Cutting a demi john

Well I do intend to vacate the Demi using a vacuum pump as in

'll probably end up transparent taping the bottle to stop it totally shattering and I'll be wearing safety gear in case it does implode.I've also looked into that cutting the bottle with oil - some say it works some say it doesn't so I'm guessing it's hit and miss.I think I will have to get a few Demi's to experiment on cutting.(Once I have the Sputter chamber setup I can start making my own crude optics.)Anth

Forgot to say I've priced the commercial vacuum bells jars and they are way outside my price range. (approx £100) Anth

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.

my page on this topic.

I dunno if you have seen this link or not, but check this out:

step 18, "Aluminizing."

-- "I can conceptualize what infinity is, but I cannot imagine it." MCJ 200406

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

[snip]

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

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

My mate with the lights is

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

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 > My mate with the lights is but they may not

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.

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.

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