I have this cresting machine and would like to replace the rubber arrow holder that the nock end fits into in the second pic.  Or at least hear how you condition it to improve "Gription"  I know that is not a word but you get my idea.  

I'm not sure how your arrow chuck fits on your machine.You can get a replacement arrow chuck for Bohning cresting machine and maybe adapt it to fit on your cresting machine.You can get these chucks at KK and 3Rivers for less then $10.

A simple do it yourself fix would be to try surgical tubing.

The actual arrow holder on replacement chuck for the Bohnings is still just a rubber washer. I have trouble getting an arrow to spin true because the washer doesn't line it up straight...even carbons and aluminums look like they're not straight. I think I'll try to rig a small drill chuck on it...

I would check different sizes of rubber gas/air/water hose. Many different sizes so you should be able to find one that works or even glue a smaller one into a larger one if you need a specific OD.

Looking at you setup I'd go to a hardware store and get a 3/4" or 1" rubber cork (to fit the cup on the motor shaft).  Drill the center of the cork (be as accurate as you can) with a 1/4" bit and then "X" the large end half the depth of the cork.  Setting it in the chuck opening should get it friction tight on the motor cup and hold the shaft well enough.  There is really no stress so it can be a relatively loose fit.

Thanks for the suggestions.  I will take it up to the hardware and parts store and see if I can make up a good fit.

Bob Urban