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I'm building a piano style shell for my midi controller.

Back piece with the 2 decorative flairs on it is actually on a hinge and folds down for easy access to plugging in cables.

It's made from pine 1/4" ply.

It has bent and concaved about 1/8 inch or so.

I have 1 hinge on the left side and 1 hinge on the right side. If I put a hinge in the middle, it won't fold all the way down as the bowing puts stress on the screws.

I've tried to spray some water on the concave side and put it on a flat surface with some clamps but that didn't work.

How would I go about getting this to be more straight?

Rear View

dallaskruse
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  • Hi, welcome to SE. There are already previous Q&As on warped plywood or unbending plywood and your question may be closed as a duplicate of one of those. Take a look at the most recent one, here and then look at the Related column to the right to see more relevant Answers. – Graphus Dec 29 '18 at 09:43
  • Now about your piece, I suspect the existing piece won't be fixable (at least not permanently) and the only viable option is replacement, and I wouldn't use softwood plywood for the new back. BTW is the rest of the box also built from softwood ply? – Graphus Dec 29 '18 at 09:49
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    Possible duplicate of How to flatten 1/8" Baltic Birch Plywood for laser cutting? – Graphus Dec 29 '18 at 09:50
  • Thank you for the replies. Yes. It's build from pine ply. This is just a first attempt at building something. I'm guessing the next reply is that I should've used a better piece of wood? – dallaskruse Dec 29 '18 at 16:45
  • Yes, you'd have gotten more reliable results with a better class of plywood (or panels glued up from solid wood, which is stiffer than ply). Since you've built the whole thing though you should see how it holds up because it might be OK. Anyway for your back, as you can see from the previous Q&As what you've tried already is how you might go about taking the bow out of the plywood so it's worth trying again. Don't just clamp back to flat but instead bend it further so that you're holding it with an opposite bend, this stands the best chance of achieving flat once the clamps come off. – Graphus Dec 30 '18 at 09:43
  • Regardless of the grade of plywood, any piece of those dimensions will be highly prone to warping. The problem lies in the design. To keep the door from accidentally popping open, install a hardware clasp on the inside. – Stephen Meschke Dec 31 '18 at 18:17
  • The door is held in place by 2 latches on the inside. It doesn't pop open by accident. I was able to bend it back to straight by wetting it a bit and over-bending it for a few hours. This is my first attempt at any sort of build so I'm still learning. This is sort of my "test run". i need to have that door so I can access my piano's audio jacks in the rear. – dallaskruse Jan 01 '19 at 00:39
  • When you're starting out it's best to follow existing plans as much as possible (although you have to be selective, since there's a lot of junk out there online unfortunately!) and over-engineer everything if budget allows. Once you gain more experience, in a few years, you'll have a better idea of where you can successfully make use of lightweight materials and lighter joints.... but saying that, plenty of pros and semi-professional woodworkers make mistakes so don't be too hard on yourself! – Graphus Jan 01 '19 at 09:33
  • To be honest ... I didn't have "plans" per se. I drew them out myself ... so i guess they're "plans" but as I'm learning, I'm finding cutting test cuts to be the best thing I can do since I've messed up a few pieces thus far :) – dallaskruse Jan 03 '19 at 16:23

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Cut a piece of 3/4" plywood 4" wide and 2" less than the width of the shell. Glue and screw it to the back panel to add rigidity.

Stephen Meschke
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