Swelling Dovetails? – Question of the Week
This week’s question comes from Ben who asks: Why do my dovetails dry fit perfectly – but when I go to glue them up, they no longer fit flush? It’s cheap pine (this is a test project) – and I’m using a dovetail jig: if that helps? Any suggestions?
And this was my response:
Hey Ben. My guess is that the dovetails are sucking up some moisture from the glue and swelling a bit, leading to a change in the actual fit. That means that if left alone for some time, the swelling would go down and they might get close to flush again. That being said, I very rarely shoot for perfectly flush dovetails anyway. I always aim to have my dovetails a little proud. This way, after the glue dries, I can flush them to the surface. If you aim for perfectly flush, you might wind up slightly under, which means you now have to sand or plane the entire board to get a flush fit, which of course brings with it a whole series of problems. But if you aim to be slightly proud and you wind up a little short of your target, the worst that can happen is the dovetails will be nearly flush. And if you are slightly over your target, a few extra swipes with the block plane are all you need to remedy the situation. Hope that helps.
*** Anyone else have some slick tips for perfectly-fitting dovetails?***
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Actually, if you are bit shallow on your dovetails, you may not have to sand or plane the entire board to fix things, depending on the situation. You could conceivably just work near the area around the joint itself. On a drawer that’s 20″ deep, if the board is 1/64″ narrower at the joint from making the dovetail joint a bit shallow and fixing it, that’s not going to be noticeable.
Of course, it is better to leave the dovetails a bit proud.
To fix the pine swelling with the glue issue, I think that most dovetail jigs have a method to adjust the tightness or looseness of the joint. If yours doesn’t, an easy way to loosen up the joint a little is to pare away the baseline of your tails board a little with a chisel. The tails board will seat a little deeper, and be a bit looser, which will accommodate the moisture from the glue. This also will fix the my-dovetails-are-too-shallow issue as well.
Or you can cut them entirely by hand, which is what I tend to do anyway. :@)
Well, I agree with Mark, concerning leaving your dovetails slightly proud of the mating surface. This does allow for filling any gaps and making the surfaces flush together.
Now, if I understand Ben’s question, he’s wondering why they are proud of the mating surface after glue-up. Well, water based glue would cause a tighter fit between the joints but unless you’re applying glue to the endgrain surface (which isn’t necessary) then the answer could be the simple difference between a dry fit by hand and s very snug fit after clamping. See, when we dry fit by hand we cannot physically aply the kind of pressure that clamps would.
Perhaps you’re cutting them slightly proud to begin with and the clamps just simply reveal this.
Just a thought.
Cutting by hand certainly does have its merits…….. Thanks for the input guys!
Marc is correct always leave dovetails a bit proud,the glue will cause an initial swelling ,typical wood glues are the worst…I like the bottled hide glue or plastic resin, both seem to have less moisture and the slower dry times seem to allow the moisture to release,secondly they have less of an initial tack,and actually seem to have a lubricating factor that makes assembly easier,and third ,they dry hard,and offer a little gap filling
Also don’t forget that pine swells more and faster than almost all types of hard woods.
LQQK
Hey guys,
My suggestion is to use a different glue. Polyurethane glues react to carbon dioxide to cure rather than water evaporation. Thus the wood stays the same dimensions.
Look to Charles H. Hayward’s book Antiques or Fake for further reference on how to fit dovetails, also Fine Woodworking magazine had some good methods to fit drawers.