Dessicant for drying larger bowls

[Bill Bell]

I recently acquired some dessicant to try drying some rough-turned green bowls; something I've not done before. I read somewhere that this method doesn't work well on bowls over an inch thick. A couple of my recent bowls are in the 14 -15 inch range and based on the"10%" principle for thickness of rough turnings, I left these at about 1.5 inches of thickness. Has anyone had experience using dessicant to dry bowls of that thickness? (Wood is very green walnut, BTW) Also, when using dessicant to dry, should I expect the same degree of warping that I typically get with air dyring? (I usually just seal the end grain and let the bowls sit until the weight stabilizes.) Thanks for any advice.

[Neil Strong]

... based on the"10%" principle for thickness of rough turnings, I left these at about 1.5 inches of thickness.



The 10% is a general rule.

Some woods need a bit more and some don't need so much.

If you know the radial to longitudinal shrinkage ratio of your wood you may be able to reduce the thickness of the pre-turned blanks.

I turn a lot of blackwood that grows locally and it requires less thickness than the 10% rule to accommodate warping from wet -> seasoned.

Warpage is a property of the wood and will be about the same for any one wood species regardless of the seasoning method.

The main difference between the seasoning methods are:


Loss rate due to cracking
Speed wet -> dry
Effort involved
Cost involved

The other 10% rule that I work on is the ratio of losses to usable blanks. I expect a 10% loss rate and only put more effort in if I'm getting more loss than that.

My so-called method...


I begin by just adding the pre-turned blanks to the pile of wet shavings on the floor.
Next day (or so) I put the wet blanks in cardboard boxes nested in wet shavings
Check after a few weeks to make sure that they are not going mouldy/moldy
Mould is more of a risk during our wet winters here, but summers are very low humidity
Bark is the main source of the mould but I invariably end up with some of that in the shavings
Rebox blanks stacked together without shavings when almost dry to touch
Forget about those boxes and final turn some of your previously pre-turned but now seasoned blanks.
Later I might stack the pre-turned blanks on open shelving to save space




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[Brice Rogers]

I turned some red gum Eucalyptus and it REALLY REALLY shrunk in one dimension. I started with an eight inch bowl and ended up with a 6 x 8 bowl. There wasn't enough wood left to make it round.

[Neil Strong]

I turned some red gum Eucalyptus and it REALLY REALLY shrunk in one dimension. I started with an eight inch bowl and ended up with a 6 x 8 bowl. There wasn't enough wood left to make it round.

Sorry to hear that, Brice.

The radial:longitudinal shrinkage of redgum can be quite high. Railway sleeper sized ones are used here in garden retaining walls and you can see some rather bent and twisted ones at the landscape suppliers that nobody wants to take!

I'm a bit spoiled with Red Gum (E. camaldulensis) here. I put a hoard of it aside 40yrs ago from what was being delivered to us back then for firewood ... some of it was very large stockyard fenceposts that were at least one hundred years old at the time, so as seasoned as it would ever be.

With age Redgum can become a deep rich colour that highlights the grain patterns. A few examples...


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The wood that had the largest radial to longitudinal shrinkage ratio that I've used was Irish Strawberry (Arbutus unedo). A bit of a challenge, but if you worked with its tendencies, rather than against them, it could be a delight...

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[Dave Mount]

I recently acquired some dessicant to try drying some rough-turned green bowls; something I've not done before.

What is it you're trying to accomplish using dessicant? Faster drying?

With thick-walled green bowls intended for twice-turning, the usual issue is trying to slow drying, not speed it up -- it's why you put sealer on the endgrain.

All dessicant does (AFAIK) is reduce the relative humidity of the surrounding air. The purpose of putting bowls in bags with wet shavings as Neil described is to increase relative humidity around the bowl, as that slows evaporation, which slows drying, which reduces checking, because the wood on the surface wood doesn't shrink a lot faster than the interior.

In thin bowls, having the surface dry too fast and check because the interior is still swollen isn't a problem (or is at least less of a problem) so you can withdraw moisture quickly without problems. Trying to speed the drying of thick-walled bowls by reducing the RH of the surrounding air speeds surface drying and causes the same checking problem we're all working so hard to prevent.

The exception would be if your shop environment is so humid that the equilibrium moisture content of the wood is unacceptably high, but that seems unlikely.

Best,

Dave

[Edward Weber]

+1 on that Dave.
I've had this come up every once in a while at another forum and I always advise against it.
It's typically hard enough to control the drying of wood normally. Trying to speed up the process is usually asking for trouble.

[Prashun Patel]

If you use a dessicant you will likely need to refresh it every so often.

I turn everything bigger than 6” diameter to 1” thick. Wax and time are the best for me. I also leave my bowls in the garage for a few weeks after roughing out before transferring to a dryer region like a basement.

Last I will say that in practical terms I usually come into green wood in semi frequent batches. This is to say, there is usually a long enough queue after about a year that there is little reason to actively dry stuff faster than a year.

[Neil Strong]

Bruce Leadbeatter here in Australia pioneered the use of domestic microwaves many years ago to speed up the seasoning of green wood. It works, but is far too much of a fiddle for my temperament.

https://joneakes.com/jons-fixit-database/1685-Microwave-drying-of-green-wood

[Jim Hipp]

A guy in the woodworking club I belong to uses silica beads to dry rough turned bowls. I know he puts the beads in a bucket with the rough bowl and seals it up. Weights them every day and recharges the beads as necessary. When the bowl stops losing weight he considers it dry and finishes it. I don't know all the details and he isn't on this forum.

[Reed Gray]

Cheap easy method, used by Christian Burshard, who loves pacific madrone as much as I do, put the bowl in a paper bag. Put that inside a plastic bag. Change the paper bag out every day. The paper bag holds some of the moisture so you are not taking out too much too fast. Dried wood shavings can do pretty much the same thing. I never use wet shavings though since things tend to mold.

robo hippy