In 2003, Bill had a large part of his pancreas removed, in an operation that ten years earlier would have been impossible. While “convalescing”, he designed and led construction of an unusual bridge. Off-site construction methods meant final build could be undertaken in about an hour, and without centring. Careful design and use of jigs meant even the off-site work could be undertaken using domestic tools and enthusiastic but non-professional labour. The words are Bill’s, originally posted on his blog, before he started BoM, and before Twitter even existed.

20th August: A fun job but a serious one

I am trying to design an arch bridge for use in a church service for the chaplains of the University of Exeter. The design constraints are pretty severe.
• It has to be built by amateurs
• It has to cost almost nothing
• The parts must be light enough to position by hand
• It must be strong enough to carry two people.
• It must be big enough to be seen from about 50m in a crowded Cathedral.

There are some bits that will need to fit pretty closely so it will have to be jigged if it is to work.

Arches don't like to be light. They need weight to deal with concentrated loads. The best solution I have come up with so far is prestressing with a lorry strap. I have put a picture of the design so far here. Each voussoir will be a box of 6mm ply with 50x50 timber for the main bearing pieces. The handrail pieces double as locators for the joints. I will add a 50x25 rail between them on top of the deck to provide a lip and a tread to prevent slipping. A tie over the top of the hand rail posts will provide a rail and also stress everything together to make it stable.

I will put wheels on the bases, but they will also need jack ups to make them level on an uneven floor.

Got a phone call on Thursday to say come in on Sunday and have half of your pancreas removed. Hope to be back here in about two weeks.

22nd September: A start

My colleagues, the Christian chaplains of the University of Exeter, have collected a load of second hand wood begged from the various construction sites on campus. We hope to have something like a bridge by Monday, and to have it beautified and decorated by the end of next week.

I think this suggests I am recovering, although an hour on my feet was enough!

24th September: A wooden arch, setbacks and progress

When an arch is to be built without mortar, the fit has to be perfect. Not an easy job for a group of amateurs. My right-hand man is Brian, a retired Quantity Surveyor who seems (to me) to spend an enormous proportion of his life supporting church work.

It is vital that the arch pieces fit together and form two parallel bands.

To allow for any slight misalignment of the saw (it is VERY difficult to get the blade set vertical) we alternated the direction of the pairs.

Carefully lining up the pieces produced a much more encouraging result and gave our first clear impression of the size of the finished job.

That took all morning, but at the end we had an arch that fitted.

Tomorrow I will need to re assemble it and set out the end angles for the abutments. I guess it will take an hour or so to get that to the state where I can relax and actually cut it.

Managed to get the abutments cut. they aren't perfect, but there is room for adjustment before the final fitup.

25th September: A small step for man!

Not a hugely productive day but I did get the angles worked out and the abutments cut. Laid out on the floor it begins to look like a biggish bridge.

The next step, and I hope the last difficult one, is cutting the spacers and getting the voussoirs set up parallel and square.

After that it should be relatively straightforward work to deck it and put on handrails. I doubt that we will get that far tomorrow. We will have to see.

The new workplace is somewhat cluttered. Brian managed to find room to work though.

27th September: Slow Friday

We began Friday by collecting a lot of spare materials from Canon Bruce Duncan, but when we got to the lab we found it in turmoil and full of equipment being moved.

We stacked as much as possible in the trailer and took it to my carport which is now full. That left me exhausted and I retired for a couple of hours.

At 1500 Brian came round and we unloaded and returned for the rest of the gear.

Not much to show for the day then. I think I must take a rest this weekend!

28th September: How to build a skeletal arch!

Sometimes you just need to sleep on things. I have been worried for several days about the problems of getting the two sides of each voussoir properly registered. Of course, the only way is to match build them, and preferably to build the whole arch rather than just matching pairs together.

On Monday, if we can find a flat floor to do it on I will set up the abutments, properly spaced, then fit sheets of ply along the outside where the arch faces are going to go. The faces can then be temporarily screwed into place and the cross pieces positioned in situ. It will also be useful to fasten on the deck while the vousoirs are up there to make sure things stay square and parallel.

That should be the last tricky part.

Thinking as I write, it might be easier to make a frame on which three voussoirs would sit properly aligned. Then we would build three together, move them along one and build the next one on the end.

I guess a photo is needed, but not till it has been done.

30th September: Real progress at last

This is how we jigged the voussoirs in the end.

This was the first day when Brian and I were able to work in parallel rather than waiting for each other. We got eight of the eleven voussoirs framed up (at last). The last three should not take long tomorrow.

We have been thinking about the problems of assembly by unskilled labour (students) and how the arch will be supported.

The cantilever idea is nice but allows no leeway. We have sketched out an idea but there isn't time to draw it. The main frame needs to be handed over to the painters in a couple of days or we will run out of time. That should now be OK though we will need some more wood to make frames for supporting the voussoirs and to tie the abutments together.

