Drilling Conical Holes

Bob

Thanks Bob but the hardened point needs both to 'rock' in the point of the hole whilst at the same time, maintain an accurate positional register in the detent. It's for a unipivot tonearm BTW, where minimum friction is desirable. I had thought of synthetic ruby clock bearings but they're a little on the rare side in the UK.

So you can't drill the hole, but have to grind it with maybe some brass and diamond/grinding paste.

But I guess you should get the ruby bearings somewhere. Maybe they have what you need: They do have an English page, but I didn't find rubys (just brass bushings). Don't ask me to order for you, they are a**holes.

Nick

The flat is produced by the chisel bit of the drill. The only way I can think of round this apart from tiny boring tools is to try a conical D bit. Im not even sure that would work, as at the tip there is no relative movement to do the cutting. have you tried a 'split tip' drill? Am I right in assuming the hole is conical, wide at the top, tapering to a point, but a different angle to the point on the end of the thing which sits in it? Would you get away with a round bottomed hole? the hole is in the grubscrew isnt it?

Dave (whos pondering it now...)

Could you just use the dent made by a sharp centre punch and hammer? If the hole needs to be deeper, how about drill the hole with a normal drill and then finish the bottom of the hole with an identical drill which has been accurately sharpened to a point (might work) or form the bottom of the drilled hole with a tight fitting hardened rod with an accurately sharpened point, like a countersink again.

Scrim

drill a flat bottomed hole

then turn a plug with the cone machined into the plug

press the plug in the hole

from "Avondale Audio"

Not at all rare but they wouldn't do what you hope. Clock/watch jewels have parallel holes rather than conical. Admittedly the diameter is between 0.08 and 0.32mm but not 'zero'.

If you call Cousin's technical advice on 01708 380180 they may be able to advise you as to the suitability for your purpose.

JG

And, with a little thinking, it is clear why it is that way (and has to be). If it would just be a conical (dead end) hole, the needle's point would either touch the ground and have no guide sideways, or -if the point is not sharp enough- have a guide sideways. In the later case, a through hole would do the same job.

Nick

Difficult problem. Drills will not drill to a point as the point can only be thinned by a finite amount.

How deep is this hole and what diameter?

As someone mentioned a D bit may do it, but with a real point it would be rather weak.

Now the scale of this problem might help others to help you ;)

Wayne...

Thanks again for all the tips and suggestions particularly the ones about the centre punch and the round bottomed hole.

The conical hole has to be made in an M3 grub screw and is sufficiently deep to guide in the steel point during assembly or should it become dislodged. The angle of the hole is greater than that of the pin which has to both rock and rotate about this axis. I suppose the pin diameter will be around 1.5 -

What I believed was possible was to buy a drill bit with an infinitely sharp point but thinking a little harder, this of course does not exist.

Hope that helps in the quest.

The balances on some of the cheaper end of production use cup and cone bearings (mainly in alarm clocks and others with pin pallet escapements) with a cup shaped as the OP is looking for. These are available from clock repar suppliers. They are more likely to be glass hard steel than ruby, though ruby (synthetic of course) may be available.

Cheers Trevor Jones