3 jaw independant chuck

3 jaw independant chuck

This topic has 27 replies, 17 voices, and was last updated 17 December 2016 at 23:50 by Nick Hulme.

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17 December 2016 at 13:40 #272378
Neil Wyatt
Moderator
@neilwyatt
Posted by Michael Gilligan on 17/12/2016 10:39:51:
Posted by Neil Wyatt on 17/12/2016 10:25:12:

The principle is that a three-point contact in two dimensions is always stable, four is not.

… This means adjusters at 0, 90 and 225 degrees.
.
1. … [ and the Pope is a Catholic ]
2. … not on a typical levelling tribrach [which is was I talking about
1 I'm sure you it is worth stating as the fundamental reason why three is used.

2 I should have been clear that that was meant in the context of finderscopes, which do not always use a 120-degree spacing.

I'm sure a tribrach (I have used one on a dumpy level, may years ago) would work better with this arrangement, although the range of adjustment is reduced.
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17 December 2016 at 14:10 #272383
Ajohnw
Participant
@ajohnw51620
Why 3 jaws more clearly. Things aren't truly round so a 3 jaw chuck will provide even pressure on all 3 jaws when work is loaded into it correctly. A self centring 4 jaw wont.

John

–
17 December 2016 at 23:50 #272471
Nick Hulme
Participant
@nickhulme30114
Posted by Bazyle on 17/12/2016 11:53:54:

OT but useful. If you put a 4 legged table on uneven ground one leg is in the air. So you move it and now a different leg is in the air. DOH! but that means there is a position between the two places you tried that is the transition between one leg in the air and the other. Careful movement will always find this spot and hence a 4 leg table can be just as stable as a 3 leg.

That's a poor analogy for a chuck, with a chuck there is nothing with the freedom to lift that is present in a table where only gravity is holding it down.

– Nick
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