Machine Threads in Pinblock, was WD-40

[Ron Overs]

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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