routing of sink cut out

PoorOwnerNovember 7, 2008

I am learning how to do a sink cutout for undermount installation. The counter top is 1.5" maple edge grain butcher block.

I have figured out that I need to trace the paper template in MDF, cut it out (sand, etc to make it perfect) then use a pattern bit to trace the cut out on the countertop.

The template says it is for negative reveal which is not friendly for wood around the sink, I imagine. I want a positive reveal. so I am wondering what is the best way to do this. Is there a pattern bit that would has the bit bigger than the bearing, so that after the flush cut you use it again allow an increase of the the template size on the target material?

I plan to use another MDF board to practice the cut out and check the reveal with the sink before operating on the actual material. Would this yield good simulation to check the quality of the template?

any other things I should know about? thanks..

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Are you aware of how risky it is to do an undermount sink in butcherblock? This is really a pushing-your-luck kind of idea in most climates, because the butcherblock will expand and contract with seasonal humidity changes. A 25" wide sugar maple slab could easily move by almost a quarter of an inch over the course of a year, which is more than enough enough to tear whatever sealant you use to attach the sink to the counter. You may luck out - you may live in an unusually stable climate, or have excellent climate control in your house (central air, humidifier for the heating season), or you may be planning to encase the butcherblock in a heavy film finish; but, what you're contemplating is something most professionals would decline to get involved with.

Other things that come to mind...

Changing from a negative to a positive reveal isn't going to happen with changes of bearings, because the difference is just too great. There's an outside chance that template guides which attach to the baseplate of the router could be used in this way, but you're probably better off getting a compass and straightedge and redrawing the template to the size you want.

You should use a female template that goes around the opening rather than a male template that sits directly over the opening. If you use a male template (an mdf version of the one that came with your sink) and the router drifts away from the template while cutting, your counter is toast. If you use a female template and the router drifts away from it, towards the middle of the opening, no harm is done.

The router should be fairly robust - hopefully at least 2 HP.

The cutting will be easier with a large-diameter bit than with a small one.

That bit should be essentially brand new (very sharp). Don't use the beat-up bit you've got rolling around in the bottom of a drawer somewhere.

Before you even start the router, cut out as much of the material (as close to your line) as you dare with a jigsaw. The router should just be used to clean up the last 1/8" - 3/16" of material.

    Bookmark   November 8, 2008 at 5:43AM
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Get a spiral cutting router bit to minimize tear-out. I got a really nice one from Woodcraft. Make sure the cutting head is long enough to cut through the thickness of the maple. I run routers backwards first (the direction the bit pulls as it cuts) before running it in the "right" direction to clean up the cut. This prevents tear-outs but be extremely careful the router can get away from you if you try and cut too much at once.

    Bookmark   November 8, 2008 at 8:45AM
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One idea: Pat Warner's book, "The Router Book", is a really good intro guide with lots of good safety-related information. (More than you'll get on the internet from hacks like me who neglect to mention male versus female templates...)

Another idea: a quirk at the bottom edge of the sink cutout (like the kerf you see at the underside of a traditional windowsill) would prevent water from travelling too far sideways. I think I'd do this with a scratch stock (google scratch stock quirk for pix/etc) with a small, slightly rounded fence.

Here is a link that might be useful: The Router Book

    Bookmark   November 8, 2008 at 11:11AM
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Hi Jon, I do know the block will move but I have not thought it would move enough to break the sealant, as far as I know most sinks are secured by clips with the silicone to stop water, but the clips should be similar for drop in installation. If the risk you proposed is true wouldn't it be just as risky to install a drop in sink in a butcherblock? Also the movement is distributed over the length of the caulk bead, so the tension per area (non techical term here) should be less than a full 1/4". Windows and door caulk can handle a movement of wood planks and they are not even fully silicone. Kitchen caulk like GE II is fully silicone. I think I have dealt with some of this stuff dried out and found it VERY elastic.

I have seen many folks here who has butcherblock and sinks mostly undermounted. That's not to say it will last long against moisture if not properly maintained.

I am however going to seal all edge with waterlox at least 5 coats.

The router will be bosch 1617 2.25HP with some reputable carbide bits that I could find...

    Bookmark   November 8, 2008 at 2:11PM
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When I make my MDF templates off the paper template, I adjust the size of the template during that layout. If I want the template smaller, I'll use transfer paper under The paper template and then trace a line 1/4" or so inside the template line.

