Dress millstones by the hours they have run and by what the flour tells you: a light dress of the furrow edges and lands every 40-60 operating hours, and a full re-cut of the furrows to their original depth every 200-400 hours. A village mill running 2.3-9.2 hours a week reaches the full interval in 22-174 weeks, so log the hours and dress when the flour turns coarser, hotter or slower rather than by the calendar.
Part of Community Grain Mill
How often millstones need re-dressing: the intervals the wiki gives, how to put them on one scale, the symptoms that bring a dressing forward, and the stone’s total life.
The Wiki’s Intervals Disagree Until They Are Put In Hours
Pages across the wiki quote very different intervals:
| Page | Interval as quoted | What it describes |
|---|---|---|
| Community Grain Mill | light every 40-60 h; full re-furrow every 200-400 h | a village mill |
| Mill Construction | every 100-200 h | a mill |
| Furrow Patterns | 100-150 h (soft sandstone, rye); 200-300 h (hard burr, wheat); 150-250 h (granite, corn) | a mill, by stone and grain |
| Stone Dressing (construction) | 6-10 weeks (burr), 4-6 (millstone grit), 4-8 (granite) | a mill, in calendar weeks |
| Stone Dressing: Cutting Grinding Surfaces | 8-60 h by stone | a hand quern |
The quern figures are for a small hand stone and are tied on that page to stone type, from 8-15 hours for fine sandstone to 40-60 for vesicular basalt. For mills, the hour figures agree on a full dressing every 100-400 hours, with the carrier’s 200-400 the widest. The calendar figures only make sense with an assumed workload: if the 4-10 weeks assumed about 40 operating hours a week (an assumption, not stated on that page), they equal 160-400 hours, in the same band. The hours run, not the weeks, is the unit that matters.
Light And Full Dressing Are Different Jobs
- Light dress: sharpen the edges of the furrows with the bill, re-crack the lands, and check the face with the staff. A few hours’ work on a pair.
- Full re-cut: lift the runner, flatten the faces to the staff, re-lay the harps and cut every furrow back to the depths in Dressing and Furrowing Patterns (about 10-13 mm at the eye and 3 mm at the rim). The construction page says a trained dresser can do a pair of 1.2 m stones in a day.
Let The Flour Call A Dressing Early
Dress before the interval if any of these appear (Stone Dressing):
- output drops by more than 20% for the same gap
- the flour runs warmer than usual
- the gap must be opened to hold output
- the flour is visibly coarser at the same gap
- the faces look shiny or glazed, or the lands feel smooth to a dampened hand
Dress late and the stones glaze and run hot; dress too often and you wear away stone for nothing.
Worked Example: A Village Mill’s Year
A village mill on the 0.2 m3/s wheel runs 2.3-9.2 hours a week (Throughput and Operations).
- Light dress at 40 h: 40 / 9.2 = 4.3 weeks, up to 60 / 2.3 = 26 weeks
- Full re-cut at 200 h: 200 / 9.2 = 22 weeks; at 400 h: 400 / 2.3 = 174 weeks, about 3.3 years
So the busy mill is dressed lightly every month or so and fully twice a year; the quiet one is dressed lightly twice a year and fully every few years. Either way, take the log, not the table, as the authority.
Stone Life Is Measured In Thickness, Not Years
The carrier says to replace a stone when its thickness drops below 3-4 in (76-102 mm). Each full dressing removes some thickness, and the amount depends on the stone and the dresser; no figure is sourced here. Measure it: record the runner’s thickness at the rim at every full dressing with a stick or caliper. As an illustration only, if a 250 mm runner lost 1.5 mm each full dressing, it would have (250 - 100) / 1.5 = 100 dressings; at 300 hours between them that is 30,000 hours, which at 400 hours a year is 75 years. The carrier’s remark that a stone lasts decades fits that order of magnitude. Replace this example with your measured loss.
What You Need
- An hours log (Grain Mill Maintenance)
- At least two people who can dress stones, since it is skilled work and a village with one dresser has one point of failure
- A spare pair or a spare runner, so the mill is not idle for the days a dressing takes
- A depth gauge: a stick or a nail through a card
Method: A Dressing Day
Step 1: Lock out the drive. Close and pin the gate, disengage the stone nut and let the stones stop.
Step 2: Lift the runner with the crane or tackle and set it on supports.
Step 3: Check the face and furrow depth with the staff and the gauge, and record thickness.
Step 4: Light dress or full re-cut as the hours and symptoms say.
Step 5: Refit, set the gap and run a trial batch. Throw away the first batch of meal, which carries grit and chips.
Step 6: Log the dressing with hours at the time and the thickness.
Common Mistakes
- Dressing by the calendar. The hours on the log decide.
- Re-cutting furrows too deep. It removes stone for nothing; keep to the traditional depths.
- Using the first batch. It contains grit.
Silica dust, chips, and a runner on the loose
Dressing throws sharp chips and fine silica dust that causes silicosis over years: eye protection, a damp cloth over mouth and nose, work outdoors or with all doors open, wet the stone first, and take air breaks (Dust and Respiratory Protection). A runner of several hundred kilograms crushes: lift it on rated tackle and never stand under it. Lock out the drive before touching the stones, because the person dressing cannot stop a wheel from where they stand. Do not use flame to test for flour dust.
What’s Next
- Learn next: Common Problems and Fixes - the symptoms that call for a dressing
- Combine with: Bearing and Shaft Maintenance - the other half of the upkeep