# Thread Bar Project, nothing is going right and I need help



## jlsmithseven (Jan 30, 2017)

Hi Guys
So it's my second semester at school. Our first project is a thread bar done on the lathe. It needs to be a 100% project or no credit.

I have my 2nd attempt at this turned down to size and grooved.

Basically this is what I ran into today...

My bar is like wobbling when it's between centers. I always notice when it's wobbling and on my practice piece, it did the same thing and only cut threads on one side of the bar. At one point it only cut threads on one side and didnt even touch the other side.

I've turned my dead center down to 60 degrees true to the chuck. I even indicated it as well in the chuck. I don't know why it's not turning true, can someone help?


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## Wreck™Wreck (Jan 30, 2017)

By "thread bar" do you mean single pointing external threads?

If I understand correctly you first turned an OD between centers, when beginning the threading op there was much run out?

If so the only thing that can explain this is that something moved.


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## mikey (Jan 30, 2017)

I'll take a shot at this. I'm not sure what a "thread bar" is, though. I am assuming you need an accurate OD and turned it between centers to do that. By grooved, I assume you mean a thread relief. So, things that might contribute to wobbling:

If you turned a dead center in a 3 jaw chuck then that's fine - it will still be accurate and on the spindle centerline - *but you cannot remove it* and then put it back in and expect it to be accurate. Once you remove the center from the chuck it will no longer run concentric with the spindle and the work will wobble. 

Is your lathe leveled? Did you check tailstock alignment? These things, if off, will turn a taper.

Depending on how long the work piece is you may also have some deflection from the cutting tool, both the turning tool and the threading tool. This is less of a problem if you're using sharp HSS tooling. Carbide tools, especially when used at low speeds, will deflect more and potentially cause inaccuracies. 

The accuracy of the center holes can cause issues as well. If you drilled the distal center hole using a steady rest then that hole is not going to be that accurate. If you chucked up the work so it just sticks out of the chuck, faced and then drilled each end then it will be more accurate. Also be sure you drilled deep enough to get almost the full conical section of the drill engaged but no more. If you go too deep your centers will ride on the shoulder of the hole and will not be supported by the 60 degree taper and the work will move.

The amount of pressure you apply with the tailstock ram can also cause the work to bend so be careful to only apply enough pressure to engage the tailstock center fully. As the work heats up it will expand and this will reduce clearances at the centers so check it from time to time and adjust tailstock pressure as needed; and keep the tips of the centers lubed. 

Watch your cutting speed. Turning between centers can cause vibration at higher speeds because of the drive dog. This isn't a problem when threading but it can definitely be a problem when external turning. This affects finish and accuracy.
Without a clearer idea of what you're doing, I can't think of anything else. I'm sure if I missed something the other guys will figure it out.


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## G MORSCH (Jan 30, 2017)

Not much to go on here...  I don't know how robust the bar is that you are trying to thread, but you have stated that you are turning between centers, meaning that you must be using a drive dog to rotate your part.  Be sure that the drive dog is not pushing against your chuck and puts no strain on the part.  Grab a different drive dog and see how the part reacts.  Some times old machines have been damaged and another thing to watch for is a bent lead-screw that can apply strain on the half-nut and move a light weight saddle up and down and in and out on every revolution (of the lead-screw).  This would only show up when threading because conventional feed rates are usually controlled by the feed-rod and not the lead-screw.  However, some low price point machines may only have a lead-screw that does both feeds and threading.  Try a different machine if that is possible.

Good Luck!

Gary


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## rgray (Jan 30, 2017)

Sounds to me like your bar is not true.
If you need it accurate you would start with  oversized stock. Put centers in each end, and then turn it to size between centers.
Then thread it between centers.
Till us what you're working with , like thread size and length of this rod.
If your cutting your own center that is held in the chuck...the only thing that needs indicating is the tool height and the compound angle. The center will then be correct until removed and can be skim cut to true it when installing to use later.


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## jlsmithseven (Jan 30, 2017)

Wreck™Wreck said:


> By "thread bar" do you mean single pointing external threads?
> 
> If I understand correctly you first turned an OD between centers, when beginning the threading op there was much run out?
> 
> If so the only thing that can explain this is that something moved.



But what moved? Yes you got my scenario right but how am I supposed to fix this? Is there anyway? I turned it between centers and it looked fine. I've been moving the piece from machine to machine because I can't get on the same machine every day. Do you think this could be the issue? I didn't even start threading anything yet on it, I can just see it wobble while between centers.


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## jlsmithseven (Jan 30, 2017)

A lot of helpful information here, thank you. I only have until Friday to finish this product, which is why it's urgent. SO many little things can go wrong and I think my biggest deal is applying too much pressure with the tail stock and my center drill holes are probably not right. Somehow we lost like all of our #3 center drills and they were the only ones I could get working for me. I've use a #4 for this project and had to go almost right up to the end of the taper. Is that too deep? How do I know how deep to go, I thought it was 2/3 of the way up the taper. I might have to start over on this project if it still wobbles I guess, right? THanks guys.


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## Wreck™Wreck (Jan 30, 2017)

jlsmithseven said:


> But what moved? Yes you got my scenario right but how am I supposed to fix this? Is there anyway? I turned it between centers and it looked fine. I've been moving the piece from machine to machine because I can't get on the same machine every day. Do you think this could be the issue? I didn't even start threading anything yet on it, I can just see it wobble while between centers.


If you have drilled the centers then turned the OD then the centers and OD's will be concentric even if there is a butt load of taper. If moving the part between machines then the error is in the next machine attachments, IE the centers or spindle.

In an effort to help you out, ask yourself how is the instructor going to measure the threads that you make? Over wires or with a  ring gauge, a ring gauge will tell someone that the Major Diameter is too large, measuring over wires only gives the Pitch Diameter.

Does your school not have bench centers?

http://cdn.mscdirect.com/global/images/ProductImages/0171874-11.jpg


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## jlsmithseven (Jan 30, 2017)

Specs


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## woodchucker (Jan 30, 2017)

I'm thinking that you are tightening the tailstock too much like mikey said. That was my first guess as I read this.
Good luck, I'm assuming that you should be able to ask the teacher for opinions.

One more thing, if you center drilled and did not go deep enough  (not too deep) to remove where the tip would ride, you could wobble.


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## jlsmithseven (Jan 30, 2017)

Yes, so can I fix my stock piece now or did I tighten it too much while I was turning? I tried loosening it and it still wobbled but I could loosen it more I think. I'm not sure, basically do I need to start another piece or can I somehow fix this one, because I spent a lot of time turning it.


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## mikey (Jan 30, 2017)

jlsmithseven said:


> I've use a #4 for this project and had to go almost right up to the end of the taper. Is that too deep? How do I know how deep to go, I thought it was 2/3 of the way up the taper.



Drill in almost to the end of the taper on the center drill. This gives max support for the given center drill size. Do NOT go past the shoulder of the taper; if you do, the center will ride on the sharp edge and not the taper itself. 

