These are two of my favorite hand nibblers, both ideal for cutting notches in sheetmetal.
Q: I have a project I'm working on that requires making slotted holes. My question is, how can I make a perfect slotted hole? The material I'm working with is 20-gauge 1020 cold-rolled steel. An example of this slotted hole style could be found on the mounting holes of many truck fenders to allow for adjustment, or the drain holes on the bottom panels of some musclecars. These holes need to be symmetrical and burr-free. The holes are 3/4x1/4 inches. I know how to do this with a drill and file, but I am looking for an easier, cleaner, and quicker way. As of now, I only have hand tools. What tools do you think I should get, and how and where should I buy them, or should I make my own tools? How would you go about making the holes, or making tools to make them? I am a recent graduate of Wyo Tech, and I took everything but mechanics, so I have some background in metalworking.Mark GriceVia the Internet
A: You actually have quite a few options for making the slots. Really, using a drill and a file is not a bad way to go. If you make a simple fixture, you can drill a series of overlapping 1/4-inch holes, which makes the filing part of the job much easier. You can make a guide by drilling a 1/4-inch hole through a scrap piece of steel-something 3/8-inch or 1/2-inch thick would be ideal. Then you can clamp this drill guide to the sheetmetal, and the guide will prevent the drill from wandering. Trust me, you just can't drill overlapping holes in sheetmetal without a guide like this. Machine-shop supply houses sell drill bushings made from hardened steel that make an even longer-lasting drill guide, but even a simple steel block should enable you to drill a few dozen holes with no problem.
There are some affordable hand punches on the market, such as the Whitney Jr. Punch, that will make round holes in sheetmetal much faster and cleaner than drilling. The genuine Whitney punches cost around $85, and there are import copies for about half that. You will still have to file off the bumps between holes, but if you overlap the holes quite a bit, it dramatically decreases the amount of filing needed.
You can buy a couple of different styles of hand nibblers that can help in cutting notches, too. Check out the Adel hand nibbler, PN TP 81, from US Industrial (www.ustool.com). This is a neat little tool, and I use mine a lot. It has to start on the edge of a panel, or in an existing hole, but it can cut a straight-sided notch easily. One real benefit of this tool is that the end of the notch will have a crisp, rectangular definition with very little distortion of the material. The downside for your application is that the tool's head is over 1/4-inch wide, so you wouldn't be able to start it in a 1/4-inch hole. It will start in a 3/8-inch round hole, or a 5/16-inch rectangular hole, and the notch it cuts is about 1/4-inch wide.
Another good option is the hand nibbler sold by Eastwood (PN 28191 www.eastwoodco.com). This can start in a 1/4-inch hole, and it will cut out a ribbon of metal about 1/8-inch wide. You can make a second pass to widen the slot to 1/4-inch (or more). They have a less expensive model on their Web site, PN 28012, but I've not seen that one firsthand.
One more option is to drill two round 1/4-inch holes with the spacing you want, then use a die grinder with an abrasive cutoff wheel to cut a slot out between them.
If you don't need extreme accuracy, you could make a fixture to enable a plasma cutter to make the holes. The definition won't be quite as crisp as you could get with a nibbler, but if the holes will be welded over or covered with washers anyway, this shouldn't matter much. This fixture can be made by cutting an oblong hole in some non-flammable material. First, measure the diameter of the plasma gun's cutting tip. If the diameter is 3/8-inch, for example, and you want to make a slot 1/4x3/4-inch, you add the gun diameter to these dimensions and cut an oblong hole in your guide block 5/8x1 1/8-inch. Then this block is clamped over the metal to be cut, and the cutting head's tip is placed inside the oblong window' and moved around the edges of the opening as you cut. This will make a hole very quickly with a fair amount of accuracy, and it should require only a small amount of cleanup. Of course, there are special punches designed to make slotted holes, or a milling machine could be used to cut slots, too, but these machines are quite expensive!
You can e-mail your questions to Professor Hammer at email@example.com, or mail to: Professor Hammer c/o CLASSIC TRUCKS Magazine, 774 S. Placentia Ave., Placentia, CA 92870. We'll print your name and city unless you request otherwise. Ron Covell has made several metalworking videos and offers an ongoing series of workshops across the nation covering all aspects of metalworking. Check them out online at www.covell.biz, or call for a current schedule of workshops or their free catalog of videos, books, and fine-quality metalworking tools. Phone 831-747-4631 or 800-768-0705. You can send a request by mail to: Covell Creative Metalworking, 106 Airport Blvd., #105, Freedom, CA 95019.