Monday, February 01, 2010

Cleaning up glued joints with a chisel

Part of a woodworker's life is about gluing wood together. There isn't much way around it, it stabilizes a joint, and bonds wood together.

You've probably heard that if you glue to pieces of wood together, and then try to break them apart, the wood will probably break anywhere BUT the glue joint. A glued joint is actually stronger than the wood itself.

But glue can also make life miserable if you're sloppy with it.
I have a very good friend who completely freaks out when gluing wood together, knowing how many possibilities there are for disasters. Why not take a little care in the beginning, so that you don't spend hours later, cleaning dried glue?

There are two areas of thought regarding glue clean-up. One is to clean up any squeeze-out with a damp rag, before it has dried. The other is to wait until the glue has set up a bit, and then cut it away with a chisel. Both methods work, but there are pros and cons to them.

I don't like wiping glue away with a damp rag. First, if you have the rag too damp, it can actually add water to the glue joint, and can possibly weaken the glue bond. Also, wiping it away forces glue into the pores of the wood. When it comes time to finish your piece, you might find a few surprises - areas that won't accept the oil you apply, or light spots in a sprayed surface finish.

Finally, my third reason for not liking the damp rag method is that it causes the wood grain to raise, thus forcing you to go back and do some additional sanding in the areas around the joint. All in all - there aren't a lot of good reasons to wipe away glue with a damp rag, unless you're gluing something very complex and you can't keep up with the glue dripping everywhere.

My preferred method is to wait until the glue sets up a bit, and then pare it away with a sharp chisel. It's hard to say how long you have to wait - but the glue should definitely be skinned over and about the consistency of toothpaste. Soft, but not drippy.

The downside to this method is that it takes some skill, and a little time. And there are some situations where you simply can't reach the joint with your chisel, to clean it. But this works most of the time, at least for me.

One last thing - I don't always use a chisel. Sometimes, if there is a very small bit of glue that has to be removed, I'll just slice it away with an X-Acto knife. Two simple cuts, and the residue just slices off very nicely.

So I'm working on a piece where I glued a couple of these "H" shaped parts. Using the Festool Domino joiner really makes things simple.

After the glue has set up a bit, you can see that there is some squeeze-out in the corners that needs to be cleaned.

The best way to get rid of it to to cut the glue from both sides - first putting your chisel on one side of the joint, and slicing the glue off.

Then flip your chisel around and cut it from the other side. Two cuts, that's usually all you need.

You want to cut from both sides, meeting in the middle. Keep your chisel flat on the wood as much as you can. That way you won't cut into the wood, and damage that 90˚ corner.

This method will get rid of most of the glue. Make sure your chisel is sharp!
To get rid of the little bit of glue residue that's left, gently scrape it away with your chisel.

Just a light scrape across the wood will usually leave you with a very clean joint. Now isn't that easier than letting the glue harden and then having to work a lot harder to cut away all that squeeze-out?

Here's another joint being cleaned. Cut from one side.

Then from the other side.

And you'll wind up with this.

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