Remember that heat will expand the work piece so you have to check the tailstock pressure frequently when turning with dead centers. You only need enough pressure on the tailstock ram to keep the work piece fully engaged, and keep the centers lubed.


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## mikey (Jan 30, 2017)

jlsmithseven said:


> Yes, so can I fix my stock piece now or did I tighten it too much while I was turning? I tried loosening it and it still wobbled but I could loosen it more I think. I'm not sure, basically do I need to start another piece or can I somehow fix this one, because I spent a lot of time turning it.



You might be able to save it but not knowing what it looks like right now, hard to say. I would try shaving off a small amount on each end and re-center drill it. This establishes a new taper for the centers. Then try to get the set up right and give it another try. If that fails, stay late after class and make a new bar.


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## Mark_f (Jan 30, 2017)

I picked up something reading this thread. First, A thread bar it's an exercise that many schools use where a bar is turned to several diameters and each section is threaded.
 You said you turned your center in the chuck on the machine and your part was fine. Next you said you can't always get on the same machine, that means you would need to make a new center every time you put the part in a machine. If you're moving the center you made with the part to a different machine it is not going to turn true . that is what I believe your problem is. If you move the part to a new machine you have to make a new center in that machine and not remove it until you're done with the part.


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## jlsmithseven (Jan 30, 2017)

mark_f ....I have made the new center, I cut the 60 degree angle true every time.
the piece looks fine. it's just the smallest amount of wobble that will make the threads cut deeper on one side than the other. the piece is fully turned down , but I did manage to get a new center drill in one end right before the end of class today. on the face of this side, right next to the center drill hole, there was a tiny chip. like right on the outer edge, so i center drilled it until that little chip was removed and i went almost to the end of the taper like you said. im hoping this has fixed it, i didnt check yet but will tomorrow. thanks.


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## Wreck™Wreck (Jan 30, 2017)

The pilot section of a common commercial center drill  is far deeper than a center will ever reach for obvious reasons, as long as one drills past the pilot and less than the body one has made a perfect 60 Deg. center given the accuracy of the tool.


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## jlsmithseven (Jan 30, 2017)

I think I'm tightening the tail stock way too hard. When I move my piece and the lathe dog, it barely has any give. Which in return means the lathe dog is not moving at all and sits in the same place while I'm spinning. Does that make sense?


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## woodchucker (Jan 30, 2017)

JL, you have a teacher there, explain what is going on and get some help. It's very hard to say for sure if any one or more than one problem is causing your problem. You are paying for the tech school, so make them work for it. Testing is only one part of the course, recognizing you have a problem and need to understand why is both experience and the job of the teacher when you can't resolve it yourself, Then you can really work on the thread bar.  Good luck.


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## jlsmithseven (Jan 30, 2017)

I have been asking questions believe me.


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## mikey (Jan 30, 2017)

jlsmithseven said:


> I think I'm tightening the tail stock way too hard. When I move my piece and the lathe dog, it barely has any give. Which in return means the lathe dog is not moving at all and sits in the same place while I'm spinning. Does that make sense?



That's tighter than it has to be. Back off pressure. Just snug it so there is no axial play; it will get tighter as the part heats up.

EDIT: I forgot that you're moving from lathe to lathe. Now that you've re-drilled your centers, don't forget to re-cut the taper on your headstock dead center after mounting it in the new lathe; this will get it concentric with the spindle. 

Let us know how it goes.


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## jlsmithseven (Jan 31, 2017)

mikey said:


> That's tighter than it has to be. Back off pressure. Just snug it so there is no axial play; it will get tighter as the part heats up.
> 
> EDIT: I forgot that you're moving from lathe to lathe. Now that you've re-drilled your centers, don't forget to re-cut the taper on your headstock dead center after mounting it in the new lathe; this will get it concentric with the spindle.
> 
> Let us know how it goes.



yes i re cut it every time. thanks for the help. i appreciate it.


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## Randall Marx (Jan 31, 2017)

Yes, I think you might have found the problem. You described recutting the center and that there was a piece of crap (swarf, dirt, general crud) present. That would cause a problem like you are seeing. Hopefully that is the problem. If it is, the lesson is to make sure your centers are clean before mounting workpiece.


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## bfd (Jan 31, 2017)

you can chuck up your part and indicate the of near the end and single point cut the center on each end. run a last word type indicator in the center hole after you recut the center. don't use a center drill because it will just follow the existing hole runout and all. after you recut your centers then reinstall the bar on centers and indicate the of of the bar. if its out then recut it. now you have the bar as true as it can be. thread from there. ps your threaded bar is a lot easier than the one I had to do you have all standard threads. I did on standard thread 3/4"-10 then a two lead left handed a 3 lead right handed and a 4 lead left handed acme  plus the nuts to fit each one. bill


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## chips&more (Jan 31, 2017)

So very sorry to read about your frustration. Learning the skill of a machinist is one thing. Instructor’s lack of communicating is another. The instructor should be offering you help. Even with all of the folks at HM and there combined knowledge at your service. It’s hard to find your problem without pics or better yet being there to see firsthand. If you want, you can have the instructor PM me personally…Dave


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## jlsmithseven (Jan 31, 2017)

So, first I'd like to thank you all for working so hard helping me figure this out.

I have good and bad news today, ultimately good news overall though.

So I went into shop today and took all your suggestions and combined them and sure enough, it was turning true again. First, I re-cut my center at 60 degrees. Then, I lubed the dead center and live center. I put my piece in and tightened it, not too hard this time, just enough. Turned on the lathe and to my amazement the piece was turning perfectly true and not wobbling. Step 1, done.

Step 2, check for tailstock runout. It was .004 out so I adjusted the tailstock and got it within .001 difference, so that was a win.

Step 3, which should have been set my tool height, didn't go so well. I was running my 60 degree thread cutting tool a bit too high the entire time in shop today and couldn't figure out why my piece was just hitting the end and bumping back in. One time, it caught the end and jammed the tool bit into the piece so I had to stop the machine. I had to find my threads again with the help of others. So I kept cutting passes of about .010-0.015 per pass. Eventually right before break, my machine jammed again. Then I told a co-student about the problem and he asked if my tool height was right. I said, wow I forgot to set it..

So I come back from break, set my tool height correctly and sure enough the threads were cutting much nicer. The biggest issue here was, I couldn't re-find my threads correctly. I used the compound in-feed to just scrape the right side of the thread, etc...then.... I noticed that the thread cutting tool was only cutting threads on the left side of my external threads. I should have stopped it there, but I kept going. Eventually I got to the end of the thread, like 60 passes later, got to my tolerance and saw there was a small lip to the left of my threads. Sure enough the nut didn't thread on and my piece was ruined so I have to start over because it's a 100% or 0 project.

So in all, it was quite the learning experience. The next time I am going to set my tool height and take everything I've learned today to heart. But I thank you guys again for your help and I very much appreciate it. I'll be sticking around on this forum for a while. I'll keep you guys posted and eventually get some more pics and stuff to share. My instructor has helped me throughout these issues and I'm just learning through each mistake. Hopefully I've learned all I need to so far for this project because it's been a LOT.


