AWGB Woodturning Forum
General Category => Tool tips & reviews => Topic started by: davidbrac on June 21, 2018, 10:03:09 AM
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So I took a wet, roughly turned 15" bowl in elm burr that weighed 2.3kg and registered 22 on my moisture meter. Put it in a bag of colour changing desiccant called envirogel, this is a drying agent that stays yellow when active and turns green when it is saturated.
The bowl was in a sealed bag for 48 hours and the weight has reduced to 1.8kg and meter reading of 12. (I cant get a reading on the main part of the bowl just on the spigot.
The bowl also shows minimal movement and no cracking.
This is the largest of four cored bowls and l have put the second one in today to see what happens with that.
I am also told that the desiccant can be dried in an oven and used again
Think l may try a green turned bowl that has been finished and wet sanded to see the result of that
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Would be interesting to see if they can be dried and reused again
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Would be interesting to see if they can be dried and reused again
The instruction leaflet states that the desiccant can be dried in an oven but it does not mention a temp, l think that too hot may ruin the colour changing propertied of the desiccant
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So l continued this experiment with the second 12" bowl which weighed 1.9kg and a meter reading of 21%
In 24 hours it got down to a moisture reading of 12% and 1.5kg in weight.
I have now inserted the existing two bowls in the gel and will check them in 24 hours
The first bowl is starting to stabilise in that its taking in moisture from the Argyll air and now seems to be 12% all round
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I'm not suggesting it's the same stuff, but in the Army we used to fit desiccators to electronic equipment, tubes of silica gel, which absorbed any moisture inside the casings.
We'd swap them out regularly and fit dried ones. They were heated in small oven type devices for 24 hours to dry them and be ready for the next box of electronics.
The gel beads were just like those you get in the little bags you sometimes get when you buy an electrical/electronic item. I keep several in each draw in my workshop, just to keep everything in them from condensation.
Going back to the enviroGel David is using, pulling the moisture out of timber so fast sounds like it's only extracting the moisture from the first few millimeters depth of the timber.
It might be nice if you report back after you've let the blanks rest out of the gel for a few days and let us know if the moisture level has gone up (equalised) through the timber from your last reading.
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http://www.envirotronics.com.au/images/TBREATHERS/ENVIROGEL.pdf
A pdf about the stuff
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I wonder how.4 of a kg relates to the moisture content percentage wise. Is there a formula that works? If it had been a smaller blank and it pulled .4kg's out of the wood then the percentage would be higher (?) but would it then have pulled the same percentage out by ratio?
Just thinking out loud really, will be interesting to see what happens though. If there have been a larger amount of gel would the weight of moisture removed increase?
(answers on a post card please to.....)
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I’ve used the colour changing beads and can confirm they dry in the oven ok spread out on a large tray, just above 100 centigrade.
Dried wet bowls that have been turned to a finished thickness with no problem, oak , elm and sycamore.
It seems fine if I’m in a rush for a bowl or two not lost any doing it so far.
Michael
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I wonder how.4 of a kg relates to the moisture content percentage wise. Is there a formula that works? If it had been a smaller blank and it pulled .4kg's out of the wood then the percentage would be higher (?) but would it then have pulled the same percentage out by ratio?
Just thinking out loud really, will be interesting to see what happens though. If there have been a larger amount of gel would the weight of moisture removed increase?
(answers on a post card please to.....)
22% moisture content for the 2.3kg for the undried bowl gives 0.5kg of water. It lost 0.5kg weight and then had 12% moisture content which is 0.21kg. Some inaccuracies in the moisture meter there - the initial moisture content would have had to be higher than 22%.
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Paul,
I think your are right about the inaccuracy of the moisture metre, which is why l was using weight as well. I only got a 12% reading on the spigot which is thicker than the sides of the bowl, l was getting a 0% reading on the main part of the bowl, which l discarded.
the first bowl has now been out of the desiccant for four days and seemed to have stabilised to a reading of 11% all over.
The bowls are all 1" thick
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using a moisture meter is a waste of time in my opinion as you can't get into the center of the wood to measure it unless it's a freshly cleaved log.
only use scales as it is the only reliable way to work out the percentage lost and you find out when it is dry when it stops losing weight regardless of what that moisture content would actually be...
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The wood may not be dry when it stops losing weight. At that point it has reached equilibrium with the atmosphere it is in.
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that's what i consider dry though...
other people's dry measurement will differ but all timber will eventually gain or lose weight trying to achieve that equilibrium with its surrounding atmospheric conditions at the time of year.
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The company my wife used to design for refused to sell pine kitchens to the states because they has 0 humidity and the wood shrank to a ridiculous rate after installation when shipped over from the UK. 'Dry' wood doesn't exist in reality and as Steve says how dry something is is relative to the humidity of its environment. omething to consider when mking things such as boxes etc.
pete
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I have now dried the set of four elm burr bowls so the have made it from a felled tree to usable rough turned blanks in ten days, which could have been shorter if l dried then all together but l did them separately. Hopefully l will finish turn by the end of the week.
Drying the 10kg of envirgel took a while, as l was putting three trays in the oven at 120c for two hours each and there was four batches.
In all l am happy with the experiment and l will store and use the envirogel again, I will let you know if l gain any other incites as my experience with the product grows. However Di has just realised that the envirogel can be used for drying flowers and l may have trouble getting hold of it when l want it!
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If the elm, to begin with, was truly "green", it may well have had >40% moisture content, so let's use 40% as a starting point. In which case your 2.3kg (2,300gm) piece of timber would have been 1380gm of elm and 920 gm of water.
After your drying process, you report that the timber reduced to 1800 gm, given that the only weight lost will be that of the moisture transferred to the desiccant, your "dried" piece would have been 1380gm of elm (as before) and 420gm of water, thus its new moisture content would have been 23%.
Using these figures, when your wood eventually reduces to about 1560gm, it will be 1380gm of elm and 180gm of water, which equates to about 12%mc. This suggests that you keep drying until your piece weighs about 1560gm.
Admittedly, these figure are based on a few assumptions, but should be a fairly good guide, and it serves to stress the point that even if you haven't got a decent moisture-meter, when working with green timber you can calculate useful data based on weight loss.
Les
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Les,
Now I understand your Tag Line - Education is important, but wood turning is importanter..
Great use of basic math.
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Les,
Now I understand your Tag Line - Education is important, but wood turning is importanter..
Great use of basic math.
...almost, Bryan, but where I come from, we still call it maths! ;D
Les
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Les.
You assume too much, The elm did not have a reading of 40% if it did my moisture meter would have been off its scale and it wasn't.
The tree was large and had fallen over in the wind, at the time of falling the sap had not started to rise and the leaves were not forming. The tree was damaged some years before, l think by a digger clearing the burn where it stands, over the years the inside of the tree had declined and was rotten. However l am able to salvage some of the wood as it was a very large elm.
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Les.
You assume too much.....
David....I was simply indicating one means of assessing mc if you know you have green timber. In all fairness, you did start the thread by saying that your elm was wet and you later accepted that your moisture meter was giving questionable readings.
Also, I was careful to use terms such as.....IF....MAY WELL HAVE BEEN...BASED ON A FEW ASSUMPTIONS....A FAIRLY GOOD GUIDE. I was simply trying to be helpful!
Les