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Colchester Triumph 2000 - Topslide Leadscrew Threadform

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Colin Heseltine07/05/2022 20:44:17
661 forum posts
230 photos

A quick question.

I am in need of a new topslide nut and this is going to be made by a friend on his Hardinge lathe as we need the existing leadscrew to test the nut. I have checked with Colchester Spares and the leadscrew is 5/8" diameter (0.625" ) and has a 2.5 pitch metric thread. I am trying to ascertain whether this is a 29 degree Imperial threadform or a 30 degree Metric threadform. None of the threadgauge sets we have possess a 2.5 pitch threadform they all go from 2 pitch to 3 pitch. It is very hard to see a 1 degree difference. Can anyone confirm, one way or another.

Thanks,

Colin

Edited By Colin Heseltine on 07/05/2022 21:10:08

Edited By Colin Heseltine on 07/05/2022 21:10:29

Mark Rand07/05/2022 22:28:45
1275 forum posts
28 photos

I think that you'll find that it makes bugger all difference. The feedscrew will have worn to something slightly different anyway.

Colin Heseltine07/05/2022 22:34:10
661 forum posts
230 photos

Mark,

That's a fair point. The play seems pretty consistent along the full length of the leadscrew. The leadscrew thread looks pretty good along its length and the form looks quite defined, as opposed to being worn away.

Colin

DC31k08/05/2022 07:28:21
687 forum posts
2 photos

Make it 29 1/2 degrees and then calculate the maximum possible error in both cases. Chew on that number a bit in the context of every other error and uncertainty in the making process, including the wear.

Hopper08/05/2022 08:44:39
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6421 forum posts
335 photos

Grind the toolbit to match the existing feedscrew thread. Check it with a magnifying glass against the daylight.

Or are you looking to get a tap for finishing purposes? Perhaps Tracy Tools might know from previous experience which finishing tap would suit your lathe?

Or you might be able to make your own 30 degree template cut and carefully filed from sheet steel and cut the point off so it fits down into the thread and use that as a gauge. Or cut the tip of a metal 30-degree set square out of a geometry set. (Do they still even make them out of metal???)

Or turn a 30 degree plug in the lathe, and a 29 degree plug, and use them as visual gauges to fit in the thread and view against the daylight with a glass.

 

Edited By Hopper on 08/05/2022 08:55:49

Edited By Hopper on 08/05/2022 08:58:00

Colin Heseltine08/05/2022 09:31:53
661 forum posts
230 photos

The toolbit has been ground to match the feedscrew. I was not intending to get a tap to finish.

I have just read a 2019 thread on this site, discussing someones issues with a Boxford feedscrew. I see that it was commented that many manufacturers used imperial sized leadscrews with ACME threadform and metric pitches.

Does not make it easy.

Colin

Pete Rimmer08/05/2022 09:40:44
1233 forum posts
65 photos
Posted by Colin Heseltine on 08/05/2022 09:31:53:

The toolbit has been ground to match the feedscrew. I was not intending to get a tap to finish.

I have just read a 2019 thread on this site, discussing someones issues with a Boxford feedscrew. I see that it was commented that many manufacturers used imperial sized leadscrews with ACME threadform and metric pitches.

Does not make it easy.

Colin

No it was just a nasty habit by Boxford/Denford. Most manufacturers use conforming threadforms.

I like the 29.5 degree option, You'll be hard-pressed to hand grind a tool to half a degree anyway without using a jig or rest.

DC31k08/05/2022 11:40:15
687 forum posts
2 photos
Posted by Colin Heseltine on 08/05/2022 09:31:53:

Does not make it easy.

It made it very easy (and thus more economic) for Messers Box, Den and Col.

No need to keep two sizes of leadscrew blank in stock. No need for inventory management so they did not get mixed up. Similarly for the cutting tools. Simllarly for the workholding devices. Agile manfacturing ability - at the flip of a lever on the machine either language leadscrew is produced. No need to make a batch of 20 and then call the toolsetter to alter the machine.

In prodcution manufacturing, cost is an issue. Why do so many French cars have M7 threads? Because M6 is too small to work and M8 in million-volume is too costly.

It would be interesting to look at some of the European manufacturers' machines that were available in imperial form and see what they did (e.g Deckel & Aciera mills, Schaublin lathes). Also interesting would be to look at current far-East machines and see what they do - they sell into both SI and Inch markets.

Mark Rand08/05/2022 13:54:40
1275 forum posts
28 photos

I had a Hardinge HLV cross slide feed screw with a square thread!

old mart08/05/2022 16:45:57
3775 forum posts
233 photos

I have just produced 4 leadscrew nuts for the museum's drill mill in 2.5 mm pitch. The threadform is trapezoidal for most metric pitches which has a 30 degree flank angle. The er/ir16 inserts that I used would not be suitable for a 5/8" or 16mm size, the leadscrews I made them for are around 22mm diameter, and 3/4" or 20 mm leadscrew diameter would be the minimum size that they can enter.

There are ready made nuts available from an ebay advertiser, the price varies accordingly to how sophisticated the nuts are, but are worth a look.

Edited By old mart on 08/05/2022 16:50:26

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