ACME thread identification question.

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

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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.

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

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

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

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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.

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.

Thanks, Pete

That would be really interesting to see.

MichaelG.

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

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.

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

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

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

Thread rolling is a specialised process, which most firms would sub out to the experts.

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Perhaps you could explain then, Steve [please]

Why would anyone choose to specify 16mm x some metric pitch in ACME form rather than Metric Trapezoidal ?

[my brain hurts] ... Is it just to make it difficult for customers to second-source spares ?

MichaelG.

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But why would those experts want to roll an ACME thread-form to Metric dimensions.

True ACME is [to the best of my knowledge] exclusively specified in Imperial units.

... If I am wrong; would someone please tell me

MichaelG.

ACME is standardised in imperial units but the form can be used for metric leads. If you were cutting the thread to a metric lead you'd have to convert the lead to inch pitch then grind the tool nose width appropriately. However, if you were rolling that metric thread you'd have to have a non-standard set of rolls manufactured.

Since the vast majority of the early Boxfords were inch screws I wonder if they had the metric threads cut but the inch ones rolled for cost purposes?

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< my emboldening >

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That's what I was wondering, Pete

... hence my hope that someone might know for sure how the metric screws were made.

MichaelG.

Edited By Michael Gilligan on 14/09/2019 21:20:37

I guess you'd need to find an ex-employee from the factory for that, or a drawing.

BTW I had an Denford TDS1 and the cross slide thread on that was clearly cut (or at least finished) with a die. The marks where the die stopped were plain to see.

I always put it down to one of my predecessors being stupid. I was never able to find out why but my guess was they didn’t know about trapezoidal.

Sometimes things conspire against you I designed a pneumatic cylinder 150mm Diameter with a screw on end, It was supposed to be 150mm x 2mm or something similar, had been told we had got the internal and external tips, but we hadn’t got the Internal so it was done 150mm x 12 TPI Whit. I calculated the dimension for 3 wire on the external thread and we made that fist then did the internal thread to fit.

In most of these cases its ignorance or expedience.

Steve

How are you sure it was a die? Threads cut with an Anjest attachment have a run out like a die as do modern CNC threads no need for an undercut with either.

Steve

"In most of these cases its ignorance or expedience."

... nice summary, Steve.

MichaelG.

Edited By Michael Gilligan on 14/09/2019 22:07:13

A lot of leadscrews are cut by thread wirling, The most accurate are ground.

Steve

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Yes, Steve : But the Boxford drawing that Pete posted explicitly states 'Plunge Roll'

MichaelG.