Steps that keep cuts square, lengths accurate and bends clean when preparing pipe.
Accurate measuring and marking is what separates neat, leak-free pipework from frustrating rework. Here is the good practice to follow when preparing pipe.
- Measure twice and cut once. Confirm the length before cutting, because you can always trim more off but you cannot put it back.
- Allow for the fitting. A pipe pushes into a fitting by a set amount, so include or subtract that engagement length, sometimes called the make-up, when marking your cut.
- Cut square. A square cut lets the pipe seat fully into the fitting and the seal sit evenly; a skewed cut can leak.
- Deburr the ends. Ream the inside and file the outside so there is no sharp burr to cut a seal, snag debris or restrict flow.
- Mark bends from a clear datum. For a bend, measure to the centre or the start of the bend as your method requires, and keep the mark on the correct face so the bend finishes in the right plane.
- Check before committing. Offer the pipe up and check alignment before making the joint permanent.
Careful preparation saves material and time. Check the make-up allowance and bending method for each material and tool you use.
Bending copper tube: the machine and the maths
Forming bends in the pipe itself, rather than fitting a separate elbow at every change of direction, keeps the run continuous with fewer joints, and every joint left out is one less place that could leak.
A bending spring or bending machine does not do your setting out for you; it supports the tube wall from inside or around the bend so the bore stays round instead of kinking or flattening as the bend is pulled or pressed round.
On a hand bender, the grooved former controls the bend radius and the guide and pressure roller support the tube as it is formed. The tube stop holds the tube in position; it does not measure anything. Mark the required bend and align it with the tool’s datum before applying force through the handle. Use the correct former and guide for the tube, and inspect for flattening, ripples or cracks afterwards. The Yorkshire Copper Tube guide traces the usual faults to where the bending pressure is applied: it must stay a set distance in front of the point where the former supports the tube. Too close, and the tube necks at the ends of the bend; too far, and wrinkles form along the inside radius. Replace worn guides and formers, preferably as a matched pair. Setting out matters as much as the tool. For a 90° bend in a machine, the Copper Board's method measures the end-to-centre length and adds half a tube diameter to find the bending mark. For an offset, close a 600 mm folding rule to 600 mm less the offset, so 550 mm for a 50 mm offset, and bend to the angle the rule makes. A spring-loaded bend is set out with a radius of four times the tube's outside diameter; three diameters, measured to the throat, is the tightest. The spring grips as the bend is pulled, so take the bend slightly past the angle needed and ease it back, then twist the spring the way it is coiled to draw it out. Keep springs lightly greased and free of rust: a rusty or undersized spring can wrinkle the tube or even snap it. Plastic pipe has its own limit: Wavin's minimum bending radius for Hep2O is 8 times the pipe diameter, which is 120 mm for 15 mm pipe.
For an idealised offset drawn as straight centre lines meeting at two 45-degree corners, the diagonal travel is the sideways offset multiplied by the square root of 2, approximately 1.414. A 175 mm offset therefore gives about 247.5 mm between those theoretical intersections. Actual formed bends have a radius: use the bender’s setting-out method and allowances to obtain the correct cutting and bending marks, rather than treating this calculation as an unadjusted cut length.