Printable Caliper Jaws Increase Precision, Deflect Derision

caliper jaw tools

If you’ve watched as many machining videos as we have, no doubt you’ve seen someone commit the cardinal sin of metalworking: using caliper jaws to scratch a mark into metal. Even if it’s a cheap Harbor Freight caliper rather than an expensive Starrett or Mitutoyo tool being abused, derision and scorn predictably rain down upon the hapless sinner’s head.

The criticism is not without its merit, of course. Recognizing this, [Nelson Stoldt] came up with these clamp-on nosepieces designed to turn calipers into a better marking tool. Using stock calipers as marking gauges always introduces some error, since the jaws are equal lengths and thus have to be held at a slight angle to the workpiece in order to make a mark. The caliper jaws correct for this admittedly negligible error by extending one jaw, allowing it to ride on a reference face while the other jaw remains perpendicular to the workpiece. As a bonus, the short jaw has a slot to mount a steel marking knife, saving the caliper jaws from damage.

[Nelson] chose to 3D-print his caliper jaws, but they could just as easily be milled from solid stock to make them a little more durable. Then again, you could always 3D-print the calipers in the first place, and integrate these jaws right into them.

25 thoughts on “Printable Caliper Jaws Increase Precision, Deflect Derision

  1. I have a 15€ pair of calipers specifically for scribing. Takes two minutes to stone a point back onto the jaws about once a year. This design is fine but if you attach this contraption to your calipers, you now also have a dedicated pair for scribing since you’re going to quickly get bored of putting them on and off all the time.

    If your whole motivation is avoiding derision from people on the internet however, another solution is to just learn to ignore the armchair machinists who probably can’t even read a vernier scale properly.

      1. Those rulers with a single roller are garbage, no matter what the quality is with which they are made.
        The problem with those things is parallax error because you just can’t hold them perpendicular.

        Instead, I do use my Mitutoyo for scribing, but I use the “step” / depth measurement in combination with a scribing pen.

        1. Pretty sure you mean Cosine Error and not Parallax Error, but in any case for small enough angles it’s negligible – e.g. cos(1 degree) = 0.9998, cos(2 degrees) = 0.9994 – still accurate to 1 part per thousand, which is better than my eyes can do.
          If you’re really that concerned about accuracy then you’re not cutting to a scribed line anyway, it’s more just there as an idiot check while you use more accurate gauges.

    1. > probably can’t even read a vernier scale properly
      “If only there was a way to tell where it was between marks on my caliper dial…”

      Someone who’s 20 and doesn’t know of vernier, I can understand.
      Someone who’s over 50 and doesn’t know of vernier…

      Show kids vernier “magic” and it will occupy them for a time.

  2. The whole basis of hacking is to ignore the hard and fast rules, when they don’t suit you. If you are using caliper jaws to scribe metal, then you are doing it wrong: the object is to score the INK, not the metal.

    1. Same outcome though: the calipers wear out and become inaccurate.

      Then again, the whole point is moot because there are calipers made for scribing, with the only difference of having the top jaw slightly shorter so the bottom jaw can extend over an edge.

  3. Scribing is only going to damage the caliper if the material you’re trying to mark is harder than the caliper. plastic and aluminum shouldn’t be much of a problem.

    I don’t know much about steel, but could one harden the tips of a caliper by heating and quenching?

          1. The hairs you’re cutting bend the fine edge and it eventually burrs, then chips and cracks.

            You can “recondition” a razor blade by running it backwards along your arm a few times before shaving, which buys a dozen or so more shaves out of disposable blades. It straightens out the burr (it’s basically stropping the blades).

  4. We have a pair of vernier in our metrology drawer known as the ‘welding clamps’ after they got used for a slightly inappropriate purpose. They still have some weld spatter embedded in them.

  5. I’ve been (lightly) scribing aluminum and plastic for more than a decade with my trusty Mitutoyos, and they still have no visible damage. Even if the points were to wear down very slightly, it wouldn’t effect measurements taken anywhere else on the jaws. I’ve personally never heard someone complain about doing that, but if they do who cares?

  6. I don’t know how it calls in English but try to find this stuff: “272380205 limit”. In my opinion it is perfect for tracing line on metal. With hard scriber and automatic puncture you can trace whatever you want :)

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