13

It seems that every few months, I've broken all my pilot hole drill bits because they're so easy to break (and so frequently used). So, every few months, I buy a whole new pack of drill bits and throw away everything in the pack above 1/8 inch or so (since my bigger drill bits are still in working condition). And then again, I attempt to drill gently, but inevitably, several months later, all my small drill bits break.

Does anyone else have this problem? If so, what are potential solutions. Perhaps...

  1. Is there a place that you know of that sells only the small drill bits (preferably the ones with a 1/4 in hex chuck)? I hate to keep tossing the bigger bits.

  2. Has anyone found a method of drilling through hardwoods that won't break drill bits over time?

  3. Anything else that I'm missing?

  • 1
    Yes, I I'm getting close to having all my small bits broken, buying the small ones in 'bulk' would be useful. – bowlturner Mar 24 '15 at 20:46
  • Don't worry about your drills breaking I am trying to do something and I already broke two of my smallest ones. I think I broke one of mine however because I bent it to the side to much. Maybe if you don't bend to the side to much. – Annoynomous Feb 20 '17 at 16:34
  • You are throwing away new drill bits? – Jacob Edmond Feb 21 '17 at 18:10
  • whaaaaaat ! send me all the perfectly good drill bits you would throw away. why why why would you do that. and why do you not know that you can by individual drill bits. – Alaska Man Feb 24 '17 at 17:25
9

Yes, small drill bits can break easily. Some manufacturers offer multi-packs of a single size drill bit. Multi-packs are also available for 1/4" hex shank bits.

Some high-end drill bits are more durable. Recently at The Woodworking Shows I also saw a demonstration by a drill bit vendor drilling through files and brake rotors. First he drilled through with a larger bit, then he used a small bit and flexed it all different directions--I was pretty sure the bit was going to snap, but it didn't.

  • Good link for the HF drill bits. Do you know of any with the 1/4 in chuck? – dfife Mar 24 '15 at 20:49
  • Ha, I didn't even see your comment but had just reread your question and wanted to add another link. As you can see, I did find a 2-pack from Vermont American, but I suspect there should be larger packs too. You're looking for a 1/4" hex shank. – rob Mar 24 '15 at 20:51
  • Great. Good to know the technical term ;) Thanks! – dfife Mar 24 '15 at 20:53
  • Man, that guy might actually go through more brake rotors than my old minivan! – FreeMan May 4 '16 at 17:07
6

Rob has presented the high end solution, I will present the cheap hack end of the spectrum.

For drilling pilot holes, you can use a brad or nail with the head snipped off. This works remarkably well, is cost-effective and easy to do. Depending on the the brad in question, you many not need to snip the head, in which case you can use the brad after a few drillings.

I would also take a look at some parts of the drilling equation - rotation speed, downward force, sharpness of the drill bits and the steadiness of the drill. If the drill bit is dull, rotating slowly with a great force pushing down and the drill wiggles, it is much more likely to break. So see if you can improve part of this. I find if the drill is steady and fast, the bits are sharp and there is no lateral movement, I have no issues. If that doesn't help, try a drill press and clamp your work down before drilling.

  • Those nail "drills" are almost impossible to break! – Ast Pace May 5 '16 at 1:48
2

Stop shopping at retail and/or home centers and head for the industrial suppliers. You can get any size bit (including number-sizes), any tip, and more types of steel than you knew existed, all in kilogram quantities.

They might not have boxes of 3mm x 30mm* low-twist cobalt pilot bits with 1/4 inch shank in stock, but they will know where to order them from.

  • shorter bits don't break as easily
  • Paul -- do you have any links to industrial suppliers that would ship small quantities to people (ones that would not require a large minimum order or have an account setup, etc)? – ProfessionalAmateur Apr 27 '15 at 13:09
  • @ProfessionalAmateur The major suppliers won't sell direct. You want the distributors, and you find them in the yellow pages (phone books - remember those?) under "Tools". When you call for stock and prices, start your quantities at 100 pieces. – paul Apr 28 '15 at 13:40
  • @ProfessionalAmateur - here's one link. No explicit endorsement, but I've purchased there before and been happy. And, they don't require purchase in lots of 100! – FreeMan May 4 '16 at 17:11
2

Small drill bits must be spun very fast and "pecked" much more frequently than larger bits.

