# How to make acme style threads for cap



## carandacher (Feb 8, 2019)

Hi All,

I am looking for basic instructions on how to make acme style threads on a metal lathe. Also I wonder what is the correct piece to use for the thread cutting...?
Here you can see attached a fine example of acme threads, I would love to get that same result as in the first pic where the black part seems to go all the way inside the barrel.


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## bmachin (Feb 8, 2019)

There are numerous YouTube videos on single pointing both internal and external acme threads. You May need to go a little bit beyond that to figure out the relationships between pitch and thread depth, etc. 

External thread tooling should be relatively inexpensive, but you may need to spend a bit more for internal tooling. at these small diameters.

Bill


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## BRobbins629 (Feb 8, 2019)

This would also work on a metal lathe putting the bit in the head stock. 

http://content.penturners.org/library/tools_and_jigs/incredible_threading.pdf

You could also grind internal and external bits and thread the normal way on a metal lathe. You would want a bit about .050 in width and cut at 10 threads per inch.


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## More4dan (Feb 9, 2019)

With a metal lathe you could turn external threads on drill rod and make your own taps.  Turning ID threads for small diameters is difficult.  I’ve done this for normal threads and I assume it would work for ACME threads. If interested, let me know and I could walk you through the steps. 

Danny


Sent from my iPhone using Penturners.org mobile app


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## Curly (Feb 9, 2019)

jalbert seems to have mastered the process. Message him and see if he has a few tips he can share beyond what has been suggested so far. 

http://www.penturners.org/forum/f13/green-silver-158520/


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## jalbert (Feb 11, 2019)

Curly said:


> jalbert seems to have mastered the process. Message him and see if he has a few tips he can share beyond what has been suggested so far.
> 
> http://www.penturners.org/forum/f13/green-silver-158520/



Those are actually square threads (no wall angle), not acme. I grind my own tools, so I’m not sure what’s commercially available. Besides taking a lighter depth of cut per pass, I find them no different to cut  than 60 degree threads.


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## More4dan (Feb 11, 2019)

jalbert said:


> Curly said:
> 
> 
> > jalbert seems to have mastered the process. Message him and see if he has a few tips he can share beyond what has been suggested so far.
> ...





What are you using for your bit geometry for cutting your threading tool?  I was thinking a cutoff tool but wasn’t sure if it would have the necessary side clearance as it progressed along the thread.  

Danny


Sent from my iPad using Penturners.org mobile app


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## jalbert (Feb 11, 2019)

You would probably get the best results from grinding some sort of helix angle . No machinist am I, so I don’t have a good explanation of the specifics. I just trial and error it.


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## Dalecamino (Feb 11, 2019)

I found this on youtube

https://www.youtube.com/watch?v=Ioi0mIVfvHA


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## bmachin (Feb 11, 2019)

If you're interested in single pointing a true acme threads you are going to need specialized tooling. Cheapest source is probably Ebay:

https://www.ebay.com/sch/i.html_fro...eading.TRS0&_nkw=acme+threading+tool&_sacat=0

This link shows a couple of solid carbide 12 tpi acme tools that will fit inside a pen cap for around 35 bucks. 

If you already have some sort of insertable toolholder you can probably find acme inserts that will fit it for the external threads.

Taps for the internal threads are fairly expensive. The ones at Victornet and McMaster will only work for through holes. I'm just making this up but it seems to me that the loads on something as thin as a pen cap would be dangerously high when tapping an an acme thread.

Single pointing a female thread isn't all that difficult. John Albert does it on every pen that he makes, and I've done it on many.

Another tooling source that is a lot more expensive but very good is Thinbit:

Threading and Chamfering Products

FWIW

Bill


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## carandacher (Feb 12, 2019)

Thanks a lot. I wonder also if it's possible to cast silver acme threads with some manual finishing?


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