# Threading - Something Went Wrong Here...



## Cody Killgore (Mar 18, 2015)

Hey guys,

I did my first threading a couple days ago on some aluminum. It turned out great. Fit nice.

Fast forward to today. I was going to make my first useful part that I've been wanting for my belt grinder. I did not have anything very machinable in the size that I needed so I grabbed whatever I had in the right size. This happened to be D2 tool steel.

I turned part of it down to 1/2" like I wanted. I started threading the end of it and man...something just wasn't going right. Can anybody tell what I did wrong just by looking at it? It looks like it just ripped it apart. I think I did miss a bit on the last engagement of the half nut, but regardless.....

This was supposed to be 1/2" 13 TPI

Zoomed in for your viewing pleasure


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## randyc (Mar 18, 2015)

Well, I'd first suspect the geometry/sharpness of your tool.  Looks like a LOT of chatter took place.  The workpiece may also have been extended too far from the chuck/collet.  Also need to use LOTS of cutting oil.  I'm like a stuck record in that I always recommend pipe threading oil which is available from almost any hardware store.

In addition to any/all of the above and based on what I see of the turned diameter at the left of the photo, the material may not have been especially cooperative (1018 sort of steel).

Sharpen the cutter, keep the work close to the chuck, make sure that the work is securely gripped, use lots of oil, run the lathe as slow as you can and practice, practice, practice.

PS:  you might try setting the compound around 27-29 degrees off perpendicular to the work.  Use the compound to feed the tool, not the cross slide.  Take no cuts exceeding .005.


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## Cody Killgore (Mar 18, 2015)

randyc said:


> Well, I'd first suspect the geometry/sharpness of your tool.  Looks like a LOT of chatter took place.  The workpiece may also have been extended too far from the chuck/collet.  Also need to use LOTS of cutting oil.  I'm like a stuck record in that I always recommend pipe threading oil which is available from almost any hardware store.
> 
> In addition to any/all of the above and based on what I see of the turned diameter at the left of the photo, the material may not have been especially cooperative (1018 sort of steel).
> 
> ...



I did not really notice any chatter. It seemed pretty smooth and I was running it really slow. It is really only 1/2" even though it is blown up big. I was using one of those triangular carbide inserts. I turned to a new corner for this thread cutting. I center drilled the end and had a live center stuck in it since it was sticking about 4 inches out of the jaws. The compound was 29.5 degrees and I did use it to feed. 

I think I tried to take bigger cuts than I should have. I do probably need to use more oil. I can't remember whether I put any on there when I was threading. I used it when turning down the diameter.

Thanks for the tips!


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## randyc (Mar 18, 2015)

You did nearly everything right except for the carbide cutter (and maybe DOC).

Carbide has a tendency to chip plus the manufacturing process is sintering, not cutting.  The result is that the cutting edge is not very sharp, even when honed with a diamond lap.  There ARE carbide tools made for threading but I suspect that you just have a standard turning tool.

Also, carbide produces a very poor finish unless it is run at high speeds.  High speeds and thread cutting are not compatible as you know.

A sharp, sharp HSS tool is ALWAYS preferable to a carbide insert for threading.  Even though you didn't notice chattering your photo clearly shows it.  Grind/lap a sharp HSS 60 degree tool, take light cuts and you'll produce good threads in no time at all.


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## Cody Killgore (Mar 18, 2015)

randyc said:


> You did nearly everything right except for the carbide cutter (and maybe DOC).
> 
> Carbide has a tendency to chip plus the manufacturing process is sintering, not cutting.  The result is that the cutting edge is not very sharp, even when honed with a diamond lap.  There ARE carbide tools made for threading but I suspect that you just have a standard turning tool.
> 
> ...



I will be sure to try HSS next time! Thanks.


