Re: Alignments of the Newport Tower

On 2 Feb 2007 01:52:56 -0800, ghughesarch@xxxxxxx wrote:

On 1 Feb, 20:58, Eric Stevens <eric.stev...@xxxxxxxxx> wrote:
On 1 Feb 2007 03:39:04 -0800, ghughesa...@xxxxxxx wrote:





On 31 Jan, 22:04, Eric Stevens <eric.stev...@xxxxxxxxx> wrote:

Bear in mind that the structure running on the track weighs several
tons and the track almost certainly was made of wood. It would have to
be much wider than an equivalent metal rail. The wheels would almost
certainly be made of wood also.

We have no evidence as to the material of the track or wheels. The ones
shown on the sectional drawing of Chesterton Windmill are not very wide.

http://www.warwickshire.gov.uk/Web/graphics/Graphics.nsf/graphics/che...
orhttp://tinyurl.com/2c73l3ifyou prefer shows the rails to consist
of two rectangular members lying flat on their longest side. The
lowest member is probably wood but the upper member may just have been
iron. The wheels are a mystery but they could be wood or wood shod
with an iron tread.

The construction of the Chesteron mill makes it a much higher class of
structure than the Newport Tower and if the rest of the NT mill
mechanism was of the same standard as the tower I would expect it to
be made of wood.

Eric Stevens- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

I should mention that, in its current form, the track at Chesterton is
the result of alterations in c.1860, when some modifications were made
to the machinery.

It was -and still is - quite usual (despite the weight of the cap - at
Chesterton, IIRC it's about 5 tons) for there * not * to be wheels or
rollers, but for the cap to slide round on greased timber (and
latterly iron or iron-shod) blocks with a flat-face to flat-face
contact, or for the point of contact with the timber curb on top of
the tower to be the sheers - the two main longitudinal timbers forming
the base of the cap frame.

Hmmm - 5 tons sitting on a track of say 22' dia = 11' radius.
Coefficient of friction = say 0.2, therefore frictional resistance at
the track = 1 ton. Therefore torque required to rotate cap = 11
tons.ft. Even with a lever with a working radius of 30' (19' beyond
the track) it would take a force of at least 820 lbs to turn the cap.
No wonder they invented the fan tail!


The tailpole, as seen on most surviving American mills including those
cited in my previous post, gives you a decent lever advantage to turn
the cap (especially if you harness a donkey to it). Post mills weigh
much more (typically 15 - 20 tons) but it is a surprisingly easy job
to turn them into the wind by hand (I speak from experience).

But they are sitting on a bearing of only small diameter. If for
example, the effective radius of the bearing was only 6" then the 820
lbs I calculated would be reduced to 37 lbs. Of course there are other
sources of friction and there is also the effect of wind pressure.
Nevertheless, a pole mill (and that clever French design you posted
the other day, must always be easier to turn than a cap mill.

In
addition, there's sometimes (though not always) a winch fitted to wind
the tailpole up to hooks or posts set in the ground round the mill.

Chesterton is turned by an internal winch, though in its current form
this is part of the 1860s alterations, with a significant gear
reduction between the handle and the toothed rack on the curb. Another
mill near Chesterton, at Tysoe (in existence before 1720), has ropes
which were fixed to projecting pegs round the inside face of the tower
and then wound round bollards in the cap.


There's no need for the timber curb to be exceptionally wide in
relation to an iron one - the smaller the contact area between the
fixed curb and the moving cap, the less resistance there is to be
overcome when turning the cap into the wind.

Oops - no. Within limits, the area of the bearing doesn't have any
effect on the frictional resistance.

I suspect it might in this case. If the bearing consists of two timber
rings in face-to-face contact, both say 22' diameter and 12" wide,
gives about 70sq ft of surface contact. Reduce the contact to six
blocks each 12" square, and the surface contact is less than a tenth
of what it was.

But then the contact pressure is more than ten times what it was. The
two effects more or less cancel out.


At the more "typical"
English tower mills, the overall wall thickness at the top of the
tower is in the range 12" - 18", the timber curb might be around 12"
wide.




Eric Stevens
.

Relevant Pages

  • Re: Alignments of the Newport Tower
    ... tons and the track almost certainly was made of wood. ... mechanism was of the same standard as the tower I would expect it to ... the base of the cap frame. ... the tailpole up to hooks or posts set in the ground round the mill. ...
    (sci.archaeology)
  • Newport Tower and windmills - some comparisons
    ... 16th century mill in France, near Calais, one of at least two ... as that is a nineteenth century tower ... mill fitted with a fantail to turn the cap automatically. ... so could not have been a feature of Newport. ...
    (sci.archaeology)
  • Re: Newport Tower and windmills - some comparisons
    ... seem to be an important part of the construction. ... 16th century mill in France, near Calais, one of at least two ... as that is a nineteenth century tower ... mill fitted with a fantail to turn the cap automatically. ...
    (sci.archaeology)
  • Re: Stirlings _The Sunrise Lands_ and misc thoughts
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