Hi Phil,
A few years ago I made a very basic tool grinder based on a Machine mart cross vice and a cheap 5" grinder (I think from Aldi or Lidl.) There are some pictures in one of my albums called cross vice tool grinder. It might give you some ideas. Note the hub on which the grinding wheel is mounted is keyed onto the shaft so it is safe to run the motor in either direction.

Les.

What makes you think it will make anything brilliant if, as you say, “ bench grinder which isn't particularly brilliant”

If it is no good it will likely make a “less than brilliant” anything else.

Or CBN for hard and High Speed steels – much better finish and control. Although if just putting the fine edge back, you can safely do tungstons on CBN, and HSS on Diamond. At very low DOC and if the wheel particles and tool are not allowed to get too hot, the Diamond will suffer no ill effects with HSS. I regularly mix and match with no problems.

Don't do low carbon steels on either wheel type – they just clog up.

If you are clogging a diamond wheel when grinding HSS, it is most likely due to high removal rate and heat – the diamond dissolves in the steel with high heat and the surface looses the cutting ability. Very difficult to recover. It's the heat at the particle cutting edge that is the issue, not the heat of the wheel – although that should not run at hundreds of degrees C anyway!

The particle bond method also plays a role – some have a resin bond that can soften under too much heat and smear over the particles – giving the impression of a clogged wheel – this applies to both diamond and CBN wheels.

Joe

Bob, yes diamond for tungsten carbide and CBN for HSS, the wheels can be dressed, perhaps you need a coarser diamond wheel?

This may be of some help you decide, a while ago I reground an old oil stone and I used a diamond wheel as I thought it a good idea at the time, it cleaned the diamond wheel up a treat, carnt quite remember but by the time the stone was flat I had may be took 1.5mm of it.