Can you cut dadoes into 3/4" thich wood for shelves?

[JonW]

So I tried a few things last night,with some 3/4” scrap plywood. I cut a few pieces to about 6” x 20”. I put a template collar on my router. Used the edge of one sheet to mark a line for routing. Added a little extra space for the collar. Use another board as a straight edge. And then routed out a 1/4” deep groove in 2 pieces. Put in the third piece and made a little shelf. It was plenty strong- I could stand on it, no problem (I weigh 150 lbs). Although I still want to go with 1/2” shelves for a lighter look. But one dado was tight enough that I had to hammer in the shelf. The other was a little loose. So getting a consistent groove/dado thickness will take some work. Also, I found out that it’s all a little wobbly, left to right. So I added a 1x4 piece of wood cut to slide between the 2 legs and that helped a lot. So the 1/4” dado looks like a good idea, with a small brace on each shelve (how thick do they need to be?) as long as I can figure out how to cut the dados to a consistent width. Interesting.

[JonW]

Tom-
Very slick looking jig there. Heck, making that is a project in itself. Can you actually use the shelf thickness to determine your dado thickness? Or do you want to go a little thinner to make the shelf fit tightly into the dado groove?

Pappy-
OK, 1/4” dado, 1/2” shelves. Sounds good. Then 1-1.5” piece under the shelf (just in the back, correct?) to prevent left-right wobbling, connected with a rabbet. Do I have all that right?

I didn’t say how I’m going to finish the shelves because I haven’t decided yet. I’m actually thinking of keeping the baltic birch ply edges visible for now. And see how I like that. Roundover or camfer most of the edges, but that’s about it. Maybe add a touch of stain and urethane or tung oil. Not sure. Open to ideas. This is my first real thing to build, so it should probably be kept simple.

Jim-
Interesting that dados make assembly easier. I hadn’t thought about that. What doyou mean by rigidly attaching? To prevent racking, are the 3 pieces in cjupdike’s shelves an OK way to go? I tried that last night with my test piece and it help a lot.

Cjupdike-
Great photos- thanks. So it looks like you added a rear brace for only 3 of the shelves. That looks to be stable enough? How did you connect those side pieces?
What is edge banding?

BY the way, for the sides, I have in mind 2 legs, each of 3” width. The rear legs will be straight and the front legs will have a curve. The curved leg will remain 3” wide, but curve over 8”. So no back (except the braces) and no solid sides. That’s the idea, at least. Doesn’t have to be that way, though.

General question:
You folks are saying to add a cross piece to that back of some (or all) of the shelves to prevent racking (left-right wobbling, it think). I’m not quite sure how you are saying to connect this brace. If I use dadoes for the shelves, I don’t need screws. So I’d like to avoid screws for the whole thing. If I cut a rabbet or horizontal dado into the legs with a router bit, won’t there still be a little bit at the corner that is rounded like the router bit, and the bracing piece won’t fit into that groove?

You folks have been great. I’m really just learning. Thanks.

[scorrpio]

Cutting proper width dado is not that hard. First, make a rough cut that is about 1/8" narrower than needed. Then, clamp two straightedges on either side of the dado, using the actual shelf that will go there as a spacer - now you can clean it up with a flush trim bit for an exact fit.

Attaching braces: Lay a rear leg inner face (one with shelf dadoes in it) up. In the rear edge of the leg, rout short rabbets about 1/2" deep and as wide as your braces will be thick. Yes, these rabbets will have rounded ends. Now, chuck a roundover bit with the same RADIUS as yor rabbet bit. (i.e. if you cut rabbets with a 3/4" DIAMETER bit, use a 3/8" roundover) and put roundovers on top and bottom front edges of your braces. Presto! The braces should now perfectly fit the rabbets and roundovers will give them a smoother look.

[Tom Miller]

Tom-
Can you actually use the shelf thickness to determine your dado thickness?

That's basically the idea, with this type of router bit and this jig. You set the jig separation by sandwiching your shelf stock between the two boards. You need to test the fit, and usually you'll add some kind of shim (a sheet of paper, etc.) in the sandwich to get the perfect fit. Once you determine how much shim you need, that should stay constant.

Then, once you have the shelf thickness and angle set (90 degrees in your case), tighten all the knobs. You can slide the jig up and down your stock while maintaining the width and angle.