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## Mark_f (Jan 31, 2017)

What I see here , is you are doing the most important thing...... LEARNING. We have all been in your place at one time in our life. Keep learning as you go. You will probably learn more from your mistakes than from anything else. You may forget accomplishments, but you will never forget the little mistakes. Soon you will be amazed what you can do with the new knowledge you are getting.


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## Tozguy (Jan 31, 2017)

Good on you Mr. Smith, we are proud of you.


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## rwm (Jan 31, 2017)

I am not sure how the other guys feel, but when I am cutting threads I never cut deeper than .005 at a time.
What is the best way to re-capture the thread? Meaning re-synchronize your lead screw? I have one it by engaging the lead screw and adjusting the compound and cross slide to fit into the thead. Any other ideas?
Robert


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## T Bredehoft (Jan 31, 2017)

rwm said:


> engaging the lead screw and adjusting the compound and cross slide to fit into the thread.



don't forget to hold the saddle to the _*right*_, against the lead screw when "finding" the thread.

hold the saddle to the right corrected by Tozguy, Thanks for catching that!


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## woodchucker (Jan 31, 2017)

Also I use the compound to feed in depth, so I only cut on the left side of the thread. I used to do it via the cross slide only, but I never found the threads to be as nice as only compound.  
Compound is 1 edge mostly cutting
X Slide is both edges cutting and that puts more pressure on the tool and the piece.


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## Tozguy (Feb 1, 2017)

T Bredehoft said:


> don't forget to hold the saddle to the left, against the lead screw when "finding" the thread.



To the left or right?


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## Mark_f (Feb 1, 2017)

I engage the lead screw, then turn the screw a little by pulling the belt ( takes any back lash out), and then adjust the compund and X axis to pick up the thread. Works for me all the time. I do this to pick up threads on a part that has damaged threads that need cleaned up. I repair Model T Ford Wheel hubs this way and they are 32 TPI.


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## chips&more (Feb 1, 2017)

rwm said:


> I am not sure how the other guys feel, but when I am cutting threads I never cut deeper than .005 at a time.
> What is the best way to re-capture the thread? Meaning re-synchronize your lead screw? I have one it by engaging the lead screw and adjusting the compound and cross slide to fit into the thead. Any other ideas?
> Robert


Turn your compound so its travel is the same as the work direction. Turn the lathe on engage the half nuts have the tool bit over the work. Turn off the lathe. Dial the compound and cross until the tool bit aligns perfectly with the thread you are trying to catch. Now retract the tool bit with the cross slide. Do not touch/turn the compound anymore. Just feed the cross until the job is done…Good Luck, Dave.


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## British Steel (Feb 1, 2017)

T Bredehoft said:


> don't forget to hold the saddle to the _*right*_, against the lead screw when "finding" the thread.
> 
> hold the saddle to the right corrected by Tozguy, Thanks for catching that!



I usually line up with the lathe in motion and leadscrew engaged to get it real-world accurate and take up play, then juggle topslide and cross-slide - low speed and blue on the existing thread help.

Dave H. (the other one)


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## tq60 (Feb 1, 2017)

Tool height can be problem but simple to adjust.

Use a small steel thing...A pocket rule or the "v" guide or even a short length of packing strap or hack saw blade.

Hold it vertical between your work and the cutter with lathe stopped.

Using cross slide slowly and gently bring it in until is just touches...If carbide it can break if too tight.

When it just touches it will hold it in place so now look at it from tail stock.

If too high the top will be towards back and too low top towards you and in dead center it will be vertical.

A little practice and you will get it and this is your starting point as fine adjustments based on cutter and material may be needed too.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk


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## bfd (Feb 1, 2017)

good directions on how to pick up a thread for whatever reason you need. toz you hold the carriage against the leadscrew to simulate the load against the carriage as it is moved by the leadscrew. so trick question if you are threading toward or away from the chuck. bill


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## tq60 (Feb 1, 2017)

Second comment...

Your instructor should be slapped!

It is his job to properly explain all of this in class before allowing you to touch the machine.

One question with part in hand should have had him  assist you by pointing out all of the things pointed out here.

Ask them questions and expect good and expect answers that yiu can understand as that is their JOB! 

Sent from my SAMSUNG-SGH-I337Z using Tapatalk


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## Tony Wells (Feb 1, 2017)

After this is all said and done, and you have completed a passing part, if it is possible and you can arrange it......make another one. This will help cement your new knowledge even more firmly. I don't know how rigid the class structure is, but I wouldn't think the instructor would mind. If that's not possible, get a little notebook and start a journal, making notes about things you did right, and the things you did wrong. It will be to refresh your memory next time you thread. Rarely are threading operations identical, and in real life you won't likely be faced with making a product like that thread bar (which btw I thing is an excellent teaching exercise), but you can learn a lot from it.


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## jlsmithseven (Feb 1, 2017)

I'm kinda confused on what you mean hold the saddle to the right means? Originally, when I tried to re-catch threads, I was turning the compound so it would just barely touch the right side of the thread. All I turned was the x-slide and then the compound and fed it in and it barely touched the right. I ran it across in the air and it looked fine.


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## jaded13640 (Feb 4, 2017)

I didn't read every response to your thread, there were A LOT of them. I assume you are simply making a bar with threads for the sake of being able to demonstrate you can cut threads? That would make the most sense to me. When I was in college they had us make practical items that were actually useful for something. We made a no twist clamp for example and that was my thread training. To be honest other than a fairly automatic machine I used to set up at a shot, and only because I was the only guy there smart enough to figure it out, that was the only threading I've ever done by the book so to speak. Setting up that machine was a bit different from just using a lathe because it was designed just to cut threads and do it in one cut. Also, my clamp use the type of thread that is used in a clamp...which is, of course, different from typical screw or bolt threads...so I don't think what my threading training taught me is the same thing as you have to accomplish. 

That being said, I think Mikey said it best when he pointed out that you CAN'T take it out and keep concentricity. They used to pound into us the importance of it, especially in lathe work but actual demonstrations didn't get into a lot of detail about it. I don't real the instructor showing how to check as we went to make sure thing were right, WITHOUT taking it out of the machine or what to do if we didn't have a choice. When class is done you're done.... You have to take it out. For sure, once you start cutting threads, you really can't take it out and think you can put it back in and it work. I'm sure some really good and really talented guys can do this but I just happened to have the knack for basic machining while going to school for engineering drafting and design. The only reason we had to take the machine tool sequence was to make us better designers. Most of the guys barely make it through the class, some were from the outside companies getting certifications and about a quarter were people from the "machinist program". So we were mostly looked at as, "they just need to get by and get the general concept, they aren't going to look for work making chips". But I did one time when there was one of the many layoffs at one of the many companies I worked at in the small area I lived in. Work was very seasonal but there was no season...LOL But I, again, kind of had a knack for it, probably because I'd worked on cars all my life till then and had a fair understanding of machined parts and therefore machine tools. 

