Re: [ATM] machine hogging

["Bob May" <bobmay@nethere.com>]

One thing to note when doing hogging of a hole into the mirror, one that I
often have to remind my students - touch the edge of the mirror with the
tool and you have to grind that amount away from the center also in order to
gain the depth back again.
You are digging a hole into the mirror when you are hogging with a
subdiameter cast iron tool and you have to work the center of the mirror
most.  The unfortunate thing with doing this on a spindle is that the center
of the mirror is the part that isn't moving so you have to make sure that
the tool is turning over that part of the mirror in order to get it ground
down.  This is actually where hand work across the center is better.
I do look at the various people doing the work and when they start to grind
out the bevel at the edge of the mirror, I remind them of what they are
trying to do with the hogging.
FWIW, one little trick is to take one of those 4" diameter diamond disks
that Harbor Freight sells for cheap and back it up with something (glue a
disk of wood for example) to make it easy to handle and just use the side of
it to do the hogging.  I'd use it only on 12" up mirrors tho due to its
diameter.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net


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