Wood Moisture Meters: What to Buy?

[John Maddison]

G'day All

Can you recommend an affordable wood moisture meter which represents value-for-money; maintains accuracy; reads an appropriate range of moisture percentages; possibly has pre-sets for preferred lutherie species and/or can be calibrated for other species; is easy to use, and is available in Australia.

One particular supplier in Oz, instrumentchoice.com.au, from whom I've had excellent customer service in the past, has a bewildering range of instruments from which to choose. Even more bewildering is Google's search results of Pages from Australia. All advice is welcomed.

Cheers & thanks

[kiwigeo]

John, I recall seeing a review of moisture meters in a copy of Australian Wood Review. Ill have a look through my dust covered collection and see if I can find the edition in question.

[John Maddison]

You're a champion Martin, thanks ... after several days of no posts I was beginning to think no-one here used such a thing!

[John Maddison]

Martin - I have just done a search of AWR's online magazine index and found these issues if it's of any help:

Moisture meters:
guide ... Issue 15: Page 58
buying ... Issue 35: Page 73
low-tech gauge project ... Issue 73: Page 84

Will suss out the library here at Albany TAFE where I work and see what's still on the shelves; I know for a fact they subscribe to AWR for our Carpentry & Joinery courses, but the staff only keep back-issues from the last 12 months.

Thanks for the heads-up!
Cheers

[Bruce McC]

John

Sorry I can't comment on meters as I don't own one, but if you can get hold of "Wood in Australia" by Keith Bootle,
see page 90 where he talks about meters and correction figures for timbers.

[Kim]

John,

I am not sure of today's tech but back when I was using them moisture meters were targeted at the milling/joinery industries. They did 'OK' at reading 40mm billets etc giving a ball park idea, but they were never very accurate..or, 'consistently' accurate. In fact despite the $400 price tag (it was the 90's) our unit ended up sitting in the box and we went back to surface feel on skip dressed...i.e. hardwood with a higher moisture content feels cooler and stays cooler for longer on the palm of your hand.

Anyhow aside from reductions in price through cheaper technology, I'm not certain things have changed much with meters and I can't imagine they would work reliably on thinner wood because they would necessarily be set up to ignore the first few mm of surface wood to give a more accurately reading at the meters set depth. But then who knows, maybe the technology has changed a lot and perfection is out there. But then like everything in the electronic measuring instruments world, I bet you would need to pay handsomely to rise above the market flood of 'work's, but not worth while' units that are out there for under the $200 mark.

Cheers

Kim

[kiwigeo]

Martin - I have just done a search of AWR's online magazine index and found these issues if it's of any help:

Moisture meters:
guide ... Issue 15: Page 58
buying ... Issue 35: Page 73
low-tech gauge project ... Issue 73: Page 84

Will suss out the library here at Albany TAFE where I work and see what's still on the shelves; I know for a fact they subscribe to AWR for our Carpentry & Joinery courses, but the staff only keep back-issues from the last 12 months.

Thanks for the heads-up!
Cheers

Sorry John, I dont have these issues.

Cheers Martin

[John Maddison]

Martin - thanks for checking;
Bruce - good tip ... am fairly sure there's a copy of Bootle in the TAFE library - will check it out;
Kim - thanks for the words of wisdom; since we in Albany started out in lutherie in 2005 we've collectively amassed several odds-n-sods of 'green' timber in billet and log form for which we've been thinking the need to keep tabs on moisture content as it cures. I take your good advice that a moisture meter would probably give erroneous readings on thin boards.

Cheers all!

[Kim]

since we in Albany started out in lutherie in 2005 we've collectively amassed several odds-n-sods of 'green' timber in billet and log form for which we've been thinking the need to keep tabs on moisture content as it cures.

John, it may pay to have a chat with Tim. Seasoning wood via the tradition 'year per inch' is good if the focus is to stock up on neck material, but for most back and sides wood doing so usually results in less efficient conversion. The 1" per year formula was devised by the joinery/furniture trades and is good practice for those industries because both required stability in thick solid boards they use to produce doors, windows, door and window frames, table tops and the like

The square dressed materials they require (or use to require when there was such a thing as joinery) run anything from 13mm through 50mm thick for stock production and up from there for specialised things like newel post for balustrade and stairs work etc which could often be 125mm square or more. Of course a post that size would simply be laminated these days but once, when the inch per year standard was devised, large boards were readily available and cheap, so there was no real need to bother with lamination.