This has been a good day for me. My screwdriver battery ran out of steam before I did. I went to the surgeon's clinic without the rest I had promissed myself and still seem to be going strong at 8pm. Off now for a Pizza. A test of my digestive system.

1st October: Are the final knotty problems solved?

We got the first voussoir completed and got one abutment assembled. It is hard to think we will get to the horizontal in 5 steps!

Well, we have just a week to the service. Brian and I finished the day happy that we had worked out schemes for everything we need to do.

First we had to collect more wood. That encouraged us to get an abutment together to the point where we could hang a voussoir on it.

With two assembled it becomes clearer how the whole thig will go together.

Then it started trying to rain so we had to restack all the wood to get under cover. Luckily, because the faces of the abutments slope straight down we were able to slide our voussoir down to get it under the carport and continue assembly at a lower level.

Once we had two voussoirs in place it began to be clearer that we would end up with a bridge. It was also clear that the slope would be uncomfortable and we would have to make steps at least at the ends.

Fastening the risers to the lower edge of the handrail posts means that they rest nicely on the top of the previous voussoir and provide the vertical location we needed. The only thing left is to stop the cantilevered voussoirs from rolling off before the keystone is in place. By fastening a light chord to the top of each post, we can tie it back to the abutment and provide the moment connection needed.

Hope to get to the stage of having all the voussoirs up tomorrow before I go off to Bristol for a meeting and a rest.

We want to build the arch as a cantilever rather than the traditional way of putting in centring. That means we have to stop the blocks falling off till the keystone goes in. We need something to hang each voussoir on and something to hold it back. String from the top of the handrails does the latter.
The handrail post seen here is on the upper voussoir. It overhangs slightly and so forms a lip which fits over the edge of the lower one. By fixing the step riser to the back edge of the post it hangs well back over the lower voussoir and so makes a locator to stop slipping.

3rd October: Coming together at last

Brian worked on after I left yesterday and was back long before I returned today. That meant there was some serious progress for me to see when I got back. Brian had finished the voussoirs and fitted all the uprights and Felicity was busy painting them. This was the sight that greeted me.

Once four voussoirs were up it became clear where we were heading (the fifth forms half the bridge) we will cut the keystone to fit when the two sides are fully assembled. This setup confirmed the stability of the cantilever and of our assembly scheme with light rope tie backs at the top of the handrails. We may need to relieve the joints slightly to get things to assemble easily, but the general impression was excellent. I was very pleased to find that the edges of voussoir five were exactly plumb so we should be able to get things to fit as required.

There are a few bits and pieces to clear up in the other half, but there is nothing to prevent me finishing those in an odd hour over the weekend. The keystone needs to be cut to fit, unless I recut the abutments slightly. It is interesting that the first voussoirs cut, where the angles were wrong, almost fits in the current bridge.

Painting day is Monday. In clearing away this evening, I found that we could stack three voussoirs high under the carport. That means they can be painted like this, or at least restacked when partly painted and finished in the stack. If that is so, we can do the painting here at a push.

6th October: Looking good

The bridge parts have been painted today. The painting was undertaken by Felicity, Jacqui, Paul and Brian in a room in Engineering.

Tomorrow is the big test. At 11 we must raise the whole bridge and make the keystone.

I will have to reach a final conclusion on fastening the abutments together and levelling them. Then there is a rehearsal in the Cathedral on Wednesday and the big event on Thursday.

One hour to complete the first full assembly. We will need to be quicker next time.

Here is the first picture of the almost completed bridge. Just the keystone to cut and all should be well.

8th October: Rehearsal time

What an afternoon. Well, what a day. We began at 8am removing the bridge from the room which was needed for a class this morning. Then at 1pm I began the business of final assembly and removal to the Cathedral. Brian joined me at 2pm when we took the first abutment down. The round trip took fully half an hour so it was 3.30 by the time the last bits were there.

Then we had to position things and line them up and fix them, which all took longer than enough. Finally, we got it togethr, then took it down again and re-assembled it with the students doing the work.

The Cathedral staff were very helpful, lending trolleys, and particularly allowing us to leave the abutments in position till tomorrow evening for the service.

This picture shows the finished bridge carrying Paul and Bruce the two full time chaplains. The view is from just inside the west door so it shows the most distant view available.

10th October: All over

At the end of the service, there was much enthusiasm for climbing, but this pair saw the symbolism most closely.

There is always a slight feeling of anti-climax on such a morning. It's completed. The bridge is to be carried away to store today.

The service went well. Of course, I sat there redesigning details but I have said many times that details need sleeping on.

The photos are grainy (interesting feature of low light photography even with a digital camera). Two students wanted to make a symbolic meeting after the service so here are photographs of them climbing up and meeting.

When they met in the middle, far too few people noticed!
Still, they showed the bridge off well for my photograph.

Now I must get on with something else.

143. A bridge in Exeter Cathedral