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The MA thread - AKA Everyday Fan Vault Construction for Beginners.

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Adam W.

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Currently looking for inspiration, so I've been looking at timber vaults and I've found some proper beauties.......

Ely Cathedral Lantern.jpg


Ely.

Ely-Cathedral-Octagon-Lantern-Tower.jpg


Lantern support at Ely.

St Albans.jpg


St. Albans

Winchester Abbey Timber Fan Vault.jpg


Winchester.

Winchester_College_Chapel_ceiling.jpg


Winchester College.

I've been offered a mentorship with the head mason at York Minster, who's agreed to teach me the finer points of fan vaults. It's too good a chance to pass, so I've signed on for another year of head scratching at the City and Guilds. Currently I'm attracted to the design of Winchester, but I'd like a bit more tracery.

Although the whole thing is exceptional, I don't think there's space for it in the studio.
 
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Adam W.

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So, after a night of fan vault nightmares, I have decided on the purest form of English fan vault from Winchester Cathedral.

Winchester Cathedral Timber Fan Vault.jpg


This design is based on a Norman arch, where the structural ribs are identical and curve in a single radius from the corbel to the compression ring at the apex of the vault.

The studio where I'm planning to construct it is not huge, so I'll have to scale things down. This should make it more economical, but won't have an impact on the challenges of its construction.

I'll initially make a quadrant of the vault, omitting the odd short rib, so that it occupies one corner of the studio to give me enough space to chop wood. It also means that all of the design is included in the project and that I can stand under it with it sweeping above my head.

So that's three of at least a million questions answered and I'm on my way.

Now I just need to figure out how to build it.
 
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Trainee neophyte

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Speaking of churches, I showed your stunning frame to a Catholic priest (somehow that sounds wrong), and he immediately asked if it was for sale.

On the offchance that you actually wanted to sell it, as opposed to use it to frame a photo of a cute kitten, I might have a buyer for you. It would be on show in central London in a rather splendid old church (well, I think it's old - I've never actually been in it). Feel free to say no.
 

Stevekane

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I guess that lot is just sitting on the four corbels with the compression ring taking the presure of it all? Its a very clever bit of work and I bet it gave the original carpenters a headache too,,,like a monty python sketch “he wants what” rolling eyes!
 

Adam W.

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It's a clever bit of timber engineering and I'm really looking forward to getting stuck in.

I think I've got it figured out and I'll frame it upside down on the studio floor. That way it'll stand alone with a couple of props and I can carve and fit all the ornament at my leisure. Then I'll number it, take it apart and reassemble it the right way up.

The first thing is to mock up one of the nodes to get all the joints and the boss which covers the node right. I'll do that in pine with a roughed out lime boss and attach a bit of the tracery. Once I get that right, it's just a matter of knuckling down and getting on with it.

It'll make a nice change from all the fiddly work on the chest and tabernacle frame.
 

Orraloon

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Congratulations on the offer. It's good that some of those skills are being passed on and kept alive. So far above my skill level I can only quietly admire.
Regards
John
 

MARK.B.

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Good news about the mentorship , the ceiling vaults look awesome and even scaled down will be a enormous amount of work but i think given your previous projects that you will knock one up in a week or two ;). Looking fwd to a pictorial write up on this project(y)
 

Adam W.

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So I've been doing a mock up of a node and boss and I'll have that joined tomorrow. I'm going to try and fix the node with a single peg from the back and drawbore all the pieces together at the same time.

Meanwhile, I've settled on the designs for the bosses, which is the main carving element of the project and I'll be using St. Mary Redcliffe church as inspiration.

The ceiling in St. Mary Redcliffe is particularly beautiful and well worth a look if you're in Bristol.

The bosses will all be foliage or leaf and berry, with the elements being connected by a vine. I'll have different designs using the designs from one part of the church. I might make double of each design to speed it up.

I've got about 19 bosses to carve, so I should be chugging along nicely after doing a few. I'm hoping to get the bosses done before I go to York, so all I'll need to do is draw it and concentrate on the carpentry for a few months.

Here's some of the bosses, I think they are lovely and they should look good in miniature. I'm carving them in walnut, using silver leaf to gild them with and they'll be about 5" in diameter and 3" deep.


Boss 4.jpg




Boss 5.jpg




Boss 6.jpg
 

pe2dave

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Saw that and thought ... what angles.... 3 dimensional....
and quickly moved on.

Bosses aside, that could be an intriguing project...
I was up in York when they were making the bosses after the fire. Sheesh.
 

Adam W.

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I've finally got the moulding on the rib to something I like.

I found it in a book called Pugins' Gothic Ornament as part of a drawing of some stone bosses from York Minster.



IMG_4715.JPG


I'm using some pre-loved Scots pine joists as a kind of sketchbook and just trying different types of moulding.

I need to keep in mind that the main ribs are curved, so the moulding needs to be simple as I have to make radiused planes or big profile shaves to cut it.

This one is made out of 2" by 4 1/2" and it takes 5 planes to cut it. The shop made planes will need to cut one side of the moulding in one go and I'll have to make a pair to account for the change in the direction of grain along the curved rib.



IMG_4712.JPG


So working down the planes in the photo above:
The 14 round cuts the cove on either side of the bead. The original is a complex radius of a 14 and 10, but I'm having everything as a single radius for ease.

The 8 hollow does the bead, which is a bit tricky as it's easy to cut it too small.

The quirk does the shoulders of the quirk. I've never seen one before and it came up on ebay when I was looking for radius planes and I thought it would be good for something. And it is, it's good for quirk shoulders, so I call it a quirk. Masons use a quirk to cut these mouldings and I do too.

