It may take a little extra time and effort, but achieving a professional look in the field is possible.
You did an excellent job of installing the new equipment, wiring it up, and testing it. In fact, you completed the job early, exceeded the contract specifications, and came in under budget. Yet your customer is unhappy enough to ask for a price reduction. What's the problem? The customer points to the panel with its uneven rows of switches on a scratched and wavy panel face. You remember the electricians used extra hours on that panel, and you wish they could have done a better job.
This situation is all too common. Panels and enclosures may look great when you install them, but field modifications can ruin their appearance. You may not think it's possible, but you can achieve a good, finished look in the field, and here's how.
Step one: Locate and mark the hole. Before you can start the hole, you must decide where to put it, but you also need to somehow indicate where that hole is going to be. This may not sound very complicated if you're putting only one hole in a panel, but what do you do when you want to make a row of six different-sized holes? And what if no two are shaped the same? What if you have to modify an enclosure in the field so it looks like the enclosure in Photo 1 above?
The first thing you must do is determine the clearances between the device bodies. It's critical to allow room for a maintenance person to remove and re-land wires. The best way to do this is by laying the parts out on a bench or other suitable surface. If you don't have the parts yet, review the drawings carefully. Once you know the minimum distance between the various devices, you can decide how many rows and columns you want, and what kind of layout works best for the operator. Be sure to leave room for labels on the finished surface so operators can readily identify indicators, switches, and whatever else you're mounting in the panel surface.
Many electricians will work from the back of a panel surface to avoid marring the finished surface, but this technique can cause other problems, especially if a panel is already mounted in the field. Avoid those problems by applying white shelf paper to the finished surface and then work from the front. You can peel the paper off when you're done, and you'll have no marks to clean up. It can also provide some protection against accidental scratching. If you mark all of your holes on the paper before making holes, you can see your layout before it's too late to change it. If you don't like the layout, you can peel that paper off and start over with a new piece. But remember, even if you like the layout, your customer may not — so this provides you with both an easy way to show what the panel will look like and an opportunity to get any feedback while changes are still inexpensive to make.
You may have learned from your high school shop class how to use a ruler and punch to mark a hole in a 2×4, but using this method on a thin metal panel distorts its surface. With today's variable drills and improved cutting tools, you don't need to mark the hole with anything but a pencil (Photo 2, right).
What if you want to make a small starter hole just to be sure your drill bit doesn't wander? You can use a device made just for this purpose that has a lens with crosshairs and a precise punch bit; the bit is often spring-loaded in the device to limit the amount of striking force. If you don't have such a device, you can use a small drill bit (perhaps 1/32 in.) in a variable-speed drill to start the hole. Even this technique often results in a “dancing drill bit” that mars the surface you're working on, not to mention several broken bits. Many electricians use a split-point step drill bit because it won't dance and it allows you to quickly start the hole with little risk of marring the surface or breaking your bit.
Step two: Select the right tool and method for the job. Do you punch, drill, or cut the hole? The correct answer depends on several factors: the material, thickness, hole size, and number of holes. Each of these tools comes with its own application guides. A general rule of thumb is “punch thin, saw thick.” Let's look at some particulars:
Drills. Most people will “warble” a drill bit in a hole rather than stop to use a larger bit. This causes excessive wear on the drill bearings and produces a sloppy hole. Use the correct bit for the hole you need.
Hole saw. These provide superior speed, but you sacrifice hole quality with them. You can prevent the typical “jumping” by placing a fender washer over the hole saw bit.
Punches. When doing large sizes, use a smaller size knockout to make a pilot hole. See the vendor's catalog for correct size pilot holes. A pilot hole that's too small will cause binding and warp the surface you're modifying. If you're using shelf paper or tape to protect the finished surface, it doesn't matter which surface you put the die on. Otherwise, prevent the need for finishing by putting the punch on the finished side with the die on the inside.
Square hole punches (Photos 3 and 4 above). These have alignment marks, so you can center the punch on your hole. Don't worry if the draw stud pilot hole isn't round — you need only rely on the alignment of the die.
Step three: Finish the hole, and finish the surface The amount of work you'll need to do to finish a hole depends on the method you used to make it. If you punched a hole properly, it's finished. If you cut or drilled a hole, you'll need to clean the burrs from the edges. You can buy a special deburring tool with a small blade on a swivel. Other tools people use to deburr include files, knives, pipe wrench pliers, and screwdrivers. Once you've removed the burrs, peel off the shelf-paper you applied in Step one. You now have a factory finish, in the field.
Pierson is senior project manager of holemaking products for Greenlee Textron in Rockford, Ill.