# Threading problem



## riversidedan (Aug 1, 2021)

am making a pencil type device such as 1 end screws into another. I used a 10M x1.5 tap for one end and 10M x1.5 for the I.D.
when I tried to screw the tapped end was too small even tho both tap and die were the same size...the picture might better explain it  and cant quite figure where I went wrong


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## MrWhoopee (Aug 1, 2021)

Please provide close-up picture of tap & die (with any markings showing), tap drill size and OD measurements of male thread and tap.


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## riversidedan (Aug 1, 2021)

I double checked and both tap and die are M10 x 1.5  below are some parts that have m10x 1.5 threading that fit just fine....the tap drill chart sez 8.7m  for a 10m 1.5 hole.  however think Im seeing the culprit>>>>>>>>>

when I ran the die was extremely hard to turn on the part so am thinking the die or part wasnt the right size......if I would have used 8.5 tap drill the part would have been really small, so I stopped and ran the die which was really hard to turn !

but check out the part you see sticking out of the die,  both are M10 x1.5  and fit just fine, so either the tap is too small  or the die  is too big    I dont get it!!  ..........


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## RJSakowski (Aug 1, 2021)

Plastic will stretch when machining forces are applied.  This will cause a tapped hole to be undersized and a die threaded shaft to be oversized. Dull tools will exacerbate the problem. If the die is adjustable, you may be able to reduce the diameter enough for a fit.  Otherwise, single point threading will give you the needed control.


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## MrWhoopee (Aug 1, 2021)

The male part should have been turned to 10mm dia., the female would would be drilled 8.5 mm. For future reference, for metric threads the tap drill is simply the major diameter minus the pitch. (10-1.5=8.5) No chart necessary. This works for USC (inch) threads too, but you have to calculate the pitch from the TPI.

Measure the OD of the male part, it should measure something around .390. If the OD was too large to start and the die loosely contained (25mm OD in 1 in. holder), the die may have spread a little. Have you run the die back over the part?

edit: looking closely at the picture of the parts, the end of the male part should be chamfered, as should the mouth of the female part. Re-run the tap and die after doing this to cleanup any deformation.


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## brino (Aug 1, 2021)

I'm sorry, I don't understand.
Your question requires a few more details to answer properly.

1) You double-checked that both the tap and die were M10X1.5. Right?

2) Exactly what diameter did you turn the male piece to before using the die?

3) Exactly what diameter did you drill the female piece to before using the tap?

Thanks,
-brino


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## riversidedan (Aug 1, 2021)

will get your answers soon , but am thinking the problem was  the male was too small, cuzz I tried it on 3 diffrent 10Mil.  female parts and it was loose in all 3 

also the metric chart said 8.7 mil for the tap drill "which I dont have" so I got as close to 8.7 as I could..


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## benmychree (Aug 1, 2021)

Could the problem just be cheap taps and dies?  Also threads cut with cheap dies not precisely guided can "cam" axially and produce a "drunken" thread which may not fit in a tapped hole, much better to single point the thread nearly to size and perhaps finish it with the die.


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## riversidedan (Aug 2, 2021)

I just had good luck with a diffrent tap/die size but dont ask me why.........and yes I agree with that cheap stuff being at fault, only thing I can say is "it got me to understand about threading


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## MrWhoopee (Aug 2, 2021)

riversidedan said:


> I just had good luck with a diffrent tap/die size but dont ask me why.........and yes I agree with that cheap stuff being at fault, only thing I can say is "it got me to understand about threading


This may have solved your problem, but it doesn't answer the why of the original one. You just can't leave us hanging like that after you've enlisted our aid. Did you measure the OD of the original thread? Is it a split or solid die? It may have just been the cheap die, or it may not. Determining the cause of your failures is part of learning to avoid them.


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## riversidedan (Aug 2, 2021)

Weather it was the male or female part still havent figured it out and is still a puzzle,    however the recent part turned out good, so your not the only one thats left hanging!  the die was not adjustable which could have been the problem. LIke I said ,the male part was loose on 3 diffrent 10x 1.5 nuts so the problem points the male part>>>>>>>>BELOW the part on the right is the male with the fancy knurl end, that thread was M7x1.0


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## Bi11Hudson (Aug 2, 2021)

Looking at the male thread, the thread appears to be incompletely formed. *Assuming* the female thread is made with a matching tap, I would consider the tooling to be of poor quality. In your post above, the male thread is too small, which confirms what I see. The die must be "mis-shapen" in its' cutting surfaces. 

Another posiblity is starting the die almost, but not quite square to the stock. That would account for the mis-shapen threads and slightly undersized finish. This could be determined by running a nut all the way down to the shoulder. If it tightens up as it approaches the shoulder, it indicates a high probability of not starting true.

I nake a practice of single pointing a male thread whenever possible for a couple of passes. Then finishing with a die.  It doesn't help much with poor quality tooling, but helps the die run true(r). I also have acquired a contraption for starting a die from the tailstock. I'm not sure if it's truely useful, but I don't do "production" work. The setup time is longer than makin a couple passes with a threading tool.

.


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## whitmore (Aug 2, 2021)

riversidedan said:


> I double checked and both tap and die are M10 x 1.5 ..
> 
> when I ran the die was extremely hard to turn on the part so. am thinking the die or part wasnt the right size......



If the die wasn't sharp, or was sharpened wrong for your material, the force of cutting
could have caused the crest of the threads to flow, making a sharp-peak thread that
has material which interferes with the blunted-valley female thread form.
It's like knurling, cutting force RAISES material beyond the intended diameter.



This happens a lot with plastic pipe threads (and one solution is to whittle the
tops off the male part).   Either honing the die, or finding the right cutting lubricant,
can help; trying a few other dies would be  interesting.


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## riversidedan (Aug 2, 2021)

just cranked out this M7 x 1.0 12L14 bolt with 2 nuts same material, other end was in the picture before but both ends fit just fine..a bit sloppy but thats my fault.


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