[CAUT] Jack speed - Teflonized cloth

[davidskolnik at optonline.net]

----- Original Message -----
From: Fred Sturm 
Date: Monday, November 13, 2006 11:37 pm
Subject: Re: [CAUT] Jack speed, (was Tight balancier
To: caut 

> On the subject of pinning friction, I have a couple questions for those
> who are talking about 6 - 8 grams for balanciers and/or jacks. 
> So we are on the same page, what precise methodology are you using to 
> measure? I assume parts are in a horizontal position. Is measurement at a 
> "standard" one inch distance from center? 

Fred - I may be wrong, and in any case, am assuming you have the part in hand (unmounted), but I have always measured at the end of the lever leather.  I'm not sure I know where the "standard 1" " comes from in this case.  Clearly this is an important question to clarify, as, lacking such consensus, we may as well be describing the resistance in colors.

>How are you eliminating the spring from the picture? 

I may be wrong, but I simply disengage the lower arm from the jack hole and, VOILA! You can measure both lever and jack.  The express version would, I suppose, be to hold the wippen in one hand from underneath, with my thumb and another finger, pull down the upper spring arm.  That works too.

I will paraphrase the points, hopefully accurately, in the remaining part of your post, as it is too long to copy completely, but difficult to edit.  I read three issues: 1) how to address current Steinway bushings; 2) how stable is any such treatment, and 3) what SHOULD the friction be at any of these centers.  I'm no expert on any of these, but I can relate my own experience and biases.

My image of this material is not really as cloth, but sort of more like putty?  Steinway, I believe, reccommends treating centers with methanol.  I think the idea is to redistribute the teflon particles in the cloth, molding around the center pin. The purity of the methanol is important in that an elevated water content would shrink the cloth, which is not the objective. I can not, at this point, offer any first hand report as to the method's efficacy.  With regard to reaming however, I do have some experience-based preferences.  I do not like use fluted reamers on this material. I don't think they are sharp enough to cut cleanly.  I make up roughened center pins which I carefully measure (to .0001" resolution) to have better control of the sizing.  With regard to stability, if Steinway can't get it right, why should you or I be able to?  I've come across extremes of tightness and looseness in newish pianos.  It may be like the original teflon.  You have to go through a few cycles, correcting the loose ones, then the tight ones, until you've stabilized things.  I would be careful if using a larger, cut centerpin, in that I would suspect that any burr could have some impact.

As far as #3 - the target friction - this would seem to be a thread in itself. (Oh yeh, I may be wrong.)  Since I haven't attended any conferences for quite a while now, my understanding of the current Steinway philosophy is a bit of a patchwork, but I have been given to understand that, as long as there is no side play, the objective (hammershank center) is as frictionless as possible.  I find this hard to accept, and would love to have the thinking explained to me.  

Regards -
David Skolnik
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