It's a piece of 4" schedule 40 pvc cap with a hold drilled to mount as flush to the base as possible.
Deano, guard? What's that?
The previous bolts that held the "spinner" assembly in place were removed (since they were only an inch) and the holes drilled to make room for the much longer bolts (3"). I drilled completely through the housing as you can see.
Also had to file a bit of the cap on the motor side of the grinder for it to fit as flush as possible.
Then, a good coating of grease both around the spindle of the grinder, and around the inside of the pvc to help keep dust contained and out of the grinder itself. You might also notice a piece of metal inside the cap with 4 holes drilled to coincide with the bolt holes, this adds reinforcement over a much broader area than having bolt heads directly in contact with the pvc cap. I like to build things once if at all possible, and knew the force would eventually crack the pvc if I didn't do this.
The rest of it is just a piece of 4" pvc pipe, also sched 40 (in other words water pipe not sewer pipe, twice the thickness for obvious reasons), and another pvc cap on the opposite end.
I thought of taking pics throughout the build, but was unsure it would work until it was all together, and then realized I had pretty much cemented everything in place when I was finished.
The blade is actually a regular diamond blade for the grinder that I cut into that shape with my good old harbor freight pneumatic rotary cutter.
Hope the description is adequate, and may a few more join me in flaunting our fingers in the face of danger.
Deano, as for heat, it seems to do quite well, doesn't build up any more heat than the grinder develops alone, which is a good thing.
Paul.