The Forestry Forum

General Forestry => Drying and Processing => Topic started by: Dough_baker on February 23, 2015, 08:41:36 AM

Title: Which moisture meter do you use for rough sawn green lumber ?
Post by: Dough_baker on February 23, 2015, 08:41:36 AM
Many types of moisture meter, their measuring range is from 0-30%. so, when measure newly milled green lumber, the choice is limited, now I am using Lignomat Scanner SD Moisture Meter.

(http://ecx.images-amazon.com/images/I/51fbh5dJxvL._SX425_.jpg)

Although it is indicated on Amazon that range is 5-99%, the instruction manual stated 5-60% as I remember.

When measure green lumber with pinless meter, does the rough sawn surface affect measure result ? should I plane the lumber before measuring ?

Is pin type meter more suitable for rough sawn lumber, like this one from Gowe?

(http://ecx.images-amazon.com/images/I/31DG3pzDDtL.jpg)

Best,
Baker
 
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: beenthere on February 23, 2015, 10:12:54 AM
Accuracy over 30% is negligible. So any reading you get over 30, just assume it means the lumber/wood is green.
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Ga_Boy on February 23, 2015, 11:14:40 AM
The moisture content of lumber is is not consistent through out the thickness.  The mositure content will be the highest in the center of the lumber and will become less as you move to the surface of the lumber. 

Pin meters will give you an average moisture content over the length of the pin that is not insulated. 
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Den Socling on February 23, 2015, 11:36:12 AM
MC is going to vary within a tree and from tree to tree. I'm wondering why you would even want to read MC of freshly sawn lumber.
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: GeneWengert-WoodDoc on February 23, 2015, 10:21:49 PM
Appreciate that the two types of meters mentioned are measuring an electrical property and then relating that property to the wood's MC.

I have tested many meters and have yet to find one that has readings above 30% that are accurate.  The problem, briefly, is that when there is liquid moisture present (above 30% MC), it behaves like a "short circuit" and so the electrical property does not vary much when the wood is a little above 30% MC or a lot above 30% MC.  For freshly sawn lumber, you can probably get a closer estimate of the MC by using the typical green MC values for the species, rather than use a meter.

I did give a rather thorough review of these moisture meters when used on kiln dried lumber.  That review, based on lots of tests, is in DRYING HARDWOOD LUMBER.  Each type has some strong advantages over the other and some disadvantages.  Together, the two are awesome.  For KD lumber, when properly used, the meter values will be within 1% of the true, oven-dried values.

When comparing the two meters, the pinless meter is measuring the average MC of the piece.  The pin meters are either measuring the wettest spot along the length of an uninsulated needle or measuring the MC at the tip of the insulated needle (the tip is not insulated).  The insulated needle allows one to measure the MC at various depths.

If you look at the article in DRYING HARDWOOD LUMBER and have any questions, let me know.
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Dough_baker on February 24, 2015, 04:18:07 AM
MC is going to vary within a tree and from tree to tree. I'm wondering why you would even want to read MC of freshly sawn lumber.

Hello Den Socling, When I asked about vacuum drying kiln at a Forestry Equipment Expo last year, they wanted to know the initial and final moisture, I didn't know the accurate value and assumed that from 60% to 16%.  :-[

They recommanded round type vacuum kiln to me, for 8/4 lumber and slab, I don't know why, obviously box type kiln is more suitable for slab, because of its width.

do you think there is any difference?
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Dough_baker on February 24, 2015, 04:25:11 AM
Appreciate that the two types of meters mentioned are measuring an electrical property and then relating that property to the wood's MC.

I have tested many meters and have yet to find one that has readings above 30% that are accurate.  The problem, briefly, is that when there is liquid moisture present (above 30% MC), it behaves like a "short circuit" and so the electrical property does not vary much when the wood is a little above 30% MC or a lot above 30% MC.  For freshly sawn lumber, you can probably get a closer estimate of the MC by using the typical green MC values for the species, rather than use a meter.

