Bantam Bearings

Hi,
Trying to get a collet chuck to clock true on my Bantam has been a impossible task. Getting a TIR of about 7/10ths total, but never in th same place - ie., 3/10ths in one part of the rotation, 3-4/10ths i another part and never in the same place twice.
My neighbour who's a toolmaker thinks there could be a problem with th headstock bearings.
Anybody got any ideas?
Thanks, Pau
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As its an inconsitent error, could well be headstock related. Have you clocked it with a small loading in situ? If there is a minute amount of end play or bearing wear this might contribute to these erratic errors, and a light load may help show this up, Just a thought..
Mike

Mr Crane wrote:
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So, why are you trying to dial in the collet, before running same dial on the spindle? As long as you are there, and set up to measure... Start as close to the possible sources of error as you can, and work your way outwards.
Check for runnout. Radially, as well as axially, on the mounting faces
Is the workpiece reliably round? A couple sizes of gage pins are a pretty cheap investment. If yer gonna buy some, get them in pairs. They are a handy tool for checking dovetails and similar tasks.
Please dont tell us you are dialling off the inside face of the collet. That would be wasted time. Dialing off the outer portion as well as the inner portion of the ground surface that the collet seats on, can give an indication as to how straight the chuck is mounted to the spindle.
That's a couple ideas, anyways.
Cheers Trevor Jones

Trevor Jones Wrote:
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We've checked the collet taper in the chuck itself, the backplat spigot and several places on the spindle nosepiece - all display thi "notching" effect, hence the suspicion that it's the bearings
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Mr Crane wrote:
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Are they Ball Bearings? Preload adjustable?
If so, try loosening off the preload to see if it smooths out.
Colchester Bantam, yes?
<shiver> Gamet bearings?
Cheers Trevor Jones

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Check the spindle endfloat first.Use a hammer and a solid block of wood on the spindle nose to seat the bearings and then adjust the endfloat.If it`s springloaded endfload as some of the Colchesters use make sure that the part the springs press upon is free to slide.When you are confident there is no end float then check radially.If the turned finish from the machine is acceptable I wouldn`t bother about it. If you need super accurate concentric parts get soft jaws and learn how to use them. By accuracy I mean better than 0.0005". Mark.

snipped-for-privacy@ems-fife.co.uk Wrote:
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There is a threaded collar on the outside (ie., non-chuck) end of th spindle which is used to take up any slack. We've followed the manual tightening it so that it is still free to turn by hand - still gettin the notching. I think it's new bearings if I want < 4/10ths, and Gamet are a bit expensive, so I hear..
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