Wood Moisture Meter

[davewarner]

Greetings Everyone.

So I've been bitten by the luthier bug and I'm having a lot of fun with it so far. Been fixing up and modding my own guitars and now I'm preparing for my first build. As it turns out it is a benefit living in Pennsylvania when looking for wood sources. I visited a local sawmill this weekend and came home with some rough cut lumber. The guy at the mill said the lumber was kiln dried (to what % I don't know), but I noticed the ends where not wax sealed and I have no idea how long the pieces have sat since coming out of the kiln.

I've read that the wood should be dried to about 6-8% for use in a guitar project. This leads to a couple of questions I have:

- Can anyone recommend a decent quality moisture meter that will work well with lumber. I'm not very trustful of the cheap meter like you can find at Harbor Freight, but I don't want to spend several hundred dollars either. Maybe something like this?

Timber Checker

- Should the wood be at 6-8% moisture content when starting the build? In other words, is it enough that the wood was dried to this moisture content previously so any checking etc., has already occurred?

- I heard about waxing the ends of boards to keep moisture out. Anyone have links that describe the process? Does the type of wax matter (can I use parrifin for example)?

Thanks a lot, I look forward to hearing from you guys.

Dave

[Mattia]

I don't own one. Cheap way to do it: slice it up, sticker it, weigh it occasionally. If it keeps losing moisture, it'll get lighter.

Any wood I get from lumber yards sits at my place for about a year (minimum) before I build with it, and definitely at least a month or two indoors, climate controlled, in billet form, before I start converting it into an instrument.

As for waxing: most woodwork places sell end sealer products for this purpose. Paraffin wax works, and I've used it on occasion.

[fryovanni]

+1 to what Mattia said. Time is your ally if you want to ensure your material has effectively stabalized.

First thing to consider is that a fixed percentage of moisture is not going to work for all situations. You want to shoot for "equalibrium" moisture levels. Meaning the wood has effectively balanced its moisture level to the relative humidity(moisture and temp) in your work space. At that point the wood should neither accept or reject moisture unless there is a change in the relarive humidity. Holding the relative humidity extreamly close year round can become expensive to maintain, so often small changes are acceptable as long as you keep the shifting gentle (note the wood will adjust, but it will limit how severe the changes are). Currently wood in my shop holds about 8% moisture, if I store wood out side it would equalize closer to 10-12%. Kiln dried lumber typically is dried and brought to the 10-14% level(effectively most of your checking, cracking, splitting, major warping and twisting, and significant shrinkage has occured by that point. The term "air dried lumber" can mean a couple things. One many times green(freshly cut) lumber is air dried to about the 25-30% level before kiln drying, and this term describes this lumber. Lumber can also be air dried to lower moisture levels(all the way to equalibrium), but this requires much more time, and space. When you recieve "air dried" wood you really need to ask how long and where the wood has been drying(get some history), and then monitor its moisture levels to ensure it has stabalized. Keep in mind where wood dries(relative humidity, air circulation rate), the type of wood that is drying(hgher density or oily resinous woods can take much longer to dry than less dense woods), and thickness of the wood effects the drying rate. A 2" thick billet of western maple may dry at a rate of about 1.5-2 years to reach equalibrium kept outside under cover with reasonable air flow in a mild climate. A piece of rosewood of the same size and dried under the same conditions could take twice as long.

During drying stages. Wood will release moisture much faster at the exposed end grain(actually accept or reject), so we treat wood with one of many types of endgrain sealer to slow that transfer down. The idea is that you want the wood to dry evenly, and this helps a bit. Wood does not dry evenly no matter how you go about drying it. The outer shell will dry faster than the core. This sets up an odd balance in the tension as wood dries. First the wood want to shrink around the shell more than the core wood shrinks(checking and cracking begin). As the shell dries more, moisture is able to start moving out from the core faster this creates a situation where the shell has stopped shrinking much, and the core begins to shrink faster than it had before (tensions shift) and you start to get heart checking and splitting becomes deeper. The bulk of this starts to calm down around 14-16%.

Anyhow, this is a broad topic and it could go on for a while(actually you can look up previous posts on this subject, or look up much of this on the web, woodworkers handbook is really handy for these topics). Key things to keep in mind. Endgrain seal is a good idea. Keep air flow to all sides of the wood even(space wood with sticks when you recieve it), allow the wood enough time to stabalize. Moisture meters are nifty tools. They give you a fair picture of where the wood basicall is in the drying process. Unless you have absolute rule over the ambient conditions in your workspace year round, you don't know exactly where the wood should be. This means you can't use a moisture meter like a ruler(wood should be at exactly 7%), but you can test several pieces of wood that have been in your shop for a long enough period to have stabalized. Using what you see those bits are at you can test and tell a piece you want to use is at about the same level (this should be a solid indicator that the wood has stabalized to your shop).

