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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):

workbench leg and skirt section

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?

  • by skirt, I think you mean the apron – ww_init_js Jun 14 '18 at 19:22
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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.

  • I would love to do it with hand tools learning along the way and it would be cheaper also, was it not for back and joint problems :( Without a workbench in the first place handling and cutting heavy stuff is difficult for me :( Assembling pre-cut pieces together looks like a physically easier task. – axk Jun 14 '18 at 14:08
  • Sorry, hadn't considered health issues as preventing doing the smaller cuts by hand. And yes there is the ever-present issue for anyone making their first bench — you could really do with a bench to make it! :-D While there are various ways around not having a proper bench to begin with really it's difficult to work with full sheets of ply at the best of times, and doing it with only hand tools is a tough ask of anyone. – Graphus Jun 15 '18 at 12:30
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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.

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    I think axk is envisioning the slats being laid flat on the router bed, preventing the square end of a cutter from making the cut you might be seeing. There are methods to create a square cut but one that involves a pigeon hole at the 90° point. I'm sure there's a different word for it, but the concept is the same. Advance the router beyond the angle, then back up a bit and continue on the next part of the angle. – fred_dot_u Jun 13 '18 at 23:15
  • I see what you mean but why not glue the slats first and then machine with the pieces in the other orientation? – WhatEvil Jun 14 '18 at 11:34
  • Marc Spagnuolo (The Wood Whisperer) just put out a video detailing this process of squaring-off rounded corners using chisels. – mmathis Jun 14 '18 at 13:04
  • I saw that, just thought plywood may be different. – axk Jun 14 '18 at 21:40
  • @WhatEvil, I don't have a CNC, planning to order this to be cut by a CNC-shop, they have a standard arrangement, I don't think they would customize their setup for one order. – axk Jun 14 '18 at 21:42

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