The Hario hand-grinder works great, it's really cheap, but it's not without a fairly annoying problem: How to repeatedly get the same grind size.
First, we'll show a dead simple way for repeated accuracy, then we'll try an experiment to further improve the grinder's precision.
Step 1: How It Works
A small gear at the top of the Hario raises or lowers the central burr grinder. This makes larger or smaller grinds.
But the gear doesn't have any sort of markings, and you need to eyeball it and use some trial-and-error to hit the exact spot you used last time.
Step 2: Spacers FTW
A spacer will provide a constant height for the gear. I made them at 1mm increments for a series of grind sizes.
1. Place the burr grinders onto a flat surface, this will push them together.
2. Push a spacer under the gear.
3. Spin the gear until it contacts the spacer.
4. Carefully remove the spacer, and insert the staple to fix the height.
If you want more options, either create more spacers or use them as a reference for slight adjustments, i.e. "1mm + half-turn down".
Step 3: Experiment! for Added Precision.
Because the central burr hangs freely, it can swing slightly and allow larger grinds through. We should be able to make the grinder more accurate by restraining its swing.
Hypothesis: By adding a bottom support, we will reduce the difference's in grain size.
Test: Grind coffee beans with and w/o the the support, compare the results.
Step 4: Experiment Results!
1. Two different grinds were compared (3mm and 4mm) with and w/o the lower support. 1 shot of beans was used in every test.
2. The ground coffee was then passed through a colander and a sieve, to separate the grains into three size groups.
3. The groups were observed, comparing the size of each group and the apparent distribution within each group.
Data (see Pictures)
Minimal difference between w and w/o the support. The grinds w/o support showed slightly more "large" grinds.
There is no apparent reduction in grind distribution by using the lower support.
I do not know if the reduction in "large" grinds is a result of a smaller distribution, or of a reduction in overall size without reduction in distribution.
I did a taste test, and I though the grinds with support tasted better, but probably totally placebo.