Cutting a Sink Hole in a Four-Inch-Thick Wood Countertop

An architect's brainchild leaves a woodworker with a tricky job: cutting out a hole for an undermount sink in a 4-inch chunk of Walnut. August 3, 2009

I'm building a walnut cabinet that will have an undermount copper sink installed. The walnut countertop is glued up, 11' long, 4" thick. I’m wondering what all my options are for cutting the 20"x30", 4" thick sink hole? I also want to make sure there aren't any odd problems with copper and walnut.

Forum Responses
(Cabinetmaking Forum)
From contributor B:
My first thoughts are to ask why anyone would need or want a countertop 4" thick. That thing is going to be a beast to move around at 11' long. The truth is, how do you plan to cut it to length and rip it to width? That would be a good indication of how you might do the cutout. It sounds like you're going to have to cut out the sink with the same saw.

From contributor G:
I would use a Sawzall.

From the original questioner:
Reason: per architect's specs. I'd prefer to use a jig saw on this if possible. What is the max cutting depth of jig saws?

From contributor B:
Sawzall is for construction grade work not fine woodwork, if you can get a clean straight line that requires little sanding let me know the secret. Figures, architects spec a lot of ridiculous things like that. I would have talked them out of it. That's really pushing it for a countertop. I'm not sure you're going to get a clean cut with a jigsaw either as even if you can get a blade that long it won't cut straight. The best bet is a plunging circular saw with guides to cut it out leaving 1/16 - 1/8" around extra. Then make a template in 1/4"-1/2" MDF with the cutout and clamp it to the top. Flush trim from one face, clip the countertop over and do the other since it’s likely the flush trim but won't do more than 2". Trying to sand sawblade marks is a lot of work and doesn't yield good results, router bits are better. Just use a brand new sharp bit with a bearing on the top not the bottom.

From contributor P:
Personally, I'd rough it out with a Skilsaw from both faces, Sawzall the corners, then make a template to run a router with a straight bit (getting the template to register accurately from each face will be a little tricky) to clean it up.

From contributor G:
I'm still trying to figure out why it has to be a pretty cut if it is a drop in sink, and the hole is smaller than the sink. Once the sink is in the hole is gone. Why does it have to look pretty? Use a circular saw (Makita 16") and then finish it off with a Sawzall. I use the Sawzall in fine woodwork on occasion to cut baseboard on the wall. One of these days I'll get a Fein MM tool.

From the original questioner:
It's an under-mount sink. I have a Fein MM. I wouldn't have thought of using it here. Is that what you're suggesting?

From contributor J:
Bore the four corners with a large bit. Then use a template and router from both sides. This should get you pretty close if not all the way through. The cut should be clean with minimal cleanup.

From contributor G:
The only way I see to do this is drill out the four corners with the correct radius bit. Use as big a circular saw you can find. Cut through the top and bottom if needed, finish off with a hand saw or a Sawzall. And break out the sander. I suggest starting with 60 grit. After you are done pick the whole thing up and smack the designer/architect across the head with it.

From contributor M:
Rough-cut the hole with whatever you want (Sawzall, jigsaw, hatchet) then, from the top of the slab, pattern cut the hole as deep as you can with a router and top-bearing bit. Finish the cut out from the bottom of the slab, again using the router but this time use a bottom-bearing bit, and use the hole itself (as cut from top) as your template.

From contributor Z:
Hole-saw the two corners and circular saw the rest from top and bottom. Now are these people all over 7' tall? Normal counter tops are at 36 " less 4" for counter less 8-10 " for sink depth. They will be very bent over to clean the bottom of the sink. What are your plans to seal all the exposed end grain in the sink cut out? Get them to sign off on long term problems with a wood counter top exposed to that much water.

From contributor C:
Why not glue it up with the cutout already removed? Careful layout and use of a knockout should do the trick. Leave the countertop long on both ends and trim to fit.

From contributor P:
The Festool jigsaw has a max cutting depth of 4 3/4", and is good at limiting blade deflection if you use their blades. The handheld PC spindle sander is great for this kind of job. It uses 4 1/2" spindles, so it would probably do the trick.

From contributor T:
My first thought was the same as contributor M using a pattern and a top bearing bit, then flipping and using a bottom-bearing bit. My other “what if” would be to cut out rough with whatever (Sawzall). Then could you get enough depth and the right blade to go around with a “Porta Band”? Drill the corners if needed. The sanding probably wouldn’t be that bad. Overall, I agree it’s a bad idea. Unless, do you need to show the 4” thickness over the sink area? Or is it just that the top has to be 4”? Could you do the glue up with the sink area already “thinned” to a more reasonable thickness, and then cut out as usual?

From contributor X:

Rough-cut it out first. Than make a jig for using a portable band saw. Cut final cuts with portable band saw.

From contributor F:
I can't add anything helpful except that I agree with this potentially being a bad idea. The faucet will also pose problems since the attachments will require removing a lot of material to allow access of a wrench. Seasonal movement will likely impair the connection between sink and wood since there's no way to allow for that movement.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor X:
My first thought was the final depth of the sink itself. Another 4 " of counter will make the bottom that much farther away, like a kid sink. As for a solution to an un-recommended application, try carving out to the depth of a normal counter then mounting the sink as per normal. The only water proofing with any shade of slim chance would be a water proof material inletted as a "decorative composite detail". Make sure the architect signs off on it as his dollar to fix.