Tools and Materials:
-Bottom wood (1/8" thick, plywood or MDF 3"x5" wide)
-Scroll saw or Band saw
Students have a tough time with this step sometimes. Make sure that as you demo it makes sense. I get kids to re-demonstrate or explain to the class to ensure comprehension.
The bottom piece ensures that the box is square so i keep a square and ruler handy to make sure the lines are all good. What i do is hold the cedar pieces together in the way that i want them . You can point out here how the long pieces have ends that are messed up and will be cleaned up shortly...
i hold the pieces over the bottom piece than slowly lower the assembly on top of the bottom. I hold the pieces down as i trace the inside of the pieces onto the bottom. I than pull off the pieces revealing the bottom with the lines drawn on it.
At this point I ask what would be wrong with just cutting it out now?
Almost always i get a student who notices that the bottom would fall through the box... it must be made larger so that the bottom will fit into the groove. I do the big high five to the kid who figures it out.
I explain that since the groove is about 3/16" deep, the bottom lines i just traced must be 1/8" bigger all the way around. I use this opportunity to make sure all the lines are square and perfect as well.
Many kids won't get this so have lots of extra bottoms around.
I use a scroll saw to cut the pieces out. You could use a handsaw of course.... give them a light sand than demo the glue-up.
I show how to rough fit everything together before gluing than i spread a nice thin even layer of glue on all of the ends and edges to be glued. Spend a LOT of time explaining how the outside groove MUST be PERFECTLY lined up so that you can stick a piece of wood in later. Check out the photos. Kids will often also not fully clamp the pieces... if your bench vices are too small you can use a jorgensen clamp or c-clamp.
Have the kids write their name on the pieces VERY clearly. The get mixed up all the time. Now is the time to be pro-active and go around with a square making sure all the pieces are perfect. Double check the outside grooves on the ends... they should line up. If not... i've attached a photo of a common fix with a chisel. Don't pull out the piece... just push it to the side and use it to fill the space.. Works really well.
If kids break off the bottom edges just glue it using a piece of masking tape as a clamp. Make sure no glue gets into the groove.