Water level sight glass

Just file a nick in it, then snap. I use a triangular diamond needle file, but an ordinary one will do as well. If it doesn't break square or cleanly, you can trim up the end by touching it against a green wheel. (Carefully!)

Phil

If you want to smooth the cut end, heat it slowly to nearly red hot in a flame. The glass will soften slightly and the sharp edge will round over. Cool slowly afterwards.

Cliff.

A small diamond cutter mounted sideways in a rod with an adjustable stop. Rotate dianond on the inside of the tube to score an internal line and if it doesn't break immediately use a little gentle heat.

I doubt that the tube was weaker then.

Thanks Chaps

I hope this stuff is stronger than we used in chemistry!

Another method for larger-bore tube & bottles: rotate tube slowly about it's axis, heating evenly where the crack should run with a fine gas torch. Touch a wire with a drop of water on onto the heated ring, and the glass breaks cleanly around it. This might not work for model-sized sight glasses, though ;)

Guy

Or you can do basically the same trick by tying a loop of string soaked in lighter fluid around the tube, set it on fire, and put it out with water after a few seconds. Works on bottles and suchlike.

-- Aamund Breivik

I seem to recollect whilst I was an apprentice the lab used high resistance wire looped across + - terminals on a 6 volt transformer. Obviously the length of wire would need to be calculated. Formula no idea. End result is the wire glows at red heat and cuts/melts its way through the tube leaving a nice edge requiring no smoothing to use. I hope some bright sparky can help with the formula. Cheers Dave