If one were to make 3/4″ shelves (plywood) that fit into dadoes on the sides of the case, would one cut the dado to less than 3/4″ and rabbet the shelves so the shelves would have shoulders? I understand that shoulders lend greater strength than through dadoes. How much of a should should there be? How wide the dado?
p.s. this technique might also eliminate the problem of 3/4″ plywood measuring 23/32″.
Replies
Around an eight of an inch is good. Have the shoulder on the top surface of the shelf, to keep the full 3/4" thickness as strength.
Around an eight of an inch is good. Have the shoulder on the top surface of the shelf, to keep the full 3/4" thickness as strength.
Could you elaborate? The shelf is 3/4 no matter which side is up, right? And the tongue doesn't change thickness. I would think the shoulder should be on the bottom to help with racking when you have the weight of books or whatever on it. I've never seen the shoulder on top in this application, which is why I ask.
If the shelf is plywood, and you cut the shoulder on the bottom, then delamination could leave less than the full thickness supporting the weight.
OK, but if you're worried about delamination, your design and/or material isn't adequate for the expected loading. With plywood shelves, I wouldn't use a rabbet anyway. It'd be easier to make two passes with a 1/2" cutter and a spacer or template than to have a whole 'nother setup for rabbeting the shelves. Then glue on a rib or nosing if you need it - and you'll probably want to hide the front edge of the ply anyway, right?
Peter, can you draw a picture of that, because either way you'll have a 5/8" thick tongue supporting the shear load, and the full 3/4" resisting bending. Rabbet up or down won't make that kind of difference.
Edited 3/10/2005 1:04 pm ET by Froed
Froed. Sorry the camera is out of the house right now. In my previous example I was actually meaning a 1/8" tongue, to exaggerate my point. So, using 3/4" thick material, if you make a 1/8" tongue and have the tongue down and the rabbet up, you will eliminate the chances of delamination [or splitting if using solid wood]. If you have the tongue up and the rabbet down then you will likely have delamination or splitting in solid woods. Peter
Alan said it exactly right. If you put the shoulder down and lets say that the shoulder is 5/8" then you will only have 1/8" supporting the books. 5/8" and the shoulder up and you will have 3/4" supporting the books. Peter
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