How to make a wide flat bottom dado?

[George Bokros]

I need to make a 1 3/8" wide dado for a mirror frame I am making. I know I can use my dado stack but would like to get a really flat true bottom. I have a dado clean out bit, aka pattern bit, I can use it in the router table to clean out the bottom of the dado. It only has 1/2" cutting diameter. Would it work and be safe to use it in the router table without the fence and make multiple passes to get the dado bottom flat. Hope I explained myself clearly.

Anyone ever do this?

[Jacques Gagnon]

George,

If I had to do this, I would use the router table after the dado set in the following sequence:

1. remove most of the material with the dado (slightly shallow and narrower dado)
2. bring the piece to the router table and work to both final depth and final width. Definitely use a fence and some form of micro-adjustment to creep to the exact width.

I am assuming here that you need "precision". If not, the dado alone with a shoulder plane would likely get you there faster.

[Lee Schierer]

That would work for the edges, but you would have 3/8" in the middle that would be missed unless you free hand the center or use a fence to guide your piece so the router bit cuts out the center portion. This assumes it is a top mounted bearing and the depth of your dado allows the bearing to ride on the edges of the dado.

[glenn bradley]

I made a modified version of the ShopNotes dado jig in issue #76.

377138

It easily accommodates wader dados like the ones I use for my tablesaw sled ZCI's.

377137 . 377136

[Marshall Harrison]

There's always the "cleanup with a chisel" route.

[George Bokros]

Oooops, it is a rabbet not a dado.

[Jacques Gagnon]

... this was my understanding from your description; I still suggest the finishing touch with the router table and fine tuning using the fence (and proper router bit projection).

J.

[Brian Holcombe]

I usually make these clean by cutting them first with a router then finishing with a shoulder plane.

I cover it carefully in this post, the majority of which has to do with dovetails but the secondary topic is a clean rabbet around the underside of the table top.

https://brianholcombewoodworker.com/2017/02/22/tea-house-table-dovetails/

I probably did not mention it specifically in the post, but I used a downcut spiral bit to waste most of the material. I can use them crossgrain to good effect, even if they are a bit slow.

[Derek Cohen]

Linking to a recent thread (on hand tools in a power shop), this is a time when a shoulder plane would be handy. A couple of quick swipes, and you are done.

Regards from Perth

Derek

Edit to add a PS: Brian, we must have posted at the same time, with the same mind! :)

[Robert Engel]

How about dado blade then cleaning up with a sanding block?

[Bob Vaughan]

https://www.infinitytools.com/routing/router-bits/carbide/groove-making-router-bits/dado-planer-router-bits

[Ted Derryberry]

Unless I had a lot of them to do I'd just use the router table taking 1/2" wide bites at a time until I got there.

[Peter Christensen]

I would do it in two passes on the table saw with a combination or rip blade. First pass with the wood on edge. Second with the wood flat to cut the waste off. Because both cuts are not through cuts you can't use a blade guard but you should have the riving knife on if the saw is equipped with one, so exercise caution.

[George Bokros]

Different take on this. I need a 1 1/2" rabbet 3/8" deep. Instead make a 3/8" rabbet 1 1/2" deep by running running the stock on edge instead of face down. First pass would be 3/8 rabbet 1" deep then raise the bit and make a second pass to get to the full 1 1/2".

What do you think?

[George Bokros]

I would do it in two passes on the table saw with a combination or rip blade. First pass with the wood on edge. Second with the wood flat to cut the waste off. Because both cuts are not through cuts you can't use a blade guard but you should have the riving knife on if the saw is equipped with one, so exercise caution.

Don't see how you can use a riving knife since cut is a through cut.

[Peter Christensen]

Don't see how you can use a riving knife since cut is a through cut.

The blade is buried during the cut except when it enters and exits the cut, therefore not a through cut. A riving knife is like a shark fin sitting just behind and a touch below the top of the blade, so it works when the blade is inside the wood. A splitter sits higher than the blade, usually holding a blade guard and anti kickback pawls, so it can only make through cuts.

[George Bokros]

The blade is buried during the cut except when it enters and exits the cut, therefore not a through cut. A riving knife is like a shark fin sitting just behind and a touch below the top of the blade, so it works when the blade is inside the wood. A splitter sits higher than the blade, usually holding a blade guard and anti kickback pawls, so it can only make through cuts.

Since I do not have a riving knife I assumed it was similar to a splitter. I stand corrected.

[Frank Pratt]

A rabbet plane will flatten the bottoms all to exactly the same depth quicker than you can set up a router & with a lot less mess & noise. They are a wonderful tool.

[Greg Hines, MD]

I would do this in two stages. First, use your table saw to cut the depth of the rabbet at the inside edge. to give you a crisp edge there. Then I would use a router, either in a table or handheld, to hog out the rest with a flat bottomed bit, starting at the end of the board and working my way to the saw cut.

Doc