For anyone, working on sheet metal, there has likely been a time when you wished you had more precisely drilled a fastener. It may not be that critical if you are just drilling rivet holes to fasten two pieces of thinner sheet metal (like .020″ up to .032″ thick sheets). If the angle of the faster (rivet) hole is not precisely at 90 degree to the surface of the sheet, the result only slightly adversely affects the installation of the rivet or the strength of the resulting joint. As the rivet is deformed, during bucking, it will handle the slight misalignment.
If, however, the fastener hole is to accommodate a more precise fastener fit like a “Hilock” or other high strength fastener; or is to be drilled through thicker or multiple layers of metal, the hole making process must result in a fastener hole which is drilled at 90 degrees to the surface of the sheets.
Even experienced craftsmen, sometimes need a bit of help in making sure, when hand drilling, fastener holes are at 90 degrees to the surface of the sheet. Drill blocks, Drill Egg Cups and other devices have been extensively employed as drilling aids by many. When adequate access is a problem, a simple “Drill Square” is a good choice.
Whether you are new to the trade; or are an experienced sheet metal/structures technician, the tools offered on this website can help you to be a better and more precise craftsman.