How to cut LOTS of dadoes into long stock

[Anthony Whitesell]

Based on the links provided in a previous thread on making drawers for my wife's craft supplies, I have constructed the first batch of four dozen drawers (I think I may need another two dozen). I decided to make the drawers first and see how many were used before making the carcass to hold them. The drawer design is a take off from this video https://www.youtube.com/watch?v=sSNLwEu1QCk. My drawers use a 3/16" hardboard bottom and 1 1/8" sides. The drawers will either hold the items directly or 2 5/8" tall organizer containers. Similar to the video, I plan to cut dadoes up the side of the carcass to act as the other half of the drawer slide. The carcass will have 1/4" dadoes every 1 1/2". The difference is the sides of my carcass is 72" long. To ensure the dadoes align horizontally when assembles, I plan to cut the dadoes into a piece of plywood 28 1/4" wide then cut to the plywood to the final 12" width.

I'm looking for options on how to cut 48 dadoes 1 1/2" apart on a 28 1/4" by 72" long piece of plywood. (about 113 feet of 1/4" dado)

I thought of a box joint type jig on the table saw, except it won't fit. My shop is not 12 feet wide. Twelve feet being the necessary clearance to start with 6' to the left and end with 6' to the right.

Any other thoughts?

[Bill Dufour]

radial arm saw with a finger on the fence that flips up/down to register into the dado.

[Anthony Whitesell]

That was one thought, only I don't own a RAS.

[Frankie Hunt]

Use a router.

Make a jig for the router to follow. Clamp it to the board, rout, move jig, rout, repeat.

[Robert Engel]

If I'm imagining this correctly, how about a router with an indexing strip fixed to the base that registers in the previous slot.

[Anthony Whitesell]

The router was the second item came to mind after I ruled out the RAS since I didn't have one. My plan was a jig with an indexing strip. I was thinking of a carbide spiral downcut bit would be best. Any idea how many feet of 1/4" wide 3/8" deep dado you can cut with one $20 router bit?

[Ted Derryberry]

Thousands, with a quality bit.

[Osvaldo Cristo]

One more for router. It looks me the best solution if you do not have an industrial production...

[Jim Becker]

Router. You can easily duplicate how I do this on my Festool MFT. I clamp a narrow board to the back fence and after adjusting the router on the track to cut the correct depth and width (bit choice for the latter) I make a cut that essentially marks that wood board the guide for where the router is going to go when it travels along the fence. Then, it's just a matter of sliding the workpiece until the groove across the wood sub-fence lines up with the layout marks on the workpiece and making the cut. Move the workpiece...make the next cut. You can make a fixed jig to accomplish the same using any router. Just have your guide rails setup such that they are exactly above the base the thickness of your workpiece plus a "proverbial hair so you can slide the workpiece through. Too loose and you'll have to clamp for each cut, although using quick clamps to insure it doesn't move is still a good idea. Too tight and you'll get frustrated.

[Jamie Buxton]

...I thought of a box joint type jig on the table saw, except it won't fit. My shop is not 12 feet wide. Twelve feet being the necessary clearance to start with 6' to the left and end with 6' to the right..

Can you turn the table saw 90 degrees? That is, is your shop 12 feet long, not wide?

[Rod Sheridan]

How about you start at one end, go 36" then flip it and do the remainder of the dadoes?

Know anyone with a sliding table saw?

Regards, Rod.

[Anthony Whitesell]

How about you start at one end, go 36" then flip it and do the remainder of the dadoes?

Know anyone with a sliding table saw?

Regards, Rod.

If my measurements aren't dead nuts on I could be in trouble when I reach the center.

I have been trying to figure out how to work from the center out. The if I start with the eight foot piece I can just cut off both ends to get to the final length.

[Anthony Whitesell]

Can you turn the table saw 90 degrees? That is, is your shop 12 feet long, not wide?

I guess I should be clearer. I don't have a 12' by 6' clear area to work. 12' being the length left to right needed and the 6' being the distance need to start and finish each cut while standing at the saw.

But you have me thinking. If I start with the 6' to the left, I could make some cuts, then move the saw to the left and make more. For all intents and purposes, only moving the plywood about 2 feet. Picture painting the outside of a house. You paint a section then move the ladder, you don't move the house. Hmmm....that has possibilities. Now to think about how to make the jig for a table saw. Thoughts? Purpose built sled?

