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ACME taps and Dies

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Vic05/01/2018 16:35:16
2920 forum posts
8 photos

I’ve never used them before and am wondering how much force is required to use them. I’ve struggled somewhat in the past cutting M12 threads in stainless steel and am wondering what to expect from say a 3/8” or 7/16” ACME tap and die. TIA.

Vic06/01/2018 17:01:10
2920 forum posts
8 photos

I’m surprised no one on here has used an ACME tap or die before.

Ian Parkin06/01/2018 17:19:03
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979 forum posts
231 photos

I would say that they are impossible to use as they are as a normal tap

I have only used them for cleaning up after single point cutting on the lathe

Ian

Oldiron06/01/2018 17:19:48
852 forum posts
23 photos

As Acme threaded rod is readily available I doubt if most people would want to run a die down even a 150mm long  piece of rod. I have used a 7/16 acme tap on bronze and it was quite difficult going. I definitely would not want to do it on SS.

regards

Edited By Oldiron on 06/01/2018 17:20:18

HOWARDT06/01/2018 18:10:23
780 forum posts
28 photos

In the dim past when I have used acme threads they have been single point cut before finishing to size with a die or tap. The problem with using any die which removes a lot of material is the torque required to turn it can twist the material being cut.

Vic07/01/2018 10:24:02
2920 forum posts
8 photos

Thanks for you thoughts guys, it confirms what I’ve been thinking. I guess they’re just intended to clean up existing threads.

Rik Shaw07/01/2018 10:48:14
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1458 forum posts
396 photos

I once made a 3/8" (if memory serve right) acme tap for clearing out after single point threading on a new bronze cross slide nut for an old Grayson lathe refurbish. It managed OK but was not easy. It would NEVER have removed the lot in one go. No, not never!

Rik

Clive Foster07/01/2018 13:30:43
2838 forum posts
103 photos

Generally good quality ACME tap sets are serial type where only the last one cuts to full size. The others are smaller diameters so as the taps are run through in succession the thread is bought out to size incrementally in a series of steps.

Tandem types are common with a roughing section and a finishing section on the same shank separated by a short blank section. I imagine these can do respectable job if your initial single pointing cuts are less than ideal. Probably a simple flat topped Vee thread would do fine as a starter. Blurb implies that you can cut a thread direct in a drilled hole without single point roughing out but in practice acceptable results are unlikely unless the material is kind and thread short. If nothing else chip control looks to be a nightmare. Probably anything much longer than the blank part is asking for trouble.

According to a sometime friend who used to work for the firm that made the CVA toolroom lathes they got themselves into a lot of trouble with ACME taps. New broom manger was sold set(s) of ACME taps on the promise that they would not only be much quicker and more accurate than single pointing but would also free up highly skilled men for other jobs. 4 or 5taps per set I think. Very, very expensive. As John told the story about a years supply of cross and topside feed-nut blanks were quickly done by semi-skilled workers. When released for production the stock was found unusable due to inaccurate and out of line threads. John reckoned they managed to re-work about 10% to useable quality by single pointing to an adjusted size and making feed-screws to match. Taps were binned, manager sacked and they went back to single pointing. I'd have thought that properly integrating the taps into the skilled man production set-up would have worked OK but John claimed time saved would have been minimal.

No idea whether the results would have been OK for a lesser machine. Saga is also an illustration of the sort of organisational traps you can fall into when the firm is based on a skilled workforce trusted to self inspect work to ensure its up to scratch.

Clive.

MW07/01/2018 15:06:41
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2051 forum posts
51 photos

I'm not surprised you struggled with stainless, to use an acme die on that is likely to put too much stress on the tool and isn't helped by the fact the material is work hardening, so you can't really use it to "neat-cut" an entire thread like you could with soft materials.

Your only option with stainless would be to single point the thread using a lathe, that way you can work up incrementally to the size needed without putting the tools under too much strain.

The only things I've used to cut acme tap/dies with material's are aluminium and mild steel, maybe at only 3/8" you could get away with it but I wouldn't expect the die to last forever. wink

Michael W

Edited By Michael-w on 07/01/2018 15:08:39

Vic31/07/2021 14:50:53
2920 forum posts
8 photos

Revisiting an old thread (pun intended) the question popped into my mind for a different project. It seems there are at least three types of ACME thread taps available. What looks like a fairly ordinary tap apart from the thread form, is no doubt intended just to clean up existing threads due to the very short lead. I have seen two other types though. One, as suggested earlier is cut as two taps in one tool. The first part has a gradual taper and cuts what appears to be a conventional looking thread. After a short gap the tap then gradually cuts the noticeable ACME form. Another type is very long and clearly removes a very small amount of material as it gradually cuts a full ACME thread. So it seems it is possible, albeit at a very high price! I won’t post links but do a Google image search if you’re interested. I shall be single point cutting if the project goes ahead but out of interest I’d like to see one of these taps in action!

old mart31/07/2021 19:21:12
3349 forum posts
208 photos

I bought one from Tracey tools to finish the X axis nuts for the Tom Senior light vertical. Having tried the tap in a bit of scrap with the correct starting bore, I decided to partially single point the thread on the lathe and finish with the tap. Their ACME taps are very long with a single taper, but I wasn't prepared to risk breaking it in gunmetal. The finished thread had some backlash on the leadscrew, but I had modified the design for two nuts with backlash adjustment, so that didn't matter.

