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Turning Eccentics in Three Jaw Chick

Formula for packing

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Alan White 1	06/11/2009 18:56:53
2 forum posts	Can anyone supply me with the formula for calculating the packing to place on one jaw of a three jaw chuck in order to drill an off centre holein an eccentric? Thanks Alan
mgj	06/11/2009 19:13:01
1017 forum posts 14 photos	Yes, and its a nightmare to write up on a computer. page 13.12 of the Model Engineers Handbook - 3rd edition. Or use a 4 jaw.
JasonB	06/11/2009 20:03:04
25215 forum posts 3105 photos 1 articles	You may also find it by looking back at a few recent back issues on line, it was covered not that long ago in "Post Bag" Jason
Michael Webb 1	06/11/2009 20:40:12
2 forum posts	One of the ways I have succesfully turned, or drilled an eccentric dia./hole is to turn a shouldered blank out of a piece of scrap material,of which can safely accomodate the eccentric offset (half the value of the actual eccentric) . Then mount it in a milling machine for boring or drilling half that value of the required eccentric.When transferred back to the 3 jaw chuck,a prefect eccentric.Simples.This is providing you have a milling machine with a DRO to accurately position the offset. Edited By Michael Webb 1 on 06/11/2009 20:44:14 Edited By Michael Webb 1 on 06/11/2009 20:46:28
Martin W	09/11/2009 18:28:33
940 forum posts 30 photos	Is there any value in using a face plate. Fix a sacrificial plate to the surface and turn this surface until true then fix your eccentric to the plate lining up the hole centre using a wobbler then drill/turn to required dimension. I think I have seen this in articles but as a relative novice I am open to correction as my recall may not be too brilliant . Cheers Martin
mgj	09/11/2009 19:38:48
1017 forum posts 14 photos	Getting a bit complicated? Put it in a 4 jaw, machine (what will be) the eccentric OD, plus any grooves etc. Put a DTI against one edge, and move it across the required throw. Drill and bore - you now have the axle/crank bore. Part off. Stick it on a mandrel, and turn any bosses needed. Turn round and do the final face. Done.
Mark Dickinson	09/11/2009 20:32:22
48 forum posts 4 photos	Alan is this what you were looking for ? http://www.steves-workshop.co.uk/tips/lathetech/eccentrics/eccentricindex.htm
Alan White 1	16/11/2009 10:55:49
2 forum posts	Thank you gentlemen I have now put it on my computer for quick calculation Alan
Malcolm BEAK	16/11/2009 23:16:05
3 forum posts	Alan I'm probably a bit late with this The equation given in Model Engineers Handbook is:>> > > T = 1.5E[1-E/2D - 3/8(E/D)³]>> > > E = the desired eccentricity>> D = the OD of the material being gripped in the chuck>> T = the thickness of the packing>> > > The portion of the equation in red is very small and can safely be ignored>> Rather than work it out each time, it’s easiest to make up a spread sheet.>> Malcolm

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