There ain’t no gettin’ away from it; if you’re going to build a car, you’re going to be drilling a lot of holes. You’ll also likely be welding more than a few up too, especially if you intend to nose, deck, or otherwise remove trim. It may sound odd, unless you’re familiar with tools or work in the automotive industry, but there’s more than one way to drill a hole.
Your first choice will likely be a regular drill bit, and these are fine for many applications (but they’re not ideal, especially for sheetmetal, if you’re after a perfectly round hole). Ever notice that a drill bit leaves a “triangulated” hole in sheetmetal, especially cheaper bits? Equip yourself with a good quality set of drill bits, look after them properly, and they’ll repay you with years of service.
A set of Roatabroaches is...
A set of Roatabroaches is invaluable when building project cars, and produce perfectly circular holes repeatedly.
However, for perfectly round holes in sheetmetal, or brackets up to 1/4-inch thick, I prefer to use a Rotabroach. They only cut the circumference of the hole, rather than the entire section you wish to remove, making them more efficient. Since the hole is perfectly round, it’ll be a snug fit for any fastener used in the hole, which is important where bolts and brackets are concerned. Rotabroaches are available from Snap-On, Blair, and other suppliers. They’re not cheap, but they’re worth every cent—if they’re looked after.
Spot-weld drill bits and step drill bits are other ways to drill sheetmetal, while hole saws can be used on sheet or heavier-gauge material. The latter will blunt very quickly unless used at the correct speed and with lubrication, which is the best way to maintain any drill bit. Speed is also a consideration with Rotabroaches, and remember, faster ain’t necessarily better, especially in this case. Take it slow, and use a suitable cutting fluid.
A good quality set of drill...
A good quality set of drill bits will last a long time if looked after. I’ve had this Bosch set for years and haven’t had to sharpen a single one yet.
OK, so you’ve finished all the fab work on your project, and are moving to the bodywork stage. Your car looks way better with all that excess trim removed, but what to do about the numerous holes left behind? Simple: weld ’em up! Sure, go ahead, but there are ways to make your life easier. First, ensure the hole is clean by filing any paint from the edges of the hole. Second, most trim holes will be on the sides of a car, so turn the wire speed up slightly if you’re using a MIG welder to compensate for this. I prefer to start at the top left of any trim hole and work my way across and down, but you may find your own preference.
Step drill bits (Unibits)...
Step drill bits (Unibits) have their uses for sheetmetal, especially when you don’t have a regular bit or Rotabroach in the larger sizes.
One sure-fire way to make the job easier is to place a piece of thick copper behind the hole, as the weld won’t “stick” to this material, you’ll use less wire, and not be left with a big blob of weld on the backside of the panel. Eastwood sells copper plates with magnets attached for this purpose, as well as a copper paddle that can be held behind the panel.
None of this is rocket science, but it’s stuff like this that’s easy to assume everyone knows. The right tools make a big difference, and can turn a frustrating job into a pleasurable one.
Need a tapered hole? Speedway...
Need a tapered hole? Speedway Motors sells this 7-degree taper reamer, which is the correct taper for early Ford tie-rod ends. Just drill a 1/2-inch hole first then slowly ream the taper. A drillpress works best for this.
Any drill bit (except a spot-weld...
Any drill bit (except a spot-weld cutter) will require an index to start, and while you can use a hammer and punch, these automatic punches make things simpler. Sprung loaded, they’re powerful little tools.
Hole saws are perfect for...
Hole saws are perfect for cutting large-diameter holes in sheetmetal and thicker-gauge material.
Here’s a hole saw cutting...
Here’s a hole saw cutting a 1/4-inch wall steel box section. Of note is the cutting fluid, which lubricates the hole saw, making for an easier cut with no “grabbing” and prevents the tool from becoming blunt owing to overheating. Select the slowest speed on the drillpress when using hole saws or Rotabroaches.
A Rotabroach will produce...
A Rotabroach will produce perfectly circular holes every time, even on thick material, such as this lower shock mount. This is important to ensure no “slop” between the bolt and the bracket.
Rotabraoches are also ideal...
Rotabraoches are also ideal for producing neat holes in sheetmetal, such as this air vent next to the pump for the air compressor on my project ’49 Chevy. Note where the Rotabroach skipped around on the surface on the three holes on the left, caused by not punching a center mark before drilling.
Here’s a good indication of...
Here’s a good indication of the different results you’ll get by using (left to right) a Rotabroach, spot-weld drill bit, and regular drill bit. Only the hole on the left is truly circular.
With the paint ground off...
With the paint ground off around the hole, use a file to clean the paint from the edges.
My preference is to start...
My preference is to start at the top left and work my way down and around the hole to fill it. Here, I’m halfway through.
Placing a thick piece of copper...
Placing a thick piece of copper behind any hole to be welded will prevent the welding wire from going through the hole, making the job easier and the weld will not stick to it.
Note how much less weld is...
Note how much less weld is left on the backside of the panel after using the copper backing, compared to the weld on the right, which was done without. It’s also a smaller weld, and has less heat distortion, as you’re for to all intents and purposes filling a recess rather than a hole.
Eastwood sells these magnetic...
Eastwood sells these magnetic copper plates for use behind holes or even butt-welds between panels.
Once the weld is ground down...
Once the weld is ground down using a soft pad-backed abrasive on a 4-inch grinder, there’s no distortion and it’s ready for sanding and filler.
Trim holes are easy to fill...
Trim holes are easy to fill with weld, but what of larger holes, such as those in the firewall of my Chevy once I’d removed the fresh air ducts and assorted cables and wires?
While the hole below was simply...
While the hole below was simply filled with weld, the larger one, which is the exact size of a penny, will have a patch trimmed to fit and welded flush with the firewall. No, you can’t weld the penny in!
I also used the same clamps...
I also used the same clamps to hold my A/C vent panels flush with the dash while I welded them in place. These clamps are invaluable, and can even be used to attach a ground clamp for the welder if need be.
Here’s a larger example of...
Here’s a larger example of a flush-fitting patch, where the air ducting used to pass into the interior. A couple of magnetic clamps hold it in place while it’s tack welded.
There were a lot of holes...
There were a lot of holes in that Chevy firewall! Now it’s ready to sand, fill, and paint.
As they’re such heavy-gauge...
As they’re such heavy-gauge steel, holes in chassis ’rails can be filled without patches, using the copper-backing method. Again, use a file or rotary air grinder to clean the edges.
Welded and ready to grind...
Welded and ready to grind smooth, this Model A chassis is now minus most original holes.
Finally, holes can be decorative....
Finally, holes can be decorative. Here, tubing has been TIG welded through holes drilled in these fabricated push bar brackets, then ground flush. There’s a lot of work here, but they look great, though they probably add weight rather than remove it!