Hope that helps,

Rich

[Jon]

I stack my pieces up and wait a good 6-12 months before using them. Right now, most of my pieces have been acclimating for about 12-20 months. All of the wood I have ever worked with has been less than 8% moisture content. So I just use time as my guideline for building. If I'm drying green lumber, that's a whole different story!

[fryovanni]

It is really important to remember equalibrium moisture level is what is most important. If your shop will not balance wood at 6-8%, and you force it to an overdry condition, the moisture level WILL rise back to equalibrium(wherever that is) and the wood will swell. If you keep your shop at a steady 72 degrees with a constant relative humidity of 45%, that is great and you will be able to hold about 6% steady. However.... If that shop is in Florida that guitar is going to swell as soon as it leaves your shops climate control, by the same token, if your shop is in the Arizona desert it will shrink. It is best (as long as your areas humidity will permit glueing and finishing) to simply knock the edge off transitions. I don't believe in assembly in a bubble, unless you know it is leaving your area for a climate that you are trying to mimic(large shops shoot for the best middle ground they can, but it is just that). Common sense type stuff here, no more no less. Jon and Mattia, as well as many other very sharp builders use time to ensure well stabalized wood (perfect solution). Note; these guys don't buy wood the month they are going to use it, they have stocked ahead a bit. Look for topics and postings by people who are having issues with lumber distorting. You will find a common thread they have either just recieved the wood recently or moisture levels have changed radically.

Peace,Rich

[davewarner]

Thanks for the replies so far. This is a lot of information to 'grok', but I'm trying. I've read back in a couple of the forums and also using search ... just a lot to process.

I'm getting the sense that since my wood source is harvested, milled, and dried locally there should not be be much in the way of acclimation issues. However if it was recently taken from the kiln there will be period of time where the moisture content is changing as the wood stabilizes to the surrounding environment. In talking with the operators of the mill the wood comes out of the kiln and is then stored in a pole barn (which is where I chose it). My shop is outside garage space so I guess that matches up ok.

I'm probably going to go ahead and get a moisture meter (any recommendations/experiences are appreciated). I do have various pieces of wood that have been in the shop for several years. Checking the moisture content of these pieces will help to establish a baseline (yes?).

So let's say the baseline is around 12%, and I have tonewood at 12%. This means the pieces are stabilized, but is there further benefit in trying to get the moisture content down in the 8% range, before building? I have a dehumidified basement where I can store the wood. Figure a small stack (with stickers) maybe with a fan blowing on the stack. I expect this would help further reduce the moisture content. Note to self, if I start collecting a tone wood stash this is probably a good long term storage solution to avoid seasonal variations in the ambient climate.

Anyway, planning on solid body construction for now and I don't expect to get it perfect this time or the next, etc. I just want to maximize the chance for success.

Thanks again,

Dave

[fryovanni]

Thanks for the replies so far. This is a lot of information to 'grok', but I'm trying. I've read back in a couple of the forums and also using search ... just a lot to process.

I'm getting the sense that since my wood source is harvested, milled, and dried locally there should not be be much in the way of acclimation issues. However if it was recently taken from the kiln there will be period of time where the moisture content is changing as the wood stabilizes to the surrounding environment. In talking with the operators of the mill the wood comes out of the kiln and is then stored in a pole barn (which is where I chose it). My shop is outside garage space so I guess that matches up ok.

I'm probably going to go ahead and get a moisture meter (any recommendations/experiences are appreciated). I do have various pieces of wood that have been in the shop for several years. Checking the moisture content of these pieces will help to establish a baseline (yes?).

So let's say the baseline is around 12%, and I have tonewood at 12%. This means the pieces are stabilized, but is there further benefit in trying to get the moisture content down in the 8% range, before building? I have a dehumidified basement where I can store the wood. Figure a small stack (with stickers) maybe with a fan blowing on the stack. I expect this would help further reduce the moisture content. Note to self, if I start collecting a tone wood stash this is probably a good long term storage solution to avoid seasonal variations in the ambient climate.

Anyway, planning on solid body construction for now and I don't expect to get it perfect this time or the next, etc. I just want to maximize the chance for success.

