Attachment 50202chebytrk...
Here is a quick pic of my carving sled. Overall is 14-1/2" x 24". Its 3/4" MDF with a glued on (replaceable) 1/4" plywood topper, T-Tracks, sliding runners and a tape measure for placement.
Dadoed out to hold the two T-Tracks jut below flush (though it has been dinged with the blade a time or two).
Runner boards are 4" wide MDF with Oval head bolts countersunk and a Jam nut to hold it to the track. (Have these in different standard thicknesses to match the project thickness).
A shallow Dado in the center holds a stick-on metal measure that you can get at Wally World.
I just center my project (L to R) at the front edge....place the runners tight against the project. Usually add a small piece or two of double sided outdoor carpet tape to the back of the project, then use masking tape to extra secure the board to the runner tops. I also add a piece of blue tape to the sled at the back of the project board and to the outside edges of the runners....seems to measure better with the contrast. Also, put a piece of masking along the bottom where the sled runs on the brass roller. (This will last several dozen projects before needing replacement).
Hope this helps...let me know if you have question.
Brad