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In defence of green oak


People often ask why it is that we make oak frames out of freshly sawn green oak with a high moisture content rather than using more stable dry oak.

Well, having laboured hard this week over a small glazed gable frame made from bone dry oak, I’m feeling well placed (and motivated) to answer.

BECAUSE IT’S EASIER!

Green oak will bend to your will, cleave along the grain, respond compliantly to a reasonable sharp chisel or saw, and pretty much do what you ask it to do. Air dried oak on the other hand will sap your strength, blunt all your tools in a heartbeat, mess with your mind and leave you weeping on the workshop floor in a dusty heap.

Here’s the fruit (dried?) of my labour:-

Oak Frame Gable by Castle Ring Oak Frame

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Jack Rafters


Rafters usually span from the apex of the ridge to a connection on the wall plate and are designed to support the roofing material – slate, tiles, shingles etc. When a roof has hips, some of the rafters are shortened to land on the hip rafter – these are called jack rafters. They can either be designed to attach into the side of the hip rafter, or to connect to an opposing pair on top of the hip rafter.
Either way you are going to have to get your calculator out, dust it down and remember how to operate the trigonometry functions.

If only I’d paid more attention in maths lessons at school all those years ago. I didn’t realise that it was actually going to be useful for something one day!

Check out these douglas fir hip rafters on our new cartshed.

Castle Ring Oak Frame

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Waist Rails


Half timbered oak frames

Waist rails are the horizontal timbers that span from stud to stud and are more commonly seen in half-timbered frames. They break up the long vertical infill panels into more manageable chunks for wattle and daub or brick infill, whilst at the same time showing off to your neighbours how much oak you have in your frame.

Oak Timber FrameFun to do in the workshop as it’s an easy joint to cut and you can churn out dozens in a day. Putting it all back together again can take a little head scratching though…….

Castle Ring Oak Frame

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Rebating


The issue of glazing oak frames is one that can keep timber framers busy arguing into the wee small hours. Of course the problem begins and ends with the nature of oak timber – it’s cut and jointed when it’s green and easy to work, but will shrink and may twist as it dries out over time. Is there a glazing system that can cope effectiveness with such movement and uncertainty and keep the British weather out?

Oak Frame Eco House

Rebating the oak frame to accept the double glazed units is one of several glazing methods employed. As you can see from this massive gable it is very fiddly and adds considerably to workshop time. Definitely time to switch the music off and concentrate hard!

Oak Framed House

Can’t wait to see it up though.

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Cheeks and Shoulders


Cutting cheeks and shoulders. Sounds like something you’re more likely to hear at the abattoir than in the workshop.
No blood involved however – at least we hope not!
A frame is made up of hundreds of joints and machining tenons is a repetitive task that we can almost do in our sleep. Nowadays a fancy dan hand held circular saw is the quickest and most accurate tool for the job.

Castle Ring Oak FrameConfidence and commitment are a must when plumb cutting the cheeks vertically, the ability to cut to a line essential for the shoulder cuts.

Rob Dawson Castle Ring Oak Frame

Rob Dawson – Castle Ring Oak Frame workshop

 

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“Shrinkage” – don’t be alarmed‏!


Green Oak and Timber Framing

Timber framers work with green oak because it can be sawn and chiseled easily. Dry oak is merciless and will blunt your edged tools as if you were cutting through metal.

The down side of using wood with a high moisture content is that as it dries it shrinks. Not only does it shrink, but it shrinks in different directions – tangentially (lots), radially (quite a lot) and longitudinally (barely at all). What all this technical stuff means in lay terms is that timbers will invariably develop big splits or shakes, and in addition will twist and cup to varying degrees.

Green Oak

It’s an important part of the framer’s job to be aware of likely movement and shrinkage so that the timbers can be selected and oriented appropriately. In this way the structural integrity of the frame is maintained.

The cracks can sometimes look alarming as they appear, but rest assured, they will settle down, and one of the many extraordinary properties of oak is that as it gets older it gets harder.

Green Oak

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Sand Blasting


Picking up where we left on the last thread…. Your beautiful (and expensive) oak frame which you have scrimped and saved for years, or even decades for, is standing proudly to attention for all passing traffic to see.

Everything fitted, the groundworks miraculously matched the frame, joints are tight…..and yet the damn thing is covered in unsightly staining from mud, water and metal reacting with the tannins in the green oak.

Sand blasting the frame with grit particles is the most popular method of returning the timber to an even clean finish and is carried out by a specialist.

Sandblasting oak timber frameThe grit is blasted at the surface of the oak removing a thin layer and a pale finish – care must be taken not to get carried away otherwise your frame will end up looking like a pile of driftwood in a seaside pub!

Even more care must be taken to make sure your sandblasting contractor is using the right grit that contains no iron particles. Iron blasted at high pressure into the oak will turn your oak, and your mood, quite literally, black!

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Tusk Tenon


The tusk tenon is a useful joint to choose when you need to connect horizontal timbers (such as in a floor layout) without weakening either beam too much. The tenon extends from some point up from the bottom surface, usually at the central or neutral axis of the beam into which it will locate.
Castle Ring Oak Frame tusk tenonsThis is all about preserving continuous beam fibres at the top and bottom of the morticed beam. What does “continuous beam fibres” mean? It means your house won’t fall down!The upper shoulder is cut at an angle to increase the strength or “shearing” area of the tenon, along with a “step” below the tenon for the same reason.

Castle Ring Oak Frame timber frame tenon

The great thing is that once the joint is assembled you’ve no idea it’s there.

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