Thanks again,

Dave

Basically you have the concept, and you are on track with your "baseline" idea. One thing you need to consider is that relative humidity is just that (relates to temp and moisture level in the air). Warmer air holds moisture better than cold, by increasing the temperature of the air(given moisture levels in the air are equal), the wood will not hold as much moisture. If your garage is not heated, the wood will most likely hold more moisture than wood that is inside (warmer). I bring wood in from the garage to aclimatize, I build inside, and that is where the guitars will be when they are in service(not in my garage). Hope that makes sense.

If you have a handle on how much moisture, and how relative humidity will modify the moisture content. The next step would be to understand the relationship of how wood expands and contract in relation to the grain orientation. Wood shrinks and expands very little in relation to the longtitudinal grain (think of this as the length of a log- longtitudinal). If you think about the growth rings of a tree, changes in radial orientation(think quartersawn) will generally be about half as much as in the tangential orientaion(think flatsawn). To try to relate that to an instrument, think of an acoustic soundboard. The longtitudinal grain runs from the neck to the tail, This being the longest part of the soundboard this means you will have the least change in length of that board when moisture levels cause expansion or contraction. The next widest part of the board would be across the lower bout. Wood is traditionally oriented in the quartersawn orientation(radial) because the width of the lower bout will expand and contract about half as much as if you used flatsawn wood. The thickness of a soundboard is small(approx 1/8"), this being the smallest effective length it is the best choice for the orientation that will change the most Tangential(flat). To give a bit of perspective on movement, many commonly used woods will move approx. .00180" per. inch of material in the radial orientation when moisture is changed 1% (starting with wood that is somewhere between 6-14%). That would mean that a 10" piece of wood will expand .0180" per. 1% increase, or shrink .0180" if moisture content drops 1%. If you have a change of 3% the change would be more like .0540"(1/16"=.0625"). In many commonly used woods the change would be twice that in the tangential orientation(flatsawn). Changes in the longtitudinal would be a slight fraction of that. Not all woods expand and shrink the same amount volumetrically, and not all woods have the same ratio of change between radial and tangential. Woods like Mahogany or Khaya(african mahogany) have very close ratios(this makes them shrink and expand very evenly in both directions. Woods like Madrone have very high differences in the rations (more like 3 times, very high change in the Tangential). You can look up these ratios on the web, or find many in the woodworkers handbook.

Hope I am not overloading you with bits of info here. If you understand these concepts, many traditional methods start to make perfect sense. It also helps you understand how best to evaluate less commonly used woods, and optimise their usage.

Peace,Rich

[orgmorg]

My approach differs from Rich's a bit, but essentially achieves the same result.

I actually do shoot for a target moisture content of 6-8%

I find my wood maintains this MC well at 45% humidity.

I have a room in my shop that is insulated and can be kept at 45% humidity.

Also, I saw most of my own wood from logs, and dry it myself.

After it is sawn ( with ends sealed ) it is stacked and stickered outdoors, covered, until it reaches 16-18% moisture content.

I have found that that is the MC that most species of wood I work with tend to settle at in my climate, and generally won't get much dryer than that stickered outdoors.

At that point, I dead stack the boards ( no stickers ) in a shed until I am ready to dry them further.

I do this in the insulated room mentioned earlier.

I don't have a lot of room in there, so I don't dry the boards whole, but cut them up into the pieces I intend to use, and stack/sticker them at one end of the room, with a dehumidifier.

When the wood reaches 6-8% MC, I stack it on shelves in that room ( no stickers ) and it stays there until I use it.

The moisture meter I use is the Lignomat mini ligno E/C, it was about $120, and from what I was able to figure at the time, that's about what a decent one costs. I also have the slide hammer probe for it, which can reach the middle of a 3" board if necessary.

Rich- I would be interested to hear your feedback on this approach, partly because I am getting ready to update this thread:

http://projectguitar.ibforums.com/index.ph...m+the+beginning

You have been doing a great job providing info on drying wood here, and I would like to avoid conflicting with that, and possibly confusing anyone who has been following your posts.

You have obviously studied this in greater depth than I, and I would value your input.

Thanks.

Edited March 18, 2008 by orgmorg

[Quarter]

... I'm not very trustful of the cheap meter like you can find at Harbor Freight, but I don't want to spend several hundred dollars either ...

I have one of the cheap Harbor Freight units.

While I don't necessarily trust the numbers it reads, I think it can be useful for relative / comparative testing.

[fryovanni]

My approach differs from Rich's a bit, but essentially achieves the same result.

I actually do shoot for a target moisture content of 6-8%

I find my wood maintains this MC well at 45% humidity.

I have a room in my shop that is insulated and can be kept at 45% humidity.

Also, I saw most of my own wood from logs, and dry it myself.

After it is sawn ( with ends sealed ) it is stacked and stickered outdoors, covered, until it reaches 16-18% moisture content.

