good checking (was: wichita) caution: contains a plug

[Susan Kline]

At 08:03 AM 3/25/98 -0700, Jim Coleman, Sr. wrote:
>Hi Henry:
>
>In your post this morning you mentioned the "problem" of the hammers
>bobbling or not checking on a very soft blow. You specifically said that
>it did not bobble enough to strike the string a second time. The answer
>which Niimi and Edwards gave you is correct. Here's an example you can
>try. Push a key down so slowly that the hammer does not touch the string,
>pash through let-off very slowly. If you have repetition spring tension
>at all, the hammer will not drop down to check on the backcheck. Sometimes
>beginners think that this is a "failure" in not checking. However, it
>is showing the proper function of the repetition lever and its spring. With
>the slightest release of the key pressure, the jack will return under the
>knuckle and the key is ready for a repeat blow. Now, with just a little
>stronger key blow, the hammer will check.
>
>What bothers most people is that when they are checking for soft blow
>conditions at the end of regulation, a few hammers will check and some will
>not. This is due to two things primarily. 1. They may be varying their test
>touch slightly, or 2. there may be a very slight difference in the spring
>tension. Of course two other things can have an effect here and that is the
>key aftertouch unevenness and the non-precision let-off. Well OK, there is
>another thing and that is the unevenness of the bushing tightness or freedom
>from excessive friction, ie key bushings and flange bushings variation.
>
>Jim Coleman, Sr.
>

Hi, Jim

I can't remember if anyone has mentioned hammer tail shape and 
backcheck adjustment as being critical to good checking after soft 
blows. The better the wedge-fit between the tail and backcheck the more 
easily it will be caught, and the more leeway one will have when 
regulating spring tension.

When installing a few sets of hammers, I've shaped the tails using 
Bill Spurlock's (simple) jig with a sanding disk. I built it from 
his plans in the Journal. It puts a true radius (arc of a circle) 
on the tail, and leaves it quite smooth. You can choose what radius 
to put on, but I stuck with his suggestion, from his article. I 
believe it was 3", though I used 2.5" once. I've never failed to 
have hammers that check beautifully without roughing the tails 
when I've used this jig. The check distance was almost completely 
uniform even after different hardness of blows.

I made an adaptation to this jig, so it will (re-) shape tails of 
hammers which have already been installed on the shanks. At the 
convention I found out that Bill is selling a far nicer version 
of this himself, now. "Grand Hammer Tail Arcing Jig" he calls it, and 
he has designed it to accommodate both new hammers and those already 
mounted on shanks. $32 and well worth it, if you've ever struggled 
to get hammers to check well.

In case anyone doesn't know his address already:
Spurlock Specialty Tools
3574 Centelow Road
Vacaville, CA 95688

Phone/fax: 707-452-8564
E-mail: 74077.3053@compuserve.com

(This was an unsolicited plug.)

Susan



Susan Kline
P.O. Box 1651
Philomath, OR 97370
skline@proaxis.com		

"Relax! Between the inconceivably big and the inconceivably
small, there's an area where everything is perfetly conceivable!"
		-- Ashleigh Brilliant