Weighing wood to determine stable MC - what do you use?

[Mike McDonald]

I know that the 'correct' way to determine if wood has reached equilibrium moisture content is to weigh it repeatedly and when its weight stops changing it's at equilibrium...

...but what kind of scale do ya'll use to weigh your wood?

I have some large (30" x 30" x 4") slabs and large (16"+D x 12"H) bowl chunks, down to small finial-sized blanks...

It doesn't seem like I would use the same scale to measure both ends of this spectrum, even if I part-turn....

 

[odie]

I know that the 'correct' way to determine if wood has reached equilibrium moisture content is to weigh it repeatedly and when its weight stops changing it's at equilibrium...

...but what kind of scale do ya'll use to weigh your wood?

I have some large (30" x 30" x 4") slabs and large (16"+D x 12"H) bowl chunks, down to small finial-sized blanks...

It doesn't seem like I would use the same scale to measure both ends of this spectrum, even if I part-turn....

You're in luck!

Postal scales are cheap and plentiful. I bought mine on ebay, and I believe it was less than $20, shipping included. You can get them elsewhere, but here's a link:

http://shop.ebay.com/?_from=R40&_trksid=p3984.m570.l1311&_nkw=postal+scale&_sacat=See-All-Categories

Mine is 35lb max, but they are available in a variety of maximum weights.......10lb, 35lb, 75lb, 150lb......

Most of them weigh in lb/oz, or kg/gram, your choice.......I use the gram scale for my roughed bowls. Most are also battery or plug into a 110v circuit.....also, your choice.

When I plug in for my monthly weighings, I use a big bolt that weighs 715 grams. If I get a reading of 715 grams with the bolt and returns to zero with bolt removed, I know that it will give me an accurate weighing, based on the true reading of that bolt.

My scale was very cheap, but all is working well after several years of constant use........

ooc

 

[Barbara Gill]

I bought a postal scale from Sam's Club. It was <$30.

 

[KellyDunn]

Mike, buy a moisture meter on ebay. Like a mini Ligno. Wood dries at about an inch a year. So your thick slabs? If you have roughed out bowls and have waxed the outsides and its your dry season they need about 3 months. But then depending on where you or yall live it could be wetter. So if you are using scales it could still be 18% or so moisture content. So when you begin to finish turn the wood is flat gonna move with the heat of your tools then sanding. So whats a boy or girl gonna do? For most stuff you build a cheap kiln from an old fridge powered by a light bulb. Where I live in Hawaii its wet. But you need to make the choices for what you do that work for you. If you got plenty of time and a dry place to store the wood do what most do and air dry. I did the scale thing here many years ago. But when it said no more loss and I turned it. Did not work for this production turner. Jamming 50 to 70 roughed out bowls into an old fridge and just checking with a meter is pretty sweet. These days I am working by myself as my wife opened a gallery so a 40 watt bulb and they dry plenty fast down to 6% for just one person. They do come back up to air moisture content. But kiln drying gets the cellular moisture down. My2c.

 

[MichaelMouse]

Moisture meters are certainly not required if you're going to weigh, and with the variety of grain presentations on a bowl it's sort of a "worst-case" reading on the flat bottom. End grain will have gone dry long before. Nice hygrometer wouldn't hurt a bit, though.

No need for monthly weigh sessions in my experience. I don't care what known wet pieces weigh, and there's an easy way to tell how things are going by measuring or eyeballing the mortise or tenon. http://i35.photobucket.com/albums/d160/GoodOnesGone/Picture-Package-10.jpg When/if it's oval, weigh, weigh one week later. While they're round, makes no difference what they weigh.

I'm sure you know that roughing to get the middle out of things will bring them down much faster than leaving them in the large. According to the wood tech types it takes three times as long to cure to 2" as 1". If your platter's going to be flat, you may not get all of that back, because it's shortening the distance to open air through endgrain that gains the most.

 

[Mike McDonald]

Thank you, all, for the great information. I knew it wasn't simple, but this is even more complicated than I thought.

I have part-turned a couple pieces, but for the most part I'm too far into instant gratification to want to part-turn. And I'm at the opposite end of the spectrum from a production turner, so how fast I can turn out multiple pieces isn't a consideration.

