Evolving a better crosscut sled

Over the past 4 years I've gone through a few versions of cross-cut sleds.

The kind we used at school was very plain, and while it worked, it was not what I would call optimal. It was basically like this one that I made for my contractor saw a few years ago. Big fences, mounted as square as possible to a huge piece of MDF. Setting up repetitive cuts meant clamping a huge L-stick to the fence, which was a huge pain in the ass. Clamping it up meant using one hand to hold up the stick in place, one hand to operate the clamp, and another hand to hold the tape measure, to make sure the stick was being clamped up in the right place. 

My first attempt at a miter bar was intended to solve most of the problem. The L-stick would have a wooden bar mounted to it that would hold the stick up in a horizontal position, and a knob would thread onto a bolt through said stick, and the bolt would engage with a T-track to clamp the thing down. In short, I could use the knob to set the position AND clamp the setting in place, while I measured with the tape measure using my other hand. Voila... I no longer need to use three hands.

This is the most recent version, and it's the first one I'm really proud of. The Kreg rails add several important advantages: Kreg's production stop is AWESOME, the adhesive scale that sticks to the rail means I don't need a tape measure anymore, all that metal adds mass, which helps the sled slide very well, but most importantly, because they bolt onto the fence, I can loosen the bolts and shim the fences to be perfectly square if I need to.

I made the floor of the sled out of 1/2" ply, ran dadoes for the rails, as well as for the fence, to make sure everything was positively square. Each side was made separately, and then joined when I mounted the fence, and the bridge in the back. I finished the whole thing with sanding sealer, so that the plywood wouldn't distort when I waxed the underside of the sled.  (Wax works wonders... the whole thing slides like it's on marbles that are rolling in a puddle of WD-40.)

I wanted to use a replaceable zero-clearance insert, and the easiest way I could think of to lay one in and have it sit flush with the rest of the floor was to lay one whole layer of the same material. So, I made the insert,  installed it, and then used contact cement to lay down the adjacent panels. With the replaceable insert, I should be able to use the sled for dados, and mitered cuts, too.