[Ken Fitzgerald]

Make a table saw sled with an indexing "pin" on it.

[Bryan Lisowski]

I would use a router a homemade jig. I would also route all the dados and then cut the piece so they match up as well.

[Edwin Santos]

2nd vote for a table saw dado sled with an indexing key. A good way to do it is to cut a t-slot or recess a t-track in the fence of the sled and use jig hardware to attach a face that you can loosen, slide, replace. I built mine for one particular project not realizing how useful it would be on an ongoing basis. You can cut each 12" side individually this way and they'll be identical, and the process will be FAST.

[Jamie Buxton]

What is the grain direction of the plywood where you're cutting these dados? Dado heads have some tendency to tear out the face grain if you're cutting across the grain direction. There's much less tear out if the dado runs with the grain direction. If you must run the dados across the face grain direction, the router has less tear out. The downside to the router is that it is much slower.

[Anthony Whitesell]

What is the grain direction of the plywood where you're cutting these dados? Dado heads have some tendency to tear out the face grain if you're cutting across the grain direction. There's much less tear out if the dado runs with the grain direction. If you must run the dados across the face grain direction, the router has less tear out. The downside to the router is that it is much slower.

Good point. Technically dadoes are cross grain and grooves are with the grain. Even though it is plywood, the cut in the outlet layer will be cross grain. Maybe I should stick with the router, but I'm concerned on how many router bits this will take to complete.

[Greg Hines, MD]

I would definitely do it with a router, and I think you should be able to do all of it with one good quality bit. If your shelves are finicky, you can do a two sided guide for it, and an undersized bit.

Doc

[Ray Newman]

My concern is plywood "quality". Once fabricated a similar drawer unit about 24" long with 1/4 x 1/4" dadoes for the runners from 3/4" ply.

However, the ply was not the best quality and internal stresses caused the sides to quickly warp before assembly. Since this cabinet will be 72", would it be worthwhile to purchase say Baltic Birch ply and maybe add some non-removable dividers to prevent warping and add structural integrity??

Also believe that a router would be your best tool for the job, especially a plunge router set to first score the work, then a second pass to cut to needed depth.

You may have already thought about the router and a shop-fabricated jig. If not, since you need to cut 48 dadoes 28+” deep, fabricate a dedicated dado jig??

Using the Porter-Cable style router template guides, construct t a T Square style jig with two arms to trap the template to prevent any cutting errors. I would also cut both sides at the same time from one piece, then rip to final width.

[Anthony Whitesell]

My concern is plywood "quality". Once fabricated a similar drawer unit about 24" long with 1/4 x 1/4" dadoes for the runners from 3/4" ply.

However, the ply was not the best quality and internal stresses caused the sides to quickly warp before assembly. Since this cabinet will be 72", would it be worthwhile to purchase say Baltic Birch ply and maybe add some non-removable dividers to prevent warping and add structural integrity??

I have been using the Home Depot poplar veneer 3/4" plywood for some time. I believe it is either 7 or 9 ply. Higher than CDX plywood, not as much as birch ply. I have built several bookcases with no fixed shelves and haven't had an issue...yet. There will be a full back on it. Due to the tighter tolerances of this built I consider adding a fixed center span.

[Art Mann]

Here is just a warning about using an indexing guide mechanism. Each cut depends on the accuracy of the previous one. If you do a lot of dados in a row, the cumulative error will get pretty far off the mark if the guide isn't sized perfectly. It is the same challenge as trying to use the old homemade finger joint jig on a table saw.

[Glen Gunderson]

Router is probably your best bet, though as Art mentions watch out for cumulative error. If your indexing guide is 1/32nd off you'll be 1 1/2 inches off by the end of 48 dadoes. You could use an indexing guide for most of them but have a few spots where you go off a measurement, say every 8 dadoes which would keep you on track more or less.

Another less dusty option just off the top of my head would be to use 1/2" plywood and do two layers of it. One full sized layer for the box and then a bunch of 1 1/4" strips glued and nailed with 1/4" gaps for the dadoes. As long you keep the nails away from where you'll saw you could do it as one large piece and then slice it into two sides.

