Allan, I think I know the one you're talking about, I'll have a look.

If I can't find it, I'll make a simple version and post photos.
(to me) It's a very simple design and easy to make.
You'll need a drill press, a disc sander and the usual things for segmented construction

I ended up using a router rather than the disc sander.
will try and explain this as best I can. The  one picture shows the router bit and the pivot pin. The pivot pin is just a long enough deck screw so you can cut off the threads and have a clean 1/8" shaft. It was welded to the black pieces of flat iron that is adjustable. I used a spiral cut router bit. Say you take a piece 3 x 3  and drill a  hole in the center and then cut it in half. Then take a piece a bit bigger than the half circle that was drilled out. Drill a 1/8" hole in the center far enough down so when rounded over you have a 1/'2 circle.Place it on the adjustable pin, I have a variable speed router and started out slow with MDF until iI has it fitting in the half circle piece. I found if you cut the pieces you want to round over long enough that you can round over both ends it keeps your finger a bit further away for the router bit
I also raised the router a bit at a time taking multiple cuts. The little round disc just rides on top of the flat iron so the toggle clamp will lock everything so you can make repeatable cuts,
that's it . My sled it held down on the router table by the 2 wing nuts and the sock guides on the fence.I am sure you can build the sled any way you want. just try and keep it as thin as you can so your bit will cut a thicker piece