From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: rec.woodworking
Subject: Re: Glass cutting
Date: Thu, 11 Sep 1997 11:43:39 GMT

On Mon, 08 Sep 1997 16:42:04 GMT, jhewitt@ctv.es (John Hewitt) wrote:


>Is there a difference between 'new' glass and 'old' glass? I see the
>guys in the shop cutting glass, it looks easy! Score the glass, give
>it a tweak and zappo, a nice straight break.
>I have some old glass, tried the same thing. Score lines were good,
>but the d*********d stuff wont break along the line. Now why's that?
>Yeah, I know, ham handed. But there has to be a reason!!!
>John Hewitt, Malaga Spain                 jhewitt@ctv.es

Tain't easy and you will have some breakage but....

More than a few years ago I was faced with replacing all of the sash
(the wood part) of the windows in a house which was 168 years old. I
wanted to change the number of lights in each window from 2 over 2 to
12 over 12. For the non-English speakers the original window had an
upper sash which contained two pieces of glass and the lower sash had
the same geometry. When I finished the upper sash would contain 12
pieces of glass and the lower sash would also contain 12 pieces of
glass.

The glass was much older and was thicker at the bottom than at the
top. I wanted to place the old glass in the new sash and was faced
with the problem of cutting the old glass. Initial attempts indicated
that I wasn't going to recover much of the old glass. I went to the
glass shop where  with my problem and was referred to an old codger
who was close to my present age. He showed me how to do it with a few
lessons and I was able to complete the job with a reasonable amount of
breakage.

This is what he demonstrated..

1. Use a cutting wheel with a good edge.

2. Use a straight edge to guide the cutter and make ONE score marking
the desired cut.

3. TURN the piece over on a surface that has some "give". I used a
flat, solid table with about 12 layers of newspaper. He used a piece
of carpet with a very short nap. NOTE: The scored line is on the
bottom side. PRACTICE until you are comfortable with the support
media.

4. Place your thumbs over the scored line on each end of the line and
gently press until the piece snapps along the line.

That is how it works. I would suggest that you get some scrap glass
and PRACTICE a bit before you risk the old glass. I did this over 35
years ago and can still cut glass with reasonable success. It takes a
certain amount of judgement to determine how much pressure to exert
and how flexible the support should be. The physics is that almost all
of the force is exerted at the score mark. The further away from the
score mark you are the less pressure on the glass.

With a bit of practice you will be able to cut curves in NEW glass.
Old glass ain't the same.