Thread: Mortise Across Grain

Originally Posted by Luke Maddux

I can't seem to find much about this, although I know it is done all the time.

i want to join the legs to a slab coffee table using M/T joinery. This will at some point require me to cut mortises perpendicular to the grain of the wood.

What at is the most efficient way of doing this? I have tried it with a only a chisel with ghastly (but useable) results.

I was was thinking about using a drill to remove the majority of the waste, then paring the sides with a chisel, then smoothing the bottom with a router plane. Anyone have any feedback on this approach?

im looking for any advice or feedback on this very commonly used joint.

cheers,
luke

I cut mortise like this all the time. I have a dedicated machine for this task.
if you are in Akl you are welcome to use my Masterwood mortiser, cut a slot of 25mm x 120mm x 120mm in 15-20 seconds

Here is a video of it cutting smaller mortise 10mm x 45mm x 60mm into wood. Did it extra slow as my other hand is holding the camera.

Yep, use a drill to remove most of the waste quickly - but make sure you use a forstner bit. Forstners cut flat bottomed holes. Also, they are difficult to deflect from their line, so you can overlap the holes.

Mark a line across the centreline of the mortise-to-be, using a marking knife. The forstner bit has a small spur in the centre which should catch in this line so all your drill holes line up. Use a chisel to clean up.

Usually, you choose both the forstner bit and the mortise chisel to exactly match the size of the mortise, so clean up is minimal (ie use a 12mm forstner bit, and a 12mm mortise chisel, and make sure you cut 12mm tenons).

Generally, you will find the only scruffy bit is the top edge of the mortise on the long axis. It gets rounded over where the mortise chisel is used to lever away waste. Make a wide shoulder on the tenon piece to hide this.

cheers
Arron