# Exact Width Dado Jig



## MT Stringer (Aug 15, 2012)

This is my exact width dado jig. It is similar to others that can be found on the internet. I built it after watching The Wood Whisperer's video a couple of years ago.

Today, I had to repair it due to a router run away,  plus it wouldn't fit the side of the baby changing station I am building.

I made it wide enough to fit a workpiece up to 24 1/2 inches wide. You can make it whatever width works for you, but that part of the jig is fixed.

The only hardware needed is a pair of 1/4 x 20 Star knobs and a pair of toilet bowl flange bolts. Note: Countersink the head of the bolts on the underside of the guides.

The way this jig works is you loosen the knobs, insert your workpiece and snug the adjustable side against it, and then tighten the knobs. That's all there is to it.

Use a pattern bit in your router. Run it down one side and then back up the other side. This eliminates the hassle of cutting dadoes for undersized 3/4 inch plywood. :dance3:

However, using a pattern bit, the smallest dado you can cut would be 1/2 inch. However, you could use a template bushing for a smaller size dado and adjust the jig to the width of the bushing. The jig would then become a straight edge guide.

The left side board is fixed in place with wood screws. My old version was glued and screwed. I had to beat it apart with a hammer so I could reuse the guides.

I cut new pieces of MDF 29 inches long so a kitchen cabinet member would fit (typical is 23 1/4 inches wide for base cabinets and 11 1/4 for the uppers).

I made the slots on the router table with a 1/4 inch straight bit (see pics). I made several passes cutting a little deeper each time until the bit broke through on the last pass.

This evening, I drew up the jig in Sketchup, so feel free to grab the pics and build your own. 

This is my gift to y'all. Hope you build one. I bet you will like it.

Merry Christmas to one and all.
Mike


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## ronheb454 (Apr 8, 2013)

Thanks, looks very good, hope to build one. Merry Christmas to you and yours, take care.


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## Willway (Aug 16, 2012)

Mike that's a nice job with the knobs on top. 

I built on of those years ago. I find the setup time to aggravating, so we are now using Whiteside plywood bits or just straight bits for hardwood. We also use a router guide base that runs in the track on the edge guide.

Anyone that's interested, Yonico (Precision Bits) is now offering a set of plywood bits in a wooden case for $23.95. If the Yonico bits I now have are any example of their quality, these are very good bits.

Yonico 14323 3 Plywood Dado Router Bits for 3/4-Inch 1/2-Inch and 1/4-Inch Plywood 1/2-Inch Shank - - Amazon.com 

Dick


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## chessnut2 (Sep 15, 2011)

Hey Mike..........I had also seen the Wood Whisperer design and was just kicking myself a couple of days ago for not having already made one. It looks like with the placement of your knobs, you've overcome the problem he had with having to leave the workpiece hanging over the edge of the workbench. Thanks. I'll use this.


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## dick in ia (Jul 23, 2007)

I made one of these years back and have been using it countless times since.
It is good to see this jig being re-visited again.


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## Web Shepherd (Feb 8, 2012)

Mike ~ You are a true gentleman. Thanks for sharing your excellent photos and sketchup drawings. Merry Christmas to you and your family.

Bob


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## Herb Stoops (Aug 28, 2012)

Good job mike , you're getting good on the sketchup too. That is good for not only making dados for new plywood thickness but any dado any size. I like it.
Herb


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## MT Stringer (Aug 15, 2012)

Thanks everyone. I have learned a lot from the folks on this forum and this is my way of giving back.

My original version was smaller but the sides of my current project are 17" + so I rebuilt it to accommodate larger work pieces.

I used this jig to cut the dado in the drawer sides for our kitchen remodel...21 drawers (42 dadoes). Each and every one was a good fit (5/8 inch thick stock).

Edit: @Willway - I have those Whiteside bits. I used the smaller one mounted in the router table to cut the 1/4 inch grooves for the bottoms of the drawer sides. They work well.


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## jw2170 (Jan 24, 2008)

Yes Mike, a very handy jig.


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## MT Born (Oct 29, 2014)

*"plywood bits or just straight bits"*

Forgive my ignorance but what's the difference?


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## JudgeMike (Feb 27, 2012)

Thanks Mike! This is now on my "Things to Make" list. I have a couple pieces of MDF that I was looking for something to make with. Wish I could get the hang of SketchUp. Tried several times using it but really slow going. Haven't given up yet, but close to it. 

Merry Christmas to you and yours...Mike


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## MT Stringer (Aug 15, 2012)

MT Born said:


> Forgive my ignorance but what's the difference?


The "plywood" bits are sized for today's plywood sizes such as 7/32 (1/4 inch), 31/64 (1/2 inch), 23/32 (3/4 inch).

My set is Whiteside Part # 470.