[glenn bradley]

I would also route all the dados and then cut the piece so they match up as well.

This is how I do critical multiples.

[Jim Becker]

Be careful with varying thickness on a lot of the import plywood that's in the mass market. I made that mistake recently when I wasn't thinking and it absolutely affected the project and not in a pleasant way. IE, it was undersized at 17.5mm instead of 18mm and still had additional thickness variation throughout the sheets...enough to matter, particularly with dados, grooves and rabbits.

[Rod Sheridan]

If my measurements aren't dead nuts on I could be in trouble when I reach the center.

I have been trying to figure out how to work from the center out. The if I start with the eight foot piece I can just cut off both ends to get to the final length.

Hi Anthony, it really won't matter.

You're going to lay them out using a tape or steel ruler and a pencil.

Let's for sake of argument agree that you make one dado 1/64" too high and one 1/64" too low.

Who cares? You'll have more than 1/64" clearance between drawer fronts, and since you're cutting both gables at the same time, they'll be symmetrical.

You're over thinking this issue.............Regards, Rod.

[Jim Dwight]

I tried a cabinet (actually two) where the drawers rode in dados in the sides. It did not work well. The drawers didn't slide well at all. If that is what you plan, I would start with a small version and make sure it works well enough for your wife.

But to cut a bunch of long dados, I would use one of my PC routers on a special base that rides my DeWalt track saw tracks. I would probably set the track for each dado rather than indexing off the previous one. Maybe I would cut 2 or 3 then use the track again. This setup is more fool proof than a table saw. The router base cannot go off the rail like a piece of plywood can move away from the rip fence.

You should be able to make a base for any router and any track saw track. It just needs a dado to ride the rail. The base for the DeWalt was not expensive, however. It even has a fine adjustment that would help with getting the dados in the right location.

[Anthony Whitesell]

These are not drawers as much as they are trays. They will be removed to access the materials contained within. To that end, the bottoms are 3/16" thick and the dadoes will be 1/4" to ease with sliding the trays in and out.

If I go with a router I was thinking of using the guide bushing to make sure the router doesn't/can't pull away from the guide. I also have a 4' AOI guide with a router base attachment but having to align that at 90* for each cut rules that out. I would like to get this project done before summer.

[Anthony Whitesell]

Luckily there are no drawer fronts. I could mark to 1/64" but then aligning and cutting, I am afraid the cumulative error there wold be tremendous. Error of 1/32" per slot would be 2%. I'm definitely leaning towards starting from the center and working to each end. That would reduce any accumulated error by 50%.

[Anthony Whitesell]

What would you call good quality? Whiteside? Amana? MLCS Katana? or?

[Jim Becker]

Whiteside, Freud, Infinity, etc., IMHO. That's what I buy for bits that get the most work. I do use less expensive "multi-colored" bits for utility or one-time profiles...mostly from Lee Valley at this point. My most recent purchase is a Whiteside. My dovetail bits are from Jessada...not sure if they are still around or not.

[Glen Gunderson]

Luckily there are no drawer fronts. I could mark to 1/64" but then aligning and cutting, I am afraid the cumulative error there wold be tremendous. Error of 1/32" per slot would be 2%. I'm definitely leaning towards starting from the center and working to each end. That would reduce any accumulated error by 50%.

If you're just marking the panel and setting the jig to those marks then there won't be any accumulated error. Just lay out a tape or a ruler and mark every 1 1/2" along it. If you're 1/32nd short on one space it just means the one next to it will be 1/32nd or so large.

I also think capturing both sides of either the router base or a guide bushing in the jig is a good idea to prevent wandering off the line. I'd make something like in this video:


https://www.youtube.com/watch?v=IsdeeQBLm2E


Throw on a fence that's 90º to the slot and you're good. Just put a mark every 1 1/2", line up the slot to that mark, and rout away.

[Anthony Whitesell]

I have tried this jig method in the past. It only works if you don't rotate the router. If the base is not perfectly centered then rotating the router either changes the position or results in a wavy cut (if you rotate and rotate it back). If/when I have to do this I use the plunge base router which has a flat on one side.