Machine Threads in Pinblock, was WD-40

[Will Truitt]

Thanks Ron:

 

I always enjoy your posts as I almost always learn something.  Likewise for
your posting below.  

 

Will

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Overs
Sent: Wednesday, June 18, 2008 6:49 AM
To: Pianotech List
Subject: Re: Machine Threads in Pinblock, was WD-40

 

Hello Terry and Will,

 

Nice to see you posting Will.

 

Hi Ron!  I also use coarse thread as you do. However, I have tried tapping
the maple and found that it made the hole too big - I used the proper tap
for the given machine screw. I figured that the maple must have enough give
in it (compared to metal), that caused the poor fit.

 

I suspect there are two factors here which may be contributing to the
outcome you've experienced. Firstly, we prefer to use older taps which have
lost their very sharp edge when cutting a thread in maple. The duller
cutting edge will cut a slightly undersize threaded hole which will help to
produce a slight interference fit. The other factor is that lower grade
nuts, bolts and machine screws will tend to be more undersized when compared
to their higher grade brethren. This may lead to a looser fit when lower
grade fittings are used. When we machine the threaded bolt for the plate to
belly rail brace, because we make them in house, we can deliberately turn
them a little larger in nominal diameter to ensure an interference fit. When
cutting the threads for the plate perimeter bolts we actually use a bolt
with an off-hand-ground cutting slot, ground longitudinally into the bolt.
This also gives us the interference fit we are looking for.

 

 I've gone to simply drilling a hole a little smaller than the thread and
simply running a buttered (wax) machine screw into the hole (just like one
does with a wood screw). I seem to get the nice tight fit that way.

 

That will certainly work, but I do like to have a reasonably large area of
thread contact with the wood (this is more important for the plate to belly
brace, since the axial loads are very high). The slightly blunt tap is
probably the ideal solution for maximising contact area. If you only have a
sharp tap on hand, the application of a little Titebond in the threaded
hole, spread around evenly with a bottle cleaning brush also provides for a
nice interference fit.

 

Ron O.

 

-- 

OVERS PIANOS - SYDNEY

   Grand Piano Manufacturers
_______________________


Web http://overspianos.com.au

mailto:ron at overspianos.com.au
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