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## PhilBa (Sep 25, 2014)

Plywood bits are the exact width of standard plywood which is slightly thinner than the nominal width. From the rockler page - 23/32" for 3/4" plywood, 31/64" for 1/2" plywood, and 15/64" for 1/4" plywood. The problem is that there is no standard so it's kind of a guessing game. That's why an exact width jig is a good idea.


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## MT Stringer (Aug 15, 2012)

And now for an update. I needed to rout a dado part way across a board. Hmmm...what to do. I need a stop block that I can set at exactly 2 inches.

So, I cobbled up a simple jig for my jig! And it worked perfectly as designed. I chiseled the round corners and the result was a good fit for my board. It turned out to be a simple solution.

The stop block jig allows the router to pass over it, yet stop when the router bit makes contact.


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## jangelini (Jan 1, 2015)

Wow! Thanks for all your help. 

Jim


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## jbroweleit (Dec 16, 2014)

Hi Mike, I see that your adjustable dado jig will provide the exact width for any size board. But here is my question: I will be building shelves all with 3/4" plywood with a 3/4" router bit. Why do I need the jig? I could just clamp down a straight piece of wood to the top of my project piece and run the straight edge of the plunge router along that side. (all carefully measured of course) I am wondering if that will be inaccurate, like maybe the plywood width varies or something and the 3/4" bit will make for a sloppy fit. Thanks for your help. Jan


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## MT Stringer (Aug 15, 2012)

jbroweleit said:


> Hi Mike, I see that your adjustable dado jig will provide the exact width for any size board. But here is my question: I will be building shelves all with 3/4" plywood with a 3/4" router bit. Why do I need the jig? I could just clamp down a straight piece of wood to the top of my project piece and run the straight edge of the plunge router along that side. (all carefully measured of course) I am wondering if that will be inaccurate, like maybe the plywood width varies or something and the 3/4" bit will make for a sloppy fit. Thanks for your help. Jan


Yes sir. Sloppy fit is correct. If I were you, I would carefully measure your plywood. It should be slightly undersize. That is the main purpose of the jig. I use a 1/2 inch pattern bit with my jig. Adjust the jig to the width of your plywood by sandwiching a sample piece in between the guides, and lock them down. Your dadoes should be a perfect fit.

Hope this helps. For more info, check out the video by Marc Spagnuolo - The Wood Whisperer. He can 'splain it better than me.
https://www.youtube.com/watch?v=7j4vGS4HY-8


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## radiorich (Mar 26, 2015)

what gret idea .
sincerely rich


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## rbs (Jan 6, 2009)

very nice!


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## MT Stringer (Aug 15, 2012)

Thanks.
I am fixing to use it on a cabinet I am building.


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## MT Stringer (Aug 15, 2012)

Almost three years since I made this jig. It has never failed me yet.

The question of making dadoes on the table saw vs using a router comes up often, so I thought I would resurrect this thread for the newcomers here on the forum.

Your ideas of cutting exact width dadoes may differ but I can assure you, this jig works! At least for dadoes larger that 1/2 inch in width because I use a 1/2 inch pattern bit to do the work.

Mike


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## Dejure (Jul 27, 2009)

*A Step Further*

Consider adding these modifications to your jig. You'll never have to go did up a clamp, or worry about losing one, and it will, greatly, reduce the time it takes you to move the jig to the next spot. I laid out what's involved in building at the following instructables web site:

https://www.instructables.com/id/Router-Dado-Jig/

Kelly


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## MT Stringer (Aug 15, 2012)

Dejure said:


> Consider adding these modifications to your jig. You'll never have to go did up a clamp, or worry about losing one, and it will, greatly, reduce the time it takes you to move the jig to the next spot. I laid out what's involved in building at the following instructables web site:
> 
> https://www.instructables.com/id/Router-Dado-Jig/
> 
> Kelly


Thanks. Mine has been hanging on the wall ever since I bought my CNC. :surprise::grin:


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## Dejure (Jul 27, 2009)

Looking for the green envy icon....



MT Stringer said:


> Thanks. Mine has been hanging on the wall ever since I bought my CNC. :surprise::grin:


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## sreilly (May 22, 2018)

I've seen this sometime in the past and wanted to build one. Now is a good time to actually build it. Seems like a solid simple design that should prove a great deal easier to use then a dado set. I've already deformed several dado shims that didn't quite make it out of the threads on the table saw arbor. No CNC on this horizon anytime soon......Thanks for the reminder.



-Steve


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## sreilly (May 22, 2018)

After getting a few more things organized in the shop I came across a a cove cutting jig that I think can be converted easily to an exact dado cutting jig making it dual purpose. This would require the use of a bearing pattern bit but the sides can be aligned with the exact width of the board, tightened down and then clamped to the plywood to be cut. The jig has knobs to tighten the adjustable bars between the two edge boards to lock into place and is long enough to cut dados up to 41-3/4" long. I'll have to experiment and see what gives. I also need to get a few quality pattern bits as well. The jig is sold by Peachtree Woodworking.


