Today Kate and I suspended the rhomboid and made bumpers for it using some McMaster-Carr frame pieces-

Kate's finger points to the upper pin vise that had not yet been tightened, while the rhomboid's full weight is on the wires.

This is frame after the addition of bumpers. Rubber sheeting was placed along the Al beams, and corners were placed on the beams to protect the other two sides of the rhomboid.

This is the clamp setup above the two upper pin vises. The wires go between the flate plates, which are adjustable. This is where the lengths of the wires can be adjusted (carefully) so the rhomboid hangs straight. 

The period of the rhomboid's oscillations was just over 23 seconds, which is about as slow as it should be. The rhomboid did not hang perfectly straight; possible factors are a weight imbalance or an unevenness of the wires due to different pin vise heights. When the left upper pin vise was tightened, the rhomboid did hang closer to straight, suggesting that the height of the pin vises does affect the balance of the rhomboid. 

The rhomboid was left suspended when we left this afternoon, to see if the wires and pin vises can hold its weight for a long period of time.