Sheetmetal is used in a variety of ways on our rigs. A thin, flat sheet of steel can be flimsy and weak toward bending. Use of thicker sheet can add strength and rigidity, but also adds cost and something we try to avoid, extra weight. Production factories add rigidity to panels such as a pickup bed by corrugating it with ridges. In the aftermarket fabrication world one might use a bead roller to add raised ridges, but flaring holes with dimple dies is possible. Cutting holes sheds more weight and adding flared holes restores panel stiffness. Lighter means faster.
With a set of dimple dies and a hydraulic press, you can do your own flared holes in your home shop. We visited with fabrication maestro Rob Bonney of Rob Bonney Fabrication in Peoria, Arizona to garner some dimpling tips we could share with readers doing their own work.
To begin with, Bonney suggests making your holes slightly oversized to make the flare process smoother. A hole size about 0.030 inches larger than the nominal hole size of the die seems to work well. If cutting holes with a hole saw, you’ll usually get a slightly oversized hole anyway, so this usually works out well for this method. It’s also a good idea to deburr your holes with a die grinder or similar tool before you flare with the dimple dies. Small imperfections in the drilled hole may result in a crack or tear as the metal is stretched during the flaring process.
Bonney shared with us that there are two basic methods of metal bending: air bending and coining. Air bending is a process where a die pushes on a workpiece to form or bend it, but the die(s) never fully contact the piece. Coining occurs when the metal is stamped under extreme pressure between two mating dies that fully bottom against the formed metal, resulting in greater bend precision. When dimple dies are used they are coining the sheetmetal, so the harder the applied pressure the more accurate the flare will be with less metal spring-back.
Aluminum sheet is the easiest common metal to flare and typically the least likely to crack. Mild steel is a bit harder and requires greater effort to dimple. Chromoly sheet tends to be the most resistant to flaring and can be prone to tearing the metal when flared, especially very thin sheet. A bit more oversizing of the hole can help reduce the tendency for the sheet to tear.