Where's the threading sticky?

J

joe_m

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I thought there was a sticky thread on threading but can't find it. If there's one then please delete this and point me in the right direction. I'm trying to do threads and I'm getting oh so close but I'm still not there. The goal is to put about .75" of 1/4-28tpi thread on the end of a 3/8" rod. The best I could do is the first pass where it outlines the threads and after that it just all fell apart. I decided then to try and make something easier like a bit fat 3/4-16. I'm using a threading insert that I lucked upon. I've got the layout down pat, the feeding part is good, I've almost mastered the half-nut on/off.

I was able to make a decent 3/4-16 thread but then I think I went just one pass too far and I can screw a 3/4x16 nut onto it but it's very very loose. So I'm down to a few small questions.

1. Major diameter. For a 3/4x16 do I start with 3/4" rod or slightly fatter? (I guess the same question backwards applies for internal threads.)
2. Thread depth. After the first pass I used the little arrow-shaped tool to check thread distance and it was good. Then as the threads got deeper I checked with the thread gauge (the one that has 50 different pieces and you pick the one with the number of teeth you want to check). Was I supposed to stop when the thread gauge didn't touch bottom, when it just touched everywhere, or some other criteria? This was my biggest problem when I tried the 28tpi. It seemed like one pass just wasn't enough but 2 was way too much no matter how little I moved the bit in. I've got to learn when to stop cutting.
3. 60 degree on the cutter. Is that for ALL standard threads (not counting the acme, the whitworth, the metric etc.) or is that just for the bit fat threads like 8tpi or 16 tpi? Before I found the threading insert buried in a drawer I was trying with a free-hand ground HSS bit that was probably not realy exactly 60 degrees and may have been part of the initial problem I was having.
4. I can release the half nuts, move the carriage out of the way, stop the lathe, let it coast to a halt, and then check with a real nut. If I do that and then start it back up then I can keep threading right? (Meaning is the whole leadscrew and dial thing all still in magic alignment?)
5. I heard there was a way to do threading in one pass with something different than your usual cutting tool - like part of those big threading tap and die sets where the dies are in four pieces. Was that a dream or is it real and if so where can I get more info?


Thanks in advance for any help. Remember I'm a newbie and I'm a visual learner so a picture would be a great help. A video would be even more tremendous. And a pop-up book with pull-out tabs and maybe even scratch-n-sniff would be perfect.
thanks
Joe
 
I don't remember if there was a sticky on threading or not, and if there was I have no idea where it went, but I may be able to help you out just the same. I would recommend that you watch a few videos on threading, I believe you will find them very helpful.

These two cover the basic steps to follow:

https://www.youtube.com/watch?v=9y0MmvscBzg

https://www.youtube.com/watch?v=5-bTfflIPlc

This one covers more of the other detailed information as well as how to pick up a "lost" thread, and this should be helpful:

https://www.youtube.com/watch?v=1IqN0sHupQE


As for your direct questions:
1. The major diameter is usually slightly LESS than the nominal diameter. This is because you almost never make a thread to 100%. To do so would require everything to be absolutely perfect for the thread to work and not bind.
2. You don't use a TPI guage as a thread depth gauge. That gauge is intended to be used to determine the Threads Per Inch of an existing threaded part. It is not made in a fashion to be accurate for cutting depth. I always use a new nut as my gauge. Once I think I have cut far enough, I stop and try a nut to see how it fits. When it gets to where it fits but binds a bit, I usually just take a couple of cleanup passes with the crossslide and the compound at the same settings as the previous pass. Tool flex will allow a small amount to be removed for a couple of additional passes.
3. Try setting your compound to 29 degrees or 29 1/2 degrees instead of 30 degrees, as shown in the third video above. You never want to exceed 30 degrees. Make sure that your cutting tool is properly ground, or if using an insert, make sure it is the correct angle and is set truly perpendicular to the work.
4. Correct. As long as you do not change any of the gearing that connects the lead screw to the spindle, you should be just fine. If you would happend to "lose your place" the third video above also shows you how to pick up the thread again if you lose it.
5. Threading can be done in one pass with a die, which is actually taking a series of cuts with multiple cutting edges. Commercial threads such as on bolts are rolled and not cut. Rolling a thread requires special equipment that usually is not found in the home shop.