The jig was extremely easy to make, BTW. In the configuration shown it guides a bearing bit. Flip the top pieces over, and it's a wider guide for guiding the router's baseplate.

Regards,
Tom

[LarryG]

One point I don't THINK Tom mentioned about his jig ... if you don't need to cut angled dados, the jig can be even simpler. My router-dado jig consists of two pieces of 3/4" MDF, each about 7" x 14", and each with an oak fence screwed across one short edge, perpendicular to the long edges. IOW the jig has two completely separate but identical parts.

To cut a dado, I place the oak fence of one jig-half against the edge of the workpiece and clamp it down with a couple Quick-Grips. Then set a scrap of the actual shelf material against the jig's edge and slide the other jig-half up into position and clamp it down. Then pull out the spacer scrap and make the cut, using a top-bearing bit as Tom does. This is about as simple and as foolproof as it gets since there's no measuring (other than locating where the dado goes, of course), no moving parts, no knobs to tighten.

Which is not to suggest Tom's jig is a Bad Thing. It'll do more than mine will; but if your needs are simpler, your jig can be simpler too.

[JonW]

All these jigs seem to be a variation on a theme. Good to hear about all of them. It sounds like you can use the actual shelf as a spacer and not worry about having to narrow the dado width to get a tight fit for the shelf.

Tom- I like that jog a lot. What did you buy for those knobs, screws, etc.?

Larry- I’m not 100% sure how what you’re describing is different from just using two straight edge pieces clamped to where the dado should be cut. You put half of your jig on the edge of the work piece, but doesn’t that make it perpendicular to the dado groove you want to cut?

Maybe just lining up two straight edges, as suggested by scorrpio, is an easy thing to do.

[JonW]

Cutting proper width dado is not that hard. First, make a rough cut that is about 1/8" narrower than needed. Then, clamp two straightedges on either side of the dado, using the actual shelf that will go there as a spacer - now you can clean it up with a flush trim bit for an exact fit.

OK, makes sense. And this will make for a tight enough fit? And I should not bother making the dado slightly narrower than the shelf- I thnk that woulkd complicate things.

Sounds like this will require a flush trim bit with the bearing on the top. I've got one with a bottom bearing. Something else to buy, I guess.

Attaching braces: Lay a rear leg inner face (one with shelf dadoes in it) up. In the rear edge of the leg, rout short rabbets about 1/2" deep and as wide as your braces will be thick. Yes, these rabbets will have rounded ends. Now, chuck a roundover bit with the same RADIUS as yor rabbet bit. (i.e. if you cut rabbets with a 3/4" DIAMETER bit, use a 3/8" roundover) and put roundovers on top and bottom front edges of your braces. Presto! The braces should now perfectly fit the rabbets and roundovers will give them a smoother look.

OK, that's really clever.

[LarryG]

Larry- I’m not 100% sure how what you’re describing is different from just using two straight edge pieces clamped to where the dado should be cut. You put half of your jig on the edge of the work piece, but doesn’t that make it perpendicular to the dado groove you want to cut?

It IS basically the same thing, yes. The oak fences that are permanently attached to the jig halves simply make everything self-squaring, self-aligning (other than the gap between the two jig halves, which is set using the scrap spacer). You set the oak fence tight against the long edge of the workpiece, and then run the bit's bearing along the edge of the jig that's perpendicular to the fence edge.

Like many simple things, this one is hard to describe in words. I'll try to take a few pictures tonight and will post them tomorrow.

[JonW]

So the oak is actually perpendicular to the MDF. Such that it actually sticks out over the surface of the MDF? And then you touch the oak to the edge of the work piece. And then the MDF runs parallel to the work piece, with it's edge at the edge of where the dado will be? And then you run the router along the edge of the MDF.

I may have this totally wrong. But it sounds like a decent setup if I can figure it out. Yeah, a photo might be the thing.

[greencat]

I think its like having 2 carpenter squares with a bottom that will square with the stock.

Is that a common router bit? And I assume that you make a slight cut into the jig if you run the dado to the edge?

[LarryG]

I think its like having 2 carpenter squares with a bottom that will square with the stock.

Is that a common router bit? And I assume that you make a slight cut into the jig if you run the dado to the edge?

The two carpenter's squares analogy is pretty close, if you imagine that the short legs set the jig halves square and the router bit runs between and is guided by the long legs. Main difference is that instead of each jig half being L-shaped, it's a rectangular piece of MDF. Otherwise, it's the exact same principle.

