Re: [ATM] Preparing to trepan for the first time - Success!

["Chris Dalla Piazza" <dalchri@hotmail.com>]

For anyone who googles this thread later on...

I did end up going with my home made biscuit cutter.  I made the bottom of
the cutter level by bringing it down on some sandpaper until all the teeth
showed wear and I could also keep the sandpaper in place without much of a
grip.

I also verified the side to side wobble was small by bringing in a felt tip
pen from the side.  Then I turned off the drill press, removed the cutter,
and inspected which teeth were marked by the pen.  Those that were marked
needed bent inward and those that weren't needed bent outward.

Once I was happy with the cutter, I marked the glass for cutting by making a
paper cutout in AutoCAD with two circles, one of the outside diameter of the
glass and the other for the diameter of the desired hole.  This ended up
getting me within 1/64" when coming in from opposite sides.

Since I didn't mess up, my suggestions are for efficient cutting.  I found
that keeping a supply of fresh grit in the cutter was helpful.  I did this
by making a small pile next to the hole.  As the noise died down during
cutting, I would push some more grit into the cutter which was accompanied
with an immediate increase in noise, just like when you start a fresh wet.
The grit wore out pretty fast.  When cutting the teeth into the cutter, they
will need to be slightly higher than the depth you intend to cut for you to
be able to push more grit into the cutter in this way.

It also helped to make sure that the groove stayed clean, especially as I
got deep into the glass.  I would spray the top clean, wipe off the spent
grit, and then run the cutter without grit just to clear out the groove.

I had trouble figuring out when I was at the bottom of the groove as I got
deeper too since the grit will make noise around the edges of the cutter and
not just as it bottoms out.  I found that my cutter would just barely start
to make a squealing sound as I bottomed out and used this to gauge my
pressure.

I had to trepan two disks.  The first disk off by about 1/64" and I found
breaking through was not instantaneous.  The first thing I noticed was that
the water had started draining through the groove.  About 1 minute more of
cutting was needed to separate the core.  The second disk, however, was
almost dead on and breaking through was almost instantaneous.

If you are concerned about doing damage as you break through, it may be
useful to intentionally offset slightly to prolong the time it takes to do
this.

The resulting holes are a little larger than the cutter which was made the
exact outside diameter of the sleeve that is to be used so this may be a
useful guide for what to shoot for when making the cutter so as to have
sufficient clearance when the cut is complete.

Thank you for all of your suggestions and I am relieved that this part is
over!






-----Original Message-----
From: Dave Smith [mailto:smithersscope@yahoo.com] 
Sent: Tuesday, November 14, 2006 6:29 PM
To: Chris Dalla Piazza
Subject: Re: [ATM] Preparing to trepan for the first time



--- Chris Dalla Piazza <dalchri@hotmail.com> wrote:

> I have created a biscuit cutter by wrapping 22GA
> steel sheet metal around a round wood block.  
> 
> This means that the end of the edge will be
> cutting deeper into the
> glass as it spins than the beginning of the edge.

Hi Chris,
You probably want to correct this if you plan to apply
any pressure from above. The uneven cutting action may
lead to an undesired wobble and slanted or tilted edge
on your resultant glass disk. 
 
> Also, I have not cut teeth into the cutter yet.  

I suggest cutting teeth into your tool. These teeth
will definitely speed the trepanning process by
allowing "slots" for the grit mixture to seep into the
cutting groove.
 
 
> I'm thinking of making a paper cutout to layover the
> disk to center the
> trepanning cutter.  I plan to come in from both
> sides and meet in the
> center.

To cut in from both sides is an excellent way to avoid
clamshell chipping upon "breakthrough" when the cut
completes. Inevitably the cut will not complete as a
circle, but rather an arc. And the section that
remains uncut will likely "fracture" due to any weight
on the tool. When you get close to "breaking through",
ease way back on any weight on your cutting tool. To
keep your biscuit cutter in place until you have a
groove cut into your glass, I recommend trepanning or
routing a masonite disk (1/8 to 1/4" thick) just
smaller (1/16") than the diameter of your biscuit
tool. Silicone this disk in place on your glass and
let this wooden disk guide the biscuit cutter. This
worked well for me. Your mileage may vary! 
 
> Does the glass disk need to be clamped down?

Absolutely! Leave the flying glass to airplane
windows!

Good luck and let us know how it goes!
Dave
 



 
____________________________________________________________________________
________
Do you Yahoo!?
Everyone is raving about the all-new Yahoo! Mail beta.
http://new.mail.yahoo.com

_______________________________________________
ATM mailing list http://www.atmlist.net/