3 Jaw GS Chuck – maintainence / stripdown?

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3 Jaw GS Chuck – maintainence / stripdown?

This topic has 5 replies, 3 voices, and was last updated 4 November 2010 at 12:53 by Beagle.

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3 November 2010 at 12:16 #5274
Beagle
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@beagle
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3 November 2010 at 12:16 #58057
Beagle
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@beagle
Hi all,

I’ve just bought a second-hand Pratt Burnerd 4 inch, 3 Jaw GS chuck, with the factory fitted “made for Myford” backplate. It looks to be in excellent cond. and of low use.

However, the chuck is quite tight to operate and has a slight notchiness to it as it rotates. I’ve already removed the jaws, cleaned and lubed the scroll face, but it’s not much better. I also quickly tried removing the backplate to gain access for a full stripdown, but it wouldn’t budge easily so I left it for now.

Is this tightness / slight notchiness just a symptom of low use and tight manufacturing tolerances and will free-up over time, or does it sound like it would benefit from a strip down and clean? If the backplate is removed and goes back on in the same orientation, I assume accuracy won’t be affected? Any top tips for removing tight backplates?!

Thanks,

– Clive
3 November 2010 at 16:43 #58066
KWIL
Participant
@kwil
You probably have some swarf trapped in or around the scroll plate itself. Mark the backplate and body with a marker. The backplates can be very tight, I have put genuine PB backplates onto PB chucks and they can be very tight indeed when new. I had to loosen the bolts and tap each in turn with a soft faced mallet to remove the plate again. Only loosen the bolts a half turn so that you do not end up trying to drive the plate off one sided, when it has moved equally, try another half turn. Worked for me.

Edited By KWIL on 03/11/2010 17:02:37
3 November 2010 at 23:29 #58096
ady
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@ady
Wots the runout like?

With old brit stuff…

If it aint broke, don’t try to fix it.
4 November 2010 at 12:52 #58144
Beagle
Participant
@beagle
KWIL – cheers I’ll perhaps give it another go when I can find a spare half-hour.

Ady – The guy I bought it off DTI’d it for me with a test bar in it and it was reading between 2-3 thou about an inch from the jaws. (I’ll confess to having not yet checked it on my own machine yet). I subscribe to the if it aint broke theory, but I guess that was partly my original question – it’s stiff to operate and a bit notchy, and cleaning the scroll through the jaw slots hasn’t helped – therefore is it broke, or just tight?!

The two old Pratt 8 inch 3 jaw GS chucks on my grandfathers Colchester Master were both loose enough that you could whizz the key around with 1 finger. I’m guessing that’s too loose, but it’s all I really have to go off.
4 November 2010 at 12:53 #58145
Beagle
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@beagle
Sorry for the double post – got a website error the first time, but it appears to have posted anyway. Can’t see a delete post button…

KWIL – cheers I’ll perhaps give it another go when I can find a spare half-hour.

Ady – The guy I bought it off DTI’d it for me with a test bar in it and it was reading between 2-3 thou about an inch from the jaws. (I’ll confess to having not yet checked it on my own machine yet). I subscribe to the if it aint broke theory, but I guess that was partly my original question – it’s stiff to operate and a bit notchy, and cleaning the scroll through the jaw slots hasn’t helped – therefore is it broke, or just tight?!

The two old Pratt 8 inch 3 jaw GS chucks on my grandfathers Colchester Master were both loose enough that you could whizz the key around with 1 finger. I’m guessing that’s too loose, but it’s all I really have to go off.

Edited By Beagle on 04/11/2010 12:55:35
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