That's the unmentioned of the 1" per year standard, it was from a time of plenty and would see a fair bit of wood from the outer stack lost during the drying process to splitting from end check (yes even if you do seal the end grain), cellular collapse from too rapid or uneven drying or air flow, warping and twisting from uneven grain (this is why the mills use to burn most figured wood, nobody wanted it, too unstable) and other issues before the rest of the stack would finally season out to be ready for machining. But the loss did not matter much, it was considered natural attrition and just part of the process....

That's my point, we no longer have the wood to waste with the 'wait and see' approach of days gone by. From what I understand the best recovery form most hardwood that is to be sawn into guitar sets is done when the wood is only semi dry. You cut the sets a few mm over and sticker them out with a gentle air circulation. Doing this gets the water out the wood the fastest way possible, and because the wood is so thin it has a huge surface area to allow this to happen safely so you don't face the same issues of thick cants and billets which have moisture 'locked in' the wood.

Aside from the benefit of resawn sets drying to a usable moisture content within a matter of months, the other big bonus is that most species of hardwood are far easier to resaw when still semi green, the blade stays sharper for longer and the whole operation runs cooler but you do need to sticker out as usual and seal the endgrain.....plumbers PVC glue works really well for this, it seals without penetrating the wood at all.

Cheers

Kim

[John Maddison]

Kim, very glad you've chimed in on this thread. Such a great knowledge base are we building here?!

[J.F. Custom]

Hi John.

Sorry for the late pickup here - after being away, I am working my way through some of the old threads.

Moisture meters vary quite dramatically in price and this tends to relate to both accuracy of readings within given percentages and versatility across a range of material. You can basically split them into two types - pin style (invasive) and electromagnetic (non-invasive).

So some info from my basic and limited knowledge and use of them; though I'm no expert so take this with a grain of salt. The pin style readers are resistance type readers - that is, they are reading the resistance of the signal sent between pins. The practical side of this is that they are reading the moisture roughly at the depth you insert the pins to. Therefore they are "invasive" in that you must drill two holes into your timber to get a reading - not the best thing in expensive tonewood. Some just push the pins in without drilling but you will have difficulty, not to mention risk breakage, inserting them to more than, say 5mm. This obviously varies according to timber hardness/density. But there is no point reading 5mm deep in a 30mm board - you need to get your reading at 15mm deep in that case which requires the drilled holes. You will find the cheapest model moisture meters are pin style readers that only give very basic results such as - moisture is between 12 and 17%; with a +/- 2% accuracy or similar. There are also very expensive pin type readers too. Usually these have much larger pins capable of reading to larger depths, coupled with better accuracy, but also have more adjustment according to timber density/species. I don't have any experience with the more expensive pin style readers.

The other style is "non-invasive". These have a 'sensor plate' that throws an electromagnetic arc/field which the unit draws its reading from. The upshot of which obviously is that you are not left with stab wounds in your timber. This style usually kicks into the mix at around the $200 mark. At this end of the range, they are usually reading to a fixed depth, say 15mm, and may have a range of settings available such as 1-10 for 'hardness' of timber. Note though that they are often pre-calibrated to within a certain range. If it is made in Europe, their range of hardness may be from 200kg/m3 to 800kg/m3 as this suits their timbers. It therefore would not read our 1200kg/m3 timbers very accurately - but they often have other units calibrated in the heavier ranges too. The more expensive units have more features and versatility. One I have used that was about $990 or so was excellent. It allowed you to adjust your reading depth from 2mm? to 40mm. It also had built in settings for timber by species averages (maple, cedar, ash etc) for quick readings - which gave you reasonable results. But it also had a setting for kg/m3 so you could adjust the setting exactly to the piece in your hand giving very accurate results.

I guess the summary of this is you do get what you pay for. The cheapest models are only to give a basic indication of wet or dry - much as you are likely to be able to tell yourself by feel ; the mid range is more accurate but still must generalize across a range of densities or pre-calibrated figures; the expensive models are more fully adjustable in every setting.

That's according to my limited knowledge. No real recommendations but food for thought on what to consider in your purchase, should you decide to go ahead with one.

Hope it helps in any case.

Jeremy.

[John Maddison]

Jeremy, thank you for taking time to write a long post; from your knowledge base and that of Kim's we now have a greater appreciation of this technology. Cheers!

[stopper]

I have a deltron moisture meter that works well. It is the prong type with a slide hammer. After taking a reading I look up the conversion tables to make the corrections for timber species, temp. etc. It gives a good estimate.
For accurate moisture content I use the microwave to dry a clean sample and make calculations based on the weight difference. Care must be taken not to burn the sample. This method is simple, accurate and practiced by many timber timber suppliers.
cheers
steve