I'll post pictures.

The top-bearing bit is fairly common ... you may not find one at HD/Lowe's, but all the major bit mfrs make them.

With Tom's jig, the bit will indeed cut the connecting piece (or at least it appears so). With mine, it won't since the jig consists of two halves that are not connected.

I'll post pictures. Really.

[JonW]

Sorry, I'm still not seeing it. I'll wait for the photo. And once I see that, I'll probably go "Ooooooohhhhh I see. That's easy."

Any more ideas for how to add in the cross brace at the back of the shelves, without using any screws or nails? I might (or might not) try this out this weekend. And I won't be able to order the bits described by scorrpio in time.

What if I made another dado on the rear of the legs, that goes all the way through the edge of the leg. And rest the brace in that? I think someone mentioned it, but it sound to me less stable - the brace touches the leg on 3 sides. But the way scorrpio described it the brace touches the leg on 4 sides of the brace- that seems much more stable to me. (Well, to me with no exprience.)

And I'm still concerned that a dado cut to the width of the shelf (from setting the jigs to a piece of the shelf) might have too much play. I'll add glue, of course. Maybe I just need to practice on scrap first and see how that goes.

[LarryG]

And once I see that, I'll probably go "Ooooooohhhhh I see. That's easy."

Guaranteed.

What if I made another dado on the rear of the legs, that goes all the way through the edge of the leg. And rest the brace in that?

You can do that, if you don't mind seeing the plywood plies in the end of the brace.

Alternatively, you can inset the braces in non-through dados as previously described except forget the rounded-over jazz. Use the router to cut as much of the dado as possible and square up the rounded ends with a chisel. This is SOP. But, that said, there's no end to the different ways to do this. Half the fun of woodworking is figuring out how to design the joinery so that it is strong, looks well, and is reasonably easy to build, especially if you have limited tooling.

And I'm still concerned that a dado cut to the width of the shelf (from setting the jigs to a piece of the shelf) might have too much play.

Why do you think this? Theoretically the dado should match exactly the shelf thickness. In practice you need a TINY amount of clearance to facilitate assembly, and to give the glue somewhere to go (hence the sheet-of-paper shim that Tom mentions).

The LAST thing you want to do is cut the dados undersize so that you have to bodily force everything together with a hammer. That will cause your legs to bend, opening up the dado and possibly even breaking the leg (and DAMHIKT).

[Tom Miller]

What did you buy for those knobs, screws, etc.?

I usually get this kind of jig hardware from Rockler. They occassionally sell their "t-track" kit for half price.

The jig I showed was just meant to show how easily you can set the dado width. Like Larry said, you may find it a little unwieldy since it's meant for non-perpendicular dados (I'm in the process of making a loft ladder). If you build the right angle into the jig, you don't have to get out a square to set the thing, and you don't need all the hardware.

I think this is what Larry's talking about (hopefully save him the effort of dusting off his Kodak Brownie ):



Regards,
Tom

[JonW]

Chisel out the corners. OK, good idea.

Why do you think this? Theoretically the dado should match exactly the shelf thickness. In practice you need a TINY amount of clearance to facilitate assembly, and to give the glue somewhere to go (hence the sheet-of-paper shim that Tom mentions).

The LAST thing you want to do is cut the dados undersize so that you have to bodily force everything together with a hammer. That will cause your legs to bend, opening up the dado and possibly even breaking the leg (and DAMHIKT).

OK, I didn't think of things bending if the fit is too tight. I was thinking everything should be jammed together with a hammer, to get the tightest possible fit. Not the correct way to look at it, apparently. I've never built anything without screws (and few things at that), so I'm concerned about things not being tight enough.

Forget the camera- Tom's picture is perfect. And here is where I say "Oooooohhhh, that's easy." Even I can make one of those.

This question is probably beyond me, but I'll try: I was thinking about having a curve in the front leg of the shelves. So the dado would have to be parallel to the floor, but at a funny angle to the curved wood. And Tom's jig, in the photo, might or might not work because you won't be able to clamp the jig sides to the wood sides and have the wood and jig touching completely flush. Any ideas how to do this? I might still be able to use Larry's 2 piece jig (or Tom's as well), just not have the jig side flush with the curve. That should work, I'd think. OK, got it.