Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Standard lab technique is to simply score the tube on one side with a fine triangular file, then placing thumbs together on the opposite side from the score, do a quick snap to break the tube. If you wish to "seal" the break, use a blow pipe in an alcohol flame (a propane or butane torch will work as well) to bring the edges of the break to a bright orange and observe the sharp corners rounding off. Don't go too far with this "healing" of the break or you will likely bulge the tube O.D. by rounding the end excessively and make a final fit in your compression nuts more difficult.

Hope that helps.