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

[JonW]

OK, I just had another idea of how to make a jig for cutting a dado. Something I could try this weekend with my router and the 1/2” straight cut bit I have (no bearing). My router (Hitachi M12V) has a collar you can add to follow a template. Kind of like the bearing on a bit we’ve been talking about, but it’s not a rolling bearing and the diameter is a little larger than a 1/2” straight cut but such that the bit rotates in the collar.

I could make a template. Say, out of a 1’x1’ board, 3/4” thick scrap. Cut a straight groove, all the way 3/4” through, this board such that I can follow it with the router collar. But just have it as a groove in one board- don’t cut it to the edges to make it 2 pieces, keep it as one. The groove will be wide enough to be the width of the dado I want to cut. And the width of the groove will allow the collared router bit to move just enough to get the exact dado width I want (say for a 1/2” thick shelf). So it's one piece, no moving parts, and just for one width. I’d just clamp this jig to the work piece wherever I want to cut the dado. The only tricky part is cutting a precise groove in this jig.

But now that I've seen a picture of Larry's jig, I'm really liking that.

[LarryG]

(hopefully save him the effort of dusting off his Kodak Brownie):

HEY! I'll have you know I'm thoroughly modern ... I got me one of those 110 cameras. Uses flashcubes, even.

Your little drawing indeed captures the basic concept. But I'll still be dusting off the Brow^H^H^H^H 110 because I just remembered that I promised someone else some pictures of another jig, one I use on my router table. (Next trick will be remember to whom I made said promise, and in which thread.)

EDIT: Jon, do you get television's DIY Network? If not, you need to see if your cable system or satellite provider offers it (DirecTV does; that's what I have) so you can watch a show called WoodWorks. It's hosted by furniture-maker-extraordinaire David J Marks. He builds stuff like you're contemplating all the time ... curved shapes, angles, stuff that requires a lot of templates and inventiveness to accomplish.

Failing that, spend some time on the DIY Network web site, looking at the pages for Marks' show. Unfortunately the pictures are very small but they and the write-ups will still be of help. This one in particular ought to help:

http://www.diynet.com/diy/shows_wwk/..._26938,00.html

and this one too:

http://www.diynet.com/diy/shows_wwk/..._26935,00.html

He used bent laminations for the legs on the first one, but the method he used to cut the shelf dados level with the floor is almost exactly the problem you're facing with your curved front legs.

[JonW]

HEY! I'll have you know I'm thoroughly modern ... I got me one of those 110 cameras. Uses flashcubes, even.

Your little drawing indeed captures the basic concept. But I'll still be dusting off the Brow^H^H^H^H 110 because I just remembered that I promised someone else some pictures of another jig, one I use on my router table. (Next trick will be remember to whom I made said promise, and in which thread.)

Well then your next step in photo progress would have to be a Polaroid.

I may now have to pick up a top bearing bit to try out your jig.

[greencat]

Jon - Are you still thinking about a design with 4 - 3" plywood legs? Are you doing this because you like the design or you want a simple design?

Cjupdike's design will be a lot stronger and not too difficult to make. By the way the shelves look nice. – Is that oak plywood?

If you like the clean lines of your design you could also make the legs out of 1 1/2 inch plywood by gluing 2 - 3/4 pieces together.

This would give you enough strength so that you would not require a back brace. You could even do this without a dado. For example – cut the 4 - 3” x 48” legs and then glue on shorter pieces to the leg. Leave a gap between the short pieces to form the groove where the shelf would go. If you have some flexibility I would adjust the shelf size so all of this could come out of 1 sheet of ¾ plywood.

[LarryG]

Oh, and another thing ...

Here's another trick for getting the dados in a curved leg parallel and level to the floor: cut the dados first, in a rectangular piece. THEN cut the rectangular piece into the curved shape of the leg.

