Drill Bit Gauge Is Interdenominational Black Magic

Oh, sure – when you buy a new set of drill bits from the store, they come in a handy holder that demarcates all the different sizes neatly. But after a few years when they’ve ended up scattered in the bottom of your toolbox for a while, it becomes useful to have some sort of gauge to measure them. [Caspar] has the solution, and all you need is an old steel rule.

The trick is to get a ruler with gradations for inches and tenths of inches. After cutting the ruler off just after the 6″ point, the two halves are glued together with some steel offcuts and epoxy. By assembling the two halves in a V shape with a 1 mm drill bit at the 1″ position, and a 5 mm drill bit at the 5″ marker, a linear slope is created that can be used to measure any drill bits and rod of the appropriate size inserted between the two.

It’s a handy tool to have around the shop when you’ve amassed a collection of bits over the years, and need to drill your holes accurately. Additionally, it’s more versatile than the usual method of inserting bits in appropriately sized holes, and can be more accurate.

Now that you’ve organised your drill bits, perhaps you’d like to sharpen them?

62 thoughts on “Drill Bit Gauge Is Interdenominational Black Magic

  1. Or alternatively, take care of you drill bits and don’t leave them rattling around the bottom of your toolbox or in a drawer? Take care of your tools, especially around a shop.

    I agree it’s a tool that could come in handy and it’s a great hack, but I think it is a solution to a problem that shouldn’t happen in the first place (atleast in the way the HaD writer describes it)

    1. if you have a limited set of bits and work at a measured pace in a single workshop, that’s not an unreasonable suggestion. but that’s not everyone’s workflow.

      1. I’m not sure I would call ‘throw everything haphazardly into the nearest bin / pile’ exactly qualifies as a workflow since you take longer finding tools than using them.

    2. I have both — random assortments of bits and organized, well taken care of, non-abused, non-DPS (Drill Protection Services) liable bits. Some of us spend most of our time actually working in our shops and producing things, and take the occasional organizing frenzy. Some spend all their time organizing and never really get any work done. This is a great hack for all!

      1. “take the occasional organizing frenzy”

        I’m in desperate need of this. In part because we moved into a smaller home (empty nesters now). My old home’s workshop was pretty much the entire basement. Now I have 1/4″ of a basement. But it nicer, for what’s that worth.

    3. My drillbits are stamped with a number.

      If your eyesight is bad, you could just grind the shaft of the bit with 1 to 5 grooves and 1-3 dots between the grooves to form a code that tells you what the bit is to 0.25mm

      Two lines, three dots, 2.75mm

  2. Great idea and simple to produce, congrats :-)
    I also have an oldie RS PCB hole gauge, just a conical tensile
    steel spire with a vernier on the end, has stood the test of some
    35years just fine despite exposure to kids.

    Should be possible to integrate maybe in the shaft of a classic
    150mm digital vernier with perhaps option to display the hole size.

  3. This looks like a good use for a laser cutter – if you’ve got your kerf width dialed in you could cut the whole thing from a single piece of material, or you could just use it to etch the scales to save having to find a decimal inch ruler.

  4. Neat trick.
    With the metric system in place in my country, I usually just whip out a ruler and measuere my bit approximately if I can’t read the imprinted diameter anymore. A 6 is somehwat under 6mm and obviously can’t be a 5 one.

    Don’t know about the imperial inch-system if they are closer together or so. But here we have drill bits from 1 – x and nearly never something like a 1.5 or so. (Dremel / handheld tools aside).

      1. As I said – most commonly used are whole numbers. But are they that common? And what is marked on them? Really 08? I would think they are not meant for powerdrills and such. So they stick out of the regular drill bits anyways, right?
        I mean the tool here has inch-markings which look wayy to big for 0.2 or 0.5mm anyways. So yeah, I would have no clue how to read these small drill bits – except for storing them in a proper container or color coding them.

        How do you keep them seperate?

    1. There’s two series of drill sizes commonly used in the USA. Fractional drills are uniformly spaced in increments of 1/64″, or about 0.4mm. The other series is progressively spaced, and designated by a number or letter, with numbers going from #80=0.0135″=0.34mm to #1=0.228″=5.79mm, and letters from A=0.234″=5.94mm to Z=0.413″=10.49mm.

      A real poverty-tier setup for woodworking and stuff might be just fractional drills in 1/32″ or even 1/16‘ increments from 1/8″ to 3/8″ (roughly 3 to 10mm); any metalworking shop will have every fractional by 1/64″ from 1/16″ to 1/2″ (1.5 to 12.7mm), and number/letter drills from #60 to Z (1 to 10.5mm). Maybe down to 1/64″ and #80, depending on the type of work they do.

