This the planer in bits.As you can see the part that carries the drum was made separate because I was working out the belt tension and wanted it to be adjustable.This added weight because the part had to be thick for rigidity and also required a reliable method for aligning the pulleys.All that is unnecessary if both pulleys are fitted to a plate on fixed centers.The grinder spindle is not designed to take a sustained side load as imposed by the belts so after realizing that I had to fit a bearing on the grinder side pulley and make the belt guard engage on it through a pin.That resulted in a heavy, structuraly strong case.If both pulleys are supported on bearings set on housings bored on the side plate the whole thing is greatly simplified and lighter as well as more rigid.Using a commercialy available grinder for power means that the attachment must be specific as all makes have different locations for the handle holes and are shaped differently so it pays to use a good quality make with good spares availability.
If you wish I can make a sketch and post it here to get you going.
If you wish I can make a sketch and post it here to get you going.