Edited to correct spelling errors/typos
 
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Keep nuts around and sneak up on the thread depth,trying the nut till it will screw on is the easiest method for a newbie. You can also thread till nearly done,then run a threading die over the shaft to finish it. There is a lot to know about threading,classes of fit,etc. Depends upon how much you really need to know for what you are doing. For threads that MUST run true to the axis of the shaft,do not finish off with dies.
 
To cut .75" of 1/4-28 thread is going to be almost impossible without support from a center or some kind of follow rest. You might be lucky to get a pass or two and use a die to finish the thread. Definitly a job using high speed steel instead of carbide.
 
Thanks for the links. It turns out I was doing everything right except the depth. The second 3/4-16 one I tried I stopped before it looked deep enough and it turned out to be perfectly on. I was going too deep because at first I thought it was supposed to take more than 3-4 passes. Now I need to make a mini-follower that will attach to the toolpost so I can turn the 1/4-28 threads. I saw one on a website somewhere and just need to track it down again.

Joe
 
Joe I agree with Terrywerm. I just think its amazing the people who think they have to always do the
math, of course you have to sometimes. Look at it this way do you have to look for the brake pedal
to stop then the gas pedal to start, so you should know by now where they are. We do moocho
threading and all I gotta do is look at it. Years ago when I had black hair or hair I made a master set
males females lefty, righty, set, of go/no go's. Only measurement is the OD then scratch it, everythings
good then make a termination cut (part it close to root of the thread) begin, when it starts even
looking like a thread, try the nut, if it wants to go on, but not, then a spring cut, (no) another spring
cut, getting better, another spring cut, until smooth no rattling. Thats the way I look at it, one screws
up with the math, the part is junk. There is absoulutly no shame on sneaking up to it. You are not
going to cut any thread in two minutes. You want to cut it once and be perfect. Has been said "there
is no hurry in a machine shop. Haste makes waste. Then I ll add here 3/8 is about it and dead center
is a must. Internal threading is .500 under that go to the hardware store, or tap & die set.
So Joe can I UPS three hundred 1/2 13s left hand male two inche pieces to you, after the first 25
without being wise guy I think you will get it.
 
ui

Success! My initial question and all the practice after it was so that eventually I could make this (the bottom piece in the pic):

threaded.jpg
It's not done yet - I still need to relieve the front edge, round the back edge, and put a hole in the back end. But then it will be one of the rods for a Stanley #46 combo plane. The thread is not 1/4-28 as I thought. It is another of those 9/32-28 oddballs for which Stanley is famous. You won't find that at ACE Hardware. Calibrated eyeballs would have spotted it across the room, but I had to get up close and personal with a micrometer to figure it out. I was also able to make the thread with no steady/follower or even a center in the tailstock so I got very lucky there. I still need to find that mini-follower article though.

The top rod is just a piece of 1" turned down to 3/4 and threaded just so I could get the hang of what to push/pull/turn on the lathe.
I could have bought this rod for about $12 online from a real machinist but instead I bought an old Leblond Regal, some tooling, upgraded to a 5C collet chuck, a VFD to run the lathe, more tooling, some reference books...
So now I figure this is a $1200-$1400 piece of threaded rod. But that's OK because I need one more, and then a pair a few inches longer. So when I get done I will have threading down pat and the rods will only have cost 300-325 each. One after the other and then hopefully eventually I can make another replacement part for another plane or brace or other vintage tool and say "well that brings my per unit cost down to $1 each!"

Joe

threaded.jpg
 
I found the huge feeling of satisfaction after turning my first thread made mere money seem irrelevant! Well done! :thumbzup:
 
Great job, Joe! Thanks for letting us know how you made out. It is always great to see the results when someone learns a new skill. :high5:
 
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