Insert for internal ACME thread?

[Adrian R2Participant @adrianr2]

Is it possible to insert tooling to cut an internal 5/8 ACME thread (8 TPI, and RH)? Web searches throw up options from e.g. Cutwell in 16mm form factor which is going to be too big to fit inside, surely, unless I have misunderstood the nomenclature?

This is for the unidentified cross slide that is fitted to my ancient Barnes lathe. The original screw + very worn nut appear to be square which I doubt I could make, but I have a new length of ACME threaded rod available.

RDG and Tracy offer hand taps, but I'm assuming I'd have to start it off somehow before using one of these, so wondering whether an insert tool is available that would do the job in one.

[Adrian R2Participant @adrianr2]

[old martParticipant @oldmart]

No, I couldn't get an insert in that small a starting bore. The smallest insert with 8 ACME would be IR16 size, and I have my doubts whether the insert could be cut down smaller leaving only one of the three edges to do the job and still be attached to a custom made holder. There is just a possibility that a cut down one could be silver soldered to a holder, but I am not sure at all. APT sell these inserts singly, but you would also have VAT and postage. Be careful to measure the pitch of your new leadscrew, 3mm trapezoidal is very similar to 8 ACME.

[Martin ConnellyParticipant @martinconnelly55370]

Can you get a matching ACME tap? May be the easiest option.

What material is the nut? I would be wondering if I could cut a triangular thread form and then use some of the ACME threaded rod like a tap to finish the thread if it was a soft enough metal.

Can you get a matching nut or two for the threaded rod? Bore out the existing nut, turn down the outside of the ACME nuts and fit them in the bore with suitable Loctite.

Martin C

[Dwayne ClarkParticipant @dwayneclark63130]

Just grind a tool out of high speed steel and cut the thread. This was one of the first jobs I did in my apprenticeship. Somewhat intimidating at first, but really not that difficult and a great learning experience.

[Clive Brown 1Participant @clivebrown1]

You could make a screwcutting tool from silver steel which can be machined or hand filed before hardening. Photo shows one made from 3/8" dia. ss. that I used to cut a 5/8" dia. x 8tpi square thread for a feed nut for my Raglan mill.

[DC31kParticipant @dc31k]

As others have said, 8 tpi ACME form is not available in 11-series laydown inserts.

See: https://www.rileyshutt.co.uk/ProductGrp/0016000300260001 for example where the coarsest 11-series pitch is 10 tpi.

If you want a pre-ground tool, have a look at these and then try to find a UK-stockist

http://internaltool.com/products/lathe/19/acme-threading-tools

https://www.carbideanddiamondtooling.com/Carbide.ID.Acme.Threading.Tool.29.Degree.4.5.6.8.10.14.16.TPI

https://www.micro100.com/products/standard—threading-tools—acme-threads

On edit:

go here: https://www.premierformtools.co.uk/ and look for SimTurnDX as that meets your requirements. Whether it meets your budget is another matter.

Edited By DC31k on 19/11/2020 20:32:29

[Anonymous]

Square threads are not difficult to cut, but are a pain to get the fit correct. These are 1/2" x 8tpi:

I made a set of serial taps to cut the nut:

But it would be simple enough to grind a tool as shown by Clive. I chose to make taps just to prove that I could, and a 1/2" OD means the ID is 3/8" which I thought was a tad small for single pointing.

Andrew

[Ronald MorrisonParticipant @ronaldmorrison29248]

Do a quick search for the word "evanut". Near zero backlash.

[Adrian R2Participant @adrianr2]

OK, so forget about inserts, either not available or prohibitively expensive.

Not sure I'm up to grinding an accurate tool, but I might be able to grind a near-ish tool and then finish with a tap. There's a tandem tap on amazon that looks good, but unf. from a US seller which doubles the price.

The delrin idea is interesting, I can see that working for CNC with many light cuts but whether it would stand up to my ham fisted lathe turning is another matter.

This is what I'd like to make, and to add to the fun I need to make it on the lathe that it will be used for.

Edited By Adrian R2 on 20/11/2020 15:47:57

[old martParticipant @oldmart]

You might post some drawings of the leadscrew and nut with dimensions. There is a possibility that a leadscrew and nut from another make of lathe could be made to fit.

The crossslide leadscrew and nut for the Museum's Smart & Brown model A was worn out, pretty long and 1/2 X 8 LH ACME. I managed to get one similar which was new and it had two bronze nuts with it. I was rather dissapointed when I checked the pitch and found it was a 3mm trapezoidal thread. When I contacted the seller, he generously refunded the money and said keep it. I ended up using it and having both nuts for antibacklash. Then a new scale had to be made with 0-118 on it rather than the original 0-125. There is a slight error between 118 thousandths of an inch and 3mm, but its not noticable in normal lathe use.

[Adrian R2Participant @adrianr2]

Hopefully sketch is attached to previous post – can you see it?

I would love to know what the cross slide is actually from, looks like someone has made a tidy job of milling the top of the original carriage flat and then bolted this one on. I don't have a picture of it assembled to hand, will take one over the weekend but this is the lower part in place with nut and leadscrew refitted.

I did consider going metric (I have an ARC digital scale on it anyway) but decided not to confuse any future keepers further.

[Adrian R2Participant @adrianr2]

Photo of cross slide. As it's all steel with no castings I suppose it could have been fabricated from stock and not be from anything, but if anyone does happen to recognise it please shout.

Research status: Tracy Tools have a long 5/8-8 RH ACME tap and Noggin End have square bronze bar (PB102) which if sawn accurately might fit nicely without needing much machining, other than the boss.

 

Edited By Adrian R2 on 23/11/2020 14:01:20

[old martParticipant @oldmart]

Being steel would most likely point to a shop made item, manufacturers usually bought in batches of castings which took less machining.

I use this handy ACME thread calculator:

 

https://www.engineersedge.com/hardware/acme-threads-calculator.htm

Edited By old mart on 23/11/2020 15:39:24

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