I'm not going to be able to help you much with your project but I wanted to say that you came to the right place. Some of these guys, for a hobby board, are just incredible machinists! I mean WAY over my head just in general conversation! If anyone can help you get through your projects they can. But listen, you ARE going to have that "ah ha" moment and this will become far easier. It might help to think of the machines as just a tool, no different than a chisel or a wrench. They do a job and that's it. If you use the wrong wrench or don't hold it squarely, it'll slip and round the head of the bolt and probably bust your knuckles LOL. This isn't rocket science, don't get bothered because you're struggling. Most if this is not that complicated and these guys will help you with the little blocks that you run into. I shocked everyone when I aced the class and made everything perfectly and got all points available. I had better than a 4 point if you consider getting extra points here and there for test questions or extra projects. But I really thought it was cool what you could accomplish with fairly simple tools. We also learn to understand the basics of CNC programming and machining. I ended up excelling at that in the field too. This isn't that hard and you WILL get it. Just remember that there may be more than one way to do just about anything..but sometimes there's only one way. If anything moves while you're cutting...it's probably scrap. Almost every time unless you started with a lot more steel than you needed. LOL.

Keep the faith, try not to get too frustrated, there's a learning curve to peeing in the toilet, so there'll certainly be a learning curve to making a precision work piece. 

Wayne


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## TakeDeadAim (Feb 4, 2017)

Sorry I am late to the party.  It has been a week of hospital visits and doctor appointments.  When I was in school we had to complete a 4 step threading exercise twice each grade period, so 8 a year for 4 years.  The threads changed from 4 basic sizes to left hand, acme and finally dual lead.  Here is what I learned;

1) Work carefully and think things through
2) Face your stock and drill you center holes in one lathe.  (see #1)
3) Before you turn between centers make sure you align the tailstock with a dial indicator and test bar.  (see #1)
4) Rough your thread sizes but do not turn to final diameter until you are on the lathe you will thread that section on. (see #1)
5) Do not start to cut a thread unless you  can finish during that class.  (see #1)
6) Make sure you have your threading tool sharp and square to the work. (see #1)

As far as center drills use what you have, its not a problem unless you don't drill deep enough to get a taper or you go too deep and get a counterbore, (see #1).  With the size of the threads/stock your using it would be very difficult to put on too much pressure with the center, (see #1).  Standard 60* threads can be cut advancing with the cross slide or using the compound at 29.5*;  I like the compound because it cuts with only one edge of the tool and I seem to get a better finish.  When I am close I usually take very small clean up passes with the cross slide, (see #1)

I am a semi retired teacher, not in machine shop but in a technical college;  part of what needs to be taught/learned/evaluated is how to sort out problems.  Ask anyone here how often critical thinking and problem solving is used in the shop; (this is #1 !)

You will get this, perhaps not this time, but please see #1.


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## ewkearns (Feb 4, 2017)

It might be worth noting that if you are getting substandard threads using the cross slide, either the tool is not on center or it is improperly ground. One of my first real-life lessons in machining came about 50 years ago from a 90-some year old machinist, when he asked why I was using the compound slide to thread a cast iron part. At that time, I had never seen it done any other way. His lesson was that feeding using the compound was a workaround for threading stringy materials like hot rolled steel. Years later, I was able to use this lesson to revise NC tapes (yeah, really.... tapes!) to thread hard materials using a 90° feed. The particular hardened part was knocking the tip off of carbide inserts at an alarming rate. Feeding straight in fixed the issue.

[opinion]
Personally, I'm a bit concerned that the instructor is letting you teach yourself. He should be an active part of your instruction: observing, offering advice, and explaining the process and the physics involved.....   I'll be the first person to note that learning is not a spectator sport, but you are paying his salary. He needs to earn it.
[/opinion]


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## jlsmithseven (Feb 4, 2017)

Thanks for the long comment. I appreciate it. I made one more mistake with this bar and have to start over yet again. I finally set my tool height and everything was right, but completely ignored the 29.5 degree on the compound, something I did every time, just not this time. Anyways, I center drilled a new piece. While I was center drilling, the chuck in the tailstock moved to the right. It didn't move per say, but like twisted very slightly while I was cutting. It wasn't the drill chuck that was loosen, it was the head. Do you think this is a scrap piece now since it twisted to the right as I was cutting or should I be OK with it? If I can turn it down and it holds concentricity I am probably fine correct? Thanks guys.!


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## T Bredehoft (Feb 4, 2017)

Chuck in tail stock moved/rotated.  Not good, could gall the Morse taper in the tail stock, causing non concentric with spindle condition. 
Remove chuck, check for metal attached to taper. If it's galled, well. it should be fixed. If it's not, forget about it. Go ahead and work on your part.


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## Wreck™Wreck (Feb 4, 2017)

chips&more said:


> Turn your compound so its travel is the same as the work direction. Turn the lathe on engage the half nuts have the tool bit over the work. Turn off the lathe. Dial the compound and cross until the tool bit aligns perfectly with the thread you are trying to catch. Now retract the tool bit with the cross slide. Do not touch/turn the compound anymore. Just feed the cross until the job is done…Good Luck, Dave.


Picking up an existing thread with a CNC lathe is a different kettle of dead stinking fish.

An encoder tells the control how to move the tool in relation to the spindle orientation, there is no gear train, you can not stop the feed once started so even if you E-stop it the spindle and tool go out of sync. The only way that I have done it is to jog the tool into the thread and note the Z Axis dimension, adjust the start Z Axis input in the correct direction and run it with the tool slightly inside the thread and run as slow as possible and eyeball it. Repeat again and again until you have it, this is very very time consuming. The few circumstances where this may be required are in the event of a power failure/control lockup or error such as a low lube oil shut down, assuming that the part wasn't ruined when the tool stopped moving but the spindle carried on rotating, this will also break the insert. If the shut down occurs when the tool is in a rapid move on the way back for the next pass then you are fortunate indeed.

I have found picking up an existing thread far faster on a manual lathe.


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## jlsmithseven (Feb 4, 2017)

I will check with a test bar to make sure it runs concentric but I should be OK right? Thank you.


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## chips&more (Feb 4, 2017)

Wreck™Wreck said:


> Picking up an existing thread with a CNC lathe is a different kettle of dead stinking fish.
> 
> An encoder tells the control how to move the tool in relation to the spindle orientation, there is no gear train, you can not stop the feed once started so even if you E-stop it the spindle and tool go out of sync. The only way that I have done it is to jog the tool into the thread and note the Z Axis dimension, adjust the start Z Axis input in the correct direction and run it with the tool slightly inside the thread and run as slow as possible and eyeball it. Repeat again and again until you have it, this is very very time consuming. The few circumstances where this may be required are in the event of a power failure/control lockup or error such as a low lube oil shut down, assuming that the part wasn't ruined when the tool stopped moving but the spindle carried on rotating, this will also break the insert. If the shut down occurs when the tool is in a rapid move on the way back for the next pass then you are fortunate indeed.
> 
> I have found picking up an existing thread far faster on a manual lathe.


