The question comes up most weeks: a groundworker has been quoted for a dual-grade rotating laser, sees the price, and wants to know whether the single-grade model will do. Sometimes it will. Sometimes it will cost you a day of re-setting every time the fall changes direction. This is how we work through it.
What the terms mean
A level laser spins a beam that is dead level in every direction. A single-grade laser lets you tilt that plane along one axis, so you can set a fall of, say, 1 in 80 along the line of a pipe run while the plane stays level across it. A dual-grade laser lets you tilt both axes independently, so the plane can fall in two directions at once, like a car park that drains to a corner gully.
Jobs where single grade is enough
- Drainage runs, where the fall is along the trench and nothing else.
- Kerb lines and haunching along a road that falls in one direction.
- Ramps, driveways and access roads with a straight gradient.
- Any job where you can set the laser up in line with the fall. If the laser can sit at one end of the slope and point down it, one axis is all you use.
Most single-grade models, the Spectra LL300N with a grade adaptor, the Topcon RL-SV1S and the Nedo Sirius 1H, will cover this comfortably, and they are typically 30 to 40 per cent cheaper than the dual-grade version from the same range.
Jobs where dual grade earns its keep
- Car parks, yards and forecourts falling to a gully or channel drain.
- Sports pitches and large slabs with a designed crossfall.
- Landscaping and earthworks where the design surface is a plane rather than a line.
- Machine control. If you are feeding a dozer or grader a plane, it needs both axes.
- Any site where you cannot get the laser in line with the fall, for example because it has to sit on a raised platform out of the way of plant.
The last point is the one people miss. Dual grade is not only about surfaces that fall two ways. It also means you can set the laser wherever is convenient and dial the fall in on both axes to suit, rather than walking the tripod round until it lines up.
Things worth checking before you decide
- Grade range. Cheaper units manage a few per cent; the Spectra GL622N and Topcon RL-200 series go to 25 per cent on one axis. Check it covers the steepest fall on your drawings.
- Automatic axis alignment. Some dual-grade lasers will find the direction of the fall for you by tracking a receiver. It saves a lot of time on large slabs.
- Receiver compatibility. Grade work at range needs a receiver with a fine deadband. Budget for a good one.
- Hire first. If you have one dual-grade job a year, hire the laser for that job and buy the single-grade unit for the rest. We keep both on the hire fleet for exactly this reason.
If you can send us a drawing of a typical job, we will tell you honestly which class of instrument it needs. Ring 01522 697777 or email the sales desk.
