Jamie t wrote in message
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N_Cook wrote:

Jamie t wrote in
message
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N_Cook wrote:

Dave Plowman (News) wrote in message
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In article ,
Eeyore wrote:



We only use LH bits only in the hopes that maybe the remainder will
spin out as we're drilling. Mostly for small holes where easy outs are
not practical. Even with that, our machinist still don't have much
better luck, than just simply drilling out the hole as close as possible
with a RH bit and run a tap down through it.

Most of the problems I hand over to the machinist have loctite broken
screws heads..

http://webpages.charter.net/jamie_5"



This is the situation I commonly find, small screws, written up as a tip for
others

To free seized equipment knobs
For the situation where the knobs are seized onto the shaft by rusted
grub screws,especially where the screw penetrates the shaft;
after you have butchered the grub screw slot try this.
And it is one of ten virtually irreplaceable knobs.
Make up some guide tubes,small enough to just slide into the hole
in the knob containing the grub screw,these tubes drilled on a lathe with
a clearance bore to take a drill bit. This drill bit usually needs to be
extended by brazing onto a longish rod (so the chuck of the
drill misses the face of the equipment).
Use some cutting oil and drill into the grub screw.
Ideally use left hand drill bits and left-handed power drill
rotation, such drill bits are available from specialist suppliers.
To convert a right hand drill bit well enough for this use grind the
cutting face back on the opposite rake angle, swarf clearance
is not relevant here. Often the bite into the drill bit
into the screw or the localised vibration or heating is enough to
shift the screw.
Now use a small "easi out"(maybe this is a UK trade name),but consist
of a coarse left-handed cutting thread on a coarse taper.
Wind into the hole in the grub screw and hopefully extract.
I don't use easi-outs as the smallest ones for this
purpose are very week and if it breaks you have
a lump of high carbon steel just where you don't want it.
Maybe appropriate for very large knobs only.
If this fails repeat the first procedure with larger diameter drill bits
and appropriate protection sleeves
until nothing remains of the grub screw,retap a larger hole and use
a larger grub screw for knob reuse.


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