Metric Screwcutting on Super 7B with 127 Tooth gear

[Pete RimmerParticipant @peterimmer30576]

Posted by Michael Gilligan on 02/11/2021 17:16:51:

Posted by Pete Rimmer on 02/11/2021 16:36:19:

[…]

but 32DP would do just as well being ever so slightly finer than 0.8MOD.

.

To the extent that, in some circles, they are considered interchangeable and meshable !

… purists, of course, cry: “perish the thought”

MichaelG.

At barely half a thou per pitch you would never notice, in fact it's probably less error than you would get from low-end gears and less difference than a perfectly acceptable profile shift would produce.

One of my nephews brought a stripped plastic gear to me from his RC car because it was the third set he had stripped. He asked me if I could make stronger gears for him. When I measured the gears the problem wasn't that they were not strong enough – the shop was selling a pair of gears one of which was 48DP the other was 60DP.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Pete

My post was really just a light-hearted ‘reality-check’ on your

“ever so slightly finer than 0.8MOD”

MichaelG.

[egaParticipant @ega]

Posted by DC31k on 04/11/2021 15:03:01:

…

How many imperial threading charts do we see that include 6 1/2 tpi or 15tpi or 9 1/2 tpi?

Here is the gearbox chart from my Willson slantbed which offers both 6 1/2 and 9 1/2 TPI. Some of the metric pitches are non-standard, too.

Incidentally, the lathe has an interesting change gear arrangement using a 125/127T pair with the same OD thus permitting rapid changes between metric and English. The system is covered in detail on lathes.co.uk.

[Pete RimmerParticipant @peterimmer30576]

9 1/2 qnd 6 1/2 are only there because they are half of 19 and 13. It's either have them on the gear chart or have a space.

There are 9.5tpi threads but they are so uncommon you wouldn't deliberately add that pitch to a selection if it weren't for the above.

[egaParticipant @ega]

Posted by Pete Rimmer on 05/11/2021 14:32:02:

9 1/2 qnd 6 1/2 are only there because they are half of 19 and 13. It's either have them on the gear chart or have a space.

There are 9.5tpi threads but they are so uncommon you wouldn't deliberately add that pitch to a selection if it weren't for the above.

Of course, but I was responding to DC31k's (possibly rhetorical) question!

I will pose one of my own: how many gearboxes provide standard pitches only?

[Pete RimmerParticipant @peterimmer30576]

Posted by ega on 05/11/2021 14:37:34:

Of course, but I was responding to DC31k's (possibly rhetorical) question!

I will pose one of my own: how many gearboxes provide standard pitches only?

No idea, not many I expect.

The HLV offers different imperial pitches depending if it's a UK or USA machine, and non-standards are incidental.

Of course, screwcutting isn't the only reason for using the leadscrew. Spring winding or coil winding might use odd pitches. I used my lathe gearbox to wind a coil with the pitch set to the wire diameter.

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