[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: [ATM] Scratches keep forming on edge of mirror
Hi Adam,
Sorry for the delayed response. I'm currently polishing my first mirror.
Consequently I don't have as much experience as the others. I had
trouble beveling with a sharpening stone. For some reason I kept getting
small chips on the outside edge of the blank.
So, I switch from a sharpening stone to wet sanding paper. I found this
gave a nice smooth bevel. I'll probably just use wet sanding paper on my
next mirror.
-Anthony, Round Rock TX
> -----Original Message-----
> From: atm-bounces@atmlist.net
> [mailto:atm-bounces@atmlist.net] On Behalf Of Dominic-Luc Webb
> Sent: Friday, August 17, 2007 2:29 AM
> To: ATM Superheros
> Subject: Re: [ATM] Scratches keep forming on edge of mirror
>
> On Thu, 16 Aug 2007, Adam Krause wrote:
>
> > I have made my tile tool and it now has good contact with
> the mirror
> > surface (8" f/6.2)
> SNIP
> > knife sharpening oil stone. When I get scratches, I have
> gone back to
> > rebevel the tile tool.
> SNIP
> > stroke (4" total stroke length) with MOT to try to bring
> the surface
> > to spherical. That is when I noticed the scratches coming
> up again.
> > I will be grinding along fine, and then I will feel resistance from
> > the edge of the mirror.
>
>
> To add something new, I got chips on my first tile tool,
> which was concrete. In my case, I definitely had small rocks
> coming off the concrete. Sealing solved this problem. The
> sides are important to seal as well. Small rocks can fall
> from the sides onto the glass. I think some of the tiles were
> also a bit loose and broke chips off the mirror as well.
> Tiles were better embedded in my later tools.
>
> As for the the bevel, I have tried a few angles without any
> effort to quanitiy this. Suffice it to say this is much more
> problematic with the plate glass that I generally work, and
> the angle may be much more critical. The pic below shows a
> surface I have baffled on top of another piece that I have
> not bevelled at all. Notice the way the lower plate glass
> chips on the corner.
> I have quantified this and these are a lot bigger and more
> frequent than what I get with optical borosilicate. For
> scale, consider that the glass is 6 mm thick (Schmidt
> corrector plates).
>
> http://www.canit.se/~dlwebb/catadioptric/310schmidt/corr_col.jpg
>
> Looking at the upper plate glass, you can sense the angle
> used, and this has worked very well for me. In terms of the
> grit size for this bevel (notice, I also work the sides of
> plate glass because these can also chip, BTW), I use a
> roughly 200 mm long combination coarse/fine sharpening stone,
> like this one:
>
> http://www.soonerstateknives.com/NT-JB6.JPG
>
> I have never found specs for the grit size for my stone, but
> similar ones I have encountered specified that they are
> silicon carbon, just like we use for grinding mirrors. My
> guess is that the fine side is probably finer than #600, and
> probably about #1000. I have had/used this tool for many
> years and it has worked very well for bevelling. My bevels
> end up nearly polished, and this brings up my final point.
> Sharpening stones can be found with grits of any sizes, so it
> is nice to see that when we discuss this, there is mention of
> the grit size. Look here for instance.
>
> http://www.fine-tools.com/japwas.htm
>
>
> Dominic
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>
_______________________________________________
ATM mailing list http://www.atmlist.net/