Turning Eccentics in Three Jaw Chick

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Turning Eccentics in Three Jaw Chick

This topic has 9 replies, 7 voices, and was last updated 16 November 2009 at 23:16 by Malcolm BEAK.

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6 November 2009 at 18:56 #4825
Alan White 1
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@alanwhite1
Formula for packing
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6 November 2009 at 18:56 #44826
Alan White 1
Participant
@alanwhite1
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
6 November 2009 at 19:13 #44828
mgj
Participant
@mgj
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.
6 November 2009 at 20:03 #44829
JasonB
Moderator
@jasonb
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
6 November 2009 at 20:40 #44831
Michael Webb 1
Participant
@michaelwebb1
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
9 November 2009 at 18:28 #44893
Martin W
Participant
@martinw
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
9 November 2009 at 19:38 #44896
mgj
Participant
@mgj
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.
9 November 2009 at 20:32 #44900
Mark Dickinson
Participant
@markdickinson21936
Alan is this what you were looking for ?

http://www.steves-workshop.co.uk/tips/lathetech/eccentrics/eccentricindex.htm
16 November 2009 at 10:55 #45141
Alan White 1
Participant
@alanwhite1
Thank you gentlemen I have now put it on my computer for quick calculation

Alan
16 November 2009 at 23:16 #45174
Malcolm BEAK
Participant
@malcolmbeak51569
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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