bcd mill - stuck key

I am cleaning up a BCA mill / jog borer. It is preety old.

I was removing one of the nuts holding the dial collar on and the spindle broke , - about the last 5 mm. Nut was coming off fine. Anyway , I am trying to see if it means a new leadscrew which would be a real pita. I can't get the parallel key out of the keyway. Any suggestions or indeed bca renovation advice gratefully received.

Edited By capnahab on 25/02/2012 17:13:21

Try holding the key with a Toolmakers clamp and wiggling it out or get a thin bladed screwdriver under the exposed end of the key and lever it up.

Tony

Could try a coid chisel (small) make a groove on both sides of the key then side cutters to remove

VC

Two ideas come to mind.

One is to use something like a centre punch on the exposed end and try to hammer that end up. Once it is moving, then it should be possible to lever it out.

The other idea may be to put something between the other end, and what looks like a thrust washer and then lever it out.

I have used the first idea reasonably successfully although it does rather write off the key.

Regards,

Peter G. Shaw

just grab it with the side cutters . Works . but marks the key .file up or replace key

Try a small chisel(narrower than the key)on the open end of the key way under the key, with a long taper it should lift the key out without damage, just go easy with the hammer. Maybe the key had been loose, and someone loktited it in, works well, even worse/ better if it locks the shaft as well. Ian S C

1/ Small thin (Watchmakers) screwdriver under the key if any/enough gap rap with mallet.

2/ Hold a Centre punch to the front edge angling it upward and tap with hammer should drive it up and out leaving only a puch mark to dress out on the end.

Is it the last portion of thread in the pic that you have broke off? if so screw on a old die of the right thread offer up a bit of bar to the existing screw end and weld a chunk on, machine/file/dremel to suit diameter then unscrew the die thus ensuring the thread is cut matching the remainder.

Regards

Paul

Old aircraft engineers proverb, if in doubt give it a clout.

regards Mark P

Or Mark P,if at first you don't succeed, get a bigger hammer. Ian S C another a/c engineer

These keys are normally tapped in from the threaded end. They often use a special jig/die to keep the key ‘fair’ in the slot. That is why the key is rounded the led in end and is usually a little oversized.

To get it out all the way suggested are valid except I would a narrow ‘Keyway’ cold chisel rather than a punch and would start my attempts with a pair of ‘Side Cutters’.

One gets a lot of these little devils in small chain saw engines.

Rdgs

Dick

PS do not use _Paul_'s die trick.  Dies do not cut being when being un-scerewed! 

Edited By Richard Parsons on 26/02/2012 10:37:58

Edited By Richard Parsons on 26/02/2012 10:39:15

If all else fails, and most of the above should work, try drilling down thru the key and tapping the biggest possible size. Then turn the first two threads off the end of a screw and try jacking it out, works on big keys, might not be enough room in your small key.

A clever feller would perhaps put the die on "backwards" so it cuts it's way off

Thanks Chaps, just for interest it came out with these side biters that I found eventually , think they were my dads. pints to mark and richard.

now back to the broken lead screw spindle.

I am likely to end up replacing it with something more user friendly but has this screw got a name ?.

cheers.

Edited By capnahab on 26/02/2012 12:03:33

Right, now that you have done the difficult bit it is time to do the easy job. Scrounge, buy or make a piece of stud, turn off some thread to fit the hole you are going to drill in the leadscrew and Loctite (638 for choice) the two together. I would have said drill, tap ans screw in (with Loctite) but there does not look like a lot off meat due to the keyway slot.

chriStephens

PS if you don't trust 638, you can always add a cross pin to be doubly sure.

How about making a longer nut with one end shouldered down to just less than the diameter of the shaft where the key is. Make the shoulder just long enough for it to grip the handle that the nut holds. I think the length of thread remaining would be enough to retain the handle.

Les.

With reference to the comments about the die, does a die cut both ways?

If not is there a correct 'way round 'to use the die. I was looking at this only a few days ago and the die seems to have the same 'start' both sides.

Hi Capnahab, depending on your skills and confidence, you could always build the end of the broken thread up with weld to the length required without distroying to much of the thread you have left, and then turn the new bit to size, then with a screw cutting tool line it up with the thread that is left and recut.

Regards Nick.

Hi David

"Does a die cut both ways?" - in my experience yes - but - I'm given to understand that the die should be used with the side with the information marked on leading, as the entrance to the die is chamfered to some extent to help with starting the cut. Using the die the other way round you haven't got this lead-in so you're trying to cut full depth right from the outset. I've got a chipped M12 die that tesitifies to this!

Now the other bit of the "but". On one job I that did, I needed to thread as close to a shoulder as I could, as the length of thread was only about 3 turns maximum, and I didn't want to extend the thread any more than I had to for aesthetic reasons as well as avoiding the shaft end projecting beyond the rest of the finished apparatus. This short thread length was quite adequate, as what was being screwed on was a flange to stop a hand wheel coming off the end of the shaft with the thread, and as everything was "handraulically" operated there were no large forces. Using the die the normal way round left only just over 2 turns engagement for the flange, but by reversing the die and following down the already cut thread I was able to extend the thread to very nearly the shoulder and got the best part of an extra turn engaged. The flange then just needed a small countersink to allow it to snug right up to the shoulder. The result was a much more secure fastening.

So yes in my experience they will cut both ways but it isn't necessarily recommended.

Keith

well gents , after a bit of cleaning its back together. The key required major gender reassignment surgery and is now a much better fit.

the double slotted screw goes on about 2 turns of thread. Haven't tightened it up yet but I think i will see how it goes for the time being.

Interestingly it seems to be the same thread as this bolt , which I think i metric 0.8mm/

Edited By capnahab on 26/02/2012 22:08:42