Change-Wheel Mystery

[Michael GilliganParticipant @michaelgilligan61133]

The  little Jason lathe came with only the auto-traverse gearing

• Driver on headstock spindle: 32
• Compound Gear: 32/16
• Compound Gear: 56/20
• Driven Gear on leadscrew: 64
• Leacdscrew tpi: 16

This gives a traverse equivalent to 179.2 tpi.

… Fair enough, I suppose; but why choose those counts?

Now the plot thickens: it appears that the Cowells ME90 comes with the same numbers, except that they are all seperate gears, and it [now] has a metric leadscrew.

Brian Perris was the original designer of both machines, so perhaps it just reflects his preference [or the gears he had in-stock at the time] … but I would be grateful if anyone could provide a logical reason

MichaelG.

Edited By Michael Gilligan on 05/01/2015 18:04:33

Edited By Michael Gilligan on 05/01/2015 18:06:27

[Michael GilliganParticipant @michaelgilligan61133]

strange choice for auto-traverse …

[BazyleParticipant @bazyle]

They are all multiples of 8 (20 being a compromise for 40). Common change gear sets are either multiples of 5 or multiples of 8 with a few strays thown in. I suspect the full set for the ME90 filled in the gaps.

A cunning salesman would have arranged that the supplied gears didn't quite give the most wanted threads pushing the user into an early purchase of a few more.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bazyle on 05/01/2015 18:56:34:

… (20 being a compromise for 40) …

.

Aha !! … That's the 'logic' I had missed

… I kept focussing on the factor of 5

Thanks

MichaelG.

[Neil WyattModerator @neilwyatt]

Brian Perris was apparently measured at exactly 5' 10.551" during a visit to the NPL. I think it's probably his little joke

Seriously, why 56 rather than the more usual 57 (oft needed for 19tpi)?

Neil

[duncan webster 1Participant @duncanwebster1]

Screwcutting 19tpi on a cowells sounds a bit optimistic to me, the chip width is 40 thou. Mie wouldn't do that, at the very least the chuck would not grip (perhaps I need another chuck, it's a lever scroll thing)

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