Environmental Engineering Reference
In-Depth Information
rest. Note that the brake wheel has a large diameter, so that a high torque could be
produced by the friction on its rim band. The braking device had an element of “fail-safe”
in that it had to be lifted to the “off” position.
It was advantageous to have the brake be capable of operation at a distance, with the
miller on the lower working loor. Application of the brake in a high wind or with full sail,
either by design or accident, could start a ire from sparks of metal or ignition of wood
because of the heavy friction effect. The miller must have had to keep a sharp eye for
sudden storms that might catch him with his sails up, so to speak. There was on auxiliary
action he could take to control over-speeding, and that was to absorb as much energy in the
grinding process as he could — for as long as the supply of grain held out.
The post mill was a triumph of mechanical engineering and the most complex power
device of medieval times, even up to the beginning of the Industrial Revolution, which was
initiated by the steam engine of Newcomen at the beginning of the eighteenth century. A
cutaway view of a complete post mill [Freese 1957] is given in Figure 1-11, and Table 1-1
lists its major parts. This is a view of the mill at Brill, Bucks, England, which was built
in 1686; it was largely restored by knowledgeable hands, so it is quite representative of the
English post mill. The drawing shows many devices and mechanisms, such as those for
grinding the grain, dressing the millstones, and hoisting the sacks. The cramped operating
quarters will no doubt be noted, and this brings us to the other major type of horizontal-axis
European windmill, the
tower mill
,
which was larger than the post mill.
This description gives the basic construction of the post mill, but designs change in
detail from mill to mill, region to region, and country to country. This is necessarily true
with respect to materials available locally. It is very dificult to date mills, because even
when a date is carved into the wood, who knows when it was actually carved? Some
documentary evidence is required before the date can be authenticated. Of course, all the
Table 1-1.
Parts List of the Brill Post Mill Shown in Figure 1-11
[Freese 1957]
1.
Brick piers
24.
Sail cleat
47.
Hopper
2.
Main post
25.
Brake wheel
48.
Damsel
3.
Crosstrees
26.
Brake
49.
Feed shoe
4.
Quarterbars
27.
Brake chain
50.
Spring stick or “rabbet”
5.
Retaining straps
28.
Brake lever
51.
Feed adjustment cord
6.
Heel, or tongue of main post
29.
Wallower
52.
Feed adjustment screw
7.
Centering wheels
30.
Upright shaft
53.
Meal spout
8.
Crowntree
31.
Glut box on spindle beam
54.
Bell alarm
9.
Side girt
32.
Bridge beam
55.
Sack-gear “take-off”
10.
Diagonal brace
33.
Great spur wheel
56.
Sack bollard
11.
Cap ribs
34.
Stone nut
57.
Sack control lever
12.
Steps or ladder
35.
Crossbar or bridgepiece
58.
Sack chain
13.
Weather beam
36.
Upper or runner stone
59.
Sack trap
14.
Windshaft
37.
Rhynd or mace
60.
Dresser case
15.
Tail beam and bearing
38.
Bridgetree
61.
Auxiliary “take-off
16.
Sail stock
39.
Brayer
62.
Auxiliary gear frame
17.
Poll head or canister
40.
Tentering rod
63.
Dresser gears
18.
Sailshaft or whip
41.
Tentering screw
64.
Dresser
19.
Sail bars
42.
Steelyard
65.
Wire brushes
20.
Uplongs
43.
Governors
66.
Dresser spout
21.
Hemlath
44.
Grain bin
67.
Tail pole
22.
Windboard
45.
Grain spout
23.
Curtain rail
46.
“Horse”
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