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## chips&more (Mar 18, 2015)

I think you answered your own question when you said you missed the mark on the threading dial. In doing so you took way too big of a cut. Under certain conditions, D2 does not cut that well and that is an example of one of them. If you miss the mark it will just tear it up.  Use cutting oil. If all you have is carbide, that’s fine. When you get the hang of threading. Try threading the depth of cut with just the cross feed. This method will make the threading tool cut equal amounts on both sides of the “V”. And you will not need to set the compound to 29.5° or whatever. Also, the finish on the threads can be more rewarding doing this way….Good Luck, Dave.


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## Wreck™Wreck (Mar 18, 2015)

Cody Killgore said:


> Hey guys,
> 
> I did my first threading a couple days ago on some aluminum. It turned out great. Fit nice.
> 
> ...


Without a scale in the photo for reference it looks like the tool took 2 slightly different tracks, this happens when one is is slightly off engaging the half nuts, I am assuming you are doing this manually. If it went well the first few passes and then went to hell all of a sudden at near minor diameter depth of cut that is probably what happened.

Place a 1/16" scale along the threads and take the picture again, it may help show the cause.
I imagine that it did an excellent job of destroying the insert as well.


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## stupoty (Mar 18, 2015)

randyc said:


> Take no cuts exceeding .005.



I've found recently that 005 is quite a good for most of the cut, i tend to work down to 0.002 once the thread get deeper and the width of the cut becomes very large.

Stuart


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## randyc (Mar 18, 2015)

Wreck™Wreck said:


> Without a scale in the photo for reference it looks like the tool took 2 slightly different tracks, this happens when one is is slightly off engaging the half nuts, I am assuming you are doing this manually...



Good call, my old eyes missed the cross-tracking !



chips&more said:


> Try threading the depth of cut with just the cross feed. This method will make the threading tool cut equal amounts on both sides of the “V”. And you will not need to set the compound to 29.5° or whatever. Also, the finish on the threads can be more rewarding doing this way….Good Luck, Dave.



No offense but the point of using the compound set at 29 degrees is NOT to cut both flanks of the thread at the same time.

The tool skims the right flank, producing a good finish, while removing most of the metal on the left flank.  At least this is the way that I was taught and to the best of my memory, literature supports the method.

Here's a pretty good discussion from "Practical Machinist"

http://www.practicalmachinist.com/vb/general/setting-compound-angle-when-thread-cutting-278289/

PS:  I missed the "D2" material, which changes the process a bit


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## JimDawson (Mar 18, 2015)

+1 on most of the above. There are defiantly two starts, that will tear things up pretty good on the last cut.  D2 is a PITA under the best of conditions. it's a balancing act between feed/speed and work hardening.  You also have to maintain a pretty healthy DOC in D2.   A good, sharp HSS tool would be the best here.


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## stupoty (Mar 19, 2015)

randyc said:


> Good call, my old eyes missed the cross-tracking !
> 
> 
> 
> ...




I saw an interesting video or article on the left half cutting thing, they used a half shaped tool  so the right hand side dosn't rub.

Stuart


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## Cody Killgore (Mar 19, 2015)

Thanks for all the advice guys. I do appreciate it. 

I think I'm going to order some 12L14 for this little project and see how much that helps. 

The reason I went with carbide was because I haven't had experience grinding tool bits yet.

I have been studying up on grinding tools this morning. I got a right cutting hss bit ground this morning. Now to do the threading one...


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## Franko (Mar 19, 2015)

Yes, pretty obvious the last pass was on the crown of the threads caused by engaging the half-nut on the wrong mark.

Mostly through a not too clear understanding of the benefit of engaging and disengaging the half-nut, I've always just left it engaged. I make a pass with the tool,  stop the motor at the relief cut, then back out the cross slide 10 thousandths and reverse  the motor to back the carriage past the end of the piece. Then move the cross slide back to it's original setting and advance the compound 3-5 thousandths and make another pass through the work. Rinse and repeat until the thread is satisfactory.

