Hello,

    This is my first post here, but I have been lurking around for quite some time. I am planning to make an 8'' telescope including the mirror. I came across the following page while looking around for some info.

http://www.geocities.com/asatsi/atm/atm.html
 

The guy there uses a plaster tool with glass pieces stuck on it instead of tiles. Are there any pros/cons to doing this? Cost and availability is of course an advantage. But does the glass pieces wear faster than the porcelain tiles? Will I have to change the glass in between grinding?

 
~

Thomas 

I personally use porcelain tiles so I can't vouch for the glass pieces.  I also use solid glass tools occasionally which also works well, so the plaster/glass pieces might also work.  Premature wear-out might be a concern.  Procelain tiles hold up well, but you could use just about anything for the tool.  Remember that your only hogging out the sphere and performing rough grinding at this stage.  The thought of potentially having to change the glass pieces during the grinding stage, or remaking the tool, is a step I'd just as soon avoid.

If you cruise around the web, you'll find all sorts of useful information about mirror grinding and the various techniques (and materials) used.  A while back I switched to using a diamond edged cup saw mounted in a drill press to do the "caveman" rough grinding work... as John Dobson refers to it.  Saves gobs of time and effort, but there's very little Zen involved. :)