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Jan 20 2012

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Notes from the Workshop: 20120120

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Filling Knots with Epoxy

Usually I’ll just layout a project so I don’t have to deal with knots, but in the case of this beautiful walnut board, the knots and surrounding wood are the whole point. To make the board usable, I needed to fill in the knots.This is the first time I’ve tried epoxy to fill knots and it worked pretty well, but I would have done a few things differently, but let’s start at the beginning.

First I used a card scraper on the walnut to produce some fine dust to mix into the two-part epoxy. After collecting all the dust, I mixed a test batch of epoxy and added dust until the epoxy was an even color. I dolloped the epoxy onto a piece of wax paper and waited a few hours for it to dry. Then I took the sample and compared it to the areas I wanted to fill.

I was pretty happy with the color so I mixed a larger batch of epoxy/sawdust and started filling holes. On the smaller knots I just spread a thin layer over the top and let the epoxy seep in. On the large through-knot I put a piece of wax paper on the down then clamped the board on top of the wax paper to keep the epoxy in place. Then I just filled the hole to the top.

After the epoxy cured for about an hour (I figured if I let the epoxy completely harden removing the waste would be tougher), I used a chisel to remove most of the epoxy above the plane of the board and then used a card scraper to make the patch flush.

For the smaller knots the epoxy patches look pretty good, but it seems that the outer surface of the epoxy is darker than the scraped surface. This make the epoxy lighter than I was hoping. In the large knot, the patch color is way lighter than the original knot, and doesn’t look as good as I’d hoped. I should have punched the entire knot out before patching. I also should have taken a bit of advice from Shannon Rogers and tried using dye to darken the epoxy, but I didn’t have any dye on hand at the time.

Be sure to check out the pictures, especially the ones where I caught the epoxy expanding.

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Experimenting with Wood Glue

After Stephen Shepherd posted his article last year on hide glue I decided to buy some and experiment. I picked up a small bottle of TiteBond liquid hide wood glue (+Titebond Adhesives). I know purists would have me use something like Old Brown Glue, but I was able to find this on the shelf locally.

I tested the hide glue on two different projects, a dovetailed box I made a while ago and never glued together and a sample dovetail out of a piece of scrap oak that I’ll eventually try reverse the glue bond and pull apart.

When I started pouring the hide glue out of the bottle, I noticed it was more viscous and gooey than wood glue. It was like pouring honey out of a bottle. This meant that I had to be careful when I pulled the bottle away so I didn’t get strings of glue all over the place. It isn’t a real con, you just have to be aware of it and be more careful. Then when I spread out the glue with a brush, the glue really stuck to the brush. I don’t see spreading this as thin as I do with wood glue.

After I spread glue over all the box’s mating surfaces, I put the box back together and wiped up all the squeeze-out with a wet paper towel. There really doesn’t seem to be a difference in ease of cleanup between the hide glue and regular wood glue. I didn’t end up clamping the box because the dovetails were tight enough to hold it together — actually I was just too lazy to break out the pipe clamps. Luckily the joints didn’t blow apart as the glue dried. Given how open (or poorly cut) the dovetails were, the hide glue held the box together well even after I hit the joints hard a few times with a mallet.

I glued the pieces of oak together the same way. This joint was a little tighter, but the glue also seemed to hold well. Next when I get some time I’ll see If I can pull it apart.

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