Annular cutting in steel: speed, feed and cutting fluid

The figures below are taken from Rotabroach's data sheets for the machines and annular cutters in the catalogue.

The pilot pin first

The pilot pin centres the cutter on the centre-punch mark, but has two more jobs. It meters cutting fluid to the cutting edge, and Rotabroach states that it reduces the risk of the cutter breaking. The Raptor Rail TR cutters use the SRA25 for 25 mm cutting depth and the SRA50 for 50 mm.

The sequence in the operating manual for the Rhino 2 rail drill is as follows: the machine must be switched off, the pilot pin is inserted into the shank, the cutter is inserted into the spindle bore with the drive flats aligned, and the locking screws are tightened with an Allen key.

When the cutter breaks through, the core is pushed out. Rotabroach warns that the core can cause injury, and the machine must not be used if the core has not come out.

Starting the cut: light pressure

Rotabroach recommends light feed pressure when starting the cut. Higher pressure does not necessarily increase the cutting speed, but can damage the cutter. Once the teeth have cut into the material, you can switch to a steady feed.

The feed pressure should be steady and high enough for the machine's speed to drop. According to Rotabroach, this gives the right cutting speed and chip load, while too little or uneven pressure is on the list of reasons why the cutter wears abnormally fast.

Speed by diameter and material

Large annular cutters should run more slowly than small ones, and hard steel more slowly than soft. That is why the machines for the largest holes have the lowest gears.

Machines with a fixed speed are a compromise. The Lynx K, with one gear and constant speed, is described in the catalogue as best suited to softer types of steel, and the capacity of the Commando is stated for steel of grade .2/.3C. This is how it looks in the catalogue:

• Scorpion — Ø100 × 100 mm, lowest gear 45–110 rpm
• Cobra — Ø65 × 50 mm, low gear 150–330 rpm
• Falcon — Ø50 × 50 mm, low gear 100–280 rpm
• Element 40 — Ø40 × 50 mm, 300 rpm in low gear
• Adder K — Ø35 × 25 mm, fixed 650 rpm

Cutting fluid

Rotabroach writes that its cutting fluid gives the cutter better performance and longer life and the hole a better finish. Too little cutting fluid, or the wrong type, is on the list of reasons why annular cutters break.

The Adder K, Lynx K, Panther CS K, Falcon and Scorpion are specified with automatic cutting fluid feed, and on the Panther CS K the tank is adjustable. Since it is the pilot pin that meters the fluid to the cutting edge, it must be in place for that reason too.

Manual or automatic feed

The Lynx K is semi-automatic: the operator chooses between automatic and manual feed, and the machine has three feed settings. With automatic feed, the cutter goes through the workpiece by itself, but the feed has to be returned by hand.

The capacity is slightly lower with automatic feed: Ø35 × 45 mm, compared with Ø35 × 50 mm with manual feed.

When the cutter jams

An annular cutter can jam in the workpiece. The machines have different forms of protection against this:

• CutSmart on the Element 30, Element 40 and Panther CS K. On the Element machines it is described as overload protection for motor and cutter
• Clutch on the Cobra, Element 40, Falcon, Scorpion and Panther CS K
• Electronic overload protection on the Adder K, Commando, Lynx K, Falcon and Scorpion, among others
• Centrifugal clutch on the petrol-powered Rhino 4 (RD074)

When you contact us

If you would like our help with cutters, pilot pins or a machine, it is useful to have this ready:

• Machine model, or a photo of the spindle
• Diameter and depth of the holes, and roughly how many
• The material to be drilled
• What happens when it goes wrong — ideally with a photo of the swarf