Popular Woodworking 2005-11 № 151, страница 20

Q & A

Are Dados A Good Joint for Casework?

Nail set

Dado

Are Dados Alone a Strong Enough Joint for Bookcase Construction?

I'm in the beginning stages of a solid-wood bookcase with doors. It has solid-wood shelves joined to the case's sides with dados.

As I research traditional j oinery for Arts & Crafts-style cabinet and bookshelf pieces, I'm seeing that the joinery for solid-wood casework is almost always simple dados.

What are your thoughts on this method of j oining solid wood ? It seems to me that a dado joint gives you virtually zero long-grain-to-long-grain glue surface in solid-wood carcase assembly. The piece I'm making is almost all solid wood except the back. I'm interested in this piece specifically but also the overall philosophy with this method of joinery.

I'm debating several options: biscuits, screws, sliding dovetails, and simply to quit worrying about this and regard it as an acceptable method of joinery.

Kevin Bradley Battle Creek, Michigan

Dados alone stink. They have no strength against wracking forces. Every long-grain surface of a dado is mated to an end-grain surface, so glue alone is weak. These joints need to be reinforced for when the glue fails — and it will. Sometimes, the face frame of the cabinet will keep the case together. But not all projects have a face frame.

So for reproduction pieces, I use cut nails toenailed through the shelf and sides through the underside of the shelf — a historically correct way to go about it. Sliding dovetails are another

option. They offer a mechanical interlock, though they can be fussy to execute.

For more modern projects, I use dados with pocket screws driven into the sides through the underside of the shelves. Screws alone and biscuits alone don't provide the same resistance to shear forces (gravity). So my advice is to use a combination of dados, glue and some sort of mechanical fastener that's concealed. This provides strength against gravity, wracking and time.

— Christopher Schwarz, executive editor

What Sanding Grits Should I Use When Power Sanding Plywood?

I need to sand a chest built out of plywood. The problem is, because the face veneer is so thin, I don't know what sandpaper grit to start with and end with. Can you help?

Trevor Anderson Bronx, New York

For solid wood, #80 grit is a good place to start, ending up with #220grit. Most plywood veneers have been sanded after manufacture, so the initial #80-grit sanding that you might do on solid wood isn't necessary.

Power sanding with plywood is always something to be careful with and I'd recommend no coarser than #120-grit paper to start, moving up to #220 grit for a final finish. Take it easy on the edges of the sheet where it's easiest to roll the sander a little and burn through the veneer. If you're hand sanding, then you're still OK with the grits mentioned.

— David Thiel, senior editor

How Long a Piece of Wood Can My Powered Jointer Handle?

This question seems almost dumb to me, but I can't seem to get this straight in my head.

Recently I had to glue up some long boards to make long 3" x 3" square posts for a bed. I have a 6" jointer, and when jointing the stock, I seemed to have a problem with truing some but not all of the pieces. And so I started thinking about stock that is longer than my jointer's infeed table.

If I have a bow in the stock and the back edge isn't even on the jointer's table yet, isn't that going to cause the stock to raise up while I'm passing it over the knives? Is there a "trick" to flattening stock longer than your jointer's infeed table, or is this something that just can't be done? Would extending my infeed table with carefully placed medium-density fiberboard extensions help, or am I missing the whole function of the machine?

Rick Schuster Coraopolis, Pennsylvania

The length of the bed absolutely controls the accuracy of your jointing. The rule of thumb is that you should be able to joint boards that are as long as your machine's infeed and outfeed tables combined. Most cabinetparts are shorter than 48", so it should come as no surprise that most 6" jointers have a bed that's about that length.

It's possible to true reasonably straight but over-long boards on short-bed jointers if you're careful. In general, it's best to first work on the concave face of a board. I'll remove the high spots continued on page 20

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Popular Woodworking November 2005