Saturday, November 8, 2014

Hide Glue, Or How I Intend to Fix my Rocker

Something's not quite right here...
As a rookie woodworker, there's few things that go through my mind more than all the mistakes I'll make. "What if I cut the board too short?" "What if my glue doesn't hold?" "What if...?" Especially concerning for me are those first cuts into good, expensive wood. Once those cuts are made, there's no turning back.

Sadly, some of these mistakes will inevitably happen. It's knowing how to recover from them that's really key. Some mistakes are easy to fix, such as the board that's too long. It's always possible to make a board shorter. Other mistakes, like the board that's too short, can sometimes be fixed by simply gluing more wood to the board. Or, the project dimensions can be adjusted to compensate. Still other mistakes become "artistic design opportunities."

But one mistake, the failing glue joint, is harder to recover from. Most often, failed glue joints will result in your project coming apart in some unsightly way. Sometimes, a more catastrophic failure occurs. It's this kind of failure I'm most concerned about as I build my rocking chair. All chairs take a beating — idle movements as you sit grinding the seat into the legs, causing the legs to spread and after time ultimately come loose. How many Windsor-style chairs (or indeed any chairs with spindles) have you found with loose spindles? Loose legs? Cross stretchers that rotate in place? It's a very common problem, and can be a nightmare to deal with.

Hide glue granules.  (via Simon Eugster)
Let's face it — there's no such thing as a perfect chair design. Every wood chair will eventually work its way apart (though you hope not for a good hundred years or so). Going in with this realization gives you power though, as you can try to design and work your project with this in mind. For my project, two things will help counter this: tapered mortise and tenon joints, and hot hide glue.

Hide glue is a natural glue made up of basically animal byproducts. It comes in two forms, ready-made liquid and granules. I'm not going to go into the details of how this stuff works. It's been covered many many many times. Suffice it to say, you melt down the granules, heat it up nice and hot, and glue your project together with it.

Mostly congealed glue.  Once it's a gelatinous
mess, it's ready to heat.
The truly great thing about hot hide glue comes time for correcting mistakes or repairs. Hide glue can be reversed simply with a hot moist rag around the glue joint or a heat gun. The glue will release along with the joint, and repairs can be made easily. Then, just a little more hide glue and the joint goes back together, just as well as it originally was. No need to scrape the old glue away either; the new glue will melt into the original glue.

Easy, right? Well, my early attempts at using it didn't so much pan out. The glue never solidified into a syrup like it's supposed to. Why? Because I used way too much water.

Everything I've seen online about how to use hide glue seem to suggest using lots of water. Or at least, that's how I interpreted it. But, words are least for me. When the instructions say "enough water to cover the glue," they mean "only enough water to cover the glue." In short, I was using too much water, so my glue was melting out to a very thin consistency.

My hot hide glue rig.  Roughly $30 worth of parts.
There's two ways to fix this. One, don't use so much water. But, if you're in the situation I'm in, the watery glue can be gelled simply by letting it cook off some of the water. Once it gets to the right consistency (more like maple syrup), you're done!  As I found out, this worked marvelously to restore my earlier attempts to a usable consistency, and I had indeed used too much water. Cooking solidly for about 8 hours was enough to cook off the water I'd added and give the glue a nice syrupy consistency which grabs onto wood like crazy. ■

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