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?
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1Breaking bits is caused by not holding the drill perpendicular to the surface ( tipping the drill).– blacksmith37Oct 14, 2019 at 15:39
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6Worrying about breaking bits is because you still buy expensive ones, instead of bottom of the barrel kits of 20 each that will last a DiYer the rest of their lives.– MazuraOct 14, 2019 at 20:11
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1In my experience, drilling a larger hole just makes the problem bigger, once you're not with <3 mm drillbits.– user3445853Oct 15, 2019 at 10:51
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6 Answers
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.
answered Oct 14, 2019 at 16:50
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My fairly cheap Ryobi is supposed to be 1600RPM on (2) with the trigger right in. The new DeWalt 20v thing goes to 2000RPM. Which is still short of 2700, but not as bad as you suggest? Also, Ryobi make a cheap (USD200) drill press that goes to 2430.– RichOct 15, 2019 at 4:26
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1+1 for "Jig it". Breaking has much to do with not-drilling-straight, the two main dimensions are the angle of drill vs tube (two minor dimensions: sliding around -- centrepunch relieves that; irrelevant dim is rotation; forward/backward dim = your pressure). So fix the drill in a neat way (parallel to surface = one main dimension plus 2 minor are fixed), clamp the 'on' button, and slide your tube towards it: Pressure you control now, and you only have to watch parallel-ness for the main source of variation (longer tube = more precise; equal pressure on both sides is the main thing). Oct 15, 2019 at 10:58
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In my limited experience of drilling steel, I've found high speeds tend to make the bit too hot and blunt it. I've had better results by using a bit large enough to allow me to press down hard and keeping the speed down. The optimal speed is a function of the diameter of the bit (smaller diameter requires faster speed) so while for 1/8" you need to go as fast as your drill will allow you (as you indicated), for 1/4" you only need half that speed.– CarlOct 15, 2019 at 11:56
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@Frank_Vr needs to focus on your last paragraph! No matter how steady you hold your drill, it will wander against the smooth face of the back wall of the tubing. If the wandering is bad enough, the bit will snap. An important note for Frank: This will happen even with a drill press. You need to punch the inside surface of the back wall of the tubing to give the bit a divot to start in. I find that a lot of DIYers think a drill press will solve all their bit-wandering and bit-breaking issues, when all they need is a punch!– dwizumOct 15, 2019 at 14:43
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1@Carl Too fast, too slow, too little pressure, too much - all will do the same thing. They also work-harden the metal, making it even tougher. You need to be near the sweet spot (or have a big drill budget :) Machinists leave none of that to chance; they have formulas and tables for feeds and speeds. Oct 15, 2019 at 15:06
If I have to drill square tubing with a hand operated electric drill I will use a square and mark a line all the way around the four sides of the tubing at the location along the length where the hole is to be located. Then mark the center locations of the holes on the two faces of the tubing on opposite sides.
Then use a center punch to dimple the center mark for the holes on both sides. Next step is to drill a small diameter pilot hole, one from each side, at the center punch locations.
Now you are ready to drill the finished hole size with the appropriate sized drill bit. The pilot hole helps to guide the larger sized drill bit. Drill each hole separately from its side.
Using careful marking and measurements this technique is the best way to get the two holes aligned nicely across from each other. It removes the worry of the angled drill bit not making the hole in the second side in the right place. It eliminates the possibility of an angled drill bit binding in the first drilled hole and breaking. And finally it gives you the benefit of the pilot hole on the second side which you do not get when trying to drill the second hole from the inside of the tubing.
answered Oct 14, 2019 at 9:38
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12The center punch is so important. Those small drill bits will travel all over the place.– JACKOct 14, 2019 at 13:02
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3Seconding @JACK but to use center punch effectively it is best to use a scratching awl (Any sharp thing would work in a pinch) to scribe the center points, Used exactly like a pen/pencil with a ruler or t-square but you leave a small scratch on the surface instead of an ink line, The intersection of two scratches will inherently center a fine center punch and keep it centered when you whack it, the wider hole with the hole punch will center your pilot drill. Which in turn will center subsequent drills.– crasicOct 14, 2019 at 18:40
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Good advice, except that the OP stated that he does not have access to the opposite side. Oct 16, 2019 at 3:28
One dirty hack is an old optical disk, a CDROM or a DVD or similar.
Lay this on the stock, or tape it on if the stock is not flat. Make sure the silver reflective side is facing your drill.
Put your drill through the hole in the middle, and its really easy to see when the drill is not square by the reflections. Check in two different directions separated by about 90 degrees and it will be square-on.
See how the reflection is in-line with the real drill bit?
Second option is to use a mag-drill. This is either a holder for your electric drill, or a complete unit with a motor and chuck embedded.
These are essentially drill presses, but have a switchable magnet in the base. Turn the magnet on and they will clamp down on a ferrous surface with enough tenacity to resist the pushback of the drilling.
If this is beyond your budget, consider making something similar that will fit your standard square tube size. Consider that the drill's handle could point sideways or even upward perfectly well while drilling horizontally, and you could strap the drill to some kind of moving sled on a wooden frame that clamps to your stock with ratchet-straps.
As Criggie suggests there are options to create or buy such tool like some kind of "drill holder/base":
Of course, check if it's calibrated.
I usually drill a pilot all the way through and "drill craft" is paramount...
If you let the drill change angle from upright as you go through, then that sideways load on the bit will snap it.
answered Oct 14, 2019 at 4:35
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2If you are using some large steel tubing a standard length pilot drill bit may not even make it to the 2nd side.– Michael Karas ♦Oct 14, 2019 at 15:02
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If you've got a drill that has a removable front handle, your best bet is to buy a drill press accessory for it. The cheapest are under £/$/€20 and you'll save that in drill bits over a few years. I keep my mains drill in my press as I've got a good cordless for other jobs.
Screw/clamp the press to your workbench, and clamp down the workpiece. These presses are more versatile than mag drills if you don't have steel around for the magnet to attach to (I work in wood, plastic, and aluminium more than steel, and have a wooden workbench).
