Guide to good Drilling Practice
Produced to help you get the best possible performance from your new Magnetic Drilling Machine, this guide contains simple, sensible pointers for the safe, effective and long term use of the equipment. Please read this carefully before using a magnetic drill unit.
- Check that all the relevant components and accessories for the machine are included and undamaged, the list of contents is included on the machine instruction leaflet.
- Assemble the unit according to the instructions, and make any necessary adjustments.
- Ensure that you have observed all the general and specific safety procedures.
If you are unfamiliar with the use of annular (or broaching) cutters, take a few minutes to read this guide – you will benefit from the better performance and longer life of the tool if you understand the concept.
Annular cutters only cut material at the periphery of the hole, rather than converting the entire hole to shavings. As a result the energy required to make the hole is lower than for a traditional twist drill.
The broaching capacity of a machine is therefore greater than the twist drill capacity. The slug ejected after the cut also has a higher scrap value than shavings
Before you start to drill. . .
- The ease with which material can be drilled is dependent on several factors including tensile strength and abrasion resistance. Whilst hardness and/or strength is the usual criterion, wide variations in machinability can exist among material showing similar physical properties.
- The cutting conditions can be dependent upon requirements for tool life and surface finish and further restricted by the rigidity of the tool and work piece, lubrication and machine power available.
- The harder the material the lower the cutting speed. Some materials of low hardness contain abrasive constituents leading to rapid cutting edge wear at high speeds.
- Feed rates are governed by rigidity of set up, volume of material to be removed, surface finish and available machine power.
- It is preferable to set and maintain a constant surface speed (RPM) for a given material and vary the feed rate within defined limits.
- Machine feed is measured in inches or millimetres per minute and is the product of RPM x number of teeth in the cutter x feed per tooth. Too light or excessively high feed rates will both cause premature cutter failure. Heavy feeds on hard materials will cause chipping of the cutting edge and excessive heat generation.
- Slender and long shanked cutters are restricted in feed rate due to deflection, and wherever possible the largest and most robust tool must be used. This is important for harder materials. Steel up to 400 HB is the potential limit for conventional M2 HSS tools. Above 300 HB, cobalt alloy cutters should be considered for increased tool life. In softer grades of material, cobalt alloy cutters may give increased output by increasing speeds and feed rates by up to 50%. Tungsten Carbide cutters permit surface speeds and feed rates up to twice those for standard cutters.
Ensure the power is off before working on the machine
Insertion of pilot pin
The pilot pin is used to both center the cutter and to eject the slug on completion of the cut. It has a flat side to allow the coolant to run down to reach the centre of the cut where the heat is greatest. Slide the pin through the hole in the centre of the cutter shank.
Fitting the cutter
The cutter is attached to the arbor by way of two grub screws that grip on the flats of the shank on the cutter. Line up the flats on the shank with the grub screws on the arbor and slide the cutter into the arbor. The screws must be tightened evenly to ensure that the cutter does not move. The Allen key used is one of the set included with the machine.
Mark the position of the hole (not punching)
Position the Machine
- Make sure the workpiece is clean and flat and position the machine with the pilot over the centre of the hole to be cut. Fit the safety chain.
Switch on the power and energise the magnet.
- Recheck the pilot is still centred on the hole position – energising the magnet can sometimes cause the unit to move slightly from the centre mark, reposition if necessary.
The magnet will hold on all ferrous materials from a minimum of 6mm (1/4″) inch thickness.
- Cutting oil ensures longer cutter life and enables the slug to be ejected cleanly. A 500 ml bottle is included with every machine.
- Apply a reasonable quantity of cutting oil to the surface to be cut. • On machines with an internal oil arbor, fill the reservoir in the arbor through the small holes at the top.
- On machines with a coolant system, oil will be automatically delivered to the cutter when the cut commences
- When cutting on vertical surfaces or upside down, cutting paste, gel or foam is recommended. It is best applied inside the cutter before drilling.
Starting the cut
- ALWAYS lower the safety guard, start the motor and then wind the cutter gently down to the surface of the work and apply light pressure until the cutter has made the initial groove in the surface. Increase the pressure until the motor is loaded.
- Maintain steady pressure throughout the rest of the cut. Too much pressure will not speed the cut, it will reduce the life of the cutter and may cause damage to the motor. If the shavings become blue add more oil.
- If the power is interrupted during the cut, the magnet must be reset before the motor will restart.
- At the end of the cut the slug will be expelled. Withdraw the cutter from the work piece, stop the motor and switch off the magnet.
For mor detailed information download our full Guide to Good Drilling Practice.