[CAUT] Mason & Hamlin agraffes

[Douglas Wood]

A couple of things about brass that haven't been mentioned in this  
thread:

1. I'm told that machinists generally have a second set of drill bits  
for brass whose cutting edges have been ground to have the cutting  
angle greater than 90û. That is, the angled cutting edge on the tip  
has been "dulled" by running a stone across the inside of the flute  
so the part that actually contacts new metal has a sharp edge but at  
greater than 90û. Think of taking a small slip stone and holding it  
nearly parallel to the drill bit and "touching" the cutting edge.

The same can be done with these reamers. It greatly reduces the  
tendency of the bit to grab the brass. !

2. Brass gets harder and more brittle with age. (As in more prone to  
breakage, and more likely to make noise!) Crystal structure changes.  
To thoroughly renew the brass, heat it red-hot (don't quote me  
exactly on this, I've not actually done it), and quench it in water.  
The opposite of steel. It redoes the structure from getting coarser  
over time to being very fine again. Dunno how close to new you can  
get. Perhaps there's a machinist among us that can comment?

My experience is that even 20 years is enough to have new brass sound  
different.

Not to mention 3. There are different kinds of brass, as in the red  
flat-topped Steinway agraffes we all love so well. They're harder-- 
try the scratch test.

Doug Wood


On Jan 7, 2008, at 7:05 PM, Donald McKechnie wrote:

> Alan, Mark and Fred,
>
> Thanks for the tips on the proper use of the reamers. Fred, I can  
> see the radius difference by using a magnifying glass on the reamer  
> I have and zooming in the picture on the MSC site. The reamer I  
> have looks like a countersink with a pilot point. The one on the  
> MSC site has a gentle radius transition starting from the point.
>
> I will go with the polishing suggestion Alan mentioned if I can  
> find a proper polishing tip locally. Otherwise, it will be the  
> slower method as I want to try fixing the buzz as soon as possible.  
> This problem is getting on my customer's nerves a good bit so I  
> would like to be the hero sooner rather than later. :-)
>
> Thanks,
> Don
>
>
> Don McKechnie
> Piano Technician
> Ithaca College
> dmckech at ithaca.edu
> 607.274.3908
>
>
>
>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/caut.php/attachments/20080108/00cf1525/attachment.html