Tuesday, January 8, 2013

Jointing with the Router

Happy New Year! I hope 2013 is kind to all of us. The last project I took on at home in 2012 was gluing up a birch countertop for my shop cabinets. In the last post, I showed how I got the big planks ready to run through the planer. In this post, which will be shorter and easier to understand, I'll show you how to get a good, straight edge on a workpiece if you don't own a jointer, or I should say, a big enough jointer.
The jointer I have access to in my home shop is 6” wide and 42” long. These planks are a bit over 90 inches long, meaning I would have to somehow push down hard enough on the jointer bed to balance at least 70” of 8/4 birch, plus hold the wood up against the fence accurately, in order to prepare my boards for gluing up. Not likely! If the boards were only 4/4, maybe so. I guess roller stands fore and aft might work, but I decided to do this job with the router. I had heard about it being done, but never seen it, and I was curious. I'm pleased to report it works well. In fact, I'd be tempted to use this method for planks this size even if I had an 8” jointer in the shop.

The concept is simple: a straightedge is clamped on top of the workpiece, parallel to its edge. A template guide is screwed into the base of the router, and rides against the straightedge so the router moves in a perfectly straight path. A straight bit is chucked in to the router, and cuts the edge of the wood at 90 degrees to its face.

I had two main concerns going into this process: first, what can I use for a straightedge, and second, what bit or bits should I use?

The straightedge is important, because its straightness determines the quality of my glue joint. The quickest and easiest would be a factory edge on a sheet of mdf, but I didn't have one around and I didn't want to bring an entire sheet of that stuff into my shop if I didn't have to. Then at Home Depot, somewhere between the prefinished shelving and the millwork, I found the perfect straightedge: primed mdf boards 10 inches wide by just under ¾ thick. They're 8 feet long. I would provide a link, but I can't find them on the HD website.

Why mdf? Because it's dirt cheap and the manufacturing process leaves it dead flat and straight. Did I mention it's cheap? Perfect for my task.

The bit was a concern because I didn't think I had any that would be long enough to joint the entire 1-7/8” thickness of my birch. I was afraid I'd have to go as far down the thickness as I could with a straight bit and a template guide running along my shelving, then take off the shelving and use a flush-trimming bit without the template guide to finish the job. Using two different setups like that is not a good idea when you want accuracy, so I was delighted to see that my longest 1/2” spiral bit would reach far enough. When I tried it, though, I found that it could only take a very, very light cut without vibrating so much it left a choppy surface. I usually use these bits for mortising, and I guess they're stabilized by being touched by the wood on both sides of a mortise. Fortunately, at the back of my bit tray I had a gigantic 1” by 2” carbide bit. I also had a template guide big enough to handle it. The extra diameter made a huge difference, and the thing cut smoothly with far less noise and effort than the spiral bit.

The procedure was simple:
      1. Take a quick test cut (or measure) to determine the offset between the template guide and the router bit. In this case it's about 1/8”. Clamp the straightedge at both ends of the workpiece in a position that will lead to a full-length cut along the board. Also be sure whatever supports the board (in my case, sawhorses) won't be exposed to the router bit.

      2. Make light passes, which in this case means lowering the bit between passes. I found it went easiest if I took about 1/2” vertical cut per pass.

      3. After the first edge is jointed, mark a line parallel to it as a guide for clamping down your straightedge as you joint the second edge. That way your finished board will be a parallelogram instead of an irregular trapezoid. I used my fancy panel gauge because I like it and I don't get to use it very often, but a pencil against the end of an adjustable square is just as good.

      4. Clamp down your straightedge and joint the second edge.
      5. Clean up! One disadvantage compared to a jointer is that this spews dust everywhere!

      6. Test your results with an accurate square, to be sure you'll get a flat glueup. Assuming you generated nice flat faces by following the instructions in the post on how to get flat boards without a wide jointer, you should be fine, but it's foolish not to test your work before you roll on the glue and clamp it up!

This procedure went much more quickly for me than prepping the stock for the planer, so I started gluing up the countertop before the sun went down. These ended up being some of the best glue joints I've made on boards this size, so I'm quite pleased indeed.

Next up: flattening the countertop!

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