I did give a rather thorough review of these moisture meters when used on kiln dried lumber.  That review, based on lots of tests, is in DRYING HARDWOOD LUMBER.  Each type has some strong advantages or the other and some disadvantages.  Together, the two are awesome.  For KD lumber, when properly used, the meter values will be within 1% of the true, oven-dried values.

When comparing the two meters, the pinless meter is measuring the average MC of the piece.  The pin meters either measuring the wettest spot along the length of an uninsulated needle or measure the MC at the tip of the insulated needle (the tip is not insulated).  The insulated needle allows one to measure the MC at various depths.

If you look at the article in DRYING HARDWOOD LUMBER and have any questions, let me know.

Thank you Dr Wengert : ) I have downloaded DRYING HARDWAOOD LUMBER on USDA website http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr118.pdf just now, a great practice guide. Will read it in these days.
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Dough_baker on February 24, 2015, 04:29:17 AM
Thank you Beenthere and Ga_boy for replies :)
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Ianab on February 24, 2015, 04:34:29 AM
A cylinder handles the pressure better than a square box.

A square box would need a much heavier steel and more reinforcing to handle the vacuum. So the usable volume of a similar cost round chamber is probably more then a square one?

As for determining the MC of green wood, I think the only practical way is the oven and scales method. Take a sample piece of wood. weigh it, then dry it in an oven (overnight?) and weigh it again. Some simple maths and you know what the MC was. Using a microwave (carefully) to dry the sample will get you a faster result.

Ian
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Den Socling on February 24, 2015, 12:58:48 PM
D_b,
There are a couple reasons I decided to use rectangular chambers instead of cylinders. Strength is one. You can literally swing the counter-weight of a forktruck into the side of one of our kilns. The chamber might be moved but not damaged. Try that with one of the Italian cylinders. Another reason is a rectangular load in a round hole. I once saw a 10,000 bf load for a cylinder that was stacked slightly crooked. They had to tear it down and rebuild it. Another is the carts. To maximize kiln charge, carts are built with the wheels in-board so that the load will sit deeper in the cylinder. That makes for an unsteady situation that I never liked.
As far as green MC is concerned, MC drops a couple percent between the time that the tree is felled and the lumber makes it's way to the kiln. When green MC was important to me, I used 70% for Red Oak, 85% for Soft Maple, 58% for Cherry, 70% for Hard Maple, 42% for Ash, etc. These are lower than you would find for absolutely freshly felled logs.
As far as final MC out of a vacuum kiln is concerned, in our kilns with other factors kept constant, final temperature sets final MC. For example, if I want Red Oak lumber to be 7%, I run it to 140'F. If I want HM baseball bat billets to be 6%, I run to 150'F. Note that most water is removed under 120'F but the bound water needs a lot more energy.
Den
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Dough_baker on February 26, 2015, 04:42:55 AM
A cylinder handles the pressure better than a square box.

A square box would need a much heavier steel and more reinforcing to handle the vacuum. So the usable volume of a similar cost round chamber is probably more then a square one?

As for determining the MC of green wood, I think the only practical way is the oven and scales method. Take a sample piece of wood. weigh it, then dry it in an oven (overnight?) and weigh it again. Some simple maths and you know what the MC was. Using a microwave (carefully) to dry the sample will get you a faster result.

