Sand tray framing

I was wondering if this plan will cause problems with sand moving outside the window area over time since there is extra space between the limits of where the ball rolls and the 1x2 framing? I was planning on adding a thin board to 1x2 pieces and then the xy system on top of that.

Yeah. You’re thinking the surface for the sand will be at the bottom of the 1x2? Sand will go everywhere it can. If you can’t limit it somehow, it will get there.

OK, thanks. I am going to go ahead and try it how I have it now and see how it works out. I think I can add a barrier later if needed without having to take it back apart.