Are mortises with angled walls cut the same way as square mortises (handtools)?

Question

What are the usual steps to carve out a non-90degree mortise that will be married to a sliding wedge/key? Should the wedge be cut first?

When chiseling a usual mortise, plumb can be used as the reference. In tusk-tenons, the angle is generally kept low to prevent the wedge to slip out -- but much lower than the bevels on most chisels.

I've thought of different options to guide the carving, from a pilot drill hole, to a workpiece jig (that allows the chisel to be held plumb), or an angled guide block (against which the chisel can slide up and down), to altering the walls of a square mortise with a rasp. Can it be simpler than that?

Examples of angled mortises:

^{Note: Tusks for locking shelves, or tusks for locking moravian workbench legs.}

There are ways to avoid the angled wall, but they're not what I'm looking for:

1. Folding wedges, which allows the usual mortising method, but gives a different look.

2. In the second image (Moravian bench), it would be possible to use a router to make space in the center of the laminated tenon. Like an inlay plane.

Update: I've found video material online which describes one way to cut these mortises, and included links in this answer.

Answer 1

The thing with hand tools is that the angles are all arbitrary and require no resetting of stops or fixtures. If you can saw to a line, you can saw 90º and 33.4º equally well. Similarly, if you can chop a conventional 90º mortise, you can do any other angle.

Here, you'd chop it out the same way. It's a through mortise, so you mark both sides of the joint first. A good angle is around 5º, so you can set a sliding bevel to something around that as a way to locate the angled side of the mortise. (BTW, don't forget to make the other end of the mortise longer than necessary - it will be buried inside the vertical member, and you want to make sure the wedge never hits it.) To help guide your eye, you can do either one or both of the following:

1. Keep the sliding bevel near to your mortise as you chop the angled end, and periodically check that you chisel is parallel to it.

2. Using the sliding bevel, pencil in the correct angle on the side of the mortised piece (ie, the larger tenon), and periodically check progress.

In both cases, use a one-sided tolerance approach. Err on the side of too high an angle (coming in from the top), then when the bulk of the mortise is clear, pare away to your marked line on the lower/exit side of the mortise.

Note that the above is for the more common example seen in your first picture. For the wedges in the moravian workbench stretcher, it will probably be easier to start from the bottom of the mortise and pare to the top - the key is just always working down the grain so you don't spelch out the other side.

Answer 2

What are the usual steps to carve out a non-90degree mortise that will be married to a sliding wedge/key?

Just to clarify the need here, this isn't an angled mortise you're looking for here, it's merely a mortise with one angled surface.

Should the wedge be cut first?

Having the ability to set a given angle and then repeatably mark it is why bevel gauges exist and why they're a part of the normal toolkit for woodworkers. But yes, you can just make the wedge first and use it to mark the angles on the outside of the tenon (as well as to mark out all the subsequent wedges if your cutting method doesn't easily allow you to make duplicate wedges at the start).

I've thought of different options to guide the carving, from a pilot drill hole, to a workpiece jig (that allows the chisel to be held plumb), or an angled guide block (against which the chisel can slide up and down)

The highlighted portion is a very good idea for critical chisel work in joint making generally (if needed) but really not needed here. You're just chopping out a mortise with three vertical walls and one angled one, you'll find it's not actually that much more difficult than doing a conventional mortise once you have pencilled lines on the exterior to guide your chiselling.

As with all mortises you should chop in from both faces, the primary intention of this being that you don't 'blow out' (chip out) at the back if you chop right through. But this has another advantage here in that you'll easily create good top and bottom edges to your mortise, and if between these the internal surface is a bit undercut that actually doesn't matter. Ditto if it ends up a bit ragged due to end-grain tearout.

While any irregularity inside the mortise often bothers the person doing the chisel work :-) it'll basically never be seen by anyone else and on this joint it doesn't matter in the slightest in terms of functionality — if the angled face of the wedge bears only on the top and bottom edges it should still work perfectly well.

Answer 3

The technique for the key and tenon in the Moravian workbench (the image on the right in the question), was publicly published (Sept 2018) in a YouTube miniseries called "Make a tusk tenon joint with hand tools", which consists of 5 segments probably taken from the full-length DVD.

In the video, the woodworker first cuts the key, then uses the key as a stencil to mark angled lines on the outside of the tenon, and then chisels out the mortise, using the pencil lines to guide the orientation of the chisel.

• Making the Key: part 3/5.
• Marking the mortise: part 4/5, and
• Cutting the mortise: part 5/5.

Not that it's the only way to do it, but it would seem that Myers' technique involves a lot of "just eyeballin' it down the back of the chisel". Which matches some aspects of the answers here. It's not as daunting as it may seem, because precision is not super critical (not in that project, anyways).

The tenon in the bench is formed by laminating two 2x4 boards. It would be possible in theory to use a router to cut out half the mortise from each board, and sandwich them, but in the video the mortise is chiselled out after lamination, not before.