FW: ATM beginner tool questions

["mlbrown@everstrive.com" <mlbrown@everstrive.com>]

>>I want to make two mirrors out of the kit, an
f/4.5 first, then an f/8. 

Do the f/8 first, then the f/4.5, which is a tad harder.

>>1) Is it practical to make a tile tool for a 6" blank?

Absolutely.  Find a dental supply store in the yellow pages and buy 25lbs
of dental stone.  Then find some tiles (see recent posts regarding Daltile
1" tiles in a sheet).  Put a layer of something on the blank, wrap the
blank around the outside to make a form, then the tiles, and pour the
dental stone inside and vibrate the air out.  Easy.  

>>2) Will the blank make good contact with the tiles during the chordal
stroke?  I'm thinking there will likely be dead zones where there are
no tiles close enough to the edge.  Will this be a problem?

Probably not a problem on the f/8 (sagitta is something like 0.046), but
the f/4.5 will be deep enough that you might grind thru the edge tiles and
have to retile the tool.  Don't worry about the 'dead zones.'

>>3) Should I use something else to hog out and then pour the tool once
I get the general curve going?

Absolutely.  Get a chunk of metal -- a chunk of pipe works fine -- and hog
away directly across the center, rotating the blank random amounts, until
the depth is about right.  This is faster than the usual grinding, and a
lot more noisy and fun.  Then build your tile tool off of the blank and
finish coarse and fine grinding.  See my 4.5" website where I do just what
you want to do:

http://host67.everstrive.com/~mlbrown/ASTRONOMY/FourInch.html

Oh, and don't bother trimming the tiles like I did.  Just use whole tiles,
or maybe knock the corner off a few tiles that stick out, but it is just
fine to leave huge gaps along the edge.  Note the condition of my tools at
the end.

Oh, and the WB kit has more than enough materials to make 2 mirrors.

=Matt


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