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I need some help. I'm trying to design a dice dispenser / tower where dice will slide or roll thorough a channel with a square cross-section. Many sources show that a typical d20 has a "diameter" of 22mm, so a 25mm channel should suffice. I'm trying to make free STL for 3d printing folks, not a product for sale.

I have only a few sets of dice, and they are of slightly different sizes, so if anyone has reliable data on what sizes are actually popular on the market, or what size is assumed for off-the-shelf dice towers, it would help me greatly. I want this to be usable with most of RPG dice, no matter if system is d20-, d10- or d6- based. My first tests will be with D&D, but if it works, I want my design to be useful to many people.

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    \$\begingroup\$ You mentioned below that you’re trying to make an STL for printing. That’s a detail worth mentioning here. Unfortunately, it also makes your task harder: “sliding” is going to be material dependent, and (unless you are far more skilled than I!) very dependent on the printer and slicer. This is a very cool idea, but it’s as though you’ve decided that your first hike will be to the top of Kilimanjaro. Maybe take a look at some existing designs on thingiverse as a starting point? \$\endgroup\$
    – fectin
    Apr 22, 2022 at 18:26
  • \$\begingroup\$ @fectin as long as it fits, size won't affect sliding. And I want to ask one thing at a time, so for purpose of this question I believe exact method of fabrication does not matter. \$\endgroup\$
    – Mołot
    Apr 22, 2022 at 20:37
  • \$\begingroup\$ How can you talk of "square cross-section" and "d20" at the same time? Unless you're suggesting smaller dice will have trouble in larger channels, why would it be problematic to start with the largest die you know, and double its dimensions? \$\endgroup\$ Apr 24, 2022 at 0:14

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Unfortunately, I don’t think a solution is possible for the use case you describe.

There are definitely some popular dice sizes. Conveniently, my experience even suggests that the dice other than a d6 (cube) tend to be more standardized: 20-22mm for a d20 (icosahedron) is common enough that something different is obvious. Here is a set of detailed dimensions I found for dice that would be recognizably “normal”.

There are two problems. First, from extensive personal experience, the variation is greatest in d6s. Not only do people play with the size, they also play with the shape. Most RPG dice aren’t like sharp-edged casino dice. Instead, they have a strong tendency to be chamfered, even to the point that the face is a circle. That means that even if you could perfectly predict the dimensions, you would have trouble keeping the dice sliding instead of rolling. If you want them to slide through an enclosed channel, it’s even worse: they are likely to tumble and jam.

Second, you have a similar problem with the non-d6 dice. The dimensions measure total outer dimension, point to point. Except when they measure face size, like for d6. It is exceedingly rare to see RPG dice with the same outer size, and it looks “wrong” to see them as a set. With good tuning, you might be able to get channels to work for cubes; I have a very hard time seeing them work for cubes and also larger icosahedrons and taller tetrahedrons.

The usual approach to a dice tower is a channel significantly larger than the dice, with baffles that strike the dice and make them tumble on the way down.

All that said, your idea sounds really neat, and I would love to hear of it working. You might be able to make it work for a game like Warhammer, Fate, Traveller, etc. All those games use only d6 rolls. If you package your tower with dice that specifically work for that tower, you might be able to avoid the issues above. And then the answer to your question is easy: the dice are whatever size you select.

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It's anecdotal, but this set on Amazon.com was one of the top results for RPG dice; with over 8k reviews, it's good evidence that it's a popular size. It's d20s have the largest single dimension, at 27mm (the shorter dimension is 22mm, so I think they'd be called 22mm dice).

My own experience is that that that size is typical, and is the largest non-novelty die size people I've seen people actually play RPGs with. This is backed up by my personal visits to FLGSs (Friendly Local Gaming Stores), where most of the dice are 22mm or smaller.

FWIW, I'd recommend bumping the channel up to 28 or even 30mm, to account for slight manufacturing defects in the dice, especially if the tower isn't easy to disassemble and re-assemble. I'd also recommend finding an FLGS that might be interested in carrying your tower; they (or players there) will almost certainly have dice you can test your tower with, and they might be willing to give you a few dice sets in exchange for the first few towers. They can also be a great place to get valuable feedback about the towers, both functionally and aesthetically (though, take aesthetic feedback with a giant grain of salt). My FLGS has sold plenty stuff made by regulars (dice bags, towers, etc.). YMMV, of course.

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  • \$\begingroup\$ I'm trying to make free STL for 3d printing folks, not a product for sale :) \$\endgroup\$
    – Mołot
    Apr 22, 2022 at 18:02
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Another factor to consider: the smallest dice that work. I know players who use tiny D6s, as small as 3mm. You'll need to make sure that small dice don't fall through gaps in the path, and that they get adequately randomised.

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    \$\begingroup\$ I have small plastic jar full of hundreds of cheap plastic six-sided dice, about 3mm on each side. They're really low quality and probably unbalanced as heck, but they let me run a one-shot game with stuff I can comfortably fit in my jeans pocket: pencil, paper, lots of d6. :) They're also multicolored, so I can use them as map tokens for combat. And I paid like maybe 1€ for them. \$\endgroup\$ Apr 22, 2022 at 18:22
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    \$\begingroup\$ Actually, I might've exaggerated the smallness — I found some quite similar dice for sale online, and they're claimed to be 5mm, not 3mm. :/ Unfortunately I don't have the actual dice here, so I can't check. I do have a ruler, and looking at it, 5mm looks wider than I remember the dice being. But maybe my memory is playing tricks on me. \$\endgroup\$ Apr 22, 2022 at 18:52

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