Im in the middle of making up a guard for a 6" wire brush that I have fitted onto a motor to bench mount, but i cant decide whether it will be safer to add a tool rest or not any advice would be most welcome
NO NO NO - no tool rest
The wheel will grab the work and pull it out of your grasp, probably smashing your fingers in the process and rip wires out of the wheel, these will ricochet off the tool rest and head straight for your chest/face area.
Use tool rests with grinding wheels (with a clearance of 1 or 2 mm), but never with wire wheels or polishing mops.
Regards Jugs (and don't forget to use eye protection, full visor best)
Any close fitting tool rest is safe and is designed to stall the motor if any thing should get stuck.