An actual woodworking question - routing a deep slot

[Theo]

Suppose I have a roughly 100x100mm post of (green) oak, that I want to route a 1m long slot out of the back for cables - let's say 20mm wide by 20mm deep. I have a 1/4" trim router but nothing bigger. I also have a 65mm cutting depth circular saw.

Is that something I can do with the trim router, in which case what kind of router bit would I need? Or should I do depth cuts with the circular saw and then try to chisel out the remains? Or some combination of the two tools?

Once this is done, I'm thinking of drilling a hole at the end of the slot and having the cables turn to go through to the other side of the post. To do that they will have some kind of turn radius, so how could I make the end of the slot gradually deeper to meet the hole? Drilling a series of holes of increasing depth and chiselling them out is one option I suppose. I don't really want to make a huge hole to accommodate the bend inside the hole itself.

Any better ideas?

Thanks Theo

[Bill]

I don't think a trim router is designed for this sort of work. I would make multiple passes with your circular saw and then it should be very easy to chisel out what you want. I'm assuming your post is square, otherwise I think you would require a fancier set up, or it could be dangerous (IMO, but lots of folks here know more than I do).

[pyotr filipivich]

Theo <theom+ [e-mail]> on 24 Feb 2024 20:28:05 +0000 (GMT) typed in rec.woodworking the following:

Use the saw, chisel out the remains. One issue is that you will not have a "square" end to the slot because of the saw blade curve. But it is in back, so who will see it?

Depends on how deep the slot is, and can you just let the cables "rise up" to point out the hole. Other wise, drilling a series of holes is pretty much the "easiest" solution. Could drill that hole first, the cut to it with the saw. "Like this {Insert sketch}!"

Alternately, you could work the sides down with a chisel and chisel out the middle, much as you would for a mortise and tendon.

[Scott Lurndal]

With your tools, I'd go for the latter. Note that it will be tough going for a 8mm trim router (I saw that switch in units, above) to route a 3/4" x 3/4" x 39" slot.

Set the saw for a 3/4" deep cut and build a jig to guide the saw, don't try to freehand it.

If you have a drill press, you can hog out the waste with a 3/4" forstner bit, then trim with a chisel.

Again, that's probably your best option.

[Theo]

Thanks, that makes sense. Alas it's not a track saw which would make it easier, but can probably jig something up.

That's a good thought, rather than trying to chisel out big chunks of material. I don't have a drill press but I suppose doing it by hand might be safe enough (then tidy up the edges).

A forstner bit to make stepped depth holes might work too. I should have a play...

Thanks all, Theo

[Bill]

Note: If you run the circular saw, having an 1/8" inch blade (!)--not a thin one, multiple times up the post, there won't be any big chunks to chisel out. If you can put the post on a sturdy table or bench, a clamped 2-by-4 ought to give you an ample jig to support the circular saw. Clearly the post should also be clamped/secured. I used this technique (on an admittedly smaller scale) once, and was really impressed with it! I do not take any credit for it.

I don't have a drill press but I suppose doing it by hand might