Hahaha, my mistake, talking about a sled for grinding the ends of the limbs?
I just run mine at 20% or so on the belt, and carefully hold them to the bed. I built a sled for the limbs but it's significantly less work doing it by hand and not using the sled lol. So I do that.
One consideration I have is to make a "base" of sorts, which essentially would be a sled. However smaller, just to aid in keeping the limb at 90 degrees. Just haven't gotten to it yet.