"N Cook" wrote in message
...
"Peter" wrote in message
...
Wanted: an 1/8 inch or so hole in the porcelain of a bog cistern.
I've used this tile-hole cutter drill-bit on tiles before with no
problems.
But on cistern porcelain got through the glaze ok but no further in
than
about 1/8 inch deep.

Drilling porcelain is addressed in the DIY FAQ
http://www.internode.co.uk/diyfaq/drillfaq.htm

But on this usenet group I posed the same question (4 Aug 2005
16:02:47 +0100) and was recommended to use an ultrasonic drilling
machine. It's like an pillar drill SDS but with the bit driven at
multi-khz frequencies and plenty high impact force.
See: http://www.sonicmill.com/machine.asp

I am presently seeking inspiration as to how to track down a local
machine shop with one of these useful machines. I tried glass/masonry
companies but drew a blank.

Let me know how yo get on.


I made a dam from blue-tac and made a crude drill bit from the shank of an
old HSS drill bit.
Grinding two flats on the shank end to make a sort of screwdriver blade.
Repeated sharpening
3 or 4 times.
With this got down to about 1/4 inch but then got concerned about breakout
on the inside.
This cover is hollow on the edges so presumably made by all angle rotation
of slip/paste
in a mould. I doubt if the central area is hollow though.
Tried firstly finding the internal matching point by putting some bits of
magnet
in the hole and tracing with iron filings but didn't work convincingly.
Then thought I'd try a Megger and presumably because of the dam
of water it gave a resistance trace so could find minimum position.
Could even use a 30 Meg ohm DVM as order 10 to 20 Meg ohms.
I will continiue tomorrow as I don't know how thick the central area is .




Worked a treat.

Found a small rod magnet and waving that about the outside hole gave
a very clear indication in the iron fillings on the inside.
With successively smaller "lollypop" grind stones in a hand drill
gradually zeroed in from the inside. Thickness about 10mm.

A tennis ball (if dislodged won't smash things) ,made a small hole and a cut
into it
to load inside with
bits of lead. Glued a locator/protector to the ball valve to take the end of
the bit of brazing rod.
Cut a slot in a wooden wedge and for a refinement added
a 'crapometer' scale to the top surface of the wedge. Now just a
matter of working out a self return mechanism to the wedge to take it back
to the minimum flush setting.

Ah DIY

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/