[pianotech] Brass Rail

[Roger Gable]

John,
The thread used by many (if not all) manufacturers for the brass rail is a 3 
x 56, where 3 = clearance diameter of .099", and 56 = threads per inch. At 
the time these pianos were manufactured the Unified Fine Thread (UFT) 
standard (which actually wasn't standardized until 1918) called for the 
number 3 shank to incorporate 56 threads per inch. It wasn't until after 
W.W.II that the standard was changed to the current 48 threads per inch. I 
suspect the clearance diameter may have been changed slightly, but I can't 
find any reference to that. Looking through my machinist catalog, which 
contains 143 pages of taps alone, there is no mention of a 3 x 56 (and 
consequently no dies), but only the 3 x 48.  I noticed this change when I 
exhausted the last of the original specification brass butts and screws from 
an American Piano Supply package. American Piano Supply went out of business 
about 1995. They must have had, or obtained their taps and dies from, 
someone who still had the original pre W.W.II tooling equipment. I suspect 
Schaff exhausted their supply of the original screws and butts about 10 
years ago. The Schaff's machinists would have most likely been unable to 
obtain any taps or dies to manufacture to the original specification, hence, 
they used the closest thread available today..
Roger Gable

----- Original Message ----- 
From: "John Ross" <jrpiano at eastlink.ca>
To: <pianotech at ptg.org>
Sent: Sunday, September 19, 2010 11:15 AM
Subject: Re: [pianotech] Brass Rail


> Thanks Ron.
> What brought it to mind was that Micro-Mart is having a sale, and they had 
> some small taps and dies, 1/2 price.
> #4-40 is the only one for #4.
> John Ross
> Windsor, Nova Scotia
> On 2010-09-19, at 3:13 PM, Ron Nossaman wrote:
>
>> On 9/19/2010 12:25 PM, John Ross wrote:
>>> Hi Joe,
>>> I have forced the screw to rethread, but thought if the proper die was 
>>> available, I would buy it.
>>> Thanks.
>>> John Ross
>>
>> Hi John,
>> It's a #4 screw, but a non-standard thread pitch. I don't have a thread 
>> gauge that goes finer than 40tpi, and these screws seem to be a finer 
>> thread than that. They're somewhere around 42tpi, I think. If they exist 
>> anywhere in the world new, I sure don't know where it would be unless 
>> someone makes a M2.5 x .6 metric screw.
>>
>> Ron N
>
>