Square corners in CNC-cut plywood

Question

I'm thinking about making a workbench out of CNC-cut plywood with the legs as several layers of plywood.

I'm thinking about attaching the legs to the skirt (top frame to make rigid or whatever it's name is) like this (this only shows one leg, the horizontal part is the skirt, it will extend further after I mirror the leg to get the other 3 legs in the CAD):

In this design I need inside square corners which the CNC cutter cannot do.

The question is if I design it with square corners, then round the corners right before sending the files to the CNC shop to accommodate for the limitation of the cutter, will it be easy to cut the square inner corners manually afterwards with enough precision for the parts to match?
Or is it better to accommodate for round corners in the design somehow so that it all connects with round corners?

Answer 1

will it be easy to cut the square inner corners manually afterwards with enough precision for the parts to match?

Yes. This sort of trimming is a trivial job (a couple of minutes) and can be done with a purpose-made tool, the corner chisel, with a conventional chisel or using a rasp or file if necessary*.

But in reality you don't have to get the inside corners here that perfect for structural reasons. Only if you remove too little material would there be a problem as the the apron piece would be held away from the vertical and horizontal joint surfaces. If they are slightly overcut (just a little too much material is removed) that won't affect joint strength in any way.

Have to say it, cutting flat components like this on a CNC machine seems like complete overkill to me. Squaring the corners could even be done using the right type of hand saw, which of course could be used to cut the entire notch, as well as to saw the pieces perfectly to length and dead square in the first place..... ;-)

Another option, no hand tools
I presume the CNC can drill holes, if so you could have it drill a small hole at the corner, do the straight cuts and then after assembly you'd be left with a portion of small, perfectly neat holes that could be left as a feature. But if you can't stand the sight of them you can of course surface fill all the holes (the void behind the fill is irrelevant, no need to worry about it).

---

*Doing it with either type of chisel the workpiece should be firmly clamped down to the bench or onto a sacrificial piece of wood. If doing it by rasp/file the workpiece should be held upright in a vice.

Answer 2

There's actually nothing in that drawing that a CNC router can't do... you're thinking of square internal corners of a pocket but this is not that. If you're doing a rabbet with a square-tip cutter then you absolutely can achieve what you've drawn, unless there's some part of that drawing I'm misunderstanding.

Edit: If you do need to machine them in the orientation such that a rounded internal corner is produced, it should be easy to cut out the rounded part by hand as needed. I would typically try to pare it off bit by bit with a sharp chisel. You can make this easier by clamping a piece of wood or board with a straight edge such that it lies adjacent to the straight surface you want to cut, this can then act as a guide for a saw or chisel.