Thanks guys for the input and especially to Don for the reminder on the importance of considering dust control. Don, don't tempt me with those expensive tools, I'm generally fiscally responsible but tools are a weakness of mine. This job I needed to do on the cheap. The job is done and I kept it under $3, none of that for bandaids. I went with the fiber disk approach. Spent $2.50 for a 10 pack of the cheap 3" ones from Harbor Freight. Spent another $0.30 for a 3/8X1 1/4" bolt with nut and 2 washers. I used the later to make a 3/8" arbor to hold the disk so I could chuck it in my drill press. Duct tape to hold shop vac nozzle to catch dust. I took it slow, about 1/2 hour of grinding time to complete. The resulting hole was a bit ragged looking but did not affect performance. It turns out that my initial cut resulted in the reflector being about 0.060" too long for tightest spot focus with a 1W HD. I spent another hour taking about 0.010" off at a time, checking performance after each pass. Initial performance looks good, I will post further after I have a bit more time to evaluate it. For those considering modding with MR style reflectors, this was a bit of a PITA. Their attraction, however, is that they come in a variety of optical shapes, Flood, Narrow Flood, Spot, Narrow Spot. This affords some flexibility depending on your objective. If I had it to do over, I would try to find a diamond disk if available in 3".