My understanding of the benefit of using the half-nut is it is supposed to be a little faster operation in production work. If you are like me, fairly inexperienced (I've been using a lathe less than 10 years), and don't do lots of threading, the reversing method is less prone to disaster, not that there aren't other factors to make disasters. 

I've had a similar thread result because my ways had gotten loose and my tool was a tad above center. The tool grabbed the work, rotated down causing it to gouge in too deep, and jerked the QCTP out of position.


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## Cody Killgore (Mar 19, 2015)

Franko said:


> Yes, pretty obvious the last pass was on the crown of the threads caused by engaging the half-nut on the wrong mark.
> 
> Mostly through a not too clear understanding of the benefit of engaging and disengaging the half-nut, I've always just left it engaged. I make a pass with the tool,  stop the motor at the relief cut, then back out the cross slide 10 thousandths and reverse  the motor to back the carriage past the end of the piece. Then move the cross slide back to it's original setting and advance the compound 3-5 thousandths and make another pass through the work. Rinse and repeat until the thread is satisfactory.
> 
> ...



That is a pretty cool idea that I haven't thought of. Thanks for the tip! I might just have to try that out.


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## Bill C. (Mar 19, 2015)

If you can mount a indicator or stop on the cross slide so it stops on the same point every time it is reset will help too.  Like they said use plenty of cutting fluid.  I always had trouble threading.  Production shops use threading dies for speed. I always kept a hand die handy to finish my threads.  Just keep practicing, cut off the bad end and cut more threads.  1/2 -13 is a good thread to practice cutting.  When you use HHS be sure there is plenty of clearance ground on the sides and front cutting edges. 

Good luck


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## epanzella (Mar 19, 2015)

It looks to me that the radius on that tool was way too big. The tool you used was for turning at high rpm not threading. Having that large radius also puts more torque into the cut as it's doing too much work. This may have caused your piece to slip in the chuck which would result in a crossed thread even if you did everything right. Check the piece for jaw skidmarks. Hard to tell for sure but your DOC looks pretty aggressive. Don't take more than .005/cut. Good luck
Ed P


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## RJSakowski (Mar 19, 2015)

I was just playing around with the threading dial on my Grizzly G0602 in preparation of cutting a thread on an important piece.  I noticed the marks on the dial did not line exactly for all marks.  There are 48 teeth on the spur gear and 12 marks on the dial meaning you can engage the half nuts at three positions in between the dial marks.  For some of the marks they were off by almost a half tooth so it would be difficult to judge whether  engaging the leading or the trailing position.  If you missed by one tooth, you would end up with a thread (no pun intended) like the thread at the beginning of this thread.  

I visually lined up each mark and recorded the carriage position from the DRO.  While there is variation in duplicate readings, it is clear the dial marks are not evenly spaced.  The gear is running true and there is no noticeable runout in the dial wheel which leads me to believe that the dial markings are not concentric with the wheel or that they are just plain sloppy. The attached graph shows the variation between marks for my dial.  Some of the observed variation was due to an inability to visually align the dial marks with the witness mark. However the four sets demonstrate a clear trend.

Four separate sets of measurements were made the last set was made after disengaging the dial and moving it by 2 inches on the lead screw before reengaging.  This was done to establish that the lead screw was not at fault.  As can be seen, the shift did not have a corresponding shift in the curve, showing that the problem lay solely in the dial itself.  The variation of 30+ thousandths is almost half the 83 thousandth of the lead screw pitch which could easily lead to engagement one thread off with the half nut.

I have not had a problem in cutting threads because the few that I have cut on this lathe were either metric or I always engaged on the same number on the dial.  My next thread was to be a 3/8-24 which should have allowed me to engage on any dial mark and could have been a disaster.
One of the next projects will be to make a new dial for this lathe.


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## randyc (Mar 19, 2015)

Ah ha - an Excel spread sheet guy, my man ! (as Denzel Washington said)


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## extropic (Mar 19, 2015)

RJSakowski,  Really useful info there. thanks for doing the work and posting.


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