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I've learned that, "Almost all drilling bits have to be rotated clockwise to achieve drilling." - Source

What is wrong, exactly, with using the "L" setting (counterclockwise setting) on my cordless power drill to drill a hole (using a standard drill bit)?

Won't the hole still be created at the end of the day, regardless of the direction? I don't understand the "real-world" difference. Are you able to visually tell the difference between the two holes (the hole drilled on the clockwise setting vs. the hole drilled on the counterclockwise setting)?

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    Yes, literally, at the end of the day. It'll take that long! – Harper - Reinstate Monica Jun 17 '17 at 2:35
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    What happened when you tried it? – jscs Jun 17 '17 at 17:07
  • You can just look at the end of a standard twist drill bit and figure this out for yourself. – CoAstroGeek Feb 12 at 18:17
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Conventional drill bits are designed to cut in only one direction, unless otherwise noted. I think one has to make special effort to find a left-cutting bit, although some screw extractors with an integrated cutter will be left-cutting.

Because a drill bit cuts, one wants the cutting edge to engage the work as it rotates. If used in the reverse direction, the cutting edge will drag and become dull in short order.

Along with the dulling, great heat will be generated from the friction. I have read on this forum of people who have used reverse direction on a conventional drill bit to effectively melt through plastic. Drilling plastic requires special bits or special technique to prevent cracking the plastic.

  • So, other than for those unusual bits, or for loosening a screw, what is the purpose of the "L" setting on a drill? – Fil Jun 17 '17 at 4:21
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    @Fil Several: if a drill bit jams in the material, it may be easier to "back it out"; when used as a power screwdriver, this is used to unscrew the screw to remove it. – DoxyLover Jun 17 '17 at 4:46
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    @Fil - You use reverse to loosen the chuck when you're changing bits (in addition to using it for screws). – Hot Licks Jun 17 '17 at 11:02
  • The reverse setting for a drill would be for removing screws as per Hot Licks' comment, but also for using screw removal tools what cut into the screw being removed. The manual for these drills suggest to not use power to tighten or loosen a chuck, but I'm willing to bet that nearly everyone does, specifically with keyless chucks. – fred_dot_u Jun 17 '17 at 12:04
  • Good answer I even use power on keyed drills but most of the time a final bump with the key. – Ed Beal Feb 12 at 21:44
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Running twist bits in reverse drags the cutting edges over the surface rather than shaving off material. In soft materials like wood you may scrape your way through regardless, in steel you'd make considerably less progress.

A more sinister issue is that the point of the bit being deprived of any bite will want to wander when starting the hole. Softwoods mask the problem to a certain degree because you can create a large starting divot by arm strength alone. On metals and engineered lumber the effect is more pronounced.

Worst of all, running a twist bit backwards greatly retards the travel of cuttings up the flutes. Rather than removing material the drill abrades it against the bottom of the hole until it piles up high enough to spill out. In deep holes this will either lead to the bit getting stuck by the cuttings forcing their way up the perimeter of the hole or cutting a hole that's out of round.

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Drilling counterclockwise is like razoring holding the razor upside down; the blade touches the thing to be cut, but it has no effect as it slides over it.

Your best bet is that if you cut wood this way, you (1) run out of battery soon and (2) burn the wood as the friction can be very large.

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I have used this technique when working with Plexiglas and fine metals and wood. First you are not drilling through the entire surface backwards, you are drilling through about 90% to 95% of the material and change the direction to pierce the last bit. This technique prevents Cracking in Plexiglas, damaging the wood when the drill bit comes through and with metal especially the last part the drill usually catches before exiting the material, by reversing the bit it prevents the metal from grabbing the bit and bending.

  • I also use this technique to drill hard plastics like plexiglass – Ed Beal Feb 12 at 21:46

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