Cutting a demi john

(The cannibalised propane cylinder chamber looks better than the glass
option)
Anth

"Anth" wrote in message
.. .
It's a good site - book marked it for future reference.
Thanks David/Mark.
Anth

Do you find that the grinding effects the strength of the glass?
Anth

"Mike Firth" wrote in message
...
Having been asked about various methods a number of times, I finally ran
some tests on using a string soaked with kerosene and lighted. I tried on
small test bottles with and without scoring and found I got roughly the
same results: The crack went all the way around and was flawed by at
least 1/4" in one or more locations. That would mean quite a bit of
grinding to reduce the edge to an even surface. The bottle ends up a
greasy black, which washes off after getting on hands and everything.
Alcohol does not work and non-cotton string does not work. The bottle
cracks as the flame goes out.
I have all the stuff to try low voltage with a nichrome wire, but have
not rigged it yet. Getting the wire to wrap the bottle all the way for
cracking without shorting where it completes the circle is my main
concern.
Don't believe putting a hot iron in oil would produce enough of a shock
to crack the scored bottle although touching a hot iron to the score where
oil inside defined the stress line might work.
http://users.ticnet.com/mikefirth/bottle.htm my page on this topic.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit47.htm Latest notes

"Anth" wrote in message
.. .
Hi
I have a glass Demi-John, I need to cut the bottom off to make a bell jar
piece of equipment for experiments.
Some techniques scour the glass and then use a heated wire to shatter
across the score.
I have seen other methods such as filling the bottle with oil and
inserting a hot piece of metal, and the bottle should cut across the
fluid line.
I have no idea if this method will work with Demi John's - has anyone got
any ideas how I could solve this problem?
Thanks
Anth

My mate with the lights is www.source-antiques.co.uk but they may not be
that cheap. The garden cloches I would look for on the web or garden
centres, he gets some of those in as well coocasionally. Regarding the
20 torr pressure, even with a perfect vacuum you only have 1 bar
pressure, 14.7 psi IIRC but that is still quite a bit to put on a demi-john.

Anth wrote:

Have you got a source/link selling these garden cloches?
Anth

"David Billington" wrote in message
k...

[snip] I know a guy that has glass light fittings that are bell jar shaped
and there are garden cloches, these have much heavier walls than a
demi-john. I think the expense in the bought items is that they are rated
to do the job but still have to be treated accordingly. Have you looked at
this site http://lerch.no-ip.com/atm/ he covers mirror silvering and other
interesting stuff.

[snip]

Just had a look at the site and couldn't see anything but he has from
time to time had industrial , aircraft carrier etc lights which have
thickwalled bell jar shaped glass in various sizes from maybe 8" high to
15". Obviously not intended as bell jars.

David Billington wrote:

My mate with the lights is www.source-antiques.co.uk but they may not
be that cheap. The garden cloches I would look for on the web or
garden centres, he gets some of those in as well coocasionally.
Regarding the 20 torr pressure, even with a perfect vacuum you only
have 1 bar pressure, 14.7 psi IIRC but that is still quite a bit to
put on a demi-john.

Anth wrote:

Have you got a source/link selling these garden cloches?
Anth

"David Billington" wrote in
message ...

[snip] I know a guy that has glass light fittings that are bell jar
shaped and there are garden cloches, these have much heavier walls
than a demi-john. I think the expense in the bought items is that
they are rated to do the job but still have to be treated
accordingly. Have you looked at this site
http://lerch.no-ip.com/atm/ he covers mirror silvering and other
interesting stuff.

[snip]

A diamond grit blade such as is used to cut ceramic tiles will do. It
needs to be water cooled. I have a small table saw with a water
reservoir that quickly cuts bottles of any size. Made by Covington.
If you can't find such a table saw you could put a tile blade in a
skilsaw (electric circular saw) and have a helper carefully lubricate
with water from a hose while you're cutting.

John Bassett

Be very careful in choosing a "table saw" for cutting glass as to where
the motor is and what gets wet.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit47.htm Latest notes

"John Bassett" wrote in message
oups.com...
A diamond grit blade such as is used to cut ceramic tiles will do. It
needs to be water cooled. I have a small table saw with a water
reservoir that quickly cuts bottles of any size. Made by Covington.
If you can't find such a table saw you could put a tile blade in a
skilsaw (electric circular saw) and have a helper carefully lubricate
with water from a hose while you're cutting.

John Bassett

The greater problem is when grinding fails to catch the last of the nick,
so that although it looks like a ground edge, it has a pre-existing crack
ready to fail. It is my judgment that all bell jars made for the purpose
have ground edges simply because blown or cast glass simply isn't flat
enough for a good seal.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit47.htm Latest notes

"Anth" wrote in message
.. .
Do you find that the grinding effects the strength of the glass?
Anth

"Mike Firth" wrote in message
...
Having been asked about various methods a number of times, I finally ran
some tests on using a string soaked with kerosene and lighted. I tried
on small test bottles with and without scoring and found I got roughly
the same results: The crack went all the way around and was flawed by at
least 1/4" in one or more locations. That would mean quite a bit of
grinding to reduce the edge to an even surface. The bottle ends up a
greasy black, which washes off after getting on hands and everything.
Alcohol does not work and non-cotton string does not work. The bottle
cracks as the flame goes out.
I have all the stuff to try low voltage with a nichrome wire, but have
not rigged it yet. Getting the wire to wrap the bottle all the way for
cracking without shorting where it completes the circle is my main
concern.
Don't believe putting a hot iron in oil would produce enough of a shock
to crack the scored bottle although touching a hot iron to the score
where oil inside defined the stress line might work.
http://users.ticnet.com/mikefirth/bottle.htm my page on this topic.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit47.htm Latest notes

"Anth" wrote in message
.. .
Hi
I have a glass Demi-John, I need to cut the bottom off to make a bell
jar piece of equipment for experiments.
Some techniques scour the glass and then use a heated wire to shatter
across the score.
I have seen other methods such as filling the bottle with oil and
inserting a hot piece of metal, and the bottle should cut across the
fluid line.
I have no idea if this method will work with Demi John's - has anyone
got any ideas how I could solve this problem?
Thanks
Anth

Decided I will go for the metal container (probably a propane or a beer keg)
due to the fact the glass containers might end up shattering under the air
pressure.
I'll have to put a window in it, which means I have to learn welding and
vacuum sealing methods.
Should be an interesting project.
Anth

"David Billington" wrote in message
...
Just had a look at the site and couldn't see anything but he has from time
to time had industrial , aircraft carrier etc lights which have
thickwalled bell jar shaped glass in various sizes from maybe 8" high to
15". Obviously not intended as bell jars.

David Billington wrote:

My mate with the lights is www.source-antiques.co.uk but they may not be
that cheap. The garden cloches I would look for on the web or garden
centres, he gets some of those in as well coocasionally. Regarding the 20
torr pressure, even with a perfect vacuum you only have 1 bar pressure,
14.7 psi IIRC but that is still quite a bit to put on a demi-john.

Anth wrote:

Have you got a source/link selling these garden cloches?
Anth

"David Billington" wrote in message
...

[snip] I know a guy that has glass light fittings that are bell jar
shaped and there are garden cloches, these have much heavier walls than
a demi-john. I think the expense in the bought items is that they are
rated to do the job but still have to be treated accordingly. Have you
looked at this site http://lerch.no-ip.com/atm/ he covers mirror
silvering and other interesting stuff.

[snip]