ACME thread identification question.

[Nick EdgleyParticipant @nickedgley74365]

Hi Diogenes,

Far from reading as egg sucking instructions I appreciate the detail and the time taken to reply.

Interestingly the measurement of the major diameter is 11mm making the thread 11 x 2.5. Nobody seems to make one of that size!

The replacement part mentioned in the link from Michael Gilligan does appear to be the correct part and I agree it would be cost effective. Having said that I enjoy the challenge and like making things!

Hi Pete,

The size quote in your post above from the ebay seller might just be what I am looking for. I cannot find that seller on ebay, do you have a link I could use?

[Pete RimmerParticipant @peterimmer30576]

https://www.ebay.co.uk/usr/reltub34

Edited By Pete Rimmer on 30/08/2019 11:58:47

[Nick EdgleyParticipant @nickedgley74365]

I contacted reltub34 via ebay and he quickly replied stating that, as Pete stated, the size is a 7/16" x 2.5mm ACME thread.

My heartfelt thanks for all of the valuable input to help me understand what I had actually got.

[Pete RimmerParticipant @peterimmer30576]

For a thread like that there must have been a factory drawing showing the departure from spec for thread cutting depth on both the nut and the screw although the screws were rolled which begs the question how did they roll an ACME thread at a non-standard pitch or why would they even do that when you could roll a trapezoidal thread on the non-standard diameter without having to have non-standard rolls made.

Somebody somewhere must have that drawing.

[Clive FosterParticipant @clivefoster55965]

Pete

ACME thread of metric pitch on imperial stock size is / was an "industry standard" whatever the books may say.

This was the normal method of producing metric machines used by British, American and, perhaps surprisingly, many continental makers back in the day. Metric trapezoidal is historically less common than you'd think. For all practical purposes the specifications are as per the nearest imperial size full depth ACME with a pitch adjustment.

Even if the thread was worked out from first principles the difference would almost certainly be too small for the likes of us to notice. Even without wear.

Clive

[Pete RimmerParticipant @peterimmer30576]

Well yes I realise that it would take nothing more than a small adjustment in half depth or tip width and it IS very small but still there must be a drawing that says more than 7/16" ACME 2.5mm pitch LH. They specified the OD for the blank for rolling the thread on the imperial cross slide screw to 4 decimals.

[DC31kParticipant @dc31k]

Posted by Pete Rimmer on 02/09/2019 14:00:47:

They specified the OD for the blank for rolling the thread on the imperial cross slide screw to 4 decimals.

But could that be because the thread forming process (rolling) is quite fussy in that respect? Maybe if checking using three wires, this is the diameter that gave correct results.

It may be similar in concept to thread forming taps: for success, you need to be a lot more careful in your tapping drill selection.

[old martParticipant @oldmart]

Tracey Tools do not list a 2.5 X 11 trapezoidal tap, but it is worth phoning them just in case. I would think about using the imperial leadscrew, at least you have a tap to make a new nut if needed. The scale is a bother if you don't have a mill and rotary table to make a new one. A lot of lathe owners have fitted a DRO to the cross slide, if you had one, the numbers on the scale could be covered up with tape.

Edited By old mart on 03/09/2019 19:27:18

[Nick EdgleyParticipant @nickedgley74365]

What a terrific company Tracy Tools are.

I rang them asking about a tap for my oddball size. They would not commit themselves over the telephone and clearly wanted to measure the item themselves. I sent them both the leadscrew and nut on Thursday last week. I received it back on Tuesday and a telephone call shortly thereafter confirmed the size as 7/16" x 2.5mm ACME. The bad news a tap was going to cost around £300 i.e. a one of specially manufactured tap.

I cannot emphasis how helpful and efficient they have been despite them being unsurprised in not making a sale.

Edited By Nick Edgley on 13/09/2019 00:10:43

[not done it yetParticipant @notdoneityet]

So what is the plan now?

Plenty of choices – well a few.

Make a new nut.

Make a screw and nut.

Buy in some trapezoidal rod plus a nut (could make a nut).

Make an acetal insert for your present nut.

Probably others.

I would probably make a new square thread screw and nut if the screw is worn in the middle. If there is enough metal in the worn nut, I would use that – bore, bush and cut the new thread.

First thing is exactly how worn the existing nut/screw combo is. They will work perfectly adequately right up until they fail. Backlash is neither here nor there with a lathe – once the backlash is taken up. Remember, there will always be some backlash with cut threads (acetal, by the ‘heat and squeeze’ process will always be a very tight fit, needing some relief after moulding).

[not done it yetParticipant @notdoneityet]

Duplicate.

Edited By not done it yet on 13/09/2019 01:42:30

[Michael GilliganParticipant @michaelgilligan61133]

It would be interesting [albeit not particularly useful] to know how Boxford went about making these 'bastard' components.

Presumably; being tooled-up to make make male screws with an ACME thread-form [whether by screw-cutting or by grinding] the easy option would have been to make their own taps to finish the nuts.

If anyone knows how Boxford produced these items, do please tell us.

MichaelG.

[Pete RimmerParticipant @peterimmer30576]

The Boxford drawing specifies that the threads are plunge rolled – for the imperial leadscrews at least.

Full marks to Tracy tools for an excellent customer service. Many would be happy to just sell an unwitting customer anything they asked for even if it was clear that it was probably not what they required. Clearly, Tracy tools places more value on their customer's satisfaction than your average supplier. Good show!

Edited By Pete Rimmer on 13/09/2019 11:21:19

[old martParticipant @oldmart]

You said you had another leadscrew and nut, could they be used?

