Ever since I have been using it, the collet aligning screw on my Bridgeport mill has been broken off. I have just realised there is a tiny nub still poking out which could be touching the collet, so yesterday I set about removing the nose cap. This was extremely tight (after removing the set screw) and it took a 4 foot bar on a pin spanner to get it off. I have now cleaned up the nose piece and tried it in a friends mill. It screws in perfectly and almost by hand, but on my mill is is still very tight. I think the thread for the set screw may be protruding into the thread for the nose piece and the threads for the nose piece may be a bit rough / burred as well.

My problem is that I can't see any way to clean the threads. This is compounded by the very limited space (about 4mm) between the threads and the piece just inside of them.

Any ideas would be greatly appreciated.

The problem I first mentioned is now solved but a much bigger problem has come to light which I will probably post a seperate question about tomorrow.

I have put a new collet locating screw in but collets still run out of true. Only about 1 thou on the side of the collet but at the edge of a 4 inch face cutter the run out -up and down- is huge.

Thanks Pete and KWIL, excuse my ignorance but when you say try a die grinder, do you mean dropping the head, removing spindle, setting it up in a lathe, using a taper adapter and skimming it, or taking a very fine stone in a Dremel and lightly touching the inside of the spindle where the locating key hole is?

I have checked the run out on the bore of the spindle and found it to be a fraction under 1 thou. I believe when new, the acceptable run out was 3/10ths of 1 thou.

As a new spindle is £800 I think I will have to put up with it for now.

Would you accept say 8/10ths of a thou run out?