We have a pile of pearwood discs around 10-12" diameter, bark still on. The y're starting to dry and cracking badly, cracking from outer edges running partway toward the centre. I take it the outer wood is drying faster than t he inner. How can I stop them cracking?
NT
Burn them
Jim K ;-)
hey're starting to dry and cracking badly, cracking from outer edges runnin g partway toward the centre. I take it the outer wood is drying faster than the inner. How can I stop them cracking?
Timber has to be dried at a controlled rate to prevent cracking. The end grain can be painted to help in this.
Timber shrinks as it drys. Cracks appear because the outer has dried too much before the inner,
A wood turner up the road from me waxes the ends of freshly felled timber he gets, so they can't dry out through the ends.
I suspect it's also important to dry slowly, at least initially, i.e. outside but out of the rain, and not in a heated house.
No, that is not the reason. The reason is that wood shrinks least along the grain (up the trunk) then least radially (the diameter of the trunk, and most tangentially or circumferentially.
Which is why wood warps cups and splits in the way it does as it dries.
How can I stop them cracking?
There is in fact only one way, and that is to soak them in a particular chemical - whose name escapes - me sold specifically for that purpose.
Ah. polyethylene glycol (PEG).
Otherwise section the logs and use the wood in parts, as described here.
I am afraid that wont work either. For sure even drying helps, but even drying wont eliminate the fact that wood is by its nature anisotropic, and shrinks differently in three dimensions. Up the bole, radially from heartwood to bark, and tangentially around the bole.
If its going to dry at all, it WILL split if its thick.
paint both sides in something that will slow the drying process. (there are propitiatory products for this, but vinyl emulsion would probably be enough)
ISTM that prayer would do if all you are after is propitiating the gods. Much cheaper.
IN the case of a lateral slice through the trunk, this will not work.
It only works with plank sawn wood, where there is a little more loss from the ends than the middle
Well I can assure you that nothing works except soaking in PEG.
When wood cells dry, they shrink at different rates in different directions.
It took many many years before people worked out how to create wood planks that did not split, and even then they still cupped and bowed and warped...
A bit late now but I think they should be in a moisture controlled environment so they dry out at a controlled rate.
I assume that they have dried out too quickly or too much.
Cheers
Dave R
too much. in that you cant dry wood *at all* without it splitting if cut that way
Thanks, I've been looking into PEG treatment.
NT
In days of yore timber was sawn radially.
Next best thing is quartering.
Most timber is just sliced these days. Hence the splitting and twisting. But speedy.
You have had a lot of replies but you need to know that wood has two stages of drying, the first down to about 25% is the cell water leaving, when this stage is finished you can blow or suck through the disc. Little shrinkage takes place up to this point.
The second stage is when water weakly bound to the cell structure is lost down to the equilibrium moisture content. This is when shrinkage occurs and as has been pointed out there is little longitudinal shrinkage but tangential shrinkage is more than radial shrinkage. The ratio of tangential to radial shrinkage differs between species but turkey oak is one of the worst.
So it is possible for the middle to remain full size whilst the outside is shrinking, this is exacerbated where the heartwood cells are filled with tyloses which hinder water movement.
Also woods that have radial weakness because of prominent parenchymous tissue (rays) will tend to pull large single cracks.
Softwoods absorb the stress internally better, I have some coasters I cut from douglas on one of my first thinning contracts that are still whole with bark intact with no special treatment.
As humidity changes boards cut through and through will cup the further from the centre they come from, those on the radius will just shrink a bit more at the outside invisibly.
I'm a bit surprise that pear should crack badly as it is both diffuse porous and with homogeneously distributed small parenchymous tissue.
So you may be suffering more from differential drying than the effects of differential tangential to radial shrinkage.
The thing about seasoning is that moisture needs to leave the surface at the same rate as the slowest parts to dry can migrate moisture to the neighbouring part.
If the discs are cut in mid winter they dry slowly initially whereas in the summer the surface dries too fast.
AJH
Talking of quarter-sawn timber...
Being the cheapskate I am, I've generally been able to buy my musical instrument making wood from fairly common sources and then stored it until it's air-dried to the standard of ready-to-use tonewoods. For instance, the last lot of mahogany I bought: I selected the sliced planks that were accidentally on the quarter and took them out of a pile of other planks.
I'm having trouble finding quartered softwood in common situations: I suppose nowadays the sapwood is stripped off for manufacturing boards as most of the planks I see are the more pest and rot resistant heartwood.
I found a couple of random "Railway sleepers" from B&Q were cut on the quarter but they had been pressure treated and I don't really want that. Does anybody have any suggestions for finding softwood boards that will be priced at normal prices but might include occasional accidentally quarter-sawn timber that I might select out?
Perhaps I ought to add that I only use the odd plank or two at a time: I don't need a lorry-load!
Nick
The simplest way might be to buy a wide section of decent softwood e.g.
2"x 8" and slice it down the middle. A waste of an expensive cut, but it would give you the equivalent of a quarter sawn 2"x 4"In message , Nick Odell writes
Any trunk slab cut with a band saw will have a few *radially* cut boards. Undoubtedly the saw mill yard manager knows this and may be financially persuaded to part with some:-)
My cousin has made a few violins. The selection of materials and their subsequent treatment appears close to a religion:-)
That's the sort of thing I'd be willing to do. The equivalent doubling up of the cost per length is still a much cheaper option than buying purpose-cut. Most wide boards I've looked at seem still to be heartwood (from bigger trees) and if they don't go right through the centre you are more likely - using your illustration - to get two 2x2s to use and throw away the middle 2x4.
I wondered whether certain grades of scaffold plank would be any good but I'd been unable to find out much visually because of the metal strip at each end.
Nick
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