Worm Gear Drive : What do they mean by that ?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 15/04/2018 20:03:27:

I thought that by problem you were querying why the 2.9mm pitch

"The problem of the 2.9mm per rev. feed rate remains"

And I noticed that they had quite a few other pitches that had no obvious (to me) use.

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O.K. thanks … I hadn't checked the others.

My query about the 2.9mm pitch was two-fold

1. it seems very coarse for a device of this size
2. It's a funny number

I've just had a quick look at the worm, and it appears to be a multi-start thread.

MichaelG.

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P.S. The original question was 'Worm Gear Drive : What do they mean by that ?'

The simple answer seems to be that 'Gear' includes 'Rack' [which is true]

[Clive FosterParticipant @clivefoster55965]

Well it is Edmunds economy range so maybe they just used the helical rack out of the small rack and pinion drive stages **LINK** . The meshed a special screw to it and figured out a fancy name that sounded a lot more meaningful than it really is. They are an American company after all. Such naming issues has always been a monumentally irritating American habit. (Knee Action suspension or Pic-O-Matic Gearbox anybody!)

Those in the above link to are basically microscope focus drive systems so the pitch is almost guaranteed to be weird. Allegedly due to the space constraints on rack and pinion for acceptable helix angle but I suspect the guy who fed me that line was trying to be clever and really hadn't a clue.

Pretty much irrelevant anyway as you'd never use graduations on any job that suited that sort of lower end kit. Dunno if Edmunds have gotten their quality up since my working days (pre 2004) but back then I'd not touch any of their mechanical stuff with a barge, let alone the pole. Optics purchases were usually desperation items when Mr Project Manager refused to pay attention!

Clive.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 15/04/2018 20:14:35:

I spent a while considering it may be some complex calculation that allows you to measure gradients using newton's rings.

Then close look at the device shows it is not graduated, so the pitch cannot be critical. Perhaps the pitch is just what turned out to be eitehr convenient to use or convenient to manufacture?

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It's just a simple positioning stage, I believe.

My original thought about the pitch was that it might relate to circular vs diametral pitch …

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Clive Foster on 15/04/2018 20:32:18:

Dunno if Edmunds have gotten their quality up since my working days (pre 2004) but back then I'd not touch any of their mechanical stuff with a barge, let alone the pole.

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It's O.K. for what I paid, Clive

Pretty sure I wouldn't buy one at list price though.

MichaelG.

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P.S. … It's made in Japan

Edited By Michael Gilligan on 15/04/2018 20:46:16

[Neil WyattModerator @neilwyatt]

Hmm, a craydford style friction drive (with speed reducer) might work very well in microscopy applications.

[Neil WyattModerator @neilwyatt]

P.S. goodnight

[Jeff DaymanParticipant @jeffdayman43397]

If yer doin microscopy with yer telescope you may be lookin in the wrong end.

goodnight indeed……

[Michael GilliganParticipant @michaelgilligan61133]

I had a quick look through the microscope, at the [greasy, and not particularly well-formed] worm screw, in situ.

It appears to be 2.9mm pitch, 3-start

That would [if my calculations are correct] mesh with helical rack of Module 0.3077 [ish]

… which is unlikely to be a popular choice.

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So; working backwards, let's try Module 0.3 [a 'commercial, off-the-shelf' item]

That would require a thread with 3-starts of 2.8274 [ish] mm pitch.

Q1. is this caculation [a] logical, and [b] accurate ?

Q2. if so … why does Ealing round 2.8274 up to 2.9 instead of down to 2.8 ?

Q3. does anyone care ?

MichaelG.

.

.

Note: My calculations were [gratuitously] to 14 decimal places.

… The screw is, of course, nowhere near that good !!

… Different rounding errors may give the 2.9 mm answer.

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