Author Topic: Chuck question... how much runout?  (Read 4413 times)

Offline AdeV

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Chuck question... how much runout?
« on: August 06, 2010, 04:26:55 PM »
OK, another daft question from my inexcusable, errr, inexhaustible I mean, supply...  ::)

You're using a 3-jaw chuck, chuck up some round bar & turn down a bit until you're pulling off a nice continuous spring-shaped chip (or fur, if your cut is light enough). Now remove it from the chuck, turn it around, and clamp the freshly faced end in the 3-jaw.

Questions:

1) Approx what runout do you anticipate getting?
2) Does it matter if there's 0.003"-0.004" (or so) of runout if you're making (for example) a piston for a model engine? If yes, what's the maximum acceptable runout?
3) How can you be sure you've got your piece absolutely straight in the chuck, if the diameter of the piece is small enough to pass through the hole in the chuck?

Thanks in advance :)
Cheers!
Ade.
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Offline Tinkering_Guy

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Re: Chuck question... how much runout?
« Reply #1 on: August 06, 2010, 04:47:31 PM »
See http://www.varmintal.net/alath.htm#Truing for Varmint Al's take on trueing up his jaws.

M'self, I'm also considering either getting some MT3 collets and a drawtube, or making a drawbar and MT3-to-R8 adapter so I can use my R8 mill collets..
Tinkering_Guy
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Offline Dean W

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Re: Chuck question... how much runout?
« Reply #2 on: August 06, 2010, 09:25:46 PM »

Hey Ade;


1) Approx what runout do you anticipate getting?

Pretty close to the same amount inherent in your chuck.  More if that end still has the factory finish.  Also, if you have two
diameters that are quite a bit different in size, the error in the chuck scroll can really show up. 

Quote
2) Does it matter if there's 0.003"-0.004" (or so) of runout if you're making (for example) a piston for a model engine? If yes, what's the maximum acceptable runout?

If you are making that piston without doing it all in one setup, that .003" will give you a lot of grief.  The piston will have a ridge
somewhere along its length that won't play well with the cylinder bore, if it fits at all.  If you do what you describe, and cut the
the complete length of the piston, then it will be straight, (as straight as your lathe can make it).  Something like a piston should
be done in one setup.  No flipping ends.

There are quite a lot of variables involved in #3.  Condition of chuck, and it's jaws.  How far the piece goes into the jaws.  The
finish of the piece, and all that.
If the piece will go through, you have a pretty good chance when it comes to runout, but you are still going to get what ever
the chuck has in the scroll.  If you need it on the button, use a 4 jaw independent.  That works for me, if that matters!

Dean
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