Will 3D Printed Dice Be Fair?

  • Is there anything to the process of 3D printing that might make the dice unfair/land on a specific side more frequently? Or will any imperfections be negligible, thus making the dice fair? I'm more concerned about making a d20 than anything else, so focus on that shape if need be.






    I am using a MakerBot Replicator+ with FDM, so take this into consideration if it affects your answer, and if you believe a different printing process would have an advantage over this don't hesitate to include it.


    In the real world, no dice are perfectly fair. But for a sufficiently loose/lenient definition of fair, yeah sure 3D printed dice can be "fair enough", depending on what your criteria are.

    It's confusing that your title asks if the dice will be fair but the question itself asks if it'll be unfair. People very often start their answer to a yes/no question with "Yes." or "No." but now it's not clear what those answers mean.

    @TomvanderZanden I believe I was clear in my question that I was concerned with the 3D printing process in general, like how it produces from the ground up or some other process that could affect a die's balance. If you must know I have access to a MakerBot Replicator+ which is what I would use for the dice, but I still don't see exactly how the specific printer would make a difference. Feel free to explain or direct me to the different printer processes and how the differences could affect the dice, I would love to know.

    "*The* 3D printing process" does not exist. Makerbot uses FDM, which builds a model by layering molten plastic. You could also use SLA/DLP, which uses light to cure photosensitive resin to form your part. You could use SLS, which uses a laser to melt together metal or plastic particles to form your part. LOM takes a piece of paper, cuts out a slice of your model, then glues these cutouts together to form the part. Moreover, even within a single process (like FDM) print settings would affect the outcome. If you ask about "3D printing in general" then the question is way too broad.

  • Icyfire

    Icyfire Correct answer

    5 years ago

    It probably won't be fair.


    Incidentally, I have a decent amount of experience with 3D printing.


    It depends heavily on the particular technology that you're using to do the 3D printing, but nearly all forms of printing aren't perfect--depending on the design you make (solid? honeycombed? hollow?), there will be slight, or not-so-slight variations across the faces, which will result in an unfair die. In particular, the faces that are parallel to the build surface will probably be different compared to the ones that are angled.


    You could probably deal with some of these problems with some kind of post-processing, but honestly at that point buying dice would be easier. 3D printing is for making custom or prototype objects, and isn't really suited to mass production of simple shapes like dice.


    Even manufactured dice have some imperfections, and a slightly unfair die probably won't make much of a difference in gameplay, but it will be hard for you to determine whether the imperfections from 3D printing are severe enough to make the die unfair without rolling it many times and looking at its distribution. Again, at that point, it's easier to just buy the dice.


    That being said, custom d20s can be super cool looking, and if you're going to 3D print something, might as well make it look cool...


    Your headline "probably not" is confusing, since the title of the question asks if the dice will be fair but the body asks if it will be unfair.

    Of course, even if your manufactured die is structurally perfect in all ways, and you roll it on a battered and scarred wooden table, an edge hitting a groove will produce imperfections in the roll that wouldn't be present on an utterly smooth table. All things are relative.

    @flith An imperfection in the table wouldn't systematically favour one roll over another, so the rolls would still be fair. *Unpredictable* imperfections are what makes a dice roll random; the problem with imperfections in the *dice* is that they can have a *predictable* effect, because they make it more likely to land in one orientation than another.

    Random imperfections in either the table or the die are one thing, but it would be all too easy to design and 3D print a die that favored one face over the others. Such an imperfection could be made undetectable without destroying the die, dynamically balancing it or doing a randomness study, rolling the die many times and tracking the results. I'd rather play whatever game I'm playing than mess around with that.

    There was another thread on SE about how to easily test the fairness of a dice. A top answer was to float it in water and poke it. If it stops spinning with the same number up each time, it's not fair, wheras a fair die will tend to spin longer and stop with different numbers up. http://rpg.stackexchange.com/q/65206/4119 has more details.

    On a practical note: if I were going to 3D-print a die, to make it as fair as possible, I'd probably make a prism-shaped die (like this), and print it such that one of the ends (ie the faces it's not meant to land on) is the "base" during printing. That would - at least for the printer types I'm familiar with - give you a better chance of a fair die, because a lot of the non-uniformity tends to be in the vertical direction and/or with sloping faces, and this way all (important) faces would be affected equally.

    It looks like all the answers are talking about theory. I have not seen any real tests. So I have decided to put my real-life test of purposely unfair d6 die - hitting and rolling plays much greater role than weight of some side.

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Content dated before 7/24/2021 11:53 AM