OK, thanks for that insite. Don’t have CNC, only a manual lathe and probably will never own a CNC lathe any time soon. Maybe a CNC mill one of these days. But thanks again, I’ll try and remember not to go chasing a thread on a CNC lathe…Dave


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## Okapi (Feb 4, 2017)

Hi,
They were a lot of things said, and I dont all understood, but if that can help you, I have some pictures about threadind and a small demonstration video.

http://www.lecollectionneur.ch/filetage-mode-automatique.html

http://www.lecollectionneur.ch/reglage-filetage/


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## Wreck™Wreck (Feb 4, 2017)

Was not directed toward you, merely an addition to the "picking up an existing thread" discussion above. unrelated to the original post yet is about threading with a lathe, relax.


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## jlsmithseven (Feb 4, 2017)

the first link didn't work and the second link doesn't really help me. we are doing 60 degree threads.

Basically at this point I know how to cut the threads. The things that I'm having trouble with still are simple and fixable.

My tool bit needs to be as sharp as possible. It looks very nice and I've gotten a lot of compliments on it. However, I annealed the tip at one point and even though I grinded it away, it's still affecting the bit. Also, it seems that every time I thread, I forget one little thing to do and the entire thing is ruined. Examples, the first time I threaded, I learned that taking off .007 with a thread file is easier than I thought. My second bar, I forgot to set the tool height, but fixed it , but didn't catch the thread in the right place. My third bar, I forgot to set the 29.5 degree angle, but everything else was perfect and my threads looked very nice. (i was quite upset). SO this time, I have a checklist printed out and I'm going to check everything before I start threading. Before I even start turning the steps and grooves, I'm going to set the compound rest to 29.5, just so I don't forget to do it when it's time to thread. SOund like a good plan?


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## Wreck™Wreck (Feb 4, 2017)

I hate to bring this up but using the compound is not required when threading, one may go straight in with the cross slide to great effect, this is not to say that it does not work but it takes longer to do, time is important.

I suspect that you are using a spindle speed that is entirely to slow even for HSS tools, wick it up a bit.

I also realize that the first time one threads to a shoulder it is a butt puckering experience at best, experience and practice will make it easy at some point, a few crashes along they way are inevitable.

Good Luck

As a side note, if you are younger then 30 and are thinking about this as a career choice then Bravo to you, I have worked in machine shops for 30 years and there are very few young people entering that workforce, it is excellent for us old guys however, they have to keep paying us a nice wage until we die or retire. Where I currently work we do a good deal of work for the manufacturing automation industry making equipment that replaces people, someone has to make the robots.


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## jlsmithseven (Feb 4, 2017)

And I'm running it at 85 rpm.


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## TakeDeadAim (Feb 4, 2017)

You can always drill the center hole a bit deeper, it does not have to be much, just a touch. Make sure the tail stock is locked in place before you drill


Sent from my iPhone using Tapatalk


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## jlsmithseven (Feb 4, 2017)

I already drilled it about 4/5 the way up the taper, I think it will be fine. Anyways here's the HSS tool bit I grinded that I have to use for threading this bar. The center point is a bit off to the left so I think I'm going to re grind it so I make the point in the middle more. It's a perfect 60 degrees though so I'm not sure if I wanna mess it up. How big of a deal would it be if it's a little to the left?

Also, would taking a TON of .003-.004 passes dull this tool quicker than taking like .010 passes with the compound at a time? Just trying to find the best way to complete an entire thread without sharpening the tool while in the middle of a thread...thanks guys

View media item 95740
View media item 95741


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## mikey (Feb 4, 2017)

You are better off if you offset the point to the left so that you can cut into the thread relief without the side of the tool making contact. I don't have a pic of my tool but it looks exactly like this (stolen from Conrad Hoffman without his consent - it was on the net so I'm posting a link): http://conradhoffman.com/shop_images/thread_tool.jpg

Also, at the very tip, just put a very tiny flat. If the radius is too large you will have that profile at the root of the thread. There are specs for this but for your project, a flat about 1/64" across is enough to keep the tip from cracking off.


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## jlsmithseven (Feb 4, 2017)

thank you, my tip actually does offset to the left i think. i will regrind it and put less of a nose radius on it.


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## mikey (Feb 4, 2017)

Try offsetting the tip way to the left like the pic. You'll be happy you did. Also, try for about 10-12 degrees of side relief - the tool will cut better for you.


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## jlsmithseven (Feb 4, 2017)

Thanks Mikey. When you say offsetting to the left, you mean make the left side top side shorter and the right side way long like that? That would mean when I go to fish tail center gauge it on my compound, I would be turning the tool holder to the right to compensate and have the 60 degree angle in the middle right? The way I have mine now, I have to turn the tool post to the left and it runs into clearance issues with my lathe dog spinning. Hope you understood all that. I drew a picture to show you what I mean. also do you have a better pic that i can see without turning my head upside down lol and clearer one. Here....

View media item 95742


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## mikey (Feb 4, 2017)

No, I'm referring to the shape of the tool itself. If you look at the pic I linked to, you will see the 60 degree point is not in the center of the tool. Its off to the left side. This allows you to get closer to the thread relief before the body of the tool gets in the way. I also suggest you use a larger relief angle when you regrind as I said and incorporate a smaller flat at the tip. The flat does not need to be round; it is there to prevent the tip from cracking off in use. There is actually a spec for the width and shape of the tip but few use it unless your thread form must pass inspection.


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## jlsmithseven (Feb 4, 2017)

Gunrunner you need to order a set of these for the Z axis hand crank. Bill did you just spit coffee on your monitor? :rofl:

View attachment 253356


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## mikey (Feb 4, 2017)

Yes, that's what I meant. The included angle at the tool's tip must still be 60 degrees but if you shift that point to the left side of the tool you will have more clearance when cutting your threads. I mentioned it because your project has shoulders on it and you may hit them as you approach the end of the cut.


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## Ropetangler (Feb 5, 2017)

Its really nice to see so many people helping out a member of the group having some difficulties with some aspects of this great hobby. There has been no name calling, big noting or other objectionable behaviour from anyone, just friendly and helpful advice. I can think of a few politicians who could usefully take a leaf from your book, so well done you blokes, and best wishes to you all and good luck to JL in coming to grips with machining. I agree with those who think that your instructor should have come over to see what your problems were and he would have been well placed to point you in the right direction having seen where you were going wrong, but this is a great place for assistance, except for the fact we are not with you to see what your problems are.
Rob in sunny Australia


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## jlsmithseven (Feb 5, 2017)

Mikey - "because your project has shoulders on it and you may hit them as you approach the end of the cut."

I've never hit them yet, but I still want to make this kind of tool because it does look better and I see a lot like this. There must be a reason. Thank you for the suggestions!!


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## jlsmithseven (Feb 6, 2017)

I ground it down to more or less where I scribed it. It looks good and is 60 degrees with like 20 degree relief i think. I might fix it up a bit more to make it more to the left, I will have time tomorrow probably. What do you think?