[scorrpio]

As to the question of how to cut exact dados in something that is curved:

The answer is to cut the dados first! Take that piece of plywood when it's still a rectangular blank, cut the dadoes. THEN cut the curves.

Joinery should never be tight. It should not be wobbly for sure, but it should all come togeather with modest hand pressure or light mallet taps. And as you graduate to working with solid wood, you'll need to learn joinery that actually allows for some 'play' due to seasonal changes.

[LarryG]

And yet ANOTHER thing ...

Adding to my tip about cutting the dados before you cut the curves ...

Start with a rectangular piece wide enough to make all four legs. Cut the dados, all the way across. Rip-cut the two straight legs off the rectangle. Then rip the remaining piece, which will become your curved legs, down its middle and fold the two halves together, like you're closing a book. Layout your curves and cut both legs at the time time, being careful to align the various dados precisely with each other.

The reasons for all this are, I'm sure, obvious: cutting all the dados while all four legs are still "connected" ensures that the dados will all be at exactly the same heights off the floor; and cutting the two curved legs together ensures that they are exact mirror images of each other.

An additional bonus is that this reduces the setup time for your dados, since you only have to deal with one large workpiece instead of four small ones.

[JonW]

Wow, you guys are bright- cut the dados before carving out the wood. I like it.

OK, I won't make things too tight. Good to learn these things before I start working.

That diynet link with the shelf stand is _very_ similar to what I had in mind. I was thinking of having a curve in the front legs. Although flip his curve- put the straight part to the floor and the curve part pointing up. And for the rear leg have it just straight up and down. And 20x24" for my shelves. And add some braces to some (or all) of the shelves, between legs. I'll have to read through that project carefully.

No, I'm not set on that design. It's just something that seems like it might be nice. And maybe something I could do for my first real project.

Sorry, no TV for me so I can't watch that show. Looks good, though. Well, I have a TV but no cable and I don't want to get cable- I'll end up watching too much TV and doing fewer fun things like woodworking.

Yes, I had thought about 1.5" thick legs, gluing together 2 pieces of 3/4". But maybe with a 1/4" dado I can be OK with 3/4" legs, about 3" wide each? I want to keep the design looking a little bit on the light side. I don't want something that looks like it's made of thick tree trunks and weighs 500 lbs. But I'm open to all ideas.

[scorrpio]

Layout your curves and cut both legs at the time time, being careful to align the various dados precisely with each other.

And how do we make sure these 1/4" deep dadoes are precisely aligned? Well, we cut a couple 1/2" wide strips of shelf stock and stuff them into top and bottom dadoes between the legs!

[Tom Miller]

Geez, step away from the computer for two seconds to do some work...you guys have been busy!

What Larry said about cutting your dados first!

Failing that, there's no reason you have to register your dado jig off of each side. Both pieces could register off one side, but you'd have to re-do one of your jig pieces. (I guess the version I showed first would work alright, too.)

But the main point I wanted to make -- you should try making a test dado or two. Here's what'll surprise you:

1. When you add glue, wood swells just enough to either make a somewhat loose fit tight, or a tight fit too tight. If you can't put it together without mallet taps when it's dry, game over.

2. A test dado of 6" length isn't the same fit as the real dado you do of 24" length.

Regards,
Tom

[LarryG]

scorrpio: Ideally, aligning the facing dados with a scrap is the way to do it. Being lazy, I'd probably eyeball it.

Tom: We're tired of Monte being the only Forum Windbag, and your training is progressing much too slowly.

Jon: There are "rules" concerning proportion and such but furniture design basically comes down to what YOU want, and/or are able to build. For a piece like yours, where there are not full-width end panels serving as legs, MY eye likes to see legs that are non-directional, i.e. square ... instead of laminating two layers of 3/4" ply to create legs that are 1-1/2" x 3", I'd be inclined to use three layers and make the legs 2-1/4" square ... trading the increased heaviness of the leg's thickness for reduced heaviness in the other direction ... and then I'd make the dados 3/4" deep, maintaining the same 1/3 depth as a 1/4" deep dado in a 3/4" piece.

