[pianotech] regulating backchecks?

[Al Guecia/AlliedPianoCraft]

  From: jim ialeggio 
  Sent: Thursday, July 30, 2009 10:28 AM
  To: pianotech at ptg.org 
  Subject: Re: [pianotech] regulating backchecks?


  Al, 

  Front rail adjustment is interesting, and I'd like to consider it, but I don't quite understand it.   

  I'm assuming you have bedded the action in the piano first. This would have included adjusting the balance rail glide bolts such that they were protruding some  small amount below the flat plane of the keyframe.

  Yes

  If my assumption is correct, this means that when the keyframe is on your bench, glide bolts in their piano bedded positions, frame clamped all around, sitting on your flat bench plane, that the keyframe is probably flexed up a bit at the balance rail.

  I just clamped on the front at the far edges. Yes the action frame is generally high at the balance rail. If I have trouble with one of the glide bolts (BR) that doesn't touch the bench top, I'll put a piece of masking tape on the balance rail glide bolt to make it all fit.

  If I'm correct, by adjusting the front rail, which you can only adjust upwards, that this allows you to lower the balance rail relative position, but not raise it. It also allows you to follow the contour of the front of the keybed which may be cambered.

  Yes

  As I write this I think I'm starting to follow your reasoning....

  My approach, which as I said, I'm not happy with, made the adjustment at the balance rail.
   
  My bench top consists of a 1-3/4" commercial solid core door with with 1/8" mahogany veneer both sides  (got 10 of 'em almost free when I built my shop). 
  My staightedges tell me its a pretty decent plane. 

  I relieved an 1/8" deep x 3" wide trough under the balance rail and installed some carriage bolts in the trough, head up, as adjusters.


  Jim I

  I will send a photo this afternoon.
  Al







    I installed 5 glide bolts upside down (similar to some Baldwin grands) on the front of my bench (which is a Steinway B keybed) and use them to make the adjustments. The way I set them up is to use action springs to hold the action firm to the bench, then I raise and lower the front glides in the bench by checking the center glides as you do when bedding the action, making adjustment to the front glides bolts 'til you get it right. Then I check the key dip to be sure it's correct. Works great. I don't need to make many adjustments in the piano after that.

    Al G









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