From: "McHatten, Shawn" 
To: atm{at}shore.net, 'Richard Schwartz' 
Reply-To: "McHatten, Shawn" 


Hey Guys
        I've had a couple of queries off list on how I built this thing so I
thought I'd post it here for anyone else who is interested. Sorry for it
being a bit long.


Richard
        Sorry I don't have pictures but I will try to get some. I have no
website but will try to send individually for those who have asked.
Hopefully the description below will help. And thanks again for the idea of
using Al. It seems to let me get the qualities of using a washer like tool
without have to be pregenerated first.
        BTW just to let you know what did NOT work, I tried building the base
out of dental stone first (actually Durbond 90 in Canada) but when I
attached it to my sander it lasted all of 3 seconds before it blew up. The
Al would not stick to the Durbond. Or I didn't let it cure long enough (but
it was 24 hours so.....). But the 1/8 wall thickness of the Durbond wasn't
strong enough to hold together. It might have been ok for a hand tool
though.
        I'd still like to know whether I'm making more of this than I should.
What are some average times out there? Dan C says 10hr for a 16in on his
website. Stathis says 14-16 with glass on his 14in. I didn't see any quotes
on either Bob's or Mel's site. Richard what are your times running at.

Thanks
Shawn

-----Original Message-----
From: McHatten, Shawn
Sent: Thursday, February 20, 2003 5:46 PM To: 'Vladimir Galogaza'
Subject: RE: ATM Super Aluminum hogging tool?? I think??

Hey Vladimir
        That's great! I'll go over details of how I built it with both imperial
and metric numbers but I'm sure you can round the metric to whatever sizes
are normal in your area.
        First cut nineteen 7/8in (22mm) OD aluminum tubing into 2in (5cm)
lengths. I wanted more than half embedded within the tool for strength.
        I then cut 3/4in (19mm) shop grade plywood into two 5in (12.5cm) disks
and glued them together. Then I drew a line across the center and using a
drill press and a 7/8in (22mm) forestner bit I drilled 5 holes spaced about
1/8in (3mm) apart across this line but only about 1/16 (1mm) deep. THIS WAS
IMPROTANT because I wanted to get the layout of all the holes on the
plywood before I drilled to the full depth. Use a good bit because you want
the tubes to fit tight.
        On either side of these 5 holes I drilled 4 more holes (8) in between
each of the 5 original holes. Then next to these I drilled 3 more (6). This
gives a 6 sided figure with 3 holes on each side. To visualize what this
would look like before I drilled, I laid down 1 coin then 6 more coins
around the circumference of the first. Then 12 more around these 6. Make
sure to only drill a short depth to just lay out the holes first and to
leave some space between holes for a "wall" thickness.
        I then started on one side drilling the holes to a depth of 1.25in
(32mm). I found that while drilling the second hole there was a lot of
breakthrough to the wall of the first hole. This was even worse on the
third. To combat this I started putting the 2in (5cm) aluminum tubes into
the holes as I drilled them. This prevented much of the breakout since it
stiffened the wall up but I found it inefficient to drill one then fill
one.
        So I start drilling 3 or 4 holes that were not adjacent to each other
then filling them with the tubes. This was faster. At this point I was
really glad that I had laid out the holes ahead of time since it would have
been hard to tell where to drill next.
        I then coated all surfaces with exterior grade varnish 3 times. I paid
special attention to the bottom of each hole and between holes since there
was some break out and I wanted to make sure it sealed well.
        When complete I had a 5in (12.5cm) tool for my 16in (40cm) mirror. I
wanted about 1/3 ratio.
        When I started grinding all the tubes did not touch the glass and they
made a terrible screeching sound. But after about 20min they were all mated
quite well and I noticed the ends of the aluminum started to flare. I was
afraid this would continue but it seems to have gotten to a certain point
and has stopped. None of my tubes have flared enough to touch each other.
        I have used full size glass on glass for rough grind (on an 8in mirror)
and found it took longer than on my 16in. I also tried an 8in frying pan
turned upside down filled with dental stone (like Tom's dog food can in his
intro at GotGrit website) but found that it pushed the grit off the glass
too fast and being 1/2 size I was not getting the middle as I would have
liked.
        The great thing about this tool is that it pushes very little of the
grit off the side of the mirror. It seems to ride on top and roll the grit.
I'm not sure if I grind like everyone else. I do not clean the mirror after
every wet. On my first wet I sprinkle grit to within about 2in (5cm) from
the outside edge. And by the time it has dried out about 4-5minutes later I
have gone around the barrel 3 or 4 times and have still not pushed any grit
off the side even though my tool has come to
the side (but not over). I then wet it down again and sprinkle on more grit
and continue. I do this about 4 times before the mirror gets muddy enough
to stop and clean. So I get about 3 sets of 4 wets in about an hours work.
        I'm still not sure if my times are better than average but I'm happy
with them. I was expecting to have to hog for 10 to 15 hours even with a
pipe cap that Bob M suggests.

        I think there are three reasons why this works so well. 1, since it
does not have all the pressure just on the edge as a pipe cap does, it
allows the tool to ride on top of the grit and force it to roll and break
apart the glass in the way it is supposed to instead of pushing it out to
the edge. 2, the round edges of the tubes won't let the grit build up and
again forces it to move under the tool. 3, the aluminum is soft enough that
some of the grit actually imbeds itself in the aluminum for a short period
and digs into the glass before rolling on under. I also think the aluminum
takes the new shape of the mirror as it is being ground quite easily. I'd
like to think I can reuse this tool for several mirrors no matter the size
or f ratio.
        Anyway I can't wait to hear how you make out with it. If it works this
fast in hogging I'm tempted to see how it would work with fine grinding
like the metal washer tools but I'm more willing to experiment with hogging
than I am fine grind :). That's all I'd need is for an 80 grit grain of SiC
to get stuck in the Aluminum and come out at the 25 micron stage :). I've
read some good things about using aluminum tools for fine grind but I think
they are plates rather than this style.
        Sorry for the long post but I wanted to make sure I passed on all the
info I had. Good luck and let us all know how you make out.

Thanks
Shawn

--- BBBS/NT v4.00 MP