Drilling problem

I have been cutting over size holes in my lath, and I think I have found out why.
My drill chuck appears to be bent.
I have the chuck on a 3 MT, sleeved up to 4MT to suit the tail stock, but
when I fitted the head stock sleeve and tested a bar in the jaws it ran out 5thow close to the jaws, and 45 thow at about 9" from them, I rotated the bar in the jaws and the run out was about the same, so I presume the bar is straight, and it's the chuck that's bent.
Before I try fitting a new taper to the chuck I thought I would ask if anyone else had had similar problems and how they solved them.
-- Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
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Jonathan Barnes wrote:

Johnathan,
Machine a centre in the chuck, and then put a fixed centre in the tailstock then put up a bar beteen centres preferably a sine bar and run a TDI along its length towards the tailstock you mayfind that the tailstock is off centre which will cause oversize holes. You will find adjustment on the tail stock to bring it into line so the cetres are correct.
Martin P
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(Snip)
Watch these sleeves. I have one that I keep meaning to chuck out. When I put a drill in it in the tailstock I can *see* the tip wandering, even when the tailstock's adjusted dead-on.
Cheers
--
Nigel

When the only tools you have are a Bridgeport, a Myford, a Colchester and
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out
I have now tried checking my chucks.
I put a bar in the lath chuck and turned it so it ran true, I then clamped my drill chucks on it and clocked their tapers both at the top and at the far end.
I got the following results for the run out.
Jacobs 36 ( 5-20mm). 3MT + sleeve top 0.0095 end 0.0370 !
sleeve removed ( so shorter lengths ) top 0.0065 end 0.0205
Jacobs 34 ( 1-13mm) 4 MT top 0.0060 end 0.0080
HD Yama ( 1-13mm ) 3MT + sleeve top 0.0080 end 0.0160
Vertex keyless 1-13m R8 ( from mill ) top 0.0040 end 0.0080
It looks to me that chucks are not that accurate, but that I should replace the big Jacobs chuck arbour.
any comments or comparisons appreciated. -- Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
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On Thu, 23 Oct 2003 22:40:17 +0100, "Jonathan Barnes"

Put a clock on the bar, near the drill chuck being tested, just to eliminate bending of the bar as a cause of error. The support of the bar by the lathe chuck changes as it turns and you might see 3 per rev variations (or 4 per rev for a 4 jaw chuck).
Mark Rand RTFM
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found
clamped
replace
eliminate
lathe
rev
I turned the bar down to get it true and then ran the test without taking it out of the chuck. ( skim to finish, and with minimum protrusion from the lath chuck.) I have re checked, and it does run true though it is a little rough so I get about a thow jiggle on the dial. -- Regards Jonathan
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On Sat, 25 Oct 2003 00:23:13 +0100, "Jonathan Barnes"

So it should - turning it compensated any error in the chuck ??
-- Steve Blackmore
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it
get
That's right, my laths 3 jaw runs out a couple of thow, but the skimmed bar runs true, so I could then clamp the drill chucks to it, and measure how far their tapers ran out with a DTI on the lath top slide, turning the lath chuck by hand.
I was surprised by how far they actually ran out. -- Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
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On Sat, 25 Oct 2003 00:23:13 +0100, "Jonathan Barnes"

Sorry, I was actually referring to the _extra_ bending due to the weight of the drill chucks, not the original out of true that you have removed from the bar. More an exercise in dotting i's and crossing t's
Regards Mark Rand RTFM
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wrote:

it
get
of
the
Interesting idea.. I had not considered the rigidity of the rig.
as gravity acts at right angles to my measurement axis it should not make any difference, however a side load of 10 kgf produced a 10 thow deflection at the end.
I think that the gravity effect will not make a difference measurable on my crude set-up. -- Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
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On Wed, 22 Oct 2003 23:24:15 +0100, "Jonathan Barnes"

I would suspect worn jaws as another possibility
Cheers Tim Tim Leech Dutton Dry-Dock
Traditional & Modern canal craft repairs
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