Wood joining accuracy

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JHZR2

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I've been looking at biscuit joining as well as the festool domino system. I read something that interested me:

Quote:

If you’re accustomed to joining pieces with a biscuit joiner and then having to go back and sand the two pieces so they’re flush, the Domino precise alignment will virtually eliminate the need to sand, it’s that good.

http://www.emercedesbenz.com/lifestyle/tools/festool-domino/

Sure, it's talking of all the virtues of the expensive domino tool...

But my curiosity is, why is the claim like that? What is intrinsically sloppier, for lack of better terms, with biscuits than these loose tenons?

Any time I've had to join something, I've used dowels. I get the simplicity and ease of these things, but aren't sold on either... But if there is an accuracy difference that is real and systematic with one method vs another, I'd like to understand why...
 
I've used biscuits for a long time. They're quite accurate if done right. No sanding needed. I often biscuit a solid edge to plywood shelving, by matching the species of wood, you gain the appearance of solid wood at a fraction of the cost.

Clearly, if I was off more than say, 1/64", I would be sanding through the veneer on the plywood.

I've biscuit joined long boards to make a table top. In that case, a 1/64" error is intolerably large. But my experience is that biscuits are quick and accurate. Further, biscuits allow for a bit of lateral error. They're quite forgiving.

The only caveat with biscuits is when joining long boards for, say, a table top. The moisture in yellow glue causes the biscuits to swell, locking them in place. It also causes a minute swelling of the surrounding wood. Sand, plane, smooth, whatever, too soon after joining, and you can get slight depressions when the wood shrinks after the moisture level returns to equilibrium.

Get a good biscuit joiner (I've got a Porter-cable that I've had for a long time, at least 15, perhaps 20, years). Set it up precisely. Use it with consistent pressure. Be certain to hold it dead square to the work piece. Those elongated dowels look more sturdy than biscuits, and would be appropriate as a substitute for a mortise and tenon joint because of that strength, say, in a table leg to apron joint...but I'm not convinced they're more accurate.

Before Festool made a tool to cut the two mortises and gave it a fancy name, the joint that the Festool creates is known as a loose tenon joint. It's strong. And often easier to cut, since plunging two mortises can be a lot quicker than cutting a tenon on one piece and plunging a mortise on the other.

By the way, given your questions on the subject, may I recommend a subscription to "Fine Woodworking" magazine? Published by Taunton Press, they're the best in the field. I've subscribed for a couple of decades and it really is an education as well as a wonderful resource for the craft.
 
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I agree. A quality biscuit joiner carefully used can make flush joints consistently. I suggest lots of practice and test fits before moving into expensive stock. There have been arguments about biscuit joiners going on for many years, if not decades. I think what ever works for you is best.

Good luck!
 
The tool and system is less important than the skill of the person doing the joining. Find a joining system that works for you and that you're comfortable with, and then practice it a lot before you move on to larger projects.

I also suggest learning to do some joinery by hand. It's far more rewarding than doing it with power tools, and it will teach you a lot about woodworking.
 
Make a spline joint on your table saw using the same species of wood for the spline to equalize wood movement.
It's a stronger and more versatile joint than biscuits and can be done in three cuts.
 
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I've never made a mis-aligned biscuit joint and I use a slot cutter in a router. Not to brag but I suppose one could screw up a biscuit joint if you're careless or clumsy or the fence isn't tight. Biscuits do provide some strength, but not near as much as the glue when set.

I don't agree that biscuit joints are "inherently sloppy" by nature. Not when cut correctly.

You can also make loose tenon joints with a router. A very versatile tool. However, it's only as accurate as it's set up. That's where the education and experience of the woodworker comes into play.
 
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