Allen Screw Removal

[jackrae]

I'm sure there's been articles about how to remove broken taps but I cannot find them. I have a somewhat similar problem.

In attempting to remove an allen screw from an aluminium pulley fixed to my drilling machine drive spindle I've managed to end up with the ball end of the key broken off and stuck into the screw socket.

So I need a way of getting the ball out and then getting the screw out - without destroying the pulley. I've tried coaxing it out with a magnetised rod but no luck.

I might try a little heat on the pulley to break the bond between the screw and the pulley, but first I need to deal with the ball end stuck in the socket.

Any ideas ?

jack

[mmaidnz]

I would try a hammer and pin punch to judiciously tap the ball from side to side,which should loosen it.Can you remove the screw with vise grips?If all else fails,grind the head of,and remove the remaining bits once you have the pulley off.That's assuming you can get to it,of course.Good luck.Hans.

[cardiffpat]

Hi, possibly you could drill around the broken ball with a dremel drill & carbide or diamond burr to loosen the ball.

When the ball is out possibly silver solder an allen socket into the damaged socket to remove, or use an easyout.

It's difficult to say without seeing it, access, cap or C/sunk ect.

[SteveW]

Guy,

Slightly different but I got a wayward roll pin out using one of the odd bits of TC tooling off the JB Tooling stand. Over past years I've pick up (bought) odd items for that "nothing else does it" moment.

In this case it was a 1mm solid TC end mill on a thicker shank. The HSS drill wouldn't touch it but the TC took the middle out of the roll pin and it came out easily. There's every chance these things will take the middle out of a broken allen key.

[Noddy]

I don't know about getting the ball out, but even relatively gentle heat will expand the aluminium pulley more than it will the screw shank and anything much over 100C will start to loosen any rust sticking it. A black and decker paint stripper would be my first choice for the heating

[jackrae]

I should have mentioned that the grub screw is buried deep down inside the boss of an aluminium pulley. I suppose the lesson learned is not to use a ball ended allen key to free off stuck grub screws.

So far I've tried making a hollow drill, a bit like a hole cutter, big enough to cut an annular groove around the screw. This was working quite well until the teeth chipped off. Now I've not only got a blocked grub screw but hard chips embedded around the outside of it preventing further use of a hollow drill. The second one rubbed its teeth off as soon as they met the previous one's chips.

I also tried dripping some caustic solution into the hole and eroding it with a brass tube but to no avail.

Looks like its now a case of sawing the pulley in half and buying a new one !!

jack

[Myford Matt]

What about drilling a hole next to the grub, levering/wiggling it into the new hole and then extracting it that way. Then drill a new hole and tap it for a new grub. Got to be better than sawing it in half.

MM

[chris vine]

Hi Jack,

Have you got the pulley off or is it stuck on the machine?

If it is free, a good way would be to take it somewhere and get it sparked out on a spark erosion machine. This is the way broken taps are often removed. Maybe someone on this forum has a small one in his workshop?? There are some designs around for home built machines.

Another thought if the pulley is off the machine is to heat it up and cool it slowly to draw the temper/hardness from the allen screw. I have not found much in the way of melting temps for Al Alloys on the web but alloy 1050 melts at 650C and you would only need perhaps 300C to soften the screw. This is the way I get broken taps out of things in my workshop, soften the tap and mill out it out with a dentists burr (secondhand). The dentists burr is for small taps obviously. I won't admit to breaking big ones!!

Chris

[JohnP]

Jack,

You may be able to use an alum solution to dissolve the steel. You'd have to build some kind of a dam if the screw is on a vertical shaft.
I'm not sure if alum attacks ali though - there's bound to be a chemist lurking somewhere on the list.

JohnP

[Noddy]

Alum is Aluminium sulphate, (or aluminium chromate for chrome alum(sulphur and Chromium have very simillar chemical behaviour under certain circumstances, so chromates and sulphates will crystalise together as a complete solid solution series))so it shouldn't attack pure aluminium, I'm not sure what else your pulley's alloy will have in it though.

I didn't know it attacked steel though thinking about it Ferrus sulphate is unstable in the presence of oxygen (from the air, thats what all the ochre in mine, bog and some spring waters is from), breaking down to rust and sulphuric acid, So I hope that the resulting acid finds it's old aluminium ion when it goes back to alum, rather than robbing fresh ones from your pulley...

use bluetack or plasticene for the dam.

Spark erosion or drawing the temper and drilling out sound like the safest ideas so far.
Keith