I want to know how to quickly create the straightest possible breaks in glass pipes
I apologise if this is only borderline suitable for a physics forum - I just hope experts with a lot of experience in stress, strain, thermal expansion, material science and similar topics might have some insight into.
The glass being cut: in short, all kinds. Varying quality, some tempered and/or annealed. Varying thickness, varying diameter, varying types - lime soda, borosilicate. Typical diameter 20mm to 40mm, thickness 1-2mm.
So far, I've had most success simply using a glass scoring tool which I use to manually score round the outside. Then I apply a bending force at that cut. I have less than 50% success rate.
I found videos on youtube where amateur glass-workers use various combinations of scoring, heating over flames, dunking in water hot or cold, applying ice. But the results seem variable, and I have had even worse success applying these methods.
I've heard of professional glass tube cutting machines that use a flame and water. I don't know if they also score the glass. I couldn't find any such machines on the net, let alone how they work.
How would you design such a machine to work? I presume the key factors are glass tolerates higher compression than tension, and glass is not a good conductor of heat.
For example, would it make more sense to apply heat evenly around the tube in a narrow band, while next to it, applying water in a narrow band? Or applying one followed by the other? Or perhaps heating on one side of the tube and cooling on the other?
Addition: After seeing this post: Why does glass break at the line where you score it? Perhaps it would make sense that heat is applied at the score line, equally and simultaneously around the circumference? If so, where would the water be applied? I'm clutching at glass straws with this one.
Further addition: This PDF on glassworking, with references to M P Groover, “Fundamentals of Modern Manufacturing", explains that tubes are made in extremely long lengths, and implies they are cut by scoring and then breaking along the score line. But it doesn't say how exactly the breaking is done. I should see if I can find a copy of that book.