Summary

Sugar cube DIY

Instructions

Make sugar cubes.

This is a printed ABS mold, used to make a silicone mold which is used to make 1/2 inch sugar cubes. Each cube weighs about 2 grams, which (I think) equals 1/2 teaspoon.

The print.
No special instructions. The 4 inch square print may lift a little at the corners but precise accuracy is not necessary. A raft is optional, imo. No raft, fast speed and 0.30mm layers worked OK for me on an Afinia. 58 grams and about 2 hours. Frame piece is 20 min, 10 g.
When this mold is printed it can be filled with silicone and left to harden. No mold release is necessary.

The silicone sugarcube mold:
I used nearly equal parts (by volume) of 100% clear silicone caulk and corn starch. Three fluid ounces of silicone (~80cc) should be enough. I used a putty knife on a sheet of glass to thoroughly incorporate the starch into the silicone.
Too much material is better than not enough. Any extra can be rolled flat to make a very functional hot pot coaster or... something...

Starting in one corner, that paste is firmly, repeatedly pressed into the narrow groves until it tries to squeeze itself up, around and out, so one can be sure the bottoms of the crevasses are filled. (See photo corner failure)

It will be maybe 90% cured in about 3 hours or less, depending on conditions and on how long it is mixed, and might then be carefully tugged and pried and pulled from the mold. Silicone tears easily and leaving it longer, like overnight, makes it stronger. When the vinegar smell is completely gone it is fully cured (but that may require days).

There are a few small (useless) holes through the bottom of the mold to poke something through, meant to help remove the silicone "grid" once it is cured. Getting the removal started is slightly frustrating but makers are a patient and resourceful people. Gently pick around at a corner to loosen it up.
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Making sugar cubes:
Mix some granulated sugar and just a little bit of water (perhaps 1/2 teaspoon to a cup of sugar). Mix and stir with a fork to dampen all the sugar grains. If thoroughly mixed, very little water is needed to get the texture of very slightly damp sand. The less water used, the faster the cubes will harden.
(Add flavored extracts like almond, vanilla, coconut and/or food coloring to the water if desired. Search the net for more information.)
Filling this 36 cube mold requires a little over 1/4 cup of sugar.

The square frame part keeps the soft, flexible mold square and provides some support. Put the frame-piece around the silicone grid, and lay that assembly on a flat surface. Spoon some sugar onto it and pack that down into the cavities with your fingertips until they are firmly filled. Level off the top with a small straightedge if desired...

You should be able to pick up and handle the filled mold without any sugar falling out. Carefully place the filled mold in a warm spot... perhaps into a warm oven or use a food dehydrator. Since the bottoms and tops are exposed the cubes dry quickly. In my dehydrator set low to around 110 F, it takes about 60 minutes before the semi-dry cubes are hard enough to be pushed out without crumbling.

Note: Unlike most people I still use Imperial measurments, so my files will be very tiny when opened in a metric software setting, as 4 inches will probably equate to 4cm.
The simplist way to manage this might be to just scale these files up to somewhere around 102 mm square.

Sugar Cube Mold