Drilling problem

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

In article , Jonathan Barnes writes

(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

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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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

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

I would suspect worn jaws as another possibility

Cheers Tim Tim Leech Dutton Dry-Dock

Traditional & Modern canal craft repairs

So it should - turning it compensated any error in the chuck ??

-- Steve Blackmore

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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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

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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