I have seen pictures of extra long ACME taps with two stages of threading, they would produce a thread in one pass without the extremely high torque.

There is some information on exactly what I did in the manual machines, Tom senior threads.

 

 

_igp2378.jpg

Edited By old mart on 31/07/2021 19:23:07

Edited By old mart on 31/07/2021 19:24:23

Clive Foster31/07/2021 19:41:28
2838 forum posts
103 photos

ACME taps need to be end loaded during tapping to avoid building in backlash. The cutting forces are so large that it is very hard for the tap to screw itself through at the proper feed rate so it tends to skim cut on the back side. By the time all is sorted out and the tap fed right through to produce a full depth thread the cut is a little oversize producing backlash.

End loading reduces the feed forces so helps keep the cut to size. Push too hard tho' and you will probably skim cut off the front!

Using them to get dead on size results is something of an art form.

Tapping coarse Vee threads is pretty much as bad but a little excess backlash can be accommodated.

Clive

Martin Connelly31/07/2021 19:45:46
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1901 forum posts
205 photos

Now that CNC is available to a lot of companies and people I would think that CNC thread milling would be the most cost effective solution for a lot of needs. I know you can buy suitable tooling for it but since it is possible to machine HSS with carbide inserts I think it is something I would try making for myself if I needed to cut Acme internal threads.

Martin C

Nigel McBurney 131/07/2021 19:56:54
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925 forum posts
3 photos

recently I had to make 4 nuts for the jack screws fitted to a 100 year old smallish showmans living van.all I had to go on was a very corroded set of parts,the thread was 3/4 x4 tpi square thread, difficult ,so the owner settled to use 5 tpi Acme, as taps were available, The nuts were made from hard hex brass,I used hex as the nut could be held in lathe chuck or bench vise without slipping. The tap from tracy tools was a long tapered tap,I could not tap under power or by hand as the shank was small and a bit expensive to break,so I screwcut a vee thread and started the tap in the lathe to get it square then finished off by hand,not an easy job. Now one word of warning ,holding the tap in the tailstock via an ER collet and pushing it in by hand and when the tap bites let the work drag the tailstock along did not work, the new tap was so sharp that it did not pull the tailstock along,it stood still and the flanks of the thread acted like a boring tool turned the thread in the brass away,one scrap nut.so it was a case of pushing the tailstock along really hard and cutting a minimal amount of thread before resulting to using a very long tapwrench,the steel screw EN 8 was threaded in the lathe by single point tool ,the work supported by the travelling steady. The real problem with the job was the course pitch and the rather small diameter. For my own hobby work I would have made the correct square thread but it would not economical commercially,I have made square thread screws and nuts cut entirely on the lathe where the pitch was finer and the diameter greater eg the brake screws on a full sze TEs and and a threaded shaft for the sluice gate in a water meadow.

Paul Lousick01/08/2021 00:21:48
1862 forum posts
661 photos

I had to cut 1/2" ACME threads on the park prake for my traction engine. The male thread was screw cut on the lathe but the female thread in the nut, made with a tap.

The nut was made from brass and gave me a physical work-out while cutting it, using a 2 ft long tap handle. I would not attempt to try and cut by hand it in steel.

Paul

Vic01/08/2021 12:21:43
2920 forum posts
8 photos

I watched a video yesterday of someone cutting a female ACME thread in a brass part with a tap and it looked to need some force but doable. There seem to be some very long ACME taps out there which surely reduces the effort. Sadly they are also very expensive!

ega01/08/2021 15:12:17
2267 forum posts
188 photos
Posted by Clive Foster on 31/07/2021 19:41:28:

ACME taps need to be end loaded during tapping to avoid building in backlash. The cutting forces are so large that it is very hard for the tap to screw itself through at the proper feed rate so it tends to skim cut on the back side. By the time all is sorted out and the tap fed right through to produce a full depth thread the cut is a little oversize producing backlash.

End loading reduces the feed forces so helps keep the cut to size. Push too hard tho' and you will probably skim cut off the front!

Using them to get dead on size results is something of an art form.

Tapping coarse Vee threads is pretty much as bad but a little excess backlash can be accommodated.

Clive

In another thread I described tapping a 1/2" x 10TPI acme thread in the cast iron body of a drill vice. This was done with the work set up on the lathe cross slide and the tap gripped in an ER collet; the lathe was then set to cut 10 TPI and the thread produced very slowly under power. See at the end of:

https://www.model-engineer.co.uk/forums/postings.asp?th=139687

The result in this admittedly non-critical application is seemingly free from backlash.

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