[pianotech] Plate screw problem

[Ron Nossaman]

On 7/15/2011 9:00 AM, David Renaud wrote:
> Also I recall someone in a class suggesting they like to go with new
> screws.......perhaps someone that had this experience before and
> determined not to go there again.

New screws are my first choice, for reasons you're discovering.


> Any warnings regarding a carbide bit attempt? I don't have experience
> drilling metal. Sound right to you.

Sounds like near certain disaster to me. A decent quality bit wouldn't 
have broken drilling a mild steel bolt, unless it was a small diameter 
bit and you forced it badly. The cheap bits I've come across tend to 
either be too soft to use, or more likely too hard and brittle. A bit 
that was improperly tempered (optimistically assuming it's made of an 
appropriate steel in the first place) isn't going to do you any favors 
when you try to drill out embedded pieces with a carbide bit, assuming 
you can find one long enough. The whole thing being deeply buried under 
the plate doesn't help at all either.

I think I'd try Pianotek's 3/8" extractor first. I'd get the biggest 
soldering iron I could find with a tip that would just fit through the 
plate hole and long enough to reach the screw stub, unless it's broken 
below the block surface, which is most likely. I'd pick out whatever I 
could get by any means I could devise , any broken drill bit pieces. 
Then use the extractor to bore down to the top of the screw stub. I'd 
then chuck a 3/8" maple dowel into the drill, and spin it on the top of 
the screw until the smoke poured out in a dense cloud. That'll heat the 
screw. I'd give it a few minutes for the heat to travel the length of 
the screw then do it again, and maybe a third time. When you've got a 
screw that's too hot to touch bare handed embedded in maple, it's going 
to dry that maple out and it will shrink away from the screw slightly. 
Then, slowly and cautiously, use the extractor to try to either surround 
the screw and core it out, or engage the top and carefully back it out.

Or you can cut out the inner rim underneath the block and attack it from 
the bottom.

And just say no to cheap TiN coated drill bits.

Ron N