I have found that that is the MC that most species of wood I work with tend to settle at in my climate, and generally won't get much dryer than that stickered outdoors.

At that point, I dead stack the boards ( no stickers ) in a shed until I am ready to dry them further.

I do this in the insulated room mentioned earlier.

I don't have a lot of room in there, so I don't dry the boards whole, but cut them up into the pieces I intend to use, and stack/sticker them at one end of the room, with a dehumidifier.

When the wood reaches 6-8% MC, I stack it on shelves in that room ( no stickers ) and it stays there until I use it.

The moisture meter I use is the Lignomat mini ligno E/C, it was about $120, and from what I was able to figure at the time, that's about what a decent one costs. I also have the slide hammer probe for it, which can reach the middle of a 3" board if necessary.

Rich- I would be interested to hear your feedback on this approach, partly because I am getting ready to update this thread:

http://projectguitar.ibforums.com/index.ph...m+the+beginning

You have been doing a great job providing info on drying wood here, and I would like to avoid conflicting with that, and possibly confusing anyone who has been following your posts.

You have obviously studied this in greater depth than I, and I would value your input.

Thanks.

I agree with what you are saying 100%. Actually our methods are not too different at all, and moisture levels we achive are very similar (my "outside" levels are probably slightly lower generally, and when I move the wood to a heated space it settles at 6-8%). I have a small space that I can rigidly control moisture levels, but I would only use it if I was assembling and had a huge swing in moisture, minor changes can easily be buffered by adjusting the room temp a few degrees for short periods.

I am sure both of us have come to our understandings on drying from some study, combined with plenty of first hand experience. I doubt we are going to contradict each other much, minor differences in how we deal with our typical climates, but that is good . Understanding that moisture levels vary reginally is important.

Peace,Rich

[orgmorg]

OK, cool. I figured we were probably pretty much on the same page.

[mdw3332]

I was in the local woodworkers shop today and mentioned to the guy that I had bought a big hunk of Walnut, (Rich, the one we talked about) but I didn't have a clue about its moisture content. He said, no sweat and loaned me a meter they keep just for customers to borrow. It's a Lignomat mini. One of the nice thing about the small shops these days. BTW it's between 10 - 12%.

Rich, if we don't hook up before the show, I'll throw it in my car and you can take a look at it then. I heard from both Dan & Carl and they are planning on it. Assuming I'm not in the hospital I'll be there. Let us know what day works for you and David. Looking forward to it.

Marty

[fryovanni]

I was in the local woodworkers shop today and mentioned to the guy that I had bought a big hunk of Walnut, (Rich, the one we talked about) but I didn't have a clue about its moisture content. He said, no sweat and loaned me a meter they keep just for customers to borrow. It's a Lignomat mini. One of the nice thing about the small shops these days. BTW it's between 10 - 12%.

Rich, if we don't hook up before the show, I'll throw it in my car and you can take a look at it then. I heard from both Dan & Carl and they are planning on it. Assuming I'm not in the hospital I'll be there. Let us know what day works for you and David. Looking forward to it.

Marty

Marty,

I hopefully will be able to make the show any day that weekend (at least am planning on it). David is exhibiting, so he should be there each day (Good time to pass the word on to any people you may know that might be in the market for a custom Myka Guitar ).

I want to sneek down to check out the new Goby Walnut shop. Goby was bought by a fella hear in town and is relocated to his shop up the street from Gilmer. Have any of you fellas had a chance to check it out yet?

Hopefully you won't be in the hospital that weekend, but if so, I am sure Dan the man and I will hunt you down like a dog as soon as your feeling like putting up with us .

Rich

[DC Ross]

Sorry to hijack the thread, but Rich & Marty, what show is this?

[fryovanni]

Sorry to hijack the thread, but Rich & Marty, what show is this?

It is an instrument show they hold at Marylhurst University each year down here in Portland. Here ia a link to the shows site- link

[davewarner]

Just coming back around on this one...

I ended splurging a bit for a Wagner MMC220 Extended Range Moisture Meter via Amazon. Perhaps a bit of overkill, but I'm quickly getting hooked on buying stock from nearby sawmills and this should come in handy.

I went back and re-read the section on wood drying in Martin Koch's Building Electric Guitars book. In that section (page 19) he provides a handy chart showing the typical moisture content wood will stabilize at for a given relative humidity level. That information is consistent with the advice offered in this thread and of course I can now verify with direct observations via the Wagner MMC220.

Anyway, thanks again for the replies. I'm learning lots!

Oh, and I'll forgive the threadjack just this once

Dave