Mostert’s Mill

+27 (0)82 771 6480
Rhodes Ave, Mowbray, Cape Town

Mill Repairs 2015 - Day 2

– Mostert’s Mill Vertical Shaft and Brake Wheel

Since the last gathering at Mostert’s Mill on 14th February (See No 170), much planning has been done including a Friends of Mostert’s Mill Committee meeting, leading up to a Work Party, arranged to suit everybody, on 21st March. The proposed jobs were worked out and a tool list drawn up.

The team consisted of, in no particular order, Neville Boyd, Paul Jaques (accompanied by his brother Roger), Steve Craven, John Hammer (accompanied by his gardener, Fortune), Morne Husselman, Pieter Breeuwsma and me. Each person had a job to do and we worked well together.

This is how the plan of action looked, to start with:

  1. Inspect wear in Pintle and its housing in the sprattle beam and decide if it can be taken up by adjustment only, or more ‘engineering’ required (building up of the pintle, and machining.) Measure for spacers on tie bolts / wedges
  2. Dismantle top bearing 
So we did just that. The bearing cap was loose, even with the wedges fully inserted, yet when it was pushed firmly against the Sprattle beam, there seemed to be not much play between it and the Pintle. The two halves of the bearing are held in place in a recess in the Sprattle beam, with shims holding the two halves together. There is a similar recess in the cap. There are also shims in the Sprattle beam recess which set the meshing between the cogs on the Brake wheel and the Lantern pinion.
The bearing cap and two halves of the top bearing have been removed from the Sprattle beam, exposing the Pintle
The two halves of the bearing are made of of a very heavy wood, Pieter suggested Ebony, which is what is used on his own Mill. We held them together on the Pintle and while there was little lateral play, there was rather too much when tilting it in all directions. This is probably because the Pintle wasn’t in line with the vertical shaft. This was noticeable, just by looking at it!
Bearing cap and two halves of the bearing
Our first decision was to assess the condition of the pintle where it passes through this bearing, so we took readings. But first we decided what would be an acceptable tolerance. Considering that 200+ years ago, this would likely have been wrought by a Blacksmith, I suggested 2mm out-of-roundness and / or taper.
Measurements of out-of-roundness and taper on the Pintle
In the end, the maximum deviation was 2.3mm, most of that being taper over the full length and only about half that is actually in the bearing at any time. We might yet work on the two halves of the bearing, taking material off the mating faces and clamping them together and boring them.
The next stages were:
3 Align sails as described by Brad and lift out vertical shaft (
4 Inspect pintle and remove lantern if necessary, inspect fit of lantern on vertical shaft, wedges, etc. 
The lifting-out has been described in exact detail by Brad, but having decided that the Lantern pinion must come off, we first marked all 16 wedges and their positions between the upright shaft and the squares in the top and bottom flanges of the Lantern, then removed the Keepers (blocks of wood to prevent them working out) and Morne knocked them out with a wooden drift.
Morne knocking out Lantern pinion wedges after marking
16 wedges, all numbered for ease of assembly
The Furniture around the Millstones was dismantled early on. We then turned the sails so the flat of the Wind shaft was horizontal to give us the maximum possible lift, rigged a chain block with straps around the wind shaft and vertical shaft and lifted it out. Sounds easy? Not really! The Lantern Pinion always seems to be in the way! Paul showed off his expert knowledge of knots!
Morne guiding the top end of the Vertical shaft
Once the Fork was clear of the Rynd in the Runner stone we could tilt it over and lower the fork on to a block of wood on the Runner.
Looking upward at the Vertical shaft after removal
Removing the Lantern was then easy!
Lifting off the Lantern Pinion
The wedges between the pintle and the vertical shaft can be seen in the photo above. Some were loose, the Pintle wasn’t tight in the Vertical shaft nor was the pintle itself in line with the rotation of the Vertical shaft. We then dismantled the Pintle from the Vertical shaft. This meant first removing the iron band, held in position by 2 countersunk screws which were well stuck. One broke the other we had to cut.
Wedges holding Pintle in place in the end of the Vertical shaft
Then several through-bolts had to be removed and the block of wood facing the camera in the picture above could be withdrawn outwards, then the Pintle upwards:
Levering out the Pintle
This is what the Pintle looks like, an intricate piece of forging!
The Pintle removed
So, keeping up with the planning:
5 Remove pintle and inspect seating in vertical shaft and method of firming in vertical shaft, with the ability to remove in future. 
6 Possibly do this job, ie securing pintle in vertical shaft.
Well, we decided to do this job, but the most important thing was to make sure the pintle was in line with the rotation of the Vertical shaft. We also wanted, in theory at least to make it easier to remove the Pintle in years to come, so we wrapped the Pintle in cling-film as a ‘release agent’.
Cling film applied to the Pintle as a ‘release agent’.
We thought it might help to clamp wooden strips to the sides of the vertical shaft and measure from them to the Pintle, but there were too many irregularities in the wooden surfaces of the shaft. In the end we used a straight-edge against each side of the Vertical shaft and measured from it to the Pintle. We had refitted all the bolts loosely and slipped the iron ring into place. By tightening some of the bolts and inserting two wedges, we arrived at surprisingly even readings in line, although it was in no way possible to make it central in the shaft. This doesn’t matter, because we will make sure the Lantern turns concentric to the pintle, by adjusting the wedges.
We then mixed up Steenvas, an epoxy with a lot of ‘body’ and poured and worked it in down the cracks with a flat strip of metal.
Mixing Steenvas
As it oozed out lower down, we applied duct tape. I would have been happier if the Steenvas had been a bit ‘runnier’, but in the end we managed to work it in quite deeply.
Duct tape applied to prevent Steenvas from oozing out
Later on when the Steenvas had become quite firm, we withdrew the wedges, which had done their work and mixed up more and forced it in.
Wedges removed and more Steenvas forced in
In the meantime, we carried on with our action plan:
7 Align brake wheel. Turn sails and take readings from a fixed point perhaps at 10 places numbered around the cog face. Remove ‘keepers’ and knock in or out on wedges until the best set of readings can be obtained. 
8 Refit keepers 
Last time we had commented that the Brake Wheel was running out, causing irregular meshing of the cogs with the Lantern pinion. We had strapped and tied the Vertical shaft well out of the way so we could turn the Sails, Wind shaft and Brake Wheel. There’s a lot of traffic noise outside so we had a human chain passing messages to John outside, when to turn and when to stop. We marked 12 places equally around the face of the brake wheel and measured from it to the Sprattle beam:
First set of readings between the Brake wheel face and Sprattle beam
Steve drew up a chart for the readings, the first readings showing a 30mm run-out. Again the possibility of it running perfectly true was remote, especially as we had noticed there’s a wave in the surface. We set ourselves a target to try to halve this run-out. We were goint to jack between the sprattle beam and the brake wheel, but Pieter pointed out that all this would do would be to move the whole Wind shaft. He said that the accepted drill is to remove a wedge or two in the area where you want the Brake Wheel to move and to hammer very firmly near the centre where the clasp arms cross over:
Pieter applying force to shock the Brake wheel into alignment
We didn’t quite make it to 15mm, but we reckoned 17 was close enough:
Our best readings; 17mm run-out
Here is Secretary Steve’s chart, for the record (ignore the first column):
All the readings on Steve’s chart
We packed up at 5pm, having started just after 9, with a break at 1 for well earned lunch and think-break! Thanks to all who helped!
Article reproduced with kind permission of Andy Selfe
Original can be found here