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Re: [ATM] Quandry over steel washer tool

Unless you happen to have a short FL pre-shaped pyrex tool laying around to use I would still recommend the pipe flange over the tile tool. I've done it both ways and  was able to rough out an 8" F7 in about 2&1/2 hours total with the pipe flange. I wasn't being particularly aggressive either, because I was interested in having a reasonably spherical surface after rough grinding. The flange worked well for this. 
   
  A tile tool would take considerable longer. Another option might be to use a subdiameter tile tool (~50%) which would concentrate the effort on deepening the center first as a pipe flange does. The one big advantage to the pipe flange, though, is it's cheap and ready to use out of the box. It lasts a long time, too.
   
  Curt
   
  >After advocating a pipe flange a short while ago, I had the opportunity 
>to try out some methods for hogging out an 8" pyrex blank. 
>Unfortunately, the pipe flange was actually not as fast as I had 
>thought 
>it was from earlier attempts. What worked fastest (hogged about 80% of 
>the sagitta on an 8" f/5 in 30 minutes on my machine) was a very convex 
>10" piece of pyrex that someone had used as a tool for an f/2 (!) 
>mirror. So, I somewhat red-faced-ly retract my earlier advice on pipe 
>flanges.
>
>So now I'm suggesting a convex surface is the best. Barring that, the 
>tiles will (I now think, but I'd need more experiments to be sure) be 
>faster as other's suggested, because they will wear convex as you go.
>
>Be aware that the tiles may be too thin to use by the time you're done 
>hogging, so you may want to pour a new tool with new tiles before you 
>start 120 grit. I've seen people get all the way to 25 micron or so and 
>have a tile tool lose tiles - they not only need to make a new tool, 
>but 
>go back to 120 grit to get the tool to conform to the mirror!
  >
>Clear skies.
>-- 
>Michael Lindner



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