Coppice Timber Drying?

[chipmunk]

Yesterday I visited The Stott Park Bobbin Mill in South Cumbria.

Someone's put a video tour here...
http://vimeo.com/6794145

It was a really interesting trip out, albeit pretty expensive (£6 for a 1hr tour, £3 for the carparking), for a turner but one thing really caught my attention and I wondered whether anyone had any wisdom or insight into what/why/how...

The coppiced timber (birch, ash, alder & sycamore) in relatively small sections (up to about 4" diameter stuff) was cut into about 2' lengths and then had a few ribbons (it looked like 3 or 4) of the bark sliced off with a draw knife along their length to apparently speed up the drying, make it more even and to stop end splitting according to the guides. This was done by young lads originally!

It seemed a neat idea but I've not heard of anyone doing it before for branchwood but it must have helped otherwise they wouldn't have bothered doing it.

Does anyone use it and how/why/what please?
Jon

 

[Richard T]

It's new to me - I'm surprised that they used coppiced poles like that for turning - much better to use stuff from wider stock but maybe it was a plentiful source and had to be treated with so much drying care.
Very interesting film. Pity I can't lip read though ...

 

[tekno.mage]

I haven't looked at the video, but wonder if the name of the place gives away the reason - you say it was a bobbin mill. If so then I can understand why they were using branch wood. Bobbins usually have a hole down the middle so the pith would get drilled out, and the bobbins would be less likely to distort after making if turned from branch wood. I've made bobbins for a friend and these used hazel & birch branch wood successfully. Using branch wood would probably also keep the price of the materials down - branchwood is less useful for making other things (like construction timbers, furniture, bowls, etc) so was probably cheaper (and easier to harvest?) than larger pieces of wood.

 

[Phil Pascoe]

That makes sense because if you think about it the trees used grow fairly upright. There would be minimal distorsion in shape when they dried. There wouldn't be much difference in stress from one side to the other.

 

[chipmunk]

As Phil says this isn't branchwood, it's coppiced timber which will be close to vertically grown with a minimum of reaction wood.

... but the question still remains whether the technique of removing a few ribbons of bark would help in the drying of branchwood.

I can see that it would speed up the drying process compared to leaving the bark completely in-tact.

The part I'm struggling with is the reduction in end-splitting - not sure whether how or why this would be achieved.

All of the bobbins are effectively spindle turned (grain lengthways). If you watch the video you'll see that smaller bobbins were made from cutt-down "cakes" which are disks of cross-cut logs, roughed out with a hole-saw type cutter. The larger bobbins were made from whole lengths of coppiced wood with the pith in place.

Jon

 

[tekno.mage]

I used the term "branchwood" erroneously - meaning coppiced timber (or indeed the trunks of very small trees) as opposed to actual branches sticking out sideways from the tree (which often don't have the pith very central due to the stresses they are under).

I'd imagine that stripping all or some of the bark from branchwood or coppiced wood would help somewhat in drying without splitting - and if you paint the ends of your cut branches with PVA as well, this would help even more. Having said that, it may well depend on the type of wood and other factors (like where and how the branch grew) how much it would help in avoiding splits.

I've dried branch wood in a variety of ways and found that the type of wood and speed of drying are the most significant factors in whether the branch splits or not. I've had reasonable success with ash branch wood, less so with yew, and poor success woods like holly, cherry and hawthorn which really need splitting through the pith before drying to minimise splitting.

My preferred method of drying shorter branches is to paint the ends with PVA and bury the pieces in a large tub (dustbin size or bigger, no lid needed) full of wood shavings, leave them in a barn (cool ventilated place) and forget about them for a year. The woodshavings stop the wood from drying out too quickly.

 

[chipmunk]

Thanks Kym,
I also dry quite a lot of branchwood but haven't tried the shavings idea to slow down the drying.

With some woods like holly and sycamore I'd suggest that slowing the drying is probably not a good idea at all since it could encourage blue stain and spalt to set in and I wonder whether this may be why the shaved bark is used to actually speed things up. I've also had trouble with silver birch spalting on me in the past and this was a favourite material in this mill so there may be a link here?

It may be "stating the bleeding obvious" but they didn't coat the ends of their logs with anything :wink:

I like turning hawthorn and yew too and in big sections I know from bitter experience that it's tricky to dry without too much checking. Splitting can also a pig with these two so I tend to use the chainsaw or bandsaw to cut them down through the pith if they're thick enough.

Jon

 

[tekno.mage]

Hi John,

I've not had problems with staining or spalting unless the wood has been left lying in a wet field for a while after felling! My last batch of holly was great because my partner felled the tree and we were able to process it immediately - which resulted in nice creamy white pieces, no splits - but a lot of distortion. Previous batches of holly I've had (from other people) were stained (but not spalted) as they had simply stored the logs in a pile undercover

Stripping off the bark would probably help prevent staining/spalting - as wood keeping the peices propped upright (on end stood on a clean plank) rather than lying them down.

If you are going to use the drying in shavings method - make sure you use pale clean shavings (ie sycamore, ash etc) to avoid staining. I usually use the shavings produced by the chainsaw when my partner cuts up the wood into more handle-able pieces to dry the pieces in.