Sunday, March 4, 2012

Two simple sleds

These are sleds I made to cut parts for simple mitered boxes. In use, they're very simple, but I thought the geometry behind using each one was interesting enough to write something about it. Both are used with the blade tilted at a 45 degree angle.

The first one is a simple crosscut sled. The 45 degree detail actually makes the process simpler. On a 90 degree crosscut, you have to make the first cut over-size, to allow the other end to be trimmed back, too. In this case, the first cut cuts the board to length at 45 degrees, and the second cut is made without any change in settings, but makes an undercut. So, the board remains the same length, but the second cut miters the underside of the board.

The second sled is a little more involved. This one is used for cutting sockets for the splines that will hold the box together. The socket has to be 90 degrees to the miter, or 45 degrees, the other way. But placement of the cut is in reference to the corner of the miter, which is hanging off of the sled. I considered having a hook that hung out over the end of the sled, but I wanted to keep things simple. So, I use a block that's clamped to the fence of the table saw to set the board position before making the cut.

The idea is that this block sets the specific overhang off of the end of the sled. Then the sled moves forward from there, and the cut gets made.

This is a solution I've used on other jigs before, where the critical distance is short, and it makes more sense to hang the work out into the air like this. It's also useful when I cut the actual splines. The splines need to be cut to exact length, and it's a cross-cut, because the grain will need to run parallel to that of the sides, to maintain glue integrity over time. So in essence I'm cutting 1/4" long splines off of the end of a wide board that's already been milled down to 1/8" thick. Because the board is so thin, and because it's all too possible that the part will split and jam up between the blade and the fence, this is  not something that I feel safe doing against the fence of the table saw. So having a stop block like this makes the operation a lot safer, and very repeatable: I use a regular cross-cut fence, set the end of hte board against the stop block, and cut one spline off at a time.

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