[pianotech] Scary Experience

[Al Guecia/AlliedPianoCraft]

When installing TP bushings where none were before, do you use a drill bit 
or a reamer to enlarge the hole? What size is best?

Al

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From: <pianoguru at cox.net>
Sent: Monday, December 08, 2008 4:10 AM
To: <pianotech at ptg.org>
Subject: Re: [pianotech] Scary Experience

> Hi Will.
>
> I agree that it is a good idea to consider adding plate bushings in cases 
> where there were no bushings in the original design.  There are many 
> things to take into consideration, but today, I would never design a piano 
> without them.
>
> My experience in manufacturing has been with Baldwin and Mason & Hamlin, 
> but my experience in rebuilding has been more with Steinway than either of 
> the afore mentioned.
>
> I remember that I was shocked to find the impression of the tuning pin 
> threads in the holes in the plate in a rebuilding project, many years ago. 
> That piano was a Steinway, not to say that it might be more common in 
> other pianos.  As I said, most of my rebuilding experience was with 
> Steinways.  In any case, when I took note of certain tuning pins that had 
> a serious tic-tic-tic problem, I discovered that after removing the pins, 
> these were the very ones that revealed a clear impression of the tuning 
> pin threads in the cast iron surface within the holes in the plate.
>
> Regarding plate bushings, many manufacturers will say that they serve only 
> one purpose, to center the drill in the hole.  I would say they serve a 
> more important purpose, to prevent direct metal-to-metal contact between 
> the tuning pin and the plate.  But, it does serve to center the drill 
> bit.  I would prefer to center the drill bit at the BOTTOM of the hole in 
> the plate, but plate bushings center the bit at the TOP of the plate hole. 
> With modern CNC machines the drilling can be centered on the bottom of the 
> hole, regardless of the center hole of the bushing.
>
> Frank Emerson
>
>