View media item 95750View media item 95749


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## mikey (Feb 6, 2017)

Should work fine but you can really shift the point over to the left a bit more. If it works without contacting anything then great. The important thing is that you are able to get the job done. 

You may or may not remember everything your instructor tells you in class but I can almost guarantee you'll remember things you learned after correcting a mistake. Well, maybe I should say that it applies to me at the very least - much of what I learned came from trying to fix something I screwed up. Now I know how not to screw stuff up so much!


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## jlsmithseven (Feb 6, 2017)

I jammed the tool bit into my piece because I didnt know you had to go slow into it. well, I've definitely learned not to do that.


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## jlsmithseven (Feb 6, 2017)

So I have until Friday to complete this thread bar. I definitely got an A in the effort department, but I'm hoping I can get an A on the project as well. I'm taking every step necessary to make sure the part is right. To other beginner's out there, once you learn how to do something, make a checklist like I did here. I have one for threading too and I think it's a big help.

View media item 95751


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## brino (Feb 6, 2017)

Hi Justin,

I feel a little late to the thread, but it sounds like you have a pile of great advice above.

I just read the entire thread, and the one piece of advice I have to offer is to be very careful when moving to a new machine. Never trust that the tailstock is centred with the headstock. I was surprised that no one seemed to mention tailstock alignment until YOU did in post #25. As you said, if your last operation on the other lathe was turning the outside then use that surface and an indicator to adjust the tailstock set-over before you start trying to turn threads. I bet this was your initial problem.



jlsmithseven said:


> I applied to school when I was 30, and had to wait on the waiting list. Now I'm 32 and in my 2nd semester. When I graduate, I will be 33. I think I'm still young enough to succeed in the field. I definitely wouldn't have taken it as serious as I am if I was any younger than 25. I think I'm at the right age for someone wanting to learn the trade.



I sometimes wish I could go back to school with a more mature attitude. I am sure I'd do better now.

I believe that you will do great! You have a good attitude of wanting to learn, you know what you don't know and when to ask for help. That will set you up well to learn from the old timers before they retire, then you'll have collected some extremely valuable wisdom.

I don't fault your instructor at all. I know I could NOT do that job. (S)he is likely so busy trying to make sure they are not liable for injury that it's hard to give everyone the individual attention they sometimes need. Tough gig.

Please post back with your progress.
We're all pulling for you!

-brino


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## ewkearns (Feb 8, 2017)

brino said:


> I don't fault your instructor at all. I know I could NOT do that job. (S)he is likely so busy trying to make sure they are not liable for injury that it's hard to give everyone the individual attention they sometimes need. Tough gig.
> 
> Please post back with your progress.
> We're all pulling for you!



Well, I'm putting about 90% of the problems with the instructor... especially with this young man, who seems to be trying very hard. No student should have struggled this long with the rudiments of a task without the instructor becoming proactively involved. I picked up my first class of shop students in 1973 and in the ensuing 44 years, this would simply not have been acceptable.

I also wonder: (1) where is the syllabus? (2) where are the project sheets? (3) etc.?


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## jlsmithseven (Feb 8, 2017)

I'm ready to start threads on my bar and I wanted to see if Mikey thought this 60 degree angle looks right. I made it to the left, would this be good enough as long as the very tip of the tool fits into that fish tail angle? Thanks guys.
View media item 95755


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## ewkearns (Feb 8, 2017)

Sorry about the flu.... no fun.

Second picture.....  rotate the tool post 90 degrees counter clockwise and you won't need as much overhang.

Third picture.... I can't really make out the tip, but at the rear of the center gauge, it looks like you are nowhere near a 60 degree included angle.....


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## rock_breaker (Feb 8, 2017)

In addition to all the good stuff above my thoughts ran to the centers being out of line or a chuck jaw being defective. As you found swarf in the tapers.  Hope you get your project completed as required.
Ray


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## jlsmithseven (Feb 8, 2017)

The tip has a 60 degree included as you can see up in there. I know the rear doesn't but does it matter since it will only be cutting with that tiny portion on top? I drew in red where it touches the gauge.

View media item 95756


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## mikey (Feb 8, 2017)

Your tool looks okay at the business end; the tip of the tool is contacting the 60 degree fishtail on both sides. However, when time permits, re-grind it so that the tip is a bit more to the left side of the tool and the right side is at the correct angle. You can see that the right side, the long side, is less than 30 degrees and the point of the tool is not aligned with the shank of the tool. 

All of this stuff is not critical. What is critical is that the angle of the tip is right and that the centerline of the 60 degree tip is perpendicular to the work when you're threading; be sure you use the fishtail to carefully align your tool before you cut. You haven't ground a threading tool before so I think you're doing pretty well.


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## jlsmithseven (Feb 8, 2017)

I have grinded all my tools. It's required. We're cutting 1018 Cold Rolled Steel with HSS bits that we have to grind. I made a left-right hand cutting tool and a 90 and 60 degree tool. Do you think I would be OK with this to try it or not. I can't afford a mistake at this point. Maybe I will just start over with a new one?


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## TakeDeadAim (Feb 8, 2017)

You will need to put a slight relief angle on the top of the tool so there is a negative cutting angle, 3-5* should be enough.  Remember to work carefully, making sure you have your lathe and tool set up properly before you cut each thread.


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## TakeDeadAim (Feb 8, 2017)

Here is a link to a video on the angles of a thread cutting tool.  This YouTube creator is a former High School shop teacher and he has hundreds of machining videos.  In this case he explains the different types of tool holders and how you need to put a grind on the top of your tool depending on the type toolholder you are using.  I would suspect you have the most common at school, which holds the tool at at 16* angle.  As long as your off school you might want to watch this a couple times and study the diagrams he puts at the end of the video.  This is a good as I can do to help you without being there.

I dont mean to kick a dead horse here but I can not stress enough the importance of paying attention to all the details when working.  Even today after having been an apprentice in the late 70's I still check set ups before cutting.  Stay with this and soon doing this 4 step threading exercise will become routine, the job is no less important but your ability and confidence will increase.


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## mikey (Feb 8, 2017)

jlsmithseven said:


> I have grinded all my tools. It's required. We're cutting 1018 Cold Rolled Steel with HSS bits that we have to grind. I made a left-right hand cutting tool and a 90 and 60 degree tool. Do you think I would be OK with this to try it or not. I can't afford a mistake at this point. Maybe I will just start over with a new one?



I took a good hard look at the tool you made and I'm pretty sure it will cut threads just fine as it is. You do need be sure you are at center height and that the tool tip is aligned correctly. Put your fishtail against the work and make sure the long side of the gauge is held flat and rigid against the work. Align the tool tip so it perfectly aligns with the 60 degree notch in the side of the gauge. Use a magnifier is needed but make sure both flanks of the tool are aligned with the notch and it should work out just fine. 

