The secret to doing good work and not turning one's truck into a complete pile of junk by exhibiting poor craftsmanship is to use the right tool for the job. It's not hard to tell when a truck has been customized by a metal butcher-there are detectable scars left from one end to the other. Of course, sometimes a guy doesn't know that his truck was butchered until the Bondo has been peeled back, but that's a story for another issue.
When it comes to replacing body panels that were spot-welded on by the factory when the truck was manufactured, the best way is to undo the spot welds. It sounds simple enough. Unfortunately it's not as easy as just grabbing a drill and boring a hole to undo the spot weld with good results. The first thing one will discover when attempting to drill out a spot weld is the fused metal that makes up the weld gets hardened in the process. Attempting to drill through hardened steel means that even if a pilot dimple was made with a center punch the drill bit will "walk" off center. If one does manage to hold the drill bit relatively on center as it chatters a sloppy, wide swath, the next problem will be cutting into the second layer of sheetmetal before the spot weld is undone (separated). This is because the tip of the drill bit is at a sharp angle that cuts deeper at a much faster rate than it does wide.
In our search to find a specialized tool that addresses the problems listed above, we have tried several of the tools currently available. The first was a design that utilized a tiny-bladed drum similar to a hole saw, and it cut out the spot weld by ultimately spitting out a miniature slug. The drawback discovered with this design was with a limited amount of surface area the teeth on the tiny bladed drum wore out prematurely. The next tool we tested was the HTP Spot Mill PN 90150. As implied by the product's name, the HTP Spot Mill utilizes a bit not unlike an End Mill used on a Bridgeport mill. In addition to its appearance, just like an End Mill the HTP Spot Mill's bit is produced from a hardened piece of cobalt steel. To prevent the HTP Spot Mill's bit from walking, there is a bullet-point drill bit incorporated into the tip that serves as a pilot.
 The HTP Spot Mill comes in...  The HTP Spot Mill comes in a rugged molded case complete with four replacement cutting bits, cheater valve, and oiler. |  Twisting the Spot Mill's red...  Twisting the Spot Mill's red anodized collar clockwise or counterclockwise adjusts the tool's depth gauge, which doubles as a brace to steady the Spot Mill'w low-rpm, high-torque drill motor. |  Using the Allen wrench included...  Using the Allen wrench included in the HTP Spot Mill kit releases the cutting bit from the collar. |
 Notice the machined flat that...  Notice the machined flat that should be aligned with the set screw before the cutting bit is tightened down. |  The secret to ensuring the...  The secret to ensuring the Spot Mill's cutting bits will live a long life is to flood the cutting bit with a high-quality lubricant as the spot welds are being milled out. |  For spot welds with plentiful...  For spot welds with plentiful clearance, the depth gauge/brace works swell in the horizontal position. |