A while back I had a job cutting 30 close tolerance 3" holes in 12" I beam I tried using a guide ring but could not hold size. I came up with the idea of using a ball bearing with an inner lining to fit the tip and pressed the bearing in a machined outer housing. A 3/8 square bar was welded on the housing. A sliding pivot block fits the bar for cutting holes 2" to 6" It was small enough to work inside the I beam and I could cut the 3" holes with a -0 +1/32 tolerance. I made a spring steel bracket that clamps to the 1/2" gas tube. That made it easy to put on and take off. I think it is the handiest tool in my torch box.
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