Cutting glass tube problem

[Dave Plowman (News)]

Thing is new glass cuts far more easily than old.

[Dave Liquorice]

Well one end of the lamp crazed, was that the end put in cold water? Cutting glass is all about starting a crack and then making it propergate in the direction you want. Controlling the propergation is down to where there are stresses in the glass, either built in (toughened glass) or from external force(s) and flexing creating areas of tension.

With the vacuum in tact that lamp tube is under considerable compression(*) from all directions. I think that will translate into the wall of the tube being in compression which supresses crack propegation. The thing will also not want to flex to create localised tension.

Thinking a loud but worth trying again after releasing the vacuum I would have thought.

(*) 15 psi doesn't sound much but you pile 7 bags of sugar onto something with a one square inch support and place that support on the back of your hand that is flat on a table...

[Tim+]

I doubt it's anything like 15 psi. Most incandescent bulbs are about 0.7 bar with an inert gas fill.

Tim

[Dave Liquorice]

[Dave Liquorice]

Long day yesterday and ICBA to look up what the nominal pressure is inside a light bulb. Still have a 0.3 bar presure difference or about

4.5 psi, that's still two+ bags of sugar or two kilograms for each square inch.

[tabbypurr]

Looks like I need to try the range of methods, see what will do it. Evidently what I tried doesn't :) Thank you everyone. Will get more bulbs & try them.

NT