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Chuck backplate mistake

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Paul Ainsworth10/11/2019 18:44:51
97 forum posts
15 photos

Ooops, I've taken a smidgen too much from the nose hole of a backing plate I was making.

Should I/Can I

a: shim it (beer can fits great)

b: make hole bigger amd sleeve it/loctite

c: bin it

jimmy b10/11/2019 18:47:23
671 forum posts
38 photos

a or b.

not c!

I made one of my back plates oversize to the register to allow for fine tuning of run out.


daveb10/11/2019 19:29:18
623 forum posts
10 photos

I've always made the hole as snug as possible because it seemed to me that was how it should be. One of my original Myford supplied chucks was so tight it needed a light scrape before it would fit the spindle. I read several arguments about the fit, more than one stated that the hole should not be a close fit because the register was the back face and not the bore, the thread took care of centralising the chuck. Several of the aftermarket backplates I've bought are a good rattling fit despite which the chucks seem to fit with acceptable run out (for a 3 jaw chuck).

I wouldn't worry to much about a smidgin but you need to keep it below a gnat's whisker.


old mart10/11/2019 19:47:24
1980 forum posts
151 photos

If the spindle is threaded (you didn't say so) then just screw it on a few times to settle it down and then true up the front face ready for the chuck. I have a number of screwed on backplates with registers from 0.0005" clearance to well over 0.010" slop, and they all run true and repeat.

David George 111/11/2019 07:04:27
1333 forum posts
447 photos

Hi Paul I would bore out and bush the hole as it is the location that matters. Use the same material, cast iron and Locktite as well as a life press fit then Finnish bore after finishing.


Mike Poole11/11/2019 09:24:01
2739 forum posts
64 photos

+1 for sleeve and rebore, I have always understood that the backplate should be a close fit on the nose register. The thread should be slightly loose to let the register faces do their work. I always bore and face the register surfaces at same setup and cut the thread to ensure they are true to each other, then mount on the nose and machine the chuck register. This seems to work for me. If the register is too tight on the nose then it will wear the nose.


Paul Ainsworth11/11/2019 09:28:26
97 forum posts
15 photos

Not threaded, it's for a DB10 Super.  A slight lapse in concentration and I took 0.2mm off instead of 0.02mm, must try harder as my school reports used to point out.

David is right in that it is this part that determines the position of the chuck, register is a push fit but the slack from behind it would throw the chuck out.

Bore out and bush it is then.

Thanks gents.


Edited By Paul Ainsworth on 11/11/2019 09:48:32

Howard Lewis11/11/2019 14:40:51
3605 forum posts
2 photos

Yet another vote for bore out and sleeve it, before boring to size


old mart11/11/2019 15:41:41
1980 forum posts
151 photos

Now it is revealed in its true form, I'm in the sleeve and bore camp, it should be fairly straightforward. If the sleeve is to be thin walled when in place, it would be easier to bore the backplate to the required size and make a fairly thick walled bush. Fit the bush and bore to size. The backplate then keeps the bush round when you finish bore it. Thin walled bushes are difficult to hold without distorting them.

Do check first that the projecting spigot on the spindle is parallel and not tapered.

Edited By old mart on 11/11/2019 15:44:03

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