If going the other way, I trace a line 1/4" outside the edge of the paper template.

Then I just use my regular flush cutting pattern bit.


    Bookmark   November 8, 2008 at 5:04PM
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Sorry, I didn't mean to imply that the sink would fall into the cabinet when the sealant tears; it will, of course, be supported by clips or some other means.

You're right that the full 1/4" of movement wouldn't affect any one part of the seal. At a minimum, the front and back edges would see about 1/8" of movement, while the part towards the middle of the counter might be quite stable. Even so, 1/8" is a lot. Yes, silicone is stretchy, but when you're playing with a shred big enough to handle, you are not duplicating the forces that are in play when the sealant is pressed into a flat layer that's 1/16" or less thick.

Yes, the seals around drop-in sinks fail the same way, but the failure is further from the water, in a place less prone to cause problems.

I realize that people do mount sinks this way, and I think they're pretty to look at. I'm not saying your whole kitchen is going to implode, but I am saying that you can't expect this installation to be as long-lived and trouble-free as an otherwise similar installation in a stone countertop.

    Bookmark   November 9, 2008 at 9:27AM
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Jon gives good advice, you just need to be aware of the issues beforehand. Wood movement, type of wood, wood versus water.

That said, I have an 8/4 teak countertop in my kitchen, it's plank, edge glued (epoxy), with an undermount sink. The countertop is 2" thick by 30" deep, and about 18' long.

Can't recall how long it's been in...maybe 6 or 7 years? Still looks great. No issues. I hit it with mineral oil about every 4 to 6 months.


    Bookmark   November 9, 2008 at 11:17PM
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Thanks, Mongo.

FWIW, the shrinkage/expansion numbers for teak are less than half those of hard maple.

    Bookmark   November 10, 2008 at 7:42AM
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OK, I have selected a farm style sink instead of a true undermount, so it is installed in the cabinet instead of attached to the countertop. Althought it is still considered to be undermounted, I plan on applying a bead of silicone bead from the outside, and joint can be redone down the road (hopefully without too much trouble)

I think that is one step away from the issues mentioned here.

    Bookmark   November 10, 2008 at 11:04PM
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A number of problems occur with wood and moisture.

No finish is completely vapor proof.
All the finish does is slow down the movement of water vapor.

If you have end grin butcher block (the end grain faces up) the cutout for the sink will be in side grain and not as prone to absorbing moisture.

The side grain 'butcher block' is not really butcher block (butcher's blocks use end grain for long life and it is easier on the knives).

The side grain on the face of the counter means that end grain will be exposed on two sides of the sink cutout.

End grain soaks up moisture quickly and easily.

You also need to consider movement of the wood.

The seal between the sink and counter will not remain water tight with more than a small fraction (think thirty secondths of an inch) of movement.

The farm style sink should eliminate most of the problems, but make sure you apply both some finish and seal the edges of the counter against the sink.

A gap and a cover strip would be even better.

    Bookmark   November 15, 2008 at 1:11PM
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Yup, the minimal (when compared to other commonly used species) tangential movement and the ability to resist water were two of the reasons I chose teak.


That's one of my semantic pet peeves...the difference between true butcher block versus edge-grain plank glue ups, and how people always refer to plank as butcher block.

Anyhow, here's a 4' square by 5" thick teak butcherblock...this thing is pretty much bulletproof.

Here's the kitchen sink cutout, it sits in the midst of about 17 or 18' linear feet of 2" thick by 30" deep teak countertop.

And since I'm on a teak kick, here's a teak tub deck...

...and a couple of teak bathroom countertops. The sink countertop has a slight bow front to it.


    Bookmark   November 19, 2008 at 12:29PM
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That's nice mongo, where did you get the teak? Did you glue them up yourself?

    Bookmark   November 19, 2008 at 1:03PM
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Bought locally, well, "locally" as in a lumberyard about 25 minutes from where I live. General Woodcraft in New London CT.

Teak has skyrocketed here. Used to be able to get wide 8/4 planks about 5 years ago for $9 a bdft, now the wide boards are running upwards of $30 a bdft.

Epoxy and biscuits for the edge-glued plank tops, just epoxy for the butcher block.


    Bookmark   November 19, 2008 at 7:33PM
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