Every welded joint starts as two cuts. If they are square, burr-free and in the right plane, the joint closes with minimal gap and the weld can be run with little filler. If they are not, the fabricator is compensating for the saw rather than joining two parts.
This is easy to underestimate because the cut is invisible once the weld is finished. A badly cut tube may still produce a part that looks right from outside, while the inside of the joint carries an uneven root, a step in the bore or a stress concentration that shows up later.
A square cut gives a consistent gap all the way around, and consistent gap is what makes a weld repeatable. When the cut is off-square, the gap opens on one side and closes on the other: the wide flank needs more filler and more heat, while the tight side may not take filler at all.
On thin-wall exhaust pipe the effect is exaggerated, because the wall has so little metal to work with. A gap that would be tolerable on heavy pipe becomes a burn-through risk on thin tube. Checking squareness with a square or a machinist's rule before welding takes seconds and saves a re-cut.
Cutting leaves a burr on the inside and often on the outside. Left in place, the internal burr becomes a raised lip in the gas path and a site where a crack can start. On a titanium fab component where the part is visible and inspected, it is also an obvious quality marker.
Deburring is usually done with a hand tool or a rotary file, followed by a wipe. Clamping dents from the saw vice matter too, particularly on thin tube: an ovalised end will not fit into a slip joint or a hose properly, and no amount of welding will correct it.
Abrasive chop saws are fast but leave a rough, slightly angled face and heat the cut zone. Bandsaws leave a cleaner face with less heat but can wander on thin wall. Rotary cutters and lathe parting give the best face, at the cost of setting the tube up accurately.
For anything that has to be welded and inspected, the cleaner cut is generally worth the extra setup time. The cut quality sets the ceiling on how good the joint can be, and no welding technique can lift a joint above the standard of the faces it was given.
Mark the cut line right around the tube, not just on one face, and check it against the drawing before the saw is started. For angled cuts the plane has to be right in two directions at once, and a wrap-around mark is the simplest way to see that it is.
The first tack tells you whether the cut was good. If the tube pulls out of alignment when the tack cools, the faces were not meeting evenly. Stop and correct the cut rather than adding more tacks to force the joint closed, which only stores stress in the finished part.
Consistency comes from the setup, not from the operator's eye. A stop on the saw, a jig that holds the tube at the same angle every time, and a standard deburring method all keep joints uniform across a batch. That is what makes the tenth part match the first.
Checking a few cuts per batch, and keeping the blade or wheel in condition, prevents the slow drift that happens when a worn tool starts wandering. On stainless and titanium a dull blade also adds heat, which changes the material right where the weld will go.
