The Non-Electric Chair #5: Cleaving Wood (part 1)

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Blog entry by lethentymill posted 08-25-2008 11:32 AM 1207 reads 1 time favorited 0 comments Add to Favorites Watch
« Part 4: In Which We Get Down To Work Part 5 of The Non-Electric Chair series Part 6: Cleaving Wood (Part 2) »

So far the tree has been felled and the trunk has been cut into suitable sections. The chair I am going to make is Project 15 in the Lethenty Mill series of furniture making projects; the back legs are actually 900mm high, so the sections of tree need only be 1m long (to allow for shakes and discolouration on the ends when dry), however I am going to play safe and go for 1100mm.

This blog installment is quite detailed, if you just want a quick overview of what I’m doing, have a look at the video clip produced to accompany this section.

Some trees are inaccessible to motorised equipment or are simply not worth the effort for a variety of reasons. Some of these trees are worth the effort of felling and cleaving. Why bother? Well I think I’ll just discuss cleaving or “riving” and let you decide.

First of all, chain saws…. Yes, they are good for this kind of small scale operation, but the chain fitted to a conventional chain saw has its teeth sharpened at the correct angle for cross-cutting not for ripping, so you need another chain saw for ripping or a replacement blade if you are going to rip along the length of the trunk. You can cut along the grain in cross-cut mode satisfactorily but the butt must be little longer than the blade, alternatively you can cut from both ends and join up by splitting it through.

Some years ago I bought a Forester chain saw mill and we were able to rip boards from butts which had collected in the yard but it was slow and required two trained operatives. I also installed an antique saw mill (see picture, right), which had a 42” Yankee (replaceable tooth) saw blade and was driven by a 28 horse motor.

Without explaining the inadequacies of these systems from our point of view, let’s just say that “Woodmiser” portable bandsaws were coming into vogue then and offered greater efficiencies. I sold the chain saw mill and we continued to use the antique saw mill for a year or so “to cut up the scraps” (i.e. I didn’t want to get rid of it – it had been a big job installing it, it was fun and it still worked).

So, for a small operation like ours – determined to use local hardwoods and commercially driven – hiring the Woodmiser was the answer when enough timber had piled up in the yard.
The narrow blade cuts efficiently with less waste than conventional sawmilling and when you are converting tree trunks with their round cross sections into narrow boards, waste really does matter. Sawmilling wastes more than half the available tree (well, it does in our experience). The trees are relatively small hereabouts and have not been grown in any consistent way, i.e. they have not been forested.

They can be knotty, twisted and bent. Once we dug out a horseshoe from an ancient Yew, but more commonly it’s the barbed wire that halts proceedings.

So, if sawing is about fairly predictable board production using available machinery then cleaving is about splitting wood by hand, using wedges and a sledge hammer – and the boards are not predictable! We are entering the territory of the sculptor.

Cleaving is an old fashioned way of doing it. Lengths of timber should be as short as possible – tailored to the job – but taking into account the difficulties of stacking and drying lots of different lengths of wood, it’s probably best to stay with a convenient length for all the pieces and cross-cut them later (so I opted for 1.100mm).

The froe is an ancient implement for splitting wood but is designed for splitting short lengths of no more than 300mm for roofing shingles etc.

The timber must be knot–free whether you are using a froe or wedges. It’s tempting to try splitting timber with a knot in it (I’ve tried it) and to cut a long story short – avoid knots!

So, now you start looking at timber in a different way, you look at trees in a different way. Instead of asking “How many planks can I get out of it?” you think “How many chair components can I get out of it?”.

Some Cleaving Suggestions: Leave the cut sections of the tree trunk for a few days and radial cracks will appear in the ends – these indicate the best way to split the log.

After putting on the safety boots and making sure you are standing on clear ground (no branch wood or loose stones), cut away overhanging branches. Casual bystanders will probably gather on the day to mutter and generally put you off. Dogs will tear around with long branches. Move them all to a safe distance.

Don’t try to do this without having at least three wedges. You will need a particularly sharp wedge just to get the crack started. Put the wedges into the side of the log not the end, one after another, as the crack opens up. Sometimes putting the wedges close together prevents the wood from splintering too much.

Don’t try this on a cross-section of greater than 450 – 500mm at least for a start. Oak and ash will be easier than beech or elm. Wedges need to be long, say 200 – 300mm.

Take aim by dropping the sledge hammer carefully on the wedge for the first tap or two and get your stance right before giving the potential chair any serious consideration.

A saw is handy to sever the fibres (splinters) that prevent the cloven wood from coming apart.
Try it and learn: Sawing with a machine is a controlled operation – you decide to quarter saw or cut through and through and then you start it up and do it. The boards are as you planned and as you expected. Cleaving is not like that; the tree dictates how you cut it, to an extent, but because of this the wood is more predictable – in the way it dries and how it can be used.

My objective was to get wood that was quarter cut but as this is also the way that the log wants to split as it dries – from the centre out – this is not easy. (For those who have done this before; a natural radial crack is also what bench joiners call a shake; a serious flaw which must be avoided – so there’s no point in studiously quarter-cutting if the billet includes a shake.) Compromise will be necessary, waste will happen; it’s just that quarter cut wood will be the most stable in the long run.

I will come back to this when I start to subdivide these ragged lumps – at least a lot of the stresses are now out of them and they can be transported back to the shed.

Cleaving Wood - Part 1

-- Allan Fyfe, Lethenty Mill Furniture,

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