Action Geometry - Help

[Ron Torrella]

Avery:

When you say you duplicated key height on #1 and #88, what do you mean exactly?  How did
you do this?  Have you considered that you should try to duplicate the keybed
environment on the workbench in order to get accurate readings in letoff and drop?

The method I use involves measuring the height of sample keys in the piano (with
cheekblocks screwed into place), then duplicating those heights on the bench using
balance rail punchings under the front edge of the keyframe.  Again, the end pins (the
ones that go into the cheekblocks) are secured to the bench just as they are in the
piano.  If there is any knocking at the glide studs, I put punchings under them as well.

Once you are sure you have "duplicated the keybed" on the bench, you should find setting
letoff and drop (rough settings, anyhow) to be much easier to do.

I suspect that the jacks are "bottoming out" because the part of the bench under the
highest end of the keyframe is slightly lower than what you'd find in the piano.  Also
could be that there's a slight rise in the bench under the balance rail at that end.

Bottom line: Make sure you're duplicating the *keybed*, not just the key height.
They're dependent upon one another!

On Tue, 03 Sep 1996, Avery Todd wrote:

>  I've duplicated the old key height on notes #1 & #88 (on the bench), and
>set approximately the same hammer blow and let off on each end. I can get
>the #1 hammer to go the full dip, etc. Everything seems like it will work out
>fine. However, on #88 I can't get the key to quite go the full dip even though
>I can get app. the same let-off and drop as on #1. It won't go into check
>because the jack jams into the cushion felt preventing full key travel. The
>paper & card FR punchings are still what was there originally.
>  The only thing I can find that "might" be wrong is the action spread is
>4-9/16 on #1 and 4-5/8 on #88. Could the wippen rail being that 1/16 inch
>further out cause the problem with the jack jamming into the felt? I've
>never had to do any changing of the action spread before and I want to make
>sure I'm not opening up a can of worms here.
>  I still need to take the action to the piano to determine the best key
>height and hammer blow, etc. but wanted to at least get everything working
>approximately before I do. Maybe when I get to the piano I'll be able to
>see some other difference, but right now I can't think of what it would be.