Cutting a mortise near an edge

I'm making a spice rack for my brother. The sides are 3/8" sapele and I am planning on attaching the shelves with through mortise and tenons. The mortises are relatively thin (3/8") and wide (1.5"). I cut the mortise for the middle shelf without a problem, but trying to cut the bottom shelf (which is very near the bottom end of the sides) caused tear out (layers of the wood between the mortise and the edge) to peel away.

I will clamp a block down right to the edge of the mortise, which I'm sure will help.

Any other suggestions?

Mortises usually run with the grain instead of across the grain. for a spice rack you do not need a mortise the full width of the shelf.

One solution would be a dado to hold the bottom shelf. Easy to cut with a saw. Even a stopped dado can be saw cut with a little extra work.

Another would be to make two or three smaller mortises to secure the shelf to the sides.

jtk

I thought about the dado, since it's much easier to do. I was hoping for the visual of the long through mortise.

Just like putting a peg or pin near the end of a tenon, if your mortise is too near the end of a board blow out, failure in horizontal shear, can be a problem. That the shelf isn't loaded with little boxes of spices already is concerning, but time is also short for a couple or three major holidays coming up.

Can you post some pictures? Do you have any stock left? I have some sapele seasoning in my shop and have read about interlocking grain but haven't mortised any. If you have some stock left it might make sense to make the sides longer from new stock and then put a vertical brace under the bottom shelf, with the lower shelf in a dado and the underlying vertical brace through mortised. Maybe.

I think I understand from your description. Very common thing on that type of mortise, across the grain, and even standard mortise. You may have better luck leaving your sides longer, cut the mortise, than saw off the “horn”.
Jim

You could try scoring the other side of the board before the through mortise breaks through. Alternatively, cut the mortise about an inch or two
away from the edge of the board, then cut to length. Finally, instead of mortises, use dovetails.

I would cut a through mortise in from both sides, which should prevent any blowout. If it was very near the end I would leave the piece long and cut it to length after glue-up. For a 3/8” shelf, I would do 2 or maybe 3 square mortises instead of one long one.

But I would use a dado as the primary joint. For something like a spice rack a through mortise would just be decoration.

I should have left the pieces long and cut the mortises first as Ben noted. At after sleeping on it, I think I'll just use a stopped dado for the bottom shelf and call it good.

Thanks for all the ideas!