Mill repairs 2015 day1
Visit to Mostert's Mill 14 Feb 15
Article reproduced with kind permission of Andy Selfe
Original can be found here http://compagnesdriftmill.blogspot.com/
Secretary Steve Craven of Friends of Mostert's Mill asked me to visit and give some advice on some technical problems at this the only working Windmill producing meal in Africa.
Mostert's Mill The team of Volunteers set the Mill working, giving all of us the opportunity to observe the faults while the Mill worked lightly. Also present were Neville Boyd, John Hammer, Paul Jaques, Adam an Apprentice Miller and a visiting Windmill owner from the North of Holland, Pieter Breeuwsma. Unfortunately Brad Wallace-Bradley has decided to retire. There are two main problems, one at the top with the meshing of the brake-wheel and the lantern pinion, the other with the stones themselves.
The meshing at the top can be watched on this short clip: http://youtu.be/DNO4qh7cMh4 There are two factors to this problem, one that the brake wheel is not running true, the other that the lantern pinion is not set central to the rotation of the vertical shaft. The run-out on the pinion is exacerbated by the fact that the 'pintle' is loose in the wood at the top, and has had to be wedged in place as a temporary measure. The round bar of the pintle engages in the bearing of the sprattle-beam and that also has excessive play.
Lantern pinion meshing with brake wheel, pintle in sprattle beam bearing
One can see in the clip when watching the cog-face of the brake wheel in relation to a fixed object like a brake block, that the brake wheel has a wavy profile, but in one area of about half a revolution the distance from the pinion is excessive. Without actually measuring it looks as if the run-out is about 25mm.
The run-out on the pinion is perhaps less, but it means that about every three revolutions the meshing is either too close, with the clasp-arms rubbing against the upper disc of the lantern, or in danger of the cogs going out of mesh. If this was to happen, re-entry into mesh could easily cause a fracture of a cog or stave.
Before any attempt is made to true-up the pinion, the problem of the loose-and-wedged pintle must be properly dealt with. Discussing this with Neville who has an engineering background and Paul who is an architect, we decided that a modern material which might help would be an ABE product called Epidermix. This is close to what is called in Europe and UK Araldit(e), a two-pack epoxy which is popular in engineering and building.
Rather than the quick-fix possibility of simply pouring this into the top of the vertical shaft, making it probably impossible to remove the pintle ever again (it may need to be machined or re-sleeved in the round section at some time in the future), it would be better to apply some kind of release agent to the metal parts, even cling-film, so that it can be removed if necessary. Here is Neville's drawing of the metal part along with the wooden (?) block which holds it in place. There is a square iron band which fits over the top of the shaft which can just be seen in the picture above.
Drawing of the pintle
If the wear in the wood is not too bad and the problem can be cured simply by applying more clamping pressure all round, it might be possible to substitute the iron band with four interlocking eye-bolts similar to those around the wind shaft (see picture below) and poll end. It might be an idea to do both! The pintle with its wedges can be seen in this short clip http://youtu.be/O9yD3wn5R6w
The brake wheel also runs out vertically, causing the brake blocks to take unevenly. It would be good to reduce this when aligning the cog face, which should be a fairly straightforward operation involving adjusting the wedges. I found two of these wedges loose today.
The other problem is on the millstones and the uneven load at every turn is not helping the problem at the top. I have read Brad's notes and seen Neville's pictures of uneven wear on the bedstone. It appears that the bedstone is not flat and level and never has been. It must be remembered that in the restoration of 1995, the Dutch Millers never had a chance to completely commission the Mill. They returned in 1998, and explained the stone-dressing procedure but it still wasn't done. It is also not known whether there is play between the stone spindle and the wooden (?) bearing in the bedstone and it is suspected that the runner, even though it is on a stiff rynd, is out of balance. An added slight complication is that the stones are not a pair, one is dressed with harps, the other is sickle-dressed.
Clearly the first stage is to level and flatten the bedstone. Brad's notes mention that he picked up 13mm out-of-level using a water-tube level. It isn't possible to use an accurate builder's level while the runner is in place and to remove that means the vertical shaft has to be hoisted out of the way; no small task! However if that is done and an accurate tool is made to take the place of the cock-head of the stone spindle from which the runner can be suspended, static balancing can be done. Brad suggests skimming off some of the top surface of the heavy side. I would suggest adding weight to the light side; that was a common method with weight-boxes set into the stone top face.
Apparently furrows on the higher areas of the bed-stone have been completely worn away, so a combination of levelling, flattening (as described in Kick and Kosmin's books and which I did at La Motte) and re-cutting of the furrows and cracking if necessary, should be done.
If the stone spindle is loose in the bearings of the bedstone and if the bearings are not adjustable, then this needs to be cured by sleeving the spindle oversize (there is bound to be wear on that as well as the bearings) and honing the bearing blocks, as I had to do at Compagnesdrift. Addition of grease pipes to the rags in the spaces between the bearing blocks has proved an advantage there.
As the problem of the stones has been there for a long time, I would suggest that the irregularities at the top be tackled first, the sooner the better.
Lantern pinion, brake wheel and sprattle beam
Watch the impressive sight of the sails working in http://youtu.be/xRRzyzFZ724 and reefing the sails on http://youtu.be/jkAoedyUrPM
Regards Andy Selfe
Link to day 2