Imperial Thread Cutting on Metric Mini Lathe

Brief example cutting 1mm pitch on a 1/16" leadscrew mini lathe:

1/16 * 25.4 = 1.5875mm pitch (exactly).

So to step this down to 1mm pitch you need to divide the gear train by 1/1.5875

1/1.5875=0.62992125984 (approximately)

So if you use the ratio 63:100 in the gear train the error is:

63-0.62992 = 0.00007874

As a percentage that's 0.008% which is close enough for rough work.

Visiting this site I see their precision metric leadscrews have an accuracy of 0.08mm per 300mm.

That's 0.026%. Which is three times the error given by using a 63 tooth gear - over a foot!

Any questions?

Neil

Indeed, such as making precision leadscrews - see above

Sorry John, I know you are on my side!

Neil

Hmmm, and further down on the same page they say the lead error over the length of the rod is 0.3mm per 300mm, rather different. I would expect precision leadscrews to be ground rather than rolled.

Of course that doesn't change the fact that a 63 tooth gear is perfectly satisfactory for cutting metric pitches with the correct gear train. Personally I say hooray for quick change gearboxes; imperial, metric, DP and module all at the change of some levers, and one gear.

Andrew

.

+1

To quote Jason's recent comment on the Soba thread:

"Problem is one mans Shoddy is another mans will do the job perfectly well."

The situation seems similar with 'Precision Leadscrews'

... or indeed anything "Precision"

MichaelG.

Edited By Michael Gilligan on 08/09/2017 10:50:17

If you read to the bottom of the main page, they pre-grind the lead screws then roll them presumably to get the best of both worlds with ground accuracy and rolled form and surface finish.

I think the 0.3mm per 300mm bit is an error as the text it's in mentions 60-degree metric form threaded rod rather than precision leadscrews and the 0.05/300mm is mentioned elsewhere and 0.003"/for for v-thread precision leadscrews.

"Cold Rolled Formed Lead Screws

Abssac supplies both machined and rolled thread formats. Lead screws that are cold rolled formed have the immediate advantage of a work hardened surface on which the load bearing nut will travel. Starting with a pre-ground bar stock, the thread form is gradually rolled into the material with increasing pressure ensuring precise material deformation along the thread form as it is worked. By repeating this process the screw stock work hardens into a smooth, polished like finish with the desired diameter and lead as the finished product."

Edited By Neil Wyatt on 08/09/2017 15:33:57

Maybe drifting off the original topic, but I think you might like this, Neil:

**LINK**

https://www.helixlinear.com/

Have a look at the blog post about plastic leadscrews

... I was quite impressed.

MichaelG