When drilling all the way through square tubing, I often snap my drill bits.
If it’s not possible to drill from the other side, is it better to drill a slightly bigger hole first followed by a smaller hole?
Best way to drill square tubing (Without drill press)
drillsteel
Related Solutions
Yes, the drill chuck will mar the finish of the shelf. There is a slight chance of damage to the chuck. Plus, choking down on the bit, like that, obscures your view of the hole (the drill and chuck block it) -- making precision harder to accomplish.
The correct way to do this is to use a drill stop.
Drill stops are less likely to slip than tape or zip-ties, and are much better for precise and/or repeated drilling.
If marring the finish is an issue, clamp a piece of 1/8th plywood over the site and adjust the drill stop accordingly.
PS: A piece of wood over the hole is usually a good idea anyway, when drilling finished surfaces. It helps reduce both splintering and the scratching that occurs when flakes of drilled wood or metal whip around the bore site.
One option especially suitable for this scenario (outdoors, often drilling above your head, with the tube bending and vibrating, using handheld drill) is using special drill bits tailored for fast drilling into sheet metal. The market has numerous offers, including Irwin Turbo Max, DeWalt Extreme 2 and Ruko Fast Cut - the idea behind all those is that the drill bit looks similar to a drill bit for wood and the small tip of the drill bit helps the drill bit dive into thin metal.
One important thing is that you should not proceed to drilling the second wall until you retracted the bit from the hole and checked that there's no metal on the tip. Otherwise the following can happen: the drill bit will burst through the first wall and the metal which the tip was facing will remain on the tip and prevent the tip from contacting the second wall.
Beware of the following downsides:
- these are next to impossible to sharpen in your workshop - prepare to either throw them out or grind them into "regular" shape bits once they get dull
- the price is notably higher compared to "regular" bits
- the "metal on the tip" problem described above
- not that easy to find in an average store, so you should shop in advance
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Best Answer
Feeds and speeds
First, there is one correct feed and speed that will make even a $1 drill cut like through butter. This is an eye-opener for those new to metal work; they think they can buy effective cutting with expensive bits. Nope, it is not for sale. What you're thinking is a waterknife; you can definitely buy those! I work in metal a lot; and I don't buy the top-shelf drill bits; I bottom-shelf cobalt's and use them correctly, insofar as that is possible in the field; hence I rarely make it to 1x.)Why not buy the "3x longer" top shelf? I never make it tot 1x before they break.
So you need to have your feeds and speeds dead nuts perfect, or as close as possible. Speed means the RPM of the drill bit. Feeds means how fast the drill bit advances (to be more precise, how far per revolution). Feeds are very difficult to get on a hand drill, since you only have pressure, and most proper feed rates require high pressure and a lot of intuition. You will know it when you've found it because the drill makes lots of pretty, long chips. Speed is a matter of getting a drill that's fast enough, which drill-drivers are not. I found a dust covered $35 drill in my notoriously overpriced local hardware store; it has a 1500 RPM speed, far better than the sea of 400 RPM drill-drivers for the ideal 2700 RPM of a 1/8" drill into mild steel.
Jig it
But second, if you have access to the backside, you need to jig this. You need to make a jig that will let you place the holes on opposite sides in exactly the right place.
The simplest jig is an Ikea cloth tape measure. Wrap it around the pipe. Either it will spiral, or each wrap will land directly over the last. Make the latter case happen. Now you have fixed one dimension. Then get the hole centered (or not but matching on both sides, if that's what you‘re into) and golly gosh, that's a tape measure right there!
Even better, make a more permanent jig out of a 2x4 notched to embrace the channel. Holes in the 2x4 are positioned so you drill through them to start the holes in the channel.
Or, use a center punch
You should always use a punch to make a divot in the metal to give the drill a place to start. However, once the first hole is drilled, you can get a special type of punch called a center punch, which is a specific diameter shaft that has a punch at the end. This goes through the made hole, and correctly positions the punch for the second hole. Now the drill isn't wandering on the other side, a sure way to break it.