The most skipped step in pressing, and at the same time the number 1 cause of joints that only start leaking after months. Two minutes of work that save you a lot of trouble.
Why a burr ruins a joint
After cutting there is always a sharp edge on the pipe, however cleanly you cut. Push that pipe into a press fitting and the burr scrapes over the O-ring. The nasty part is that you notice nothing: the joint is tight straight away and passes the pressure test as normal. Only after weeks or months does the damaged O-ring start to leak slowly, usually out of sight in a wall or floor.
That is why the rule in pressing is: the joint is made in the preparation, not in the pressing. The tool will always press; the question is what you let it press shut.
How to do it by material
Copper and stainless steel
Cut square with a pipe cutter. It pushes a small burr inwards by itself, so deburr the inside.
Lightly deburr the outside as well, so the pipe slides smoothly past the O-ring.
Calibrating is not needed as long as the pipe is round. Squashed or oval pipe: saw off a piece and start again.
Multilayer pipe (PEX-AL-PEX)
Cut with sharp pipe shears, square to the pipe.
Then always calibrate with a calibration tool of the right size: it makes the pipe round again and adds an entry chamfer on the inside.
Most calibration tools deburr at the same time. Turn it calmly a few times until it runs freely.
Test after calibrating: the fitting should slide on smoothly, with a twist, up to the mark. If you have to push or lever, the pipe is not round yet or there is still a burr.
Frequently asked questions
For a one-off emergency job it will do, but a proper deburrer costs a few euros and does it evenly all round in one turn. With multilayer pipe you want a calibration tool anyway, which does both at once.
That is the classic picture of an O-ring damaged during assembly by a burr or by skipping calibration. The fitting has to come out and be replaced; a pressed fitting cannot be repaired.
No. The profile of the jaw determines how the fitting is deformed, but no jaw can seal a damaged O-ring. Preparation is everything.