[CAUT] Bushing cloth thickness

[Fred Sturm]

	Spurlock's sizing cauls for .146" are .227", #1 caul is .185", and  
final #2 is .149" (at least that's what mine measure. Bill could have  
changed his specs since I bought mine). This means that there is a  
total of .081" to make up between sizing and the pin size itself, and  
a little less to allow for "frictionless" movement. Interestingly  
there is .042" between sizing and #1, but only .036" between #1 and  
#2. I'm not sure what Bill had in mind (yes, I know, I should ask him  
<G>), but suspect he was thinking in terms of .045" or so felt, and  
that the gap between #1 and #2 would be smaller allowing for the  
compression of the first layer of felt in the clamping process (the  
#1 clamp has wood on one side, #2 has felt on both).
	Me, I use mostly BU-6 and BU-3 from Pianotek, which measure .038  
and .043 using my micrometer with its friction brake (.043" only when  
the mortise is larger than the sizing cauls). I find a very loose fit  
with the caul gives the best long term results. As I mentioned some  
time ago, I'd druther have #1 be .190 or so, to hold the felt a  
little firmer for cutting purposes. And I added a layer or two of  
scotch tape or other tape to some to experiment, and considered  
asking Bill to make me up some custom ones. But I get by just fine  
the way I do it now, so it's a low priority.
	Ed, I wonder at your using spring clamps, but saying you don't want  
heavy clamping pressure. Seems like that's a contradiction, but maybe  
I don't know what you mean by spring clamps. The cauls only apply  
pressure to the extent they are wider than the gap between the  
mortise and the felt size plus a bit of glue. Very little to none in  
my technique. The caul mostly just holds the felt in place while the  
glue dries. I have had no problem with felts falling out, so I assume  
this is all the clamping needed. I also iron all the bushings briefly  
(1 to 2 seconds tops), which probably helps with "grab" a bit. The  
short time doesn't allow the glue to become liquid enough to  
penetrate the cloth much.
Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu



On Jul 31, 2007, at 9:08 AM, A440A at aol.com wrote:

> Fred asks,
>> Do you use cauls different from  Spurlock's standard sizes? I find  
>> they require considerably thinner cloth than .053. <<
>
>      For Steinways, I use the stock felt with spring clamps on the  
> balance rail, and, usually, .162" cauls  on the fronts.  For max.  
> longevity, I try to avoid thick glue and heavy clamping pressure,  
> as I feel that it basically turns the back of the cloth into an  
> inflexible matrix, leaving less actual cloth to absorb the force of  
> keys hitting the pins.
> I once mixed up some hide glue, very thick, and began gluing the  
> various felts to wood.  I then thinned it down, and glued the same  
> felts.  Then, thinner yet.   It appeared that the thick glue  
> captured more of the felt when pressure was applied, effectively  
> rendering the "felt" to be thinner while supported by a much  
> thicker glue/felt base.  It also made it more difficult to remove.
> Since I am now rebuilding actions I did 20-25 years ago here at  
> Vanderbilt, I really enjoy the ease of removing backrail cloth,  
> damper felt, upstop rails, etc. that I glued with thin hide glue so  
> long ago.
> hope that helps,
> regards,
>
>
>
>
>
>> About humidity effects, It seems like the felt is a bigger factor,  
>> as high humidity yields sluggishness. The idea being that felt  
>> will swell, closing the gap, while the gap becomes wider due to  
>> expansion of the entire key (or button). I guess if there is  
>> crushed wood, though, that would tend to swell in high humidity,  
>> also closing the gap (kind of like what I imagine happens with  
>> pinblocks and loose pins).
>> Regards,
>>
>>
>
>
>
>
>
>
> Ed Foote RPT
>
>
>
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