Snipes bill for starting the rebates on the chamfer of the cove to make a track for the 14 hollow to ride in.

Rebate plane for the rebates.


Once the moulding is cut on straight sections the node is mocked up so that I can work out and scribe the joint and the boss is plonked on top to check the proportions.

So when you look up, the moulding is just seen as a collection of lines made of highlight and shadows.



IMG_4718.JPG


I quickly turn the boss to 4" ø before carving it, as it cuts down on the chopping out. I'll have to trench the bottom of the boss out so that it can slide along the rib, as it's part of the joint and holds the node together.

It has some sap on it and that will get carved off or gilded over, as I don't want to see it when it's finished.

IMG_4717.JPG


I should have the whole joint together tomorrow. That's the plan anyway and I'll have sorted quite a lot of the questions out about the joint and be on the carving.

I've got a slot in this years MA show in October, so I need to have something to put on the wall to drum up interest in the project.
 
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Adam W.

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So I've decided to go with some very basic timber framing joints to keep it as simple as possible. The complicated stuff is at the top of the ribs where they meet the ring and I'll possibly be using lap dovetails at that joint.

The rail is scribed to the moulding of the rib and there's a stub tenon in a blind mortice. This keeps the rib at maximum strength and the mortices are around the neutral axis of the rib. There's minimal loading on the fan vault anyway, but I don't want to weaken it as it's a long single curved piece.


IMG_4723.JPG


The scribing of the bead is of no concern, as it gets covered by the boss so I've just cut it off and pared it away if it's preventing the joint from closing up.


IMG_4721.JPG


I'm relying on the spring of the rib and the whole rail to create compression at the joint to keep it snug. It closes up ok for a framing joint and there's no need to be retentive about it, as the polychrome will fill the gaps.

When I get to York, I'll take a look behind the scenes on their timber vault to see what the joints are and it may all change.

This is intended as a preamble to get a few things sussed and there will be an increase in complexity towards the final framing of the vault, as I add more and more complications into the mix.

This is the kind of arrangement that's on a coffered ceiling.


IMG_4722.JPG


I've started on the boss and have made a paper template to position the housing joints for the rail. These need to be very precise, as they determine the angle where the rail meets the rib and in this case its 90º.


IMG_4726.JPG


So all I have to do now is cut the housing for the rib and rail and it's time to carve the thing.
 
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MARK.B.

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Would be worth a day trip ( remember when yer mam and dad bundled you into the car and put a fiver in the tank :sleep::D) out to York, word is a bloke called Adam can show you the good stuff ;);).

" So I've decided to go with some very basic timber framing joints to keep it as simple as possible."
Pressure getting to much huh :LOL: na'h just kidding my friend ,please do keep the pics and info ( the work around's are my favourite bits) coming,besides i have nothing better to do with my time o_O:LOL:
 

Adam W.

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Bear with me, it's guaranteed to hit the fan shortly when I introduce some curves and compound angles.

Luckily I have two master masons on my side. One from York, who we already know about. The other is Heather Newton from Canterbury Cathedral, who is responsible for egging me on and getting me into this predicament :winky !. Luckily, she's also the new Head of Carving at the Art School and is responsible for arranging the mentorship at York, so I'm in very good hands.

Edit:
There's also a rebate which holds the curved timber web to think about, but not today.
 
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Adam W.

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So that was last week and seeings this week has started, I've been looking at the shape of the vault and have some questions to answer.

Initially, I thought that the vault was a segment of a very large circle resting on the corbel and ending at the compression ring and that the arc was a single radius, as it would be if it was a part of a circle.

So I started to look at the theory of parabolic conoids, masonry arches and stuff like that. And came across a theory by a chap called Hooke, who was a contemporary of Wren. (That's 17th century stuff but the fan vault was a 13th century and onwards thing).

Hooke came up with a way to describe the perfect shape for a self supporting arch with no thickness.

"As hangs the flexible line, so but inverted will stand the rigid arch."

I'll try and explain what it means and it involves a chain, no computers in those days.

If you suspend a chain between two points you make a catenary. A catenary has gravity acting on it, so it hangs down in and forms a uniform curve, called a catenary curve (I'll assume that the chain has a uniform thickness and weight for simplicity, no need to over complicate things which are already a bit complicated).

This curve is called a hyperbolic cosine (a bit like a parabola). There's a formula for those, but I'm not going to use it, and I reckon master carpenters and Masons in the 14th century didn't either, but they could have used a chain to plot the curve and experimented with smaller vaults before doing the big stuff.

Below is Polenis' drawing of Hookes' theory.

Hanging-chain-analogy-Polenis-drawing-of-Hookes-analogy-between-an-arch-and-a-hanging.jpg


At the bottom is Hookes' chain catenary, which is under tension. When you make it rigid and flip it up about axis DE you get an arch which is under compression, due to gravity.

This is Hookes' perfect arch and it describes the precise load path for compression forces acting on the arch. Notice it doesn't get to be vertical at the ends BC, that's an important thing. All the timber vaults that I've looked at have a single piece of timber where all the ribs come together and load the corbel. The rest of the vault without that piece of timber look like Hookes' arch.

If you build an arch of masonry with no mortar, it has to contain all of Hookes' hyperbolic cosine catenary curve within the depth of the masonry, otherwise it will collapse into a heap on the floor.

So this weeks question is;

Did the carpenters and masons who built this stuff in 1400 know all about this before Hooke described it?

Actually there's two questions.

And;

Do timber vaults need to pay attention to this like masonry vaults do ?
 
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