I’ve been wracking my brains trying to work out what the problem is with this Chuck and Jaws. It’s not too easy to take accurate measurements of certain aspects of the design without a suitable jig and possibly specialist measuring equipment so I gave up on that idea. As a result I’ve tried a couple of different options. I tried just fitting the inner fixing screws but on tightening they wanted to move the jaws off centre so to speak. I then tried fitting just the outer ones and it was marginally better. What I believe the problem is, in spite of the fact that the accessory jaws have a “register” (tenon) that mates with the Chuck jaws, is that the screw holes are in slightly the wrong place. As a result the accessory jaws are pulled off centre by the fixing screws.
A long time ago I noticed that Axminster chucks, at least the two SK100’s I’ve owned, use standard Cap Head Socket Screws to retain the accessory jaws. There are also over size counterbored holes in the accessory jaws. As a result the fixing screws don’t overly effect the position of the accessory jaws on the Chuck. Contrast this with some other makes that, for some reason use non standard Countersunk Screws in a fairly small countersunk hole. If, big if, the holes are always in exactly the right place then this should not be an issue.
It seems on my particular example either the M5 tapped holes in the Chuck jaws are slightly off or the holes in the accessory jaws are? I think I can fix this by using different screws and perhaps a little light fettling. It shouldn’t be necessary of course. Maybe I’ve just got a rogue example or maybe there are more out there like this?