Turning Eccentics in Three Jaw Chick

[Alan White 1Participant @alanwhite1]

Formula for packing

[Alan White 1Participant @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

[mgjParticipant @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.

[JasonBModerator @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

[Michael Webb 1Participant @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

[Martin WParticipant @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

[mgjParticipant @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.

 

 

[Mark DickinsonParticipant @markdickinson21936]

Alan is this what you were looking for ?

http://www.steves-workshop.co.uk/tips/lathetech/eccentrics/eccentricindex.htm

[Alan White 1Participant @alanwhite1]

Thank you gentlemen I have now put it on my computer for quick calculation

Alan

[Malcolm BEAKParticipant @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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