But that's ME. In no way am I saying your design would be unattactive; only that it would be different from what I would probably do.

[JonW]

1. When you add glue, wood swells just enough to either make a somewhat loose fit tight, or a tight fit too tight. If you can't put it together without mallet taps when it's dry, game over.

2. A test dado of 6" length isn't the same fit as the real dado you do of 24" length.

I had no idea about either of those things.

Making these shelves should be a really interesting exercise for me. I might get the shelves I want. Or not. But I'll certainly learn a lot for the next project.

Larry- Interesting idea about the legs being more square and less rectangular. I'll think about it. The curved legs would certainly be different looking that thick. Not sure how much of the layers I will want to look at on the baltic birch ply. Also not sure my jig saw can cut that deep (it will arrive soon). But maybe. Hmmm...

I thought I could start this project this weekend, but it looks like it needs more thought. And I'll have to find a top bearing flush trim bit. Not sure I'll find one locally (I live in a somewhat small town) and may have to order one. But it will come out much better with all this great input.

[JonW]

OK, I've thought about this project some more and I think I'm all set except for 2 remaining questions...

-What router bit should I buy? Top bearing flush trim bit, I know. I figure the cutting diamater should be narrow- less than the 1/2" shelf width. But in my looking around, 1/2" is only about as narrow as I see. I'll have to measure my 1/2" baltic brch for the shelves and see if that will work or if it's too wide. Any recommendations on specific router bits to get, brands, etc? (Bonus: I just called and found a local place that has a Freud 1/2" diameter, 1/4" shank, 1" deep bit in stock)

-How many braces should I make. There will be 5 shelves. Put a brace in the back of every shelf or maybe only in for 3 shelves? 5 braces would be safer and I may do that. And with my beginner skills, maybe Ishould go the safe route. But I don't want the shelves to end up looking too heavy.

[scorrpio]

1/2" diameter bit might be too large if you decide to use 1/2" thick shelves.. MLCS has a top-bearing flush trim bit that's 5/16" diameter, 1/4" shank.

Braces - depends on how wide they are, and how tall the whole thing is. If the unit is under 36", I'd say a a couple 4" wide braces will suffice, one close to top another near bottom. If that looks inadequate, you can always add one more in the middle.

Oh, in one mmagazine, I've seen an interesting variation on Larry's jig, that is fine-tuned to use either 1/4" or 1/2" straight no-bearing bit. Take 2 pieces of hardboard that are about 1" wider than your router base. On top, along its middle, attach a piece of wood 3/4 by 3/4". Now, using that piece as a fence for your router baseplate, trim one side of each with a 1/4" straight bit, and the other side with a 1/2" bit. mark which side is which. Now, orient the two pieces so that same width sides are facing each other, and on the bottom of hardboard along the edge coser to you and square to the top fence, attach another fence. Hope the illustration below makes things clear:

It came out a bit skewed...
Viewed from top and from front. Clamp both pieces with bottom fence on same side of work, using shelf stock as spacer. For wider dadoes, put 1/2" marked sides facing each other, and chuck a 1/2" bit. For narrow ones, use 1/4" setup.

[JonW]

1/2" diameter bit might be too large if you decide to use 1/2" thick shelves.. MLCS has a top-bearing flush trim bit that's 5/16" diameter, 1/4" shank.

Yeah, I saw that. But that particular bit (#6504) has an overhang. Probably not the best thing for a newbie like me. If that same bit existed without the overhang...

Braces - depends on how wide they are, and how tall the whole thing is. If the unit is under 36", I'd say a a couple 4" wide braces will suffice, one close to top another near bottom. If that looks inadequate, you can always add one more in the middle.

I was thinking about 4' high, 5 shelves. Maybe 3 or 5 braces that are not too wide- maybe 2 or 3"?