Deliberately unfair (and fair) d20 dice

This is why I would never, ever allow a player bring a 3D-printed d20 to any of my games! It's just too easy to load the dice if you print 'em yourself. On the other hand, they would be OK for a player to use as a substitute for the standard advantage/disadvantage mechanic of rolling two d20s and picking the higher or lower value. I describe these differences on my blog.

The fair d20 is both geometrically balanced and numerically balanced, with a constant sum (plus or minus 1) around each vertex, and a constant sum of face values adjacent to each face.

The unfair d20s are not only unbalanced from an internal hollow space on one side, but also the numbers are distributed so that the high numbers are all on one half and the low numbers are on the other half. Opposite faces of the fair and unfair dice still add up to 21 just like any other d20.

To aid in identifying which d20 is which, the high-biased d20 has a smiley ☺ on the "20" face, and the low-biased d20 has an "F" (for "FAIL") on the "1" face. Even when printed with different colors, I couldn't trust my memory to remember which is which. Be glad of those markers.

Read my blog article for if you're interested in the statistical test results for these dice. Don't mind the math; it's written for a layperson. Instead of a linear probability distribution of the d20 advantage/disadvantage mechanic, the loaded dice appear to have a curved probability distribution. It is still possible to roll a 1 with the high-biased d20 and roll a 20 with the low-biased d20.

Print settings

Printer: Prusa I3 MK3S

Supports: No

Resolution: 0.20 mm layers

Infill: 30% gyroid for fair d20, 60% for biased

Filament: Generic PLA 

Notes:

Print with a 4mm brim. There is not much surface area contact between the d20 and the build surface. Reduce elephant foot compensation to 0 to ensure that the brim sticks.

Don't attempt to use STL cleanup utilities. Doing so is likely to fill in the hollow half-volume inside the unfair dice. After slicing, check to be sure that the top half of each unfair d20 is actually hollow.

Category: Dice