I've been stuck for two days on this... I had to rethink certain dimensions for a small gearbox case and it has broken all the related parts created by splitting the original box. I simply can't execute the shell command. I've placed bolt holes and recesses for access with a ratchet but THE SHELL OPERATION REFUSES TO WORK. I require a 1cm thick shell which originally was working by creating an offset from my revolved cuts (recesses) but now I believe it is these very same recesses that are cause the shell function to stop working. Dimensions are approx 150 X 210 X 120 and I require a 10mm shell.