Hole in One
“The quality of drill chucks vary and this has a huge impact on accuracy in holemaking. If your drill isn’t held securely, it will cause the bit to wobble and go off centre. We use Rohm chucks, which are known to be extremely accurate, precision made chucks. Even in the jaws, which are carbide, you get maximum grip of the bit which means maximum holding power and holemaking accuracy.”
McDonald cites Fein’s KBH25 as an example of the advances in drills. He refers to it as a “drilling system” as it can use twist drills, be equipped with a tapping chuck to tap holes and can also be used as a hole saw. “It’s the world’s first handheld cord drill designed for use with carbide tip core bits. It is designed with a safety slip clutch so that if it jams, it kicks it out and an operator won’t hurt his wrist.”
Hougen’s magnetic drills also have a built-in safety circuit, says Powers, that stops the motor when the drill lifts from the material to prevent drill bit breakage.
“Make sure the drill’s magnetic base is clear of chips and debris and is securely attached to a clean surface. Uneven surfaces or large debris buildup prevents the magnet from obtaining optimal holding power, which can cause the drill to shift or lift during operation. If it does shift or lift during the cut, it is possible the cutter will break.”
Cutter breakage and cutter wear are common problems when drilling holes and the most common cause for this is the speed at which you drill your hole. Slow feed rates will reduce the life of your cutter, while high speed rates, particularly when drilling large diameter holes, can burn out cutters. Suppliers like Fein and Hougen advise that fabricators ensure they have the right speeds for the thickness of material and for the type of material, as these two factors have a big impact on holemaking quality.
“Cutters are designed to turn at a specific feed and there are several factors you have to consider to ensure they perform. They’re designed to be strong vertically, but have a weak point on the lateral load. If you’re cutting deep holes and you don’t have the proper feedrate and coolant, the cutter may break,” warns Powers.
Some suppliers like Fein have introduced magnetic core drills with dual speeds with electronic speed control and speed memory functions.
“Some of our units are designed with the speed memory function. Once the operator has finished drilling a hole with a specific feed, he can push the speed memory button. So when he turns the drill off and then on again, it goes back to the speed you used and recorded,” explains McDonald.
If you’re working with different material thicknesses and material types (ferrous and non-ferrous alloys) and using magnetic drills, magnetic adhesion can become a problem. If you have thin material, the magnet won’t hold well, so you have to clamp another piece of metal on top or below the thinner metal to ensure stronger adhesion. In the case of non-ferrous materials, suppliers offer vacuum pads that use suction to clamp onto stainless steel or aluminum. A steel base is placed on top and the magnetic drill sits on the base to drill the hole.
“One problem we run into more today is handling materials with paint or rust proof coatings, which inhibit the magnetic hold of a drill,” says Powers. “It’s imperative to take measures, such as removing the coating so you have the bare metal, to ensure you prevent injuries that could occur if magnetic adhesion fails while using a mag drill.”
The shape of the material on which you need to drill a hole will also impact drill selection and hole quality, adds McDonald.
“A magnetic drill for drilling holes in pipes won’t fit on a pipe properly so you need drills designed with accessories for making holes in pipe. You need to select cutters specific to your application requirements. For example, one unit we offer in our magnetic drill line has a V-shaped base and you set this on the pipe, tighten it up and then you have a flat plate on which you set your magnetic drill to make the hole in the pipe. There are also specific cutters for holes in ibeam or for stack material, which have special geometries to allow you to drill down layers of material.”