How do you raise a cap?

With difficulty! There should be a word for fitting rafters to to make a windmill cap roof..... Well, if it's good enough for barns, it's good enough for windmills; so I'll call it raising. Anyway, that is the stage we reached today. We have trial fitted the ribs in place, using a temporary pattern instead of the actual finial (we'll leave that challenge until we assemble the cap for real on-site). This was a tricky procedure, especially for the first few ribs, but the more we added, the easier it became. By the end of the day, we had all the tenoned ribs in place - that leaves us with the tapered ones to fit in-between.

Wow, it's starting to look like a windmill

Other items from the previous few days:

The braces for the truck wheels have been finished and fitted;

Two of the four new truck wheel braces

and we have made a start on the storm hatch and neck block

Starting the storm hatch; the weather studs fitted to the weather beam

The old neck block (supports the bearing for the windshaft), doesn't look too bad from this angle

From beneath, doesn't look quite so good!

Starting to make a new neck block

Sunshine, and some more framing

Hoorah, dry weather. With the basic cap frame set up and lowered back onto the cap circle, attention has now turned to the additional frame members. The two diagonal braces between the weather beam and shears had somehow escaped the decay which affected the other beams, so we have reused these and fitted them into place. We have also reused the central block between these two braces, and made two new 'closers' which fill the gaps either side of this.

Diagonal braces fitted

Presumably, these braces originally helped spread the load from the weather beam to the cap circle, as well as stiffening the frame to resist thrust from the sails.

The cap is kept in position laterally by cast iron 'truck wheels' which rotate against the inside of the curb. Four of these were hung off diagonal struts running between the outside of the shears and the cap circle. We are having to remake these, as the originals had, you guessed it, decayed.

Making one of the new truck wheel supports (shown here upside down); lapped dovetail will fit into cap circle

Cap framing in the rain

Having chosen to build the cap outside, we are having to work in (brief) windows of fine weather. The sprattle and tail beam are now morticed in, so the basic cap frame is together.

The sprattle and tail beam in place

Closer view; with wedging space on the sprattle

Oh, it's raining again. What a change.

At least we've got the hang of arranging the tarpaulin now, so we don't have an olympic sized swimming pool to drain off every morning.

Heavy cap timbers

As promised, a further update on the cap construction....

Having taken delivery of some rather hefty sections of oak, we are now in a position to start building up the main cap structure. First up, the two large beams which run front to back in the cap, the 'shears'. Here we see one of the shears in position, being cleaned up prior to being notched over the cap circle. Large timbers call for large planes!

Shear being cleaned up

With both shears cleaned up and notched into place, next came the transverse beams. The next photo is looking from the front of the cap towards the rear. So, we have, from front to back, the weather beam, sprattle beam and tail beam.

The weather beam and tail beam will support the front and rear ends, respectively, of the windshaft. The sprattle beam is effectively in the centre of the mill and will locate and support the top end of the main upright shaft.

The next two shots show some detail of how these beams are located in the shears.

Dovetail joint between weather beam and shear

Tenons at ends of weather beam and sprattle

The tenons on the sprattle (upside down in this shot) are cut to allow for wedging of the beam into position. This gives some scope for adjustment, so the upright shaft can run true. In contrast, the tail beam will be a direct fit. So, next job, morticing..........

An update on Cap progress

The scaffolding has gone, the temporary cap is still there, despite the weather, and we have retreated to the relative comfort of our workshop. After a brief hiatus, we have progressed with work on the reconstruction of the cap, so here is an update.

Much of the timber in the cap was too far 'gone' to be reused. However, some of the ribs have been brought back to life, with splice repairs.

The first task was to build the foundation of the cap; the 'cap circle'. This was made in a similar fashion to the curb, with curved oak segments butted together and joined with recessed metal plates. This was built upside down, to allow us to fit the metal track on which the cast-iron wheels (trolley wheels) will run as the cap rotates.  Many of the original sections of track were reused. However, a few new pieces had to be made to match, as some of the originals had been excessively distorted as the decaying cap had sagged. These were not flimsy pieces of metal, so this hints at the total weight involved.

Joint of cap circle segments, with track also shown

The whole cap circle, upside down at this stage

Next, we made a smaller version of the cap circle, which will hold the trolley wheels. These were made of elm, which should cope with the large cutouts. Again, the segments were joined with ironmongery.

Bearing cages overlaid on cap circle

Once we were happy with this set-up, the cages were removed and the cap circle segments were turned over the right way, to allow us to start fitting the ribs. These were morticed individually, hopefully at the right angle so everything will come together at the top. Each rib comprises a lower and upper part, joined together to give a reverse ogee curve. The top end of the ribs fit into a rather cramped arrangement at the finial, with every other rib morticed in, and the others fitting in-between.

A lower rib section, with splice repair, morticed into the cap circle

The lower part of the finial, morticed ready to receive the ribs

Getting up to date, we have now moved onto fitting the main timbers of the cap structure. More of this to follow in my next blog entry, coming soon......

A temporary cap

Now that the curb is finished, we have been building a temporary roof for the tower. This will keep the weather out, allowing the scaffold to be taken down. We will then move on to the rebuild, off-site, of the cap.

Starting to board out the roof. Excuse the soulless OSB, it is only temporary!

Boarding finished, and felt going on.

The finished roof, with chicken wire under the eaves, to keep the birds out and still allow ventilation.

Curb complete!

Over the last few days we have been finishing off the curb and fixing it into position. Here are a few photos showing the developments..... 

 

The curb, with metal track let-in. This acts as a 'ball-race' for the rollers which will allow the cap to rotate into wind. The large nut just inside the track is for one of the holding down bolts. Inboard is the guide ring, which, er, guides, the cap as it rotates around the curb.

 

Under the curb, showing a holding down bolt concreted into the masonry. The curb is temporarily propped up, to be lowered later, sliding down these bolts. This method allowed us to tighten the various bolts/nuts holding the curb and guide ring sections together, prior to these being 'lost' under the curb when it was lowered.

Ready to be lowered

Lowering on three chain hoists simultaneously, onto a bed of mortar. Note the lack of overalls due to working in the 'greenhouse' section of the scaffold, in 25 degrees heat.

Level and position checked, the curb in its final (we hope!) position.