Cable tray on a radius: working out the segments

Tray will not hold a smooth curve: it is built up from a series of identical small notches, each swinging the run through a little angle. More notches bring it closer to a circle — and make it a longer job.

What the arc is made of

You set the diameter at the centre of the run and the arc angle: 90 degrees for a sweeping turn, 360 for a full ring. Then you choose how many notches, and the calculator works out the pitch between them, the size of each cut and the angle each segment turns through. Every notch is identical, and they all go on the inside of the arc.

How many notches to make

It is a trade-off between smoothness and work. For a 90 degree turn on a one metre radius in 300 mm tray: three notches leave the run about 39 mm off a true arc, and the facets show; six notches give 10 mm, a sensible middle; eighteen give a millimetre but the cutting drags on. The calculator shows the deviation as you go, so the choice is an informed one.

Length needed and joints

The length is measured along the outer edge, where no metal is removed. For a ring of any size it soon passes three metres — so a joint is unavoidable, and it is better planned in advance, landing on a straight section between notches rather than at a fold.

90° turn, 2000 mm diameter, 300 mm tray. Figures in mm.