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## CharleyL (Feb 28, 2009)

My exact width router dado jig is made a bit different, but looks very similar. It has additional rails along the two top pieces, so the edge of the router base rides against these. The edge of the main pieces of the jig get trimmed off with the router when the jig is being built, so the distance from the rail to the edge that was trimmed with the router is fixed and always the same as long as you use the same diameter router bit in the same router each time that you use the jig. When the jig gap is adjusted to fit the board that will be inserted in the mortise, the gap between the two parts of the jig will be the mortise width and if the mortise needs to be a little wider than the router bit, a pass along the right half of the jig, followed by a pass down the left half of the jig will create the correct width mortise whatever it is, without the need for a router bearing or a bit that is the exact size of the mortise. Again, the edge of the router base rides against a rail on each side of the jig and the edge that was initially trimmed off by the router bit during construction of the jig is always the same distance from it so it doesn't enter into the mortise width calculation. Just the gap between the two trimmed edges, and you set this gap for the width of the mortise that will be cut, just like you would when using a top bearing router bit in the jig shown. The only thing important is that the router bit for this needs to be the same or smaller diameter than the mortise to be cut and no bearing is needed, because the router base is riding against these upper rails To me, this design eliminates the need for top bearing bits and the need to have different lengths of bits.

As you can see in the photos, it is built much like the ones shown, except for the additional top router base guiding side rails. I have never needed a longer jig since all I've ever used it for was pine shelving, which is never wider than about 12". If I ever need longer I'll just make another longer jig.

Charley


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## Herb Stoops (Aug 28, 2012)

CharleyL said:


> My exact width router dado jig is made a bit different, but looks very similar. It has additional rails along the two top pieces, so the edge of the router base rides against these. The edge of the main pieces
> 
> As you can see in the photos, it is built much like the ones shown, except for the additional top router base guiding side rails. I have never needed a longer jig since all I've ever used it for was pine shelving, which is never wider than about 12". If I ever need longer I'll just make another longer jig.
> 
> Charley


So if you use a different bit of larger diam. it will recut the jig to a shorter distance from the guide rail? In other words, you always use the same diam.bit and same router.
Herb


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## CharleyL (Feb 28, 2009)

Well, at least the same diameter router bit and same diameter router base. I have three DeWalt DW618 routers and I use a 3/8 up spiral router bit, since every dado that I've wanted to cut was in the 1/2" - 3/4" range. You could probably use a different router if the base diameters were identical. If you use a different bit with a larger diameter it will re-cut the jig and you will be required to use that diameter bit from then on and you won't be able to use the jig to make dados smaller than that new larger diameter bit any more. For this to work, you want to make the jig for, and use a bit with a smaller diameter than the dados that you will want to cut and always make two passes, down against one rail and back against the other rail. This widens the dado from the bit diameter to the width of the dado needed and what you spaced the jig for.

The end result is the same, but the design of my jig eliminates the need for special and different size top bearing router bits, as it just uses a single standard router bit that can be straight blade or spiral, but I found that the spiral do a better job when used for cutting dados. Both designs of the jigs adjust for whatever the actual thickness of the board that the dado is being cut to fit, but a jig built like mine eliminates the need for the special top bearing router bits.

Whenever I make a jig that I will keep for future needs, I always write on it any special instructions for it's use. That's why I included the last photo. I darkened part of the text just before taking the photo because I was afraid that the original note wasn't dark enough to see in the photo. This jig is about 15 years old now, and gets used about once per year. It's dirty and the text is fading, but it still works as designed.

Charley


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## Dejure (Jul 27, 2009)

The issue of router bases sizes had much to do with my version. I have about thirteen routers (Hitachi, Porter Cable, Bosch, Dewalt, Trend), so have to be mindful of the different base sizes, which, sometimes, is extreme (e.g., 3/4 horse PC to a Bosch Colt).

With my version, as long as the bit and bearing are the same size, you can use any router and any bit, up to the size of the groove or dado. I figured it was easier to grab any router and any bit, as long as it was a pattern bit (bearing on top, for those not familiar with the difference between a flush trim bit and a pattern bit).

IF you wanted to deal with the issue of base sizes, you may be able to flip my version 90 degrees, but it would still take some careful measuring to the right and left of the bit area, rather than a quick set and go for "what you see is what you get."


In the end, your version is a WHOLE lot easier to whip out than mine. A person could mark the base for different router bases on hand and a second side slides at some point, but a second slide might just be more "buzzer and bell" than necessary, compared to yours.

Any way you go, a jig for repeating cuts in wood, even if only used once a year, will prove itself worth its weight over the years.


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