      As for only using even mm sizes, I can only imagine you’re a woodworker or some such discipline, where you don’t commonly tap holes. Since the tap drill size for UN and M threads is calculated by subtracting thread pitch from major diameter, tap drills are only round numbers for round thread pitches, e.g. M6x1.0 is drilled 5mm , or 3/8-16 is drilled 5/16″. But for e.g. 0.75mm or 1.25mm pitches, you’ll need corresponding 0.25mm or 0.1mm increments.

      1. I’ve got two sets of tools, and always have to stop and think what the next size up from 7/32″ is…

        I pity you Brits…you have to deal with all those failed standards like Whitworth as well as Englis/Metric.

        Metric’s easy — 75% of the bolts on my Toyota want a 10mm wrench :-)

        1. fractions teaches you to factor numbers in your head quickly. it’s good practice.

          I hate having to have both a metric and SAE sets of sockets, box end wrenches, drill bits, tap-and-dies, and allen keys. It gets expensive when you are also buying impact sockets. My grandfather hated it so much he never bothered to get a metric sets and worked entirely in SAE. I’d like to cut the size of my tool chest in half and scrap my SAE in favor of metric. (I ride a metric motorcycle, so I’m definitely biased on this one)

          answer: 15/64 or 1/4, depending on what you mean by “next”

    1. Don’t worry, Congress passed the Metric Conversion Act so we should be seeing it come in to effect any day now. I hope so anyway, it’s been 42 years.

      The rest of the world is almost exclusively metric, and most STEM-ish industries in the USA are as well. The construction industry is not and never will be, likewise with weather forecasts.

      However, it used to be very common to see “1.89 litre” packaged goods in Canada and Mexico, because that’s 2 quarts. Now it’s much more common to see “2.11 quart” goods in the USA, which is 2 litres.

      1. Precision machining can and still is done in inches in many US shops. You won’t find anyone measuring atomic scale with inches, they’ve moved to nanometers. So I guess it depends on what you mean by “precision work”, as it is relative.

    1. Try doing that with a set of Number drills :)
      But they drills are probably not in many people’s drillbit sets these days, my guess is because of the ready availability of sub-millimetre drills in cheap sets. Letter drills aren’t that common either.
      This guage is as far as I know quite novel and a nice quick-reference, but like others have said, put a digital caliper on small drillbits to check before using.

  5. Better tip, buy a caliper. It will also help you if you determine which drill bit to use.

    To store them get a wood block and drill sequential holes for each to rest so you have them sorted.

    1. which turn out to be, interestingly so, the account numbers of the president of the United Federations Of Antique Massphone-Ringing Arts and an unknown hooker living at the junction of Meerpsroad and Ianus-Prime-Street on Quank, eleventh planet in the double star system Farnhall.

  6. A similar trick can be used to divide a prime or other inconvenient distance in one’s measurement unit of choice by n, where n is the number of units along a ruler or tape measure held at an angle to the object to be divides, such that the n unit measuring device forms the hypotenuse of a right angled triangle, and you simply mark where the perpendiculars come down from measurements 1..n on the hypotenuse.

    Usual disclaimer’s re: metrizable topological spaces with euclidean geometry apply.

  7. I check, with a caliper, every drill bit I pull out of my drill index for size before I use it. Just a habit I guess from working in a machine shop with other people, it easy to shift the bits in the index to the next larger hole. I keep three sets of dill bits, one new index, one used index with broken or missing bits, and the coffee can bits that i use when size doesn’t really matter, like for clearance holes. My larger bits, about 1/2″ are kept in there boxes from the manufacturer.

  8. It is a shame that they invented hand tightened chucks on drills. Custody of chuck key is a requirement to use the bits from a full index. Hand tightened lug nuts, let’s go for a drive in the mountains.

    1. Keyless chucks on power tools, supposedly convenient but boy are they difficult to tighten properly, ending up marring the shank of the bits. I’ve tried them, but I stick to proper keyed Jacobs chucks with the key secured to the power cord.

  9. What happened to the plain old drill gauge? The small plate about the size of two playing cards with a bunch of holes punched in it from 1/64 inch to 1/2 inch with each hole marked – has worked fine for me for something like going on 50 years – no batteries to go dead, no fancy caliper. I also keep my regular drill bits in an index so I don’t have to rummage around in some box and waste time

  10. What I need is a device for un-breaking all those small drill bits I’ve broken over the years, which are now lying in the “discarded in disgust” layer at the bottom of the box full of broken stuff, underneath the slightly larger “bits of scrap metal that might be useful one day”, and covered in a layer of sawdust, offcuts of insulating tape, blobs of dried epoxy all gummed together with the “non volatile at room temperature” fractional distillate of WD40.

    Strangely enough, you only ever break the useful ones.. i.e. the ones you use.. can’t think why..

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