Pie cut calculator
Work out a pie cut bend before you cut: how many slices, the angle to cut them at, and the length of each side. Enter your tube, the bend you want and how you are setting the radius.
| Each slice | mm | inches | Mark at (mm) |
|---|---|---|---|
| Short side | 0 | 0 | 0 |
| Centreline | 0 | 0 | 0 |
| Long side | 0 | 0 | 0 |
Lengths are after cutting. "Mark at" is the spacing between your scribed lines: the finished length plus one blade width.
How the numbers are worked out
Both faces of a slice lean by the cut angle, so each slice turns the tube by twice that. The number of slices is the bend angle divided by that turn: six 15° slices make a 90° bend, welded between two square-cut ends of tube.
If you cut the bend out of the middle of one length of tube instead, the first and last cuts leave an angled end on the tube either side. Those two ends do the work of one slice between them, so you need one loose slice fewer: five for a 90° bend.
With R as the centreline radius, D as the outside diameter and the joint angle in radians: centreline = R × angle, short side = (R − D/2) × angle, long side = (R + D/2) × angle. Our pie cut sleeves mark a 20 mm short side at 7.5°, which fixes the radius at 76.4 mm plus half the tube diameter. Every millimetre of blade width takes about 4 mm off that radius, which is why the calculator asks for it.
For the full method, from marking out to tacking, see how to pie cut exhaust tube. Not sure whether you have pipe or tube? See SCH10S pipe vs OD tube sizes.