Julie
|
Any suggestions for...I want to turn some of my vast collection of demijohns into glass cloches by cutting off the bottoms. Has anyone done this already - or something similar - and has anyone any suggestions as to a good way to do it without smashing them?
|
misteralz
|
I'd reckon on getting a good bit of heat into them first, then multiple scribes with a stanley knife or tile cutter should see you getting a good clean cut.
|
Julie
|
Thanks, I'll give that a try.
I did also wonder if it might help if I put a band of masking tape around it to help prevent splintering, sort of like when you are cutting kitchen worktops or putting selotape on a balloon and piercing it with a pin. It takes up the surface tension in the area or something, what do you think.
|
misteralz
|
That would depend entirely on which method you used for heating it up. If you were to try it cold with a tile cutter the it would contain any glass splinters at the very least. Sort of like when you see track cars with crosses taped over the headlamps. 
|
Julie
|
Heating them up wouldn't be a problem as they would fit into the rayburn oven.
The only tile cutter I have is a large flat contraption which you place the tiles in and slide the cutter along them. I can't see any way of adapting that to do the job other than turning the demijohn against the cutter. It would probably be worth investing in a hand held glass cutter of some kind. I don't see the stanley knife blades being hard enough for the job, although I do have a small stash of them - could give it a try?
I have a sort of instinctive feeling that it might be better to try and cut a disc from the bottom rather than compromising the structural strength of the jars by cutting the bottoms clean off, what do you think? I expect the actual curve on the bottom edge will be where the glass is thickest too.
|
misteralz
|
If you get enough heat into the glass, then a Stanley blade should be sufficient - remember that provided you've not bought yours from the pound shop you can ratchet the blade out which will in effect increase its rigidity. Cutting a disc from the bottom sounds like a good plan, but how do you intend on doing it? I think you'd need a bloody big hole saw for that, and it'd probably need diamond-tipped teeth.
You ever seen one of those plastic orange peelers? You want something like that, ideally, but made in metal.
|
Julie
|
I should think a glass cutter would have an industrial grade diamond in it.
I wonder what they used to use to make a circular hole in a window pane with? Do you remember the old fashioned extractor fans that were fitted into the middle of a window pane?
I could probably use a plate as a template and score round it a million times but I can see me smashing the whole jar trying to tap the circle of glass out.
I keep forgetting to ask, what does heating the glass do? Does it render it less liable to break?
I know what excessive heating does, it melts it doesn't it, but no way am I going to get it that hot without making a dirty great deep fire in Gordon's forge.
|
misteralz
|
That's a damn good suggestion, actually! The tools they used to use were like a compass, except with a suction cup on them rather than a spike. That'd work well if the demijohn in question has a reasonably flat bottom but it'll require lots of passes.
Heating it will make it easier to cut given that it's going to be quite a thick workpiece. Let it cool naturally afterwards, although throwing the waste piece in a bucket of cold water may be interesting...
|
Julie
|
and stand well back 
|
