It’s a 12-inch sliding compound miter saw that I picked up from a guy on craigslist. It’s awesome.
However, I’ve been using it a lot lately and have been noticing that the angles need a lot of fine tuning to get exactly 45 or 90 degree cuts.
At first I thought it was just the positive lock mechanism needing some tweaking, but on closer examination, I found that the problem was the saw’s fence itself.
If I held a straight edge against the fence, I could see that both sides (although one more than the other) drifted further back as the neared the center, and the two sides were not parallel with each other.
This meant that the angle of a cut could be wrong in three ways, depending on how I held the board (one angle if the board referenced both fence surfaces, and another angle for each of the two surfaces alone if trimming the end of a board).
I know I’ve recently outed myself as something of a rebel when it comes to precision, but not being able to cut at a specific angle when needed is always a bad thing.
But how to correct this? The fence is a single piece of cast aluminum, and can’t be bent without breaking, so I couldn’t just straighten it out, I needed to fix the surface.
When I looked more closely I saw that the fence was not bent out of shape, but rather worn out of shape. The saw had been previously owned by a production shop that used it almost exclusively for cutting aluminum, which apparently, over time, had worn down the fence.
So then I thought the solution might be the milling machine (to be perfectly honest, I try to use the milling machine as the solution to almost every problem). The difficulty with milling the surfaces flat would be keeping the fence perfectly parallel to the milling table in two different clamping positions to address each side. Ultimately this seemed like a big risk.
Then I noticed two 1/4-inch holes on each side of the fence, and realized that the solution was to add an auxiliary fence to the saw.
I wanted the fence to be rigid and thin (so as not to reduce the cutting capacity too much), and I decided to make it out of 1/4-inch thick aluminum tool plate (I had some laying around that I picked up as a remnant from the local metal supply store).
I roughly cut two 3-inch wide strips and squared the edges on the milling machine (I knew I needed it!). I then marked the locations of the holes and edges in order to keep from mixing up the two parts, and then countersunk and drilled holes (in that order) to line up with the holes in the fence.
Unfortunately I countersunk the wrong side of each piece, but luckily the hole positions are mirror images of each other on the left and right sides of the fence, so I just pretended I meant to do that and casually attached them to the opposite side with beveled machine screws and nylon lock nuts.
That’s it. Now I have a straight and sturdy secondary surface that I can shim if necessary to get a perfectly true alignment and then never think about again.