Factor 1 - Cutter surface speed

The surface speed of a drill bit is how fast the cutting edge moves across the material being drilled. This is measured in surface feet per minute (SFM) and is proportional to both the RPM and the diameter of the bit.

When you get down to small sizes, say 1/16", you need high revs to be moving the cutting edge at an appropriate speed, keeping the chip load (and therefore cutting forces) low. The recommended SFM for wood is 600 to 1000.

The recommended drilling speed for a 1/16" bit is on the order of 40,000 RPM:

(SFM * 12) / (Pi * Dia.) = (600 * 12) / (3.14 * 1/16) = 36,688 RPM

which of course is higher than most folks have available. So you'll want to use your fastest speed and feed the bit proportionately more slowly.

Factor 2 - Chip evacuation

Once your hole is more than a couple bit diameters deep, you need to pull the bit out of the hole periodically to clear the chips. Failing to do this causes the bit to bind in the accumulated chips and break the bit. This periodic drill, pull out, drill action is called "pecking".

All the chips formed by a twist drill must be "stored" in the flutes. These can hold at most a few diameters worth of material before they become "packed" with chips. Continuing to drill in this state packs the chips against the wall of the hole and binds the bit, causing it to break.

Pecking is required on small bits at the same number of diameters as a big bit, but since the diameter is small, the pecks need to be what seem like very small amounts, say 1/8" for the 1/16" bit.

By keeping these two things in mind, smaller bits can last as long as larger ones, which for most home users is "indefinitely".

  • That SFM info is very interesting, but I'm having a hard time reconciling it with the remarkable drilling efficiency of a hand drill or brace. – Graphus supports Monica Feb 20 '17 at 23:08
  • @Graphus Yes, I think there's a limit to how applicable surface speed is to wood as a material, as opposed to metals. A chip is formed in very different ways (splitting or cutting vs plastic deformation) and as you mention, big honking cuts can be taken just fine in wood with an auger style bit. I think the main thing we can take away is "you have to go faster for small bits" to avoid excessive cutting pressure, and "those little grooves fill up fast on small bits" :) – scanny Feb 21 '17 at 2:51
  • But this extends to smaller bits too — the usual advice I've read re. drilling with small bits (truly fine ones most particularly) is to drill more slowly, precisely because they can be overstressed so easily and going slow allows you to take more care. This is in wood specifically I should stress. – Graphus supports Monica Feb 21 '17 at 9:09
  • @Graphus Well, I would certainly agree that one should feed more slowly, especially if you don't have really high speeds. This reduces the chip load the same way that higher RPM does. It's actually probably better advice all around come to think of it. When cutting metal, too low a SFM can cause problems with chip formation, but with wood I don't believe it matters at all (as we observed with the auger bits earlier). So a slow feed rate would compensate for lower RPM and the finer chips would reduce the torque on the bit that works to break it. I'd still use all the RPMs I had though :) – scanny Feb 21 '17 at 9:24
  • Full disclosure: I may be slightly biased towards low rotational speeds currently as recently 95% of the holes I've drilled have been with a hand drill or brace :-) – Graphus supports Monica Feb 21 '17 at 9:58
2

I assume you are using a typical hand-held powered drill? The shape and position of the handle with respect to the bit makes it hard not to apply bending force to the bit.

I like using an old-fashioned egg-beater drill for pilot holes. The handle lies on the same axis as the bit so pushing down as you drill doesn't apply bending force. The long shape of the tool also makes it much easier to line up by eye perpendicular to the surface. The biggest downside is you need to use both hands so they might not work for you.

You might also find that using wood-specific (ie brad point) drill bits helps as they tend to have larger flutes that aid chip evacuation. Since the bit doesn't clog up you don't end up having to either stop and clear the bit periodically or push hard to complete the cut (and risk snapping the bit).

However, only the better and more expensive brands make brad-point bits in small sizes and 2mm is the smallest I've found.

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