Cutting Compound Angled Mortises

[John TenEyck]

A few days ago a question was asked on how I cut compound angle mortises with my horizontal router mortiser. Why might you want to do that? Well, if you make chairs the rail between the front and back legs is often at a compound angle where it meets the legs. Typically the rail angles out and up where it meets the back leg, for example. Here's how I would handle that.

The end of the rail is cut to whatever compound angle is needed. Let's say the rail angles out at 5° and up 2° where it meets the back leg. OK, first I cut off the end of the rail at those angles.





The table on my HRM is set to 5° and the workrest angled to 2°.





And now the mortise is cut.



With both the table tilted and workrest angled the mortise ends up exactly perpendicular to the face of the compound angle cut. But if you'd rather the mortise be parallel with the length of the rail, you don't tilt the table, you just angle the workrest. Now the mortise looks like this.



If you'd rather have an integral tenon you cut those in the same way, only you start with longer parts, obviously, and you cut away material to leave the tenon rather than into the rail to create a mortise. But the principles are the same.

There are other ways to do this but I don't know of any that are easier or faster within the budget of a hobbiest woodworker.

John

[Jim Andrew]

Thanks for posting that. Way cool.

[Rick Potter]

Pretty slick, John.

A video would be even nicer.

[Jason Mikits]

Thanks for showing this. I don't often reply, but am very glad to see this. I know you've posted this before, but can you show the link for this horizontal router table build again?

[Brian Holcombe]

For maximum strength of the joint the ‘tenon’ side (skirt) should be straight and the mortise side (leg) should be angled. This is for two reasons, it minimizes short grain, increases the long grain in the mortise and maintains the dovetail effect created by splaying parts.

[John TenEyck]

Thanks for showing this. I don't often reply, but am very glad to see this. I know you've posted this before, but can you show the link for this horizontal router table build again?

Happy to: https://sites.google.com/site/jteney...outer-mortiser

John

[John TenEyck]

Pretty slick, John.

A video would be even nicer.

There is a video on my webpage for the HRM: https://sites.google.com/site/jteney...outer-mortiser It is shown with the original, non-tilting, X-table, but the operation is the same.

John

[John TenEyck]

For maximum strength of the joint the ‘tenon’ side (skirt) should be straight and the mortise side (leg) should be angled. This is for two reasons, it minimizes short grain, increases the long grain in the mortise and maintains the dovetail effect created by splaying parts.

Thanks Brian. As I showed above, you can cut the mortise (or integral tenon) in the rail either way. And the same goes for the leg mortise, so you can orient the tenon any way you like. I've seen them cut both ways but your explanation makes complete sense for integral tenons, though maybe less critical for loose tenons.

John