No, I’m not talking about expansion coefficients. What I’d like to see is a graph that shows moisture content on one axis and shrinkage amount on the other axis. Say, over a scale of 100% EMC to 6-8% EMC. I know the curve is not linear. Do the different woods have a different shape to the curve?
Most if the expansion coefficient formulas I’ve encountered are only good at the lower end of the EMC range.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)
PlaneWood
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Try this.
http://www.woodbin.com/calcs/shrinkulator.htm
You can make your own plot from the results if you want to see it graphically.
I would think that if anyone would have a chart like what you're looking for, it might be this site http://www.fpl.fs.fed.us/
Be prepared to spend some time searching here though. The sheer volume of info there can sometimes be a bit overwhelming.
If you build it he will come.
If you don't mind paying for it here's a program that will do just that. http://www.kitehillsoftware.com/
I reviewed it for Fine Woodworking a couple of years ago and gave it good marks.
Lee
Lee, did it give correct answers over all ranges of MC? Most just work in the 6-20% range where the curves are fairly linear.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
I have to confess here that I did not check every value for every wood at at every MC. There are somewhere around 500 species listed. The numbers I did check were accurate.The wettest it will go is 99%. It really doesn't take long to get wood below 99%, just let it stop dripping.Here's a print out of red alder entered at 99% MC and destined for an environment in which 6% is the low and 13% is the high. These numbers are MC, not relative humidity. The board width I entered was 10" and flat sawn.Note that it says that at 99% MC the board is 10" wide, once EMC of 6% is reached the board will be 7.48" and under the wettest conditions in Connecticut it will swell to 7.67" at 13%.Lee
I think there's something wrong with those calculations you posted for red Alder. There's no way in the world that, that wood will shrink two and a half inches from green to dry. I put the same numbers that you used into the web site that I posted, and it won't take 99% moisture content. I believe, because the fiber saturation point, is 28% for Red Alder, and it's impossible to add more naturally. So I went from 28% to zero and the shrinkage at maximum is just under half an inch. Would you recalculate your Numbers starting with 28%, and see if they match those on the other program? I'm curious to see if they will agree then.
Indeed there is something wrong with those numbers. I think Mike has it correct in that the numbers are run out from lower MCs and they forget the tiny little detail of the fiber saturation point.Plugging in 28% I get a 10" board shrinking to 9.4" at 6% and swelling back to 9.59" at 13%.Nice catch, Lee
Yeah, that 2.5" shrinkage seems a bit much!
This all is just a curiousity for me. I'm just wondering what the total shrinkage curves looks like to see if there might be a pronounced 'knee' in the curve. My guess is that it is a smooth curve with no pronounced knee. And, I'm also guessing that the shape of the curves for all woods are similar with the curves just raised or lowered a little from species to species.
I guess it's just the engineering in me trying to come back out! And, I'm thinking that having such a chart printed out for the 8 or 10 most popular woods (all on one piece of paper) would be nice to have.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
I think I know what that program is doing. It's formula is linear and based on the part of the curve from 6% to 20% which is mostly linear in that range. By back projecting a straight line it's giving an answer that is much to great.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
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