About Checking

[Paul McCloud]

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Hi, William:
    If your hammers don't find increased friction when you push them down into check, your angles may not be correct.  If you take a wedge shaped block and force it into a crack, you'd expect it to get tight, right?    The tail is arc-ed in a radius which is less than the radius of the hammer shank length, so that when the tail meets the backcheck, it acts as a wedge.  It's possible that the radius arc of your tails is too long (you may need to sand a tighter curve into them).
The backcheck is bent so that the tail will be caught in it.  The movement of the keystick is also in an arc which intersects the arc of the hammershank.  The movement of the hammer and keystick and their arcs causes them to meet and interfere with each other (a good thing!).   Where these two arcs intersect should be around the middle of the backcheck head.  The bottom of the backcheck should be closer to the hammer, and the top should be farther away (this is your backcheck angle)  This angle insures that the tail finds more friction as it goes down into it.  It sounds like your backcheck angle is insufficient to cause this to happen.  See if you can angle the backcheck back a little, and regulate the backcheck height again, while making sure it's not rubbing on the tail on the way up.  
It's too bad we can't see the action up close.  Sounds like a good subject for a Guild meeting/demo.
Hope this helps,
    Paul McCloud
    inSaneDiego


----- Original Message ----- 
From: William R. Monroe 
To: Pianotech
Sent: 11/10/2004 6:15:31 AM 
Subject: Re: About Checking


Joe Garrett, 
I have already bedded the keyframe, and double checked to make sure.

Tom,
Already repaired the balance rail holes (Onesti system - great tool!).

Joe Goss, and Paul,
Rep Springs really don't seem too strong, they have definite rise, but do not "jump-up" from check.  I will try weakening them more, though, and see what that brings.]

Terry F,
Double checked jack position, by bringing it out to the point of cheating, then just in enough to function, and no change (Drat!).

Paul,
Great ideas.  Checks are aligned, spaced, etc.  I resurfaced them prior to regulation.  Checking occurs about 1/3 of the way into the backcheck, and backcheck height is just about even or a little below the backcheck tail at drop, checks do not rub on tails on the rise.  The one thing that is giving me concern is that when the hammer is in check and I push them further into check, it does not happen.  I can push the hammer pretty much through the range of the backcheck without much increase in friction.  As as mentioned earlier, maybe the hammers being hung at a different angle are to blame (if indeed that was done).  I will be checking that, but any other thoughts on why the hammers won't go deeper into check?

Thanks everyone for your input!!!
William R. Monroe
Madison, WI
Assoc.



----- Original Message ----- 
From: Joe Garrett 
To: pianotech 
Sent: Tuesday, November 09, 2004 11:35 PM
Subject: Re: About Checking


William asked: "Also tried varying the backcheck height, which showed no noticeable
improvement with either higher or lower backchecks.  Also tried changing the
backcheck angle - again no improvement one way or the other, hammers simply
will not check on soft blows."

Lost in Wisconsin:
William R. Monroe
Madison, WI

William,
If you've tried all of that, then it has to be something you didn't try.<G> Have you checked to see if the keyframe is bedded properly? I've known that to mess up checking.
Best Regards,


Joe Garrett, R.P.T.
Captain, Tool Police
Squares R I
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