While bending some GG flex track for a low valley loop to loop run I took notice of my shop vacs which were right in front of me all along.
Simply clamp the inverted drum by it's gutter on both sides at the edge of my work table. Then slide the inside tie ends into the lip recess plus add a clamp against (not on) the outside tie ends to hold the track in place:
Then take a short piece of 2 X something and slide it against the ties around the perimeter:
My Craftsman shop vac has a neat 18" opening with a recessed edge that is perfect for accommodating the tie ends and holding them in place. No potato chip warping.
The 18" track circle relaxes close to 31" and is ready for installation, if you wait it will expand it's radius.
These reverse loops will be mounted somewhat hidden under the around the room benchwork so the flat black is used to diminish attention:
Pictured are my two reverse loops with the 031" being roughed in:
Spacer blocks are tacked into the Homasote until I have all the components cut and fitted for spiking.
Happened to have some curved sections so I did not have to bend an "S" curve to meet the switch.