I have put a fair amount of thought into this, as I designed my own dip duplicating regulation table & cordless adjustable lightweight trolley.
Flat is not necessary. Keybeds are whatever shape they are...they will seldom be flat. Its actually quite difficult to maintain a dead flat surface the sheer size of a piano keybed. So if you managed to create a dead flat surface, it would still not match a piano keybed's surface. Instead, what is necessary, is a technique to duplicate dip using a reasonably stiff board. Glass or other hard to machine substances would be a total pain in the butt, as you would be constantly fighting the material itself. So, I would recommend against glass. You want something that allows you to install elevating screws from the bottom, to protrude through the top surface. So you need a structure that allows you to reach under the table to work the elevating screws.
If you want it light, as I did, I went with aircraft aluminum honeycomb cell laminate. This makes things complicated, but I wanted it light...and love how maneuverable it is. But that is only if you want it light. If this is for shop work, any solid core doorslab, cut down to dimension would work..as dead flat is not necessary. Or, Pick up a maple dining room table top, at the dump, or something like that. Or, make a torsion box, which is a screwed together frame, with 1/2"-3/4" high quality cabinet grade plywood glued on the top...or something like that.
It doesn't matter if it is not stable over the seasons, as you only care about its dimension over the course of your regulation, and even then, only while you are setting dip and checking. No other regulation procedures require dead nuts dip duplication. On my table, I only set dip, one section at a time (not compass wide) and only set at dip time and checking.
The elevating screws need to be located every 6" or so, under where the front rail will be, and every 6" under where the balance rail will be. Long key actions , medium key actions, and short key actions, will have different distances between front rail and balance rail. I set mine up for the front/balance rail positions of a S&S A. If you want, you can just set up two different front rail locations and a single balance rail row of elevating screws.
You want the table to be stiff, but not anally flat, and not even totally immune to climate changes...just not worth the trouble. Stiff, though is helpful.
here's a pic of the structure under my aircraft aluminum table.
I no longer include the back row of elevating screws, as they are unnecessary, once you have your technique down. Plus, the back row would mess with the height precision of a string height/letoff gantry...one like I show in the video.
Ideally, some keyframes, like Steinway's which are crowned purposely, and which tend to have keybed that require glide bolts to protrude further than flat, it would be helpful if, where the balance rail row of elevating screws is located, that area was dadoed out by 1/8" of so, for clearance. But one can get around that if you don't have the dado.
Also, one needs access to the front, back and sides of this table. My first table years ago was part of my shop work table against a wall...total pain, and cuts the utility of the table seriously.
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Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
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Original Message:
Sent: 05-24-2021 13:44
From: Floyd Gadd
Subject: regulation bench flat top
I suggest you consider a regulation bench configuration that supports the front and back rail, and that gives you an adjustable rail that runs under the balance rail glides. Some keybeds are bowed -- configured such that the surface at the points the glide bolts make contact is lower than where the front and back rails make contact. I have this feature on my regulation bench, and last week had to reconfigure it so that the center support rail could move even lower. I am working with a 1965 Yamaha action, and found that even with a slightly lowered center support rail, I could not duplicate the key height I had established in the piano. At the moment, I have the treble end of the rail 2.5 mm lower than the front and back rail, which should now allow the regulation I set up on the bench to be reasonably workable when the action returns to the piano.
The Edwards Action Cart incorporates one way of setting this up. My bench has a rail with adjustable bolts under it at each end, and an additional one in the middle.
You can, of course, work with a completely flat bench top and shim the front and back rails to duplicate the conditions given to you by the keybed. I'm not sure what the perfect flatness of the regulation bench gives you, in this case, other than the ideal surface for some theoretical ideal piano. Maybe I'm too pessimistic. Maybe there are more perfectly flat keybeds out there than I realize.
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Floyd Gadd
Regina SK
306-502-9103
Original Message:
Sent: 05-24-2021 13:23
From: David Weiss
Subject: regulation bench flat top
Excellent article. Thanks.
Original Message:
Sent: 5/24/2021 12:17:00 PM
From: Wesley Owen
Subject: RE: regulation bench flat top
I prefer to use hand planes to flatten benchtops, but they require practice and I do not need my benchtops to be perfectly machined flat to within .001 of an inch.
Other methods work just as well: https://woodworking.astrosteve.com/2018/03/20/the-ultimate-workbench-part-9-flattening-the-top/#more-366
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Wesley Owen
Evanston IL
847-257-5554
Original Message:
Sent: 05-24-2021 09:06
From: David Weiss
Subject: regulation bench flat top
I want a flatter top for my regulation bench. I'm thinking of laying a piece of 1/4 tempered glass over the top of the bench. I don't use this bench for anything except regulating.
Any thoughts?
Thanks,
David Weiss