Hole in One
- February 9, 2017
Steps to ensure holemaking quality and accuracy
In today’s competitive market, fabricators can’t afford to make mistakes. Doing it right the first time, every time, is the new mantra and that’s especially important when it comes to holemaking in metal fabricating.
Holes large and small can be created in metal fabrication using a variety of processes and equipment from manual type equipment such as drills, hole punchers, hole saws and ironworkers, to more automated in-line processes such as laser, plasma and punching machines. This article focuses on manual type equipment.
When using drills...
If you’re using drills, whether they’re handheld drills or magnetic core drills used in the shop or in the field, it’s important to select the right equipment to fit your application.
Allan Powers, technical department head at Hougen Manufacturing, says for magnetic drills, there are multiple models with different functions and features to select from, so it’s important to know what style of drill will meet your needs. And that depends on several factors: the type of application, the diameter of the hole or holes you have to drill, the depth of hole, the drilling speeds, the number of holes, the type of material you need to drill and the space or physical limitations of you shop.
And it’s especially important to note that all drills are not created equal. There are “big differences” in the quality of a drill and in its performance, says Randy McDonald, national product manager with Fein Power Tool Co., Mississauga, ON.
“You need high power efficient drills with constant speed and constant torque because if you’re drill slows down, it won’t cut properly, won’t clear the chips and can result in overheating of the drill bit, which in turn will result in inaccurate holes.”
With traditional handheld drills, you should pay special attention to the quality of the drill chuck that holds the drill bit, advises McDonald.
“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.”
When using hole saws...
Hole saws are common for holemaking and are used by hobbyists and fabrication shops alike. There are a variety of models in the market, but the most common is the bi-metal hole saw, primarily because it’s compatible with a variety of materials, and cuts faster and smoother than other types of hole saws. However, Joe Novak, senior manager, product development for Lenox, part of Newall Brands, says the use of carbide teeth is growing. “As we’ve seen with band saws, drill bits, inserts and other equipment, carbides are stronger and more durable than a bi-metal cutting tool. As carbide tipped saws become more cost effective, we’ll see more growth in this segment.”
When performing hand drilling with hole saws, he adds that “it’s important to drill a pilot hole first on all handheld cutting applications. The pilot serves to hold the saw in place and prevent ‘walking’.”
Having the right drill and cutting technique is key to an accurate hole, he advises. “For stainless, you should use high pressure and low speed (rpm) on the drill. In today’s marketplace, there are a number of battery operated drills that don’t have the torque needed to cut stainless at the low speed setting. For mild steel and aluminum, you can cut with less pressure at a higher rpm.”
If you’re cutting holes in stainless, Novak recommends using a lubricant, for easier cutting. “The fluid offers both lubrication and cooling. The lubrication helps overcome friction, helps to penetrate the metal and aids with chip removal. The cooling properties keep heat under control and slow tooth wear that’s normally associated with high temperatures.”
When it comes to hole saws, consider the volume of holes you need to create in your parts. “For a low volume of holes, bi-metal saws are a tremendous value. The lower cost of the saw provides a competitive cost per cut. For a larger volume of holes, carbide may be a better option. There are annular cutters and other technologies available for cutting high volumes,” explains Novak.
If you’re considering purchasing a hole saw, the diameter size of the holes impacts selection. For large diameter holes, look for a hole saw with a rigid structure that will limit vibration and provide stability during processing. “CNC machines are the most stable and therefore the most accurate,” says Novak.
When creating large diameter holes, you typically use lower cutting speeds, so if your jobs entail a variety of sizes, then you need to ensure your hole saw is able to change speeds to accommodate different sizes, adds Novak.
When using ironworkers...
“The skill of your operator will determine the accuracy and the quality of the holes created in your parts,” explains Bradly Kuchenbecher, technical support and inside sales with Scotchman Industries, which supplies different models of ironworkers.
He advises that fabricators don’t fall into the trap of assuming that if they purchase a high end machine that it will guarantee performance.
“You can have a $10,000 machine or a $100 one and it will only function as well as the operator tells it to. What I mean by this is that the operator needs to set positive stops and not be in a hurry and try to eyeball locations, but take the time to set up a jig.”
Just as important as having a good operator is the need to ensure you have a good maintenance system, he adds.
“Inspect your tooling daily and make sure your punch and die is free of foreign material. You need to have a clean, good sharp edge that is properly lubricated to ensure the performance you need to create holes in your ironworker.”
An important consideration is the diameter size of the hole or holes you’re creating. The larger the diameter of the hole, the more power it will require from the ironworker to create the hole in metal.
“As hole diameters increase, tooling costs increase. So when you’re deciding which machine to select for holemaking, you need to factor in tooling costs and tooling life. With a punch and die system on an ironworker, you can get between 3 and 5,000 holes before the tooling starts to deteriorate. And, an ironworker performs other functions as opposed to a designated hole puncher. An ironworker can perform hole punching, plate shearing, notching and can even bend metal in thicknesses up to one inch.”
When using hole punchers...
The main reason to select a hole puncher is because of speed. “When compared to drilling holes, a hole puncher can punch a hole much faster than a drill or drill press,” says Powers.
Punching force is key and when selecting a hole puncher, ensure the machine you select is capable of punching the holes you need to create.
“In many instances, a common problem with hole punchers is that people use them for materials that these machines are not designed for,” adds Powers. “The rule of thumb is that if you’re punching holes in anything harder than standard structural steel, you need to run your hole puncher at half capacity. So if your punch unit has a maximum capacity of one quarter inch, then the maximum for harder material is an eighth of an inch.”
Keep in mind that there are different hole punch systems. One example is the UniPunch system, which the company describes as a “catalogue of units that can be used alongside one another to punch the holes and notch the edges to make a part.”
According to UniPunch, a system like the one it offers, helps fabricators improve productivity and cut costs because it gets high volume production shops into production more quickly, provides faster part to part changes and allows fabricators to reuse tooling.
A special purpose vehicles manufacturer who wanted to remain anonymous but agreed to provide a testimonial for UniPunch states online that using dedicated setups for its JIT operation has helped the company reduce steel inventory by 80 per cent, a cost savings of $5 million a year.
“Using dedicated setups allows us to pull a setup off the storage rack, put it in the press and be producing parts faster than we could set up a CNC machine. It’s also more cost effective to use UniPunch holders than to have our toolmakers build a die, or to have one built on the outside.
“It is also quicker and easier to make a changeover or to sharpen the punches, much, much easier. Pulling a punch out of a UniPunch holder compared to a hard die is a world of difference.” SMT