Urethane rubber will not stick to some metals (for example; brass or stainless steel) under any circumstances.
Urethane rubbers that exude an oil (such as PMC-121® WET or PMC®-780 WET) will not bond permanently to any metal.
To get urethane rubber to bond to steel or other common metals, we recommend using a rubber that does not exude oil such as Vytaflex®, Reoflex® or Brush-On® urethanes.
You can increase your chance of a secure bond between urethane rubber and metal by:
Options: After step 2 above, spray a high quality SHELLAC onto the metal surface as a primer. Shellac is a good bonding primer for urethane rubber. Ure-Bond® II adhesive is a better primer for bonding urethane rubber to metal and is available from Smooth-On distributors.