[old martParticipant @oldmart]

If all else fails, just get a 12 X 3 trapezoidal leadscrew and nut and graft it onto one of your existing ones?

**LINK**

[Nick EdgleyParticipant @nickedgley74365]

I was considering using my imperial leadscrew and nut but discovered the leadscrew is not the correct one, the length is different. It is most likely a Boxford part but from a different machine.

I have decided to buy a replacement nut from Boxford which is a little irritating having made one but been stymied by my inability to cut the appropriate thread in it and the fact that with postage and VAT it is £83!

[old martParticipant @oldmart]

There is a UK company selling metric leadscrews and nuts, but not in 2.5mm pitch:

**LINK**

 I have looked everywhere for 2.5mm pitch trapezoidal, and cannot find any, funny as your Boxford is not alone, the drill mill at the museum uses 2.5mm pitch screws on the X and Y table travel, although they are much larger diameter than yours.

Edited By old mart on 13/09/2019 16:34:30

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Pete Rimmer on 13/09/2019 11:16:48:

The Boxford drawing specifies that the threads are plunge rolled – for the imperial leadscrews at least.

.

Thanks for that, Pete

Did they do the thread rolling in-house, or sub-contract, I wonder.

… either way [if I understand the process correctly] that would require a serious machine and long dies.

MichaelG.

.

https://m.youtube.com/watch?v=RPcy8-6Hfqg

Edited By Michael Gilligan on 13/09/2019 23:12:25

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 13/09/2019 23:11:29:

Posted by Pete Rimmer on 13/09/2019 11:16:48:

The Boxford drawing specifies that the threads are plunge rolled – for the imperial leadscrews at least.

…

Did they do the thread rolling in-house, or sub-contract, I wonder.

… either way [if I understand the process correctly] that would require a serious machine and long dies.

MichaelG.

…

Buying parts in has long been a common commercial arrangement. Very few manufacturers make everything, for example Myford lathes came with Brook Compton motors and Dewhurst Switches. I doubt they made their own paint, and perhaps not lead-screws either.

My dusty and unreliable memory tells me precision lead-screws soon became specialist items not worth the trouble of making in-house. For some reason Bristol comes to mind, perhaps because I saw something in their long closed Industrial Museum. (Sort of makes sense because Bristol engineering went up-market during the late 19th century when local iron and coal ran out. Hi tech stuff like aero-engines. Today it's still big in electronics and aerospace.)

Hearsay unless I can find a reference. Does this ring a bell with anyone else? Who made British lead-screws?

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 14/09/2019 09:16:20:

Posted by Michael Gilligan on 13/09/2019 23:11:29:

Posted by Pete Rimmer on 13/09/2019 11:16:48:

The Boxford drawing specifies that the threads are plunge rolled – for the imperial leadscrews at least.

…

Did they do the thread rolling in-house, or sub-contract, I wonder.

… either way [if I understand the process correctly] that would require a serious machine and long dies.

MichaelG.

…

Buying parts in has long been a common commercial arrangement. [ … ]

.

Quite so, Dave … and the Pope is usually a Catholic

I am interested in how and where the Boxford screws were made, because that knowledge might help us understand why they chose to use a 'bastard' thread.

MichaelG.

[Pete RimmerParticipant @peterimmer30576]

I think it's fair to postulate that the thread rolling was farmed out simply because the drawing only specifies the blank diameter for rolling, not the specific tolerances for the rolled thread which you would expect would be on the drawing if the rolling were done in house. The integral gear on the other hand has those specifics listed on the drawing.

I'll see if I can dig it out and post it.

The South Bend lathe that the Boxford was copied from had cut threads which we know because Larry Vanice has the leadscrew cutting machine they used at the factory.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Pete

That would be really interesting to see.

MichaelG.

[Pete RimmerParticipant @peterimmer30576]

Here's the drawing, as found in the files section of the Boxford Yahoo group.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks again, Pete

So we now know [pretty much for sure] that the English version was made for plunge rolling a 10tpi LH ACME form thread … 'though I can't quite decide whether, or not, the instruction effectively includes the rolling thereof.

[my thinking is that it probably does … because the ACME form is sufficiently well-prescribed to need no further detailing]

Mystery stll surrounds the [Boxford special] Metric specification though

MichaelG.

.

https://www.amesweb.info/Screws/AcmeScrewNutThreadDimensions.aspx

Edited By Michael Gilligan on 14/09/2019 13:23:16

[S.D.L.Participant @s-d-l]

Posted by Michael Gilligan on 14/09/2019 09:50:06:

Posted by SillyOldDuffer on 14/09/2019 09:16:20:

Posted by Michael Gilligan on 13/09/2019 23:11:29:

Posted by Pete Rimmer on 13/09/2019 11:16:48:

The Boxford drawing specifies that the threads are plunge rolled – for the imperial leadscrews at least.

…

Did they do the thread rolling in-house, or sub-contract, I wonder.

… either way [if I understand the process correctly] that would require a serious machine and long dies.

MichaelG.

…

Buying parts in has long been a common commercial arrangement. [ … ]

.

Quite so, Dave … and the Pope is usually a Catholic

I am interested in how and where the Boxford screws were made, because that knowledge might help us understand why they chose to use a 'bastard' thread.

MichaelG.

Halifax Rack and Screw make precision leadscrews, Used to serve the machine tool industry.

I know they will also make Ba$tard sizes as where I work they used to make us a 16mm x metric pitch ACME in stainless steel.

Steve

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