Dave Plowman (News) wrote:
In article ,
Dave wrote:
Have you ever tried drilling a self tapper?

Going back to your comments about having tungsten carbide drills for
PCB's, could you get a pilot hole in the screws and open it up with the
right sized cobalt bit, freshly ground, of course?

I've probably got the right size tungsten carbide. Bought a load off a
workshop that closed down - including the ancient but very good PCB drill
press.

My thinking is, that if you have one of those 12 V and tiny hand drills,
it would be ideal to control where the twist drill can wander. Just
angle the drill slightly, at 90 degrees to the direction of error, until
the tip is pointing down the centre of the screw and bring it upright
again.

I'd say there's a very real chance of breaking a small tungsten carbide
used hand held.

Only if it is used in a pistol grip power drill. I also make PCB's but I
use HSS steel drill bits in a 12 Volt mini drill. (I have no problem
with regrinding them at this diam.). It has a body of about 35mm diam,
that contains the DC motor, with a very small chuck at the end. It is
very difficult to put any side force on it, unlike a pistol grip drill.
Just let the bit do the cutting without using too much force to make the
bit cut. The only problem you might encounter, is if you you do break
the bit and part of it stays in the screw, you might be stuffed at
getting the broken part out.

That didn't look right. If the twist drill is wandering to the left, you
angle it to the left, until the drill cuts back to the middle of the
screw.

I could cut a cross with a Dremel to provide the centre?

That could shatter the bit, due to the cutting edge ramping up and down
over the cut cross. I wouldn't tackle it that way.

As an aside, many years ago, I had a series of Austin Minis and they
were notorious for the brake adjusters to seize up. One was so bad I
used an easy out to try and get it to move. Needless to say, the easy
out snapped. The tungsten carbide drill I had, drilled it as if it was
butter. After that, it was out with the blow torch and use heat to
release it. That never failed. :-)

Some years ago, I bought some tungsten rotary files, one was a ball
cutter, only about 3mm in diam. Something like that would be far better
to give you a centre.

Thinking about that, why not find what used to be a Fred Aldous shop and
see if they are still available? Our local one was closed down some
years ago and it was the only place I had ever seen them. They used to
be based in Manchester.

Good luck

Dave