Next time you grind your tool, set your tool rest to between 12-15 degrees of downward angle. Now mark the tool by dividing the width of the blank into thirds. Then use a protractor set at 30 degrees and draw a line on the tool blank to intersect the first mark on the left. Grind to the line and  match the grind to the 30 degree angle on protractor. Grind to get this angle perfect. Then grind the right side of the tool at 30 degrees to make a perfect 60 degree angle at the tip. A tool ground this way is easier to align quickly because the tool's cutting tip is aligned with the shank of the tool and you can get very close to where you need to be visually. You still need to align the tool with the fishtail but its much faster when the tool is ground properly.

Be sure to hone the tool after grinding so the edges are very sharp. I don't angle the top of a threading tool. I do hone it so it is dead flat. I also make a small flat at the very tip, being sure the flat follows the angle of the nose of the tool so that the flat is even from the top of the tool blank to the bottom. This flat helps to prevent the tip from cracking off. Do not forget this flat! It only needs to be very small - maybe 1/64" across - and it does not need to be rounded unless you wish.


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## jlsmithseven (Feb 8, 2017)

Thanks guys I will look at all this.


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## 12bolts (Feb 8, 2017)

Justin, Your tool should work fine for this application. What Mikey means by offsetting to the left is more like this.
	

		
			
		

		
	



	

		
			
		

		
	
 This is a 10 mm tool bit. The left flank is about 3 mm long. You really only need to make the left flank 2-3 times longer than the depth of the thread you will be cutting. Its also easier to adjust for 60* grinding angle. If you grind the right hand flank, (long side) 1st. Then you only need to make small adjustments to the way you present the tool to the grinding wheel to get your 60* included angle, and because you are only taking off an amount over a shorter length a light touch is all that is required. I also hone all my tools with a stone after grinding, makes a big difference. And I put the radius on my tools with the stone too. Its much more delicate and you get a nice radius. Too easy to put a big flat on the nose if using the grinder. Good luck next week!

Cheers Phil


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## jlsmithseven (Feb 11, 2017)

SO I can just introduce my bit to the wheel to make the right side more flat of an angle and leave the left alone pretty much right? When you say depth of the thread, you just mean the depth I am infeeding at right? Or do I need to make the left angle as long as the thread crest to root? I think I should just start a new tool bit.


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## 12bolts (Feb 11, 2017)

Justin,
Yep, just grind the right side at roughly 30*, but trying to keep it straight all the way along the ground edge, (dont roll your hand as you grind. I sort of lock my elbows into my waist and get all my movement from the forearms). Once you have got your RH side done, move around and grind the 60* included, on the LH. Check it on your thread gauge and adjust the angle as necessary. I use a jewellers loupe to inspect the fit. Depth of thread, (the amount you are infeeding) is the same as thread crest to root amount. Your tool bit, (the ground, working part), "really" only needs to be as long as your cutting depth in a perfect world, but as perfect as we machinists like to think we are, a bit more length for imperfection is a good idea. Hence the 2-3 times. It also means that a tool ground for a 1/4" thread will also be able to cut a 3/4" thread, with perhaps a slight change to the nose radius.


jlsmithseven said:


> ...I think I should just start a new tool bit.


If your tool fits the fishtail gauge as you showed above then you will be right to cut your bar with it as is. Because you're not working to a shoulder then the non offset tip wont, (shouldn't) be a problem for you. Apart from giving you more room to work the offset tip is much easier to craft your 60* angle.
Hope this is clear? Any doubts, misunderstanding or confusion please ask. I'm sure I speak for all here when I say we hope for your success next week.

Cheers Phil


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## mikey (Feb 12, 2017)

I wanted to add that the flat at the tip of the tool should be 1/8XP, where P = the pitch of the thread you're cutting. This is important only if you're submitting your thread for inspection. Even then, I bet you'd need an optical comparator to see it so most of the time, a very tiny flat at the tip is sufficient to prevent breakage. By tiny, I mean 1/64" or so. Let us know how your project goes, okay!


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## jlsmithseven (Feb 12, 2017)

I think if I can just shave off the right side and get the 30 degrees on it, that it will make the point more to the left and I will be good to go. I'm gonna try it tomorrow.

UPDATES: I think I fixed it. I will post a pic for you tomorrow Mikey to show you what my tool bit looks like. I want to start threading tomorrow morning so please look out for it.


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## jlsmithseven (Feb 14, 2017)

Hey guys,
so after much frustration and trials, I finally got my first thread completed! Only 4 more to go. What do you think?
View media item 95774View media item 95775View media item 95776


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## mikey (Feb 14, 2017)

Looks good, Justin! Congrats!!

Does your instructor require you to check tolerances on your threads to be sure they fall within specs? I assume he is calling out for a 2b or 3b fit, right? If so, then the major diameter and thread depth will have tolerances that you can measure and meet. That will get you your "A" right there.


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## jlsmithseven (Feb 14, 2017)

We just need the thread to pass a 3-wire measurement and to thread on the test nut.


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## mikey (Feb 15, 2017)

jlsmithseven said:


> We just need the thread to pass a 3-wire measurement and to thread on the test nut.



Okay, good that he requires that. For us hobby types, we can just cut the nut to match the thread but you have to be able to make the thread to specs so that a female threaded part that is made by someone else will fit. Looks like you got this, Justin, and thanks for following up for us. A lot of guys are pulling for you.


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## 12bolts (Feb 15, 2017)

Good job Justin. Glad it worked out for you. On a side note, those threads look pretty darn good, but





jlsmithseven said:


> ....I think I fixed it. I will post a pic for you tomorrow .....


I'm not seeing a pic of your tool?

Cheers Phil


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## jlsmithseven (Feb 15, 2017)

Thanks for the compliments. I will post my tool tomorrow for you. Got another one done today, the largest one. Took so much longer to do but looks just as good. 3 more to go!
View media item 95778View media item 95779


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## Randall Marx (Feb 15, 2017)

Looking great! Glad you finally got it figured out. Keep up the good work!!!


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## jlsmithseven (Feb 16, 2017)

Got another one done today guys! Two more small ones and ( I'm all done. )


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## rwm (Feb 16, 2017)

Those are beautiful threads! Nicer than most of mine. Good work.
Robert


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## MrDan (Feb 16, 2017)

Looking good, JL! I too struggled with remembering everything I needed to do to guarantee success, a checklist helped immensely at first. Just when I was sure I had it all down, I switched to an internal thread and completely forgot that the compound must be swung to the left instead of the right when setting the 29.5° angle. Oops...


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## jlsmithseven (Feb 16, 2017)

Thanks for the kind words rwm, and yes I know what you mean. Seems I will have to do the same with the internal threading!


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## jlsmithseven (Feb 17, 2017)

I just wanted to thank this entire forum for helping me out with this project. Through many trials and errors, I have completed my project to 100% specifications. It wasn't easy, it was frustrating, but through perseverance and LOTS Of learning, I did it. THANK YOU ALL SO MUCH! I really appreciate it more than you know.
View media item 95783View media item 95784


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## mikey (Feb 17, 2017)

That looks great, Justin - congrats on finishing your project. All the best to you, and keep us posted on how you're doing.