Ian

Thank you Ian, oven and scales must be the most solid method  :P
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Dough_baker on February 26, 2015, 04:48:57 AM
D_b,
There are a couple reasons I decided to use rectangular chambers instead of cylinders. Strength is one. You can literally swing the counter-weight of a forktruck into the side of one of our kilns. The chamber might be moved but not damaged. Try that with one of the Italian cylinders. Another reason is a rectangular load in a round hole. I once saw a 10,000 bf load for a cylinder that was stacked slightly crooked. They had to tear it down and rebuild it. Another is the carts. To maximize kiln charge, carts are built with the wheels in-board so that the load will sit deeper in the cylinder. That makes for an unsteady situation that I never liked.
As far as green MC is concerned, MC drops a couple percent between the time that the tree is felled and the lumber makes it's way to the kiln. When green MC was important to me, I used 70% for Red Oak, 85% for Soft Maple, 58% for Cherry, 70% for Hard Maple, 42% for Ash, etc. These are lower than you would find for absolutely freshly felled logs.
As far as final MC out of a vacuum kiln is concerned, in our kilns with other factors kept constant, final temperature sets final MC. For example, if I want Red Oak lumber to be 7%, I run it to 140'F. If I want HM baseball bat billets to be 6%, I run to 150'F. Note that most water is removed under 120'F but the bound water needs a lot more energy.
Den

Thank you Den, the disadvantges of cylinder type you mentioned are critical. I need to study more before invest my own vacuum kiln.  :laugh:
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: YellowHammer on February 26, 2015, 09:37:02 AM
As for determining the MC of green wood, I think the only practical way is the oven and scales method.  Using a microwave (carefully) to dry the sample will get you a faster result.
smiley_thumbsup smiley_thumbsup
I have a meter that is supposed to measure up to 60% MC, but I still routinely oven dry boards to check the accuracy of the meter and to keep me personally calibrated as well.  Its hard to argue with an oven dry board and a set of scales.

Its amazing how, given enough time handling boards of different MC's, you can get the "feel" to pretty accurately estimate lumber MC by touch, weight and visual clues.  Its kind of a parlor trick, but I have won more than one bet guessing the MC of a board and then checking with a meter (I've lost a few bets, too ;D).  Dough_baker, you probably have developed skill in estimating the doneness of certain foods, its pretty much the same thing.  By the way, I send my moisture meter back to the factory occasionally to get recalibrated.
YH
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Den Socling on February 26, 2015, 06:11:34 PM
YH, Dough_baker is a businessman in Shanghai. I believe the dough he's baking is money.  ;)
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: YellowHammer on February 26, 2015, 07:07:28 PM
YH, Dough_baker is a businessman in Shanghai. I believe the dough he's baking is money.  ;)

 ::).Oops, apologies if offense was taken.  I guess I shouldn't have taken Dough_baker's forum name too literally, ;D.  Yet it seemed such a good parrallel when discussing drying wood.  ;D

YH
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Dough_baker on February 26, 2015, 10:07:37 PM
YH, Dough_baker is a businessman in Shanghai. I believe the dough he's baking is money.  ;)

 ::).Oops, apologies if offense was taken.  I guess I shouldn't have taken Dough_baker's forum name too literally, ;D.  Yet it seemed such a good parrallel when discussing drying wood.  ;D

YH

My career is designer actually  :)  I also run a business of construction materials and furniture as sort of side project. Usually, I purchase 4-6mm veneer and logs and make them into hardwood flooring and furniture, rather than simplely buy end products and sell them. Thank you for your help Den!

Fermented food making is one of my hobbies, such as aritisanal baking and cheese making. However, cheese making needs more comlpex tools I only had done it when I was in university. Baking bread, espesically basic french dough with around 50% moisture in baker percentage, is much easier.

Yellowhammer, now I could just tell 40% MC lumber from 12% MC by touch, the latter feels warmer, need much more experience to tell accurate value. :o

I'd like to post photos of a garden project I designed and built:  :laugh:

(http://gd3.alicdn.com/imgextra/i3/26659870/TB23r2rbVXXXXXpXpXXXXXXXXXX-26659870.jpg)

(http://gd2.alicdn.com/imgextra/i2/26659870/TB2t8HwbVXXXXbyXXXXXXXXXXXX-26659870.jpg)

(could you see these pictures?)
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Den Socling on February 26, 2015, 10:16:31 PM
Yes you posted pictures just fine. Pretty too.
Title: Re: Which moisture meter do you use for rough sawn green lumber ?
Post by: Den Socling on February 27, 2015, 11:37:13 AM
YH I stand corrected. He's multifaceted!  :D