Tuning Dados

[Art Greenberg]

I'm making a closet organizer for SWMBO. Ya know, to score points, so I can buy more tools. 8-)

I picked up some BB plywood for this project. Assembly involves a few dados. I found that the BB does have a little variation in thickness, so the dados needed some tuning. I used a card scraper for this, and after I figured out how to attack the side wall of the dado properly, it worked OK, but to took a long time. I found that I needed to refresh the edge on the scraper pretty often.

What alternatives are there? Would a side rabbet plane work OK in plywood?

[Charley]

Instead of making dados to fit the full thickness of the plywood, consider making narrower dados and then rabbet the ends of the plywood to fit them. A

1/8 rabbet off each side will leave a 1/2" for strength and should eliminate the surface thickness variations that are affecting your dado joint ( a good fitting 1/2" dado is better than a 3/4" poorly fitting dado). Better quality plywood like birch cabinet ply may cost a little more, but the thickness tolerances are much tighter, and therefore are easier to cut good fitting dados for.

[Art Greenberg]

I am having trouble seeing how this would get around variations in thickness. I think any method of making the rabbet that references the surface of the plywood would just transfer that variation to the remaining tongue.

I did say I used BB (baltic birch). Are there grades of that material, or sources, that have better thickness tolerance?

[Chris Friesen]

You reference from the uncut face, such that the tongue thickness is constant while the rabbet shoulder varies.

Chris

[nailshooter41]

Art- if usnig a saw to cut your dadoes, an adjustable dado cutter head should do the trick. Get it honed in on a piece of scrap them hit plywood.

If you are using a router, they make bits purposely undersized to route the dado to be the same thickness as the plywood.

You shouldn't have to scratch off the edges of a dado no matter what you are using to cut.

Robert

[Bob]

Basically, he's saying trim the board instead of the dado to fit. Its not all that easy to reliably trim a little strip (3/16" wide strip) next to the edge of a board. A straight board guide clamped to the shelf and a rabbet plane work pretty well.

For trimming a dado after the fact, the side rabbet plane set by Nielson seems pretty nifty, though not much use for anything else.

I like the approach of cutting the dados the right width in the first place. This means precutting the shelves to know what thickness is required. Then you have to play games with dado blade setup on the tablesaw or use of a router with an adjustable dado jig.

I am very surprised you got > I am having trouble seeing how this would get around variations in

[Art Greenberg]

OK. That would mean using a router "on edge", or (equivalently), stand the board up on a router table, or a table saw. Not easy with a 3-4 foot long 12 inch deep shelf.

[Art Greenberg]

Right. I wonder how well those planes will work in plywood, where its cutting with the grain in some of the veneers, across the grain in the others.

I thought that should have been the case, and that is exactly why I bought a number of sheets of the stuff to keep for projects like this one.

I dealt with my local lumber yard, which had to special order it. They're much more accustomed to dealing with construction lumber, and I was dismayed to see that they treated the BB just like construction lumber - just thrown into the truck as if it were underlayment or sheathing. An experiment that seems to have failed. It may be necessary for me to rent a truck and drive a bit to get decent product.

[Lew Hodgett]

Take your choice, stacked dado on a T/S or a router.

Make dado in two (2) passes with an undersize cutter.

PITA, but it solves the problem, just keep your dial caliper and marking chalk handy.

Lew

[Art Greenberg]

I used both a router with a jig, and a tablesaw with dado set and shims. I fussed with both using a sample piece. The problem is, the sample turned out to not be wholly representative of the batch of plywood I had to work with.

If only that were true. I bought a bunch of Baltic Birch thinking it would be consistent enough in thickness to make it so. I guess, even with BB, I'll have to hand pick each piece using a dial caliper.

Sigh.

[Leon]

Sand the surfaces of the plywood where it will fit into the dado with a ROS until they fit. Or use a top bearing pattern bit and a straight edge as a guide to widen the dado.

[Bob]

Just to confirm you were getting what you thought you were, did it come in

5'x5' sheets? That's the only form I've ever seen BB come in.

Bob

[Art Greenberg]

[Art Greenberg]

PITA is an understatement.

I don't see how to control the TS with the accuracy needed to do it this way, without one of the really cool positioner-based fences from Jointech or Incra.

Certainly doable with a simple router jig that is adjusted using the shelf as a gauge. I have a gadget from Woodline that works that way (DadoWiz), and that's what I used for most of the dados. But I did _not_ anticipate the need to reset it for each end of each shelf.

I suppose I could go back and re-cut each dado this way, that would take care of the problem. But it seems so much easier to neander it with the scraper ...

Live and learn.

[Leon]

Just to confirm, Baltic Birch is not the only plywood that comes in 5x5 sheets. There are plenty of imitators and I think he got one of the ones sold as BB.

[Lew Hodgett]

A UniFence will do the job; however, there is a way using both T/S and router.

First pass use T/S with undersize dado, then clean up to size with router and a straight edge.

Just make sure you use a common reference for all cuts, either top or bottom of T/S dado cut.

Have fun.

Lew

[Art Greenberg]

Ot-oh ... could be. Is there a way I can avoid making the same mistake again? What should I look out for?

[Art Greenberg]

I only need to take of a little - I had success with a few passes with a scaper. So setting the straightedge could be a bit fiddly, but it is certainly worth a try.

Of course.

Always!

Thanks for the suggestions.

[George]

The 5x5 5 ply can be Russian stuff, too. Not as good as the Finnish. Usually has a violet stamp on it with Cyrillic FKA (factory) and a number.

[Lew Hodgett]

SFWIW, my landlord uses Birch ply to fabricate tooling to stamp gaskets.

Absolutely refuses to use Russian material.

Lew