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## Seedtick (Feb 17, 2017)

Way to go Justin. I'm proud of you. You did a first class job.
I remember making my thread bar way back in the spring of '81. Just a few months prior to that I asked one of the other new students, 'what is that big machine?' after everyone had a few laughs they told me it was a lathe. I went OJT a couple of weeks before graduation and in the 30+ years since I've never had a job that didn't involve making chips.
Stay after it, you're gonna be a dandy machinist.
Seedtick


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## Wreck™Wreck (Feb 17, 2017)

Your next test is to make a 2 start thread.

Glad it worked out for you.


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## MrDan (Feb 17, 2017)

Very nice work! Bet you get an A....


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## Tozguy (Feb 17, 2017)

Very good Mr. Smith, looking forward to seeing more of your work but I can't for the life of me think of what machine that thread bar goes on.


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## netfences (Mar 1, 2017)

This may seem like a silly question but is the diameter of the cut in the thread the spec (ie: 3/4" x 24tpi with final product larger by the cut depth) or does it specify the O.D. of the final product?


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## jlsmithseven (Mar 1, 2017)

not sure what you're trying to say. it's 3/4 x 11 tpi i believe it was. it specifies the OD of the final product and measure with 3 wire is calculated and larger than 3/4 by a little bit. that is how we measure the thread depth.


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## netfences (Mar 2, 2017)

Thanks Contact, I think you've got the gist of what I'm trying to understand. Using an S.A.E. 3/4" x 11 tpi bolt as the example, does the 3/4" represents the material that's left? How deep is the cut into the material in this example?


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## FOMOGO (Mar 2, 2017)

Congrats on getting through your project, looks great. Cheers, Mike


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## jlsmithseven (Mar 3, 2017)

netfences said:


> Thanks Contact, I think you've got the gist of what I'm trying to understand. Using an S.A.E. 3/4" x 11 tpi bolt as the example, does the 3/4" represents the material that's left? How deep is the cut into the material in this example?



OK. yes 3/4" is the actually size of the thread. this means that the top of the thread is approx. 3/4". as far as how deep this one is, I'd say like .145 thousandths deep. I calculated it using the formula I was taught but it was always like .060 thousandths bigger for some reason. Either way it worked out.


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## mikey (Mar 3, 2017)

netfences said:


> Thanks Contact, I think you've got the gist of what I'm trying to understand. Using an S.A.E. 3/4" x 11 tpi bolt as the example, does the 3/4" represents the material that's left? How deep is the cut into the material in this example?



The "3/4" part indicates the nominal major diameter of the thread; the part measures about or slightly less than 3/4" in diameter. The depth of cut required to cut the threads is typically calculated with a formula, of which there are several. One such formula is: *0.750 / TPI*. In this instance, 0.750 / 11 = 0.0682", so you would incrementally feed in with your compound a total of 0.0682" to create a full depth thread. 

All such calculations are estimates and you are wise to check the thread depth well before reaching the calculated depth by using either the three wire method or a screw thread micrometer. The readings obtained with either of these methods is compared to a table that lists the tolerances for a given thread. These tolerances vary with the fit you are going for, a 2b or 3b and so on. Once your thread falls within the tolerances you choose, you are at the proper depth of cut and that thread should take any nut that is made to the same standards.

Hope this is clear. If not, shout out.


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## The Liberal Arts Garage (Mar 3, 2017)

Not that I'm any kind of a "precision" threader,try a follower rest ask in your shop.
I fear fear your shop doesn't  really have a Teacher ; one of the most necessary
skills lies in keeping up hope and pride in his students.  .........BLJHB.


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## jlsmithseven (Mar 4, 2017)

A 6" vise is overkill for a RF45 style mill. A 4" is more appropiate for that size mill & IMO 5" max. I have a 5" GMT vise on my PM45 & it's slightly too big. Not enough Y axis travel to make use of the 5" full capacity. Better to save your money rather than getting something too big & most importantly the weight. I take my vise of the table quite often, a 6" is still light enough for me to be carried by hand but I'm glad I have a 5". I also have a 4" vise as well. I prefer the 5" though.

But those GMT 6" Premium vises are pretty nice. I'd love to have one but don't need one on my current mill. But if you plan on upgrading to a full size knee mill in the future than the 6" will be perfect.


Here's what the 5" looks like on my mill.




I couldn't even complete this cut without my bellows & DRO scale getting in the way. Not enough Y travel & the 5" vise is not even maxed out.




Here's what a 6" vise looks like on another PM45 (gt40's)
View attachment 253544


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## woodchucker (Mar 4, 2017)

You are coming along nicely Justin.
Cheers.


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## bfd (Mar 4, 2017)

nice threads. 3/4-11 that's an oddball. 3/4-10 is standard. where is the nuts. some of my apprentices made a table lamp out of the completed project. bill


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## jlsmithseven (Mar 5, 2017)

it's probably 3/4-10, i just took a guess.


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## netfences (Mar 5, 2017)

jsmithseven said:
			
		

> One such formula is: *0.750 / TPI*. In this instance, 0.750 / 11 = 0.0682", so you would incrementally feed in with your compound a total of 0.0682" to create a full depth thread.


Noted, so with a 3/4" x 24tpi thread case, the measure will be 3/4" on the male part and 23/32" on the female part (ie: .750/24)?


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## mikey (Mar 5, 2017)

netfences said:


> Noted, so with a 3/4" x 24tpi thread case, the measure will be 3/4" on the male part and 23/32" on the female part (ie: .750/24)?



.750/24 = 0.03125" = the depth of cut taken with a threading tool to reach final depth of a 24 tpi thread. It appears you are looking for the diameter of the work piece at the bottom of the thread; this is called the minor diameter and is listed in any table that lists the specs for a given thread. The major diameter is the OD of the work piece, in this case 3/4".


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## netfences (Mar 5, 2017)

mikey
I think I've finally got it. Continuing the 3/4" x 24tpi thread example, a bolt will have a 3/4" O.D. and the nut will have a 23/32" I.D., the major diameter in each part being the same 3/4".


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## mikey (Mar 6, 2017)

netfences said:


> mikey
> I think I've finally got it. Continuing the 3/4" x 24tpi thread example, a bolt will have a 3/4" O.D. and the nut will have a 23/32" I.D., the major diameter in each part being the same 3/4".



The depth of cut (0.750/24 = 0.3125" = DOC). DOC is taken on the radius so at the base of the thread (the minor diameter) the dimension is theoretically 0.750 - 0.03125 X 2 = 0.6875". So, you are feeding in a total of 0.03125" but it is cut all the way around the work piece so at the bottom of the final cut the diameter of the work piece is 0.6875". This is all theoretical because there are tolerances involved but this is the concept.


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## jamby (Mar 6, 2017)

When in tech school in 1965 I had to make V threads, Square threads, Acme and Double Acme threads and then the cruelist twist,  had to make the nuts to screw on them.  If your thread form is not right they will screw on one way but not the other...  errrr  
I still have the samples I made back then,  thanks to my Dad.  When I cleaned out his house I found them in a box in the basement.  Thanks Dad!

Jim


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