I will be building a larger cabinet and needed a sled that could cross-cut 24" panels. I wanted a single-runner sled (cause my table saw only as one miter slot).
Wish list: (1) A runner that had no seasonal movement. I've used wood. It expands, it shrinks. (2) A runner with no slop. I have used the Incra miter runners, but they are tricky to adjust. The 24" version has only three (I think) width adjustment points and no matter what I do, there is always a little bit of side-to-side play. Plus, the 24" Incra Runner (their longest) wasn't really long enough (my sled is 27" long and I wanted a runner at least 27" long to match).
I decided to try UHMW plastic. I got a boatload of the stuff on sale from Peachtree Woodworking's sale. Included were two 48" long runners.
The stuff is flexible, doesn't glue well, and it was about .003" shy of .75". Great!
This is what I did: I routed a .75" groove in the bottom of my new sled (1/8" deep). I centered six 3/16" holes along this groove (at 6" intervals), and drilled some matching (but slightly larger at 1/4") holes in my UHMW runner.
I inserted special prongless t-nuts into the UHMW plastic (I used my woodworking vise to just squeeze them in). These nuts, BTW, are sometimes referred to as Propell nuts, sometimes as Hurricane nuts, McMaster just sells them as t-nuts. I used the #10-24 size (they have a base that is 45/65" in diameter).
Inserting the t-nuts into the runner made it "bulge" up to .752" around each nut.
I screwed through the top of the sled, through the runner, and into the t-nut. Trying the sled in my miter slot it was a little tight. A couple licks with a cabinet scraper at the "bulges" and it slid perfectly, no play and slides like butter.
The best thing is, I can actually tighten the screws from the top and the plastic bulges a little more (and the runner tightens in the slot). Loosen the screws and it slides like butter again. So, it is slightly adjustable.
And I like the fact that the runner can be removed/replaced, too.
You may wonder how to achieve this with a dual-runner sled (if you're one of the lucky ones with two miter slots). My suggestion is to make two single-runner sleds (one for left of blade, one for right). Then, with the sleds in their respective slots, attach the front and rear fences to join them together into a single unit.