Cleaning up internal thread on Bridgeport quill nose cap.

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.

This is an idea for a tool as the one pictured would not fit (or maybe it would if you removed the pin and reattached once in the hole):

https://www.zoro.co.uk/shop/cutting-tools/combined-drill-and-countersinks/rc2000-medium-reversible-countersink/p/ZT1126465X

You could get an internal screw cutting tool and run round the threads by hand to clear out any debris, worth a try!

Tony

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.

The screw is there to stop the collet turning when the drawbar is tightened. Get rid of it and see if that makes any difference. Neither of my R8 mills have the screw fitted.

Andrew

If you remove the alignment pin and fit a collet without one, does it run true then? If not, it's probably the inside of the quill that is burred from when the pin was damaged. I would die-grind a very slight low spot at the pin exit.

+1 Took it out of my BPT a long time ago. You should be able to remove any burr by careful use of grinder as suggested by Pete Rimmer.

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?

First, establish that you have a problem. Put your fly cutter in and see if it runs true or not, but make sure the slot isnt aligned with the pin hole or any burr might fall into the slot and mask the problem.

If you think there is a burr around the pin hole then yit should show up as a shiny spot. You might also try using a magic marker to black the shaft of your flycutter and then the burr will leave a shiny scratch on that.

If you fid that you do have a burr, use your dremel and remove the smallest amount possible to createa low spot instead of a hump. Don't try to chuck it up and turn it, it will almost certainly make things worse.

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?