I DO have a moisture meter, but the moisture content 1/4" into a large chunk doesn't really tell me anything about the moisture content in the middle.


For weighing wood, how far apart do the measurements have to be to be reliable? Obviously two measurements, an hour apart, don't tell you if it's stabilized. But 24 hours? 72 hours? a week? two weeks? two months?

Thanks again, ya'll!

 

[odie]

Thank you, all, for the great information. I knew it wasn't simple, but this is even more complicated than I thought.

I have part-turned a couple pieces, but for the most part I'm too far into instant gratification to want to part-turn. And I'm at the opposite end of the spectrum from a production turner, so how fast I can turn out multiple pieces isn't a consideration.

I DO have a moisture meter, but the moisture content 1/4" into a large chunk doesn't really tell me anything about the moisture content in the middle.


For weighing wood, how far apart do the measurements have to be to be reliable? Obviously two measurements, an hour apart, don't tell you if it's stabilized. But 24 hours? 72 hours? a week? two weeks? two months?

Thanks again, ya'll!

Mike.......

Roughed bowls will lose weight quickly at first, but the weight loss will taper off as you near stabilization. I use one month intervals between weighings, but that's just my choice. You will also see results in a week, two weeks, month, two months, etc.

If you go with less than weekly weighings, the roughed bowls won't stabilize any quicker.......but, if you wanted to weigh every day, that would work, too......just spending a lot of effort. I suppose it all depends on how you feel about it.....but, for me, monthly weighings work.

Right now, I have about 50 roughed bowls in various stages of the seasoning process.......it would be more work than I care to do, if I weighed them more often.

My suggestion is for you to get yourself a bunch of kiln dried blanks and have fun making bowls.......all the while, roughing and seasoning wet blanks. It will only take four or six months and you will have a nice rotating stock of seasoned blanks to work with. Although I concentrate on unseasoned blocks of wood, I have a nice supply of kiln dried blanks that I continue to use.......I NEVER run out of wood blanks to use.

I can certainly understand about your desire for "instant gratification", and you can have that, all the time, by using BOTH kiln dried blanks, and wet blanks........

ooc

 

[MichaelMouse]

For weighing wood, how far apart do the measurements have to be to be reliable? Obviously two measurements, an hour apart, don't tell you if it's stabilized. But 24 hours? 72 hours? a week? two weeks? two months?

The elephant in the corner is the relative humidity. Let the meter read 13% when the RH is 65% and that's as good as it gets. If the RH is 45%, you have 4% to go. Thus the recommendation to get a hygrometer and look at it once in a while. I'm 25% now (5%moisture), and have been for months. Summers I control to 45.

I go a week because of the percent per week in planks generalization. Has to mean a potential for two or three times as much in a rough bowl. Plus I look ahead to the next weekend in setting up my fun....

 

[KellyDunn]

Mike, if you want instant learn to do green start to finish. do the outside. After its sanded put some finish on it to prevent large moisture loss. Got that from Ellsworth many years ago. Take down your inside and sand that. Do the bottom. Put finish on all that and wait to see how it moves.
To using a kiln. A kiln gets out the BOUND moisture in the cellular structure. Folks are right that pins wont work for thick work. For roughed bowls a poke on the rim and bottom should tell you plenty. One person said they have 50 roughed out bowls. I must have a thousand. Dont want to weigh or wonder. They went through a kiln and I know the bound moisture is gone. So its relative humidity which has been said. I pop a bowl from the shelf with 18% back in the kiln and in two days its down to six. Because I have no competing slow bound moisture coming into the blank. Now, as has been said. You do not have to do that. For me its the quality of my basic blank in dryness. Most of my work does not stay in wet Hawaii. It goes to places a lot more dry in general. So I create that dryness so the buyer has a round or somewhat round bowl in its final place. When I air dried and finished I thought all was well. I then went to visit folks in Colorado Springs, Colorado. My bowls were twisted S shaped things that embarrased the hell out of me. That now does not happen because of my xtra efforts. But I am a full time turner and do it for a living. So my case is different than most. Each person has to come up with what works for them. That said. Green turning can be great fun. I did a silver dollar eucalypt nat edge piece today. It moved while turning. Should be like knarly leather in the morning and all twisted and cool in a few days. Bottom line? Have fun.