Step 1: Get Some "Pins" for the Drop-in Holes
Step 2: Measure Distance Between Holes
Step 3: Decide Depth of the Stand Tray
Step 4: Cut Tray Stand and Back Support
Step 5: Drill Holes for Support Screws in Back Support Strips
Step 6: Test the Positioning of the Support Screws
Step 7: Make Sure Stand and Front Support Line Up As Desired
The width was good.
I saw I could attach the support directly to the bottom of the back support. A direct 90 degree connection would work fine, which would make it easier to attach.
To accommodate the tilt, I put a vertical support board on top of the back support (with the screws) and tilted the back stand to where I wanted it. It looked like the easiest way to get the proper tilt would be to attach the vertical back support about 1/2 cm in from the edge.
Step 8: Attach Front Support Tray to Back
I held the tray and stand in place, and on the back/bottom I marked 4 location for screws. I wanted to predrill holes for the screws, because plywood splinters easily. I drew the marks across both pieces so that they would line up exactly.
I used 4 wood screws (1/4" diameter, about 1.25" deep). I predrilled 1/4" holes at the marks, in the middle of the short edge of the tray, and on the back of the stand. The back holes I drilled high enough so that the bottom of the back piece would line up with the bottom of the tray.
Once the holes were drilled, I started the screws into the back. Then I lined up the tray and drilled each screw a little bit into the holes in the side of the tray. I only started them in a little, so that if the holes were slightly misaligned, I would be able to get them all into their approximate locations before driving them in the rest of the way.
Just like replacing a spare tire on your car, it's better to finish driving the screws in an alternating pattern. If you just screw them in from left to right in a straight line, any misalignment will get worse by the end. By alternating, any misalignment is spread evenly across the whole piece, and not concentrated at one end.
When it was screwed in, I held it up and it looked good. The base was at a 90 degree angle, it was flat, and the screws weren't visible from the front.
Step 9: Attach Vertical Back Support to Back Piece
I marked the location of the screw holes from the front piece, onto the vertical and horizontal back supports. Then I set the vertical back support on top of the horizontal support, moved it in from the edge about the 1/2 cm I'd chosen when it was on the piano, and marked that distance in from the edge, at each screw location. I also put a mark on the other side of the vertical support, so I could see where to center the screw holes.
Predrilled holes in the vertical and horizontal supports, then screwed them together like the front tray piece.
Step 10: Attach Music Tray to Back Support
Insert the back support piece into the holes. Set the front tray and tilt as desired.
At this point I noticed a slot in the tray area of the piano. To give clearance to this slot, I moved the tray off-center to the right. It didn't overlap the right speaker, so I wasn't too concerned about it being an inch off center. If I were to do this again, I'd make the front support about an inch narrower.
I put a music book on the tray and tilted the stand. I also tested the tilt with some sheet music. It seemed adequate.
I decided to use two more machine screws, with washers and wing nuts, so it would be removable.
I measured the width of the tray, & set the washers on the tray at 1/3 and 2/3 of the width. Then I marked the center hole of each washer, so the height of the hole would accommodate them.
While holding the front support at the desired angle, pressed firmly against the back support, I drilled the first hole through the tray, and all the way through the back support. Made sure the drill hole was level with the top of the piano. Then I put a washer on the first machine screw, drilled it through the front and back hole, put a washer on the back, and tightened a wing nut.
After making sure the angle was still good, I repeated this for the second machine screw support.
Step 11: Check It, and It's Done!
Check it one last time. The angle still ended up a little steep, but the papers and books seemed ok so I'm not worried about it.
It would be easy to remove & spraypaint this black at a future date.