Magnetic drill holding force: thin material, pipes, clamping

Rotabroach states it plainly for the Commando: 8000 N applies at 20 °C and against plate at least 25 mm thick.

Magnetic force as stated in the catalogue

Rotabroach gives the following holding forces and magnet surfaces, from strongest to weakest:

• Scorpion — 30 000 N, magnet surface 230 × 110 mm
• Falcon — 18 500 N, 170 × 85 mm
• Adder K — 15 000 N, 165 × 80 mm
• Cobra — 12 000 N, 180 × 90 mm
• Element 40 — 10 000 N, 180 × 90 mm
• Element 30 — 10 000 N
• Commando — 8000 N, 165 × 80 mm
• Raven, Eagle and Gator — 7 000 N, permanent magnet

A larger surface does not mean a greater force

Adder K has a smaller magnet surface than Cobra, but a higher stated force. The surface tells you where the machine will fit and how wide a base it stands on. It is the force you should compare when the question is whether it will hold.

For Lynx K and Panther CS K, the force is given in kilograms: 1500 and 750 kg respectively. These figures cannot be compared directly with those in newtons.

The force needed increases with the size of the hole. A large annular cutter produces a greater counterforce, and Scorpion, which drills Ø100 × 100 mm, also has the strongest magnet in the catalogue.

Thin material means a weaker grip

An electromagnet needs steel to carry the magnetic field. If the material is thin, there is no room for the field, and the holding force drops. For the Commando, Rotabroach states that material thinner than 25 mm progressively reduces the magnetic force, and that a steel packing plate should then be placed under the workpiece where the magnet sits, if possible. If that is not possible, the machine must be secured in another way.

The same happens with anything that creates an air gap between the magnet base and the material: paint, rust, mill scale, swarf and unevenness. Wipe the surface, and make sure the whole base is in contact before you start.

On non-magnetic materials, such as aluminium, the magnet does not hold at all. The accessories overview for Adder K and Cobra lists a vacuum pad.

Pipes and curved surfaces

A flat magnet base does not sit well on a pipe, and Rotabroach states that a workpiece that is not flat can result in insufficient magnetic force. For pipes from 60 mm in diameter, Rotabroach has a pipe adapter kit (RD2311) for Element 30, Element 40, Commando, Cobra, Raven, Eagle and Gator. Raven, Eagle and Gator are supplied with a pipe strap in addition to a safety strap.

When the power fails

An electromagnet lets go when the power fails, whether because of a power cut, a loose extension lead or a residual current device tripping. The safety strap is then what holds the machine. It is supplied with the Commando, Element 30 and Element 40, among others, and on a wall or overhead it is the strap that takes the fall.

Element 30, Element 40, Falcon and Scorpion also have magnet detection. On the Element machines, it is described as a warning of insufficient magnetic adhesion.

Raven, Eagle and Gator have a permanent magnet that is activated mechanically and holds without power. They are driven by compressed air and hydraulics, so there is no power to lose either.

When you contact us

With this information, we can assess whether the magnetic grip will hold for the job:

• Material and material thickness where the machine will sit
• Flat surface, section or pipe — and if so, the pipe diameter
• Whether you will be drilling horizontally, on a wall or overhead
• The largest hole to be drilled
• What electricity, compressed air or hydraulics are available on site