4 jaw queries

When I stripped, cleaned and oiled my 4 jaw lathe chuck today, (it is a Buernard chuck as fitted to a Myford ML7,) I noticed that the jaws and their
slots were all numbered, presumably to ensure they are fitted together in the correct pairings. My question is why? I understand the reason for doing it on a self-centering 3 jaw chuck, but since the 4 jaws all operate independently it seems to me that as long as the threads are identical it should not matter which jaw goes in which slot. Can anybody explain?
The other thing that occured to me was how difficult it was to clean the tiny bits of swarf from the female thread in the backplate. Even gouging with a fine 1.0 mm screwdriver still left muck behind. Would a tap be a good idea or would it enlarge the thread?
Cliff Coggin.
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To clean the threads make or adapt a spring loaded pair of internal calipers with sharp ends to the legs, close under hand pressure, pop into the threadand alow to expand into the th1reagds agnd
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With the chuck resting downwards on the bench, use an old toothbrush in the thread, slowly rotating the body of the chuck.
Start with the toothbrush at the top of the thread and keep turning until it comes off the bottom of the thread.
It helps if the chuck jaws are open so that all the crud falls right out.
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Sorry, I didn't pick up on the ground-in dirt that you were implying.
Dousing the toothbrush in oil will slowly, after several applications, loosen up that dirt. The several applications being each time that you take the chuck off the spindle nose.
Of course the oil will slowly rot the toothbrush fibres, but discarded toothbrushes are ten-a-penny, at least in my household.
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On Wed, 12 May 2010 17:36:23 +0100, "Cliff Coggin"

It would only enlarge the thread if the tap was too big. I bought a tap for that purpose a while back and it works well; however,they aren't cheap!
Regards, Tony
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wrote:

Assuming that the spindle nose thread and the lead screw thread match each other metric-to-metric or imperial-to-imperial, then it should be a (reasonably?) straight forward matter to make a soft-ish (in relation to the metal of the spindle nose) tap oneself.
To alleviate any concern about widening the existing female thread my guess is that you could gash it for a very-negative rake angle (like as for brass cutting, but only much more so?)
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wrote:

clean the

gouging
be a

a
match each

(reasonably?)
spindle
my
as for

But surely the thread isn't used for location, only retention - there will be a 'register' turned on the spindle and chuck to actually locate it.
AWEM
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wrote:

Good point. I hadn't thought of that. Thanks to all for the replies about the thread.
Nobody has ventured an opinion about the jaw numbering so I guess it is as mysterious to all as it is to me.
Thanks again, Cliff.
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wrote:

Even
tap
bought
however,they
the
thread
(like
there
about
is as

I would expect that there might have been a 'select on test' assembly to get the right fit of jaw to slot to allow for tolerances in grinding the slots and jaws. If numbered you can get them back in the right slot!
AWEM
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I would agree with Andrew on this.Good quality chucks are selectively assembled for fit.Likewise if you by replacement jaws either hard or soft from Pratt-B they will require fitting by grinding the tenon slots. Mark.
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i suppose they are numbered so they get put back in the same slot and wear to that slot......mixing them would cause un-necessary wear on the other slots.lead screws.
i picked a nice one today 15 ..a four jaw that's independant...and then by swivelling a few levers at the back, it becomes a four jaw scroll..all jaws moving together...remains to be seen how accurate it is when its in scroll chuck mode.
you can also lock any of the four jaws...and move the independents in scroll mode...maybe handy for doing repetitive four jaw work ..i don't know yet .
all the best.markj
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