Seasonal humidity changes make life interesting for all of us, as wood expands and contracts across its width.
I’d like to become more knowledgeable and accurate at allowing for wood movement. Using Google I found the “shrinkulator” and the accompanying “Wood Shrinkage Table”, both of which are very helpful. I also have checked out a copy of Bruce Hoadley’s book Understanding Wood: A Craftsman’s Guide to Wood Technology. I hope to find a used copy for sale next month.
Sgian/Richard helpfully suggested planning on an average summer relative humidity of 60%, and an average winter relative humidity of 40%.
Would it be safe to “guesstimate” rel humidity of 40% Dec-Feb, 50% Mar-May and Sep-Nov, and 60% Jun-Aug?
Sophisticated topics can be challenging for my aging grey matter, are there any other statements of expansion and related besides Hoadley’s book that I might be able to obtain?
Thanks.
Replies
Without knowing where you are it's impossible to attempt to guess at the range of relative humidity. I suggest you get Hoadley's Understanding Wood. It has a chart and diagram that shows the average relative humidity in areas throughout the US.
Contact your local TV station and they can probably give you an answer.
May I also suggest you go to Radio Shack and buy a digital temperature/relative humidity gauge and put it on the wall in your shop.
Good suggestion, Howard. I keep forgetting that I have one on the motor switch box for the dust collector.
Several years ago I made some 4' and 5' sticks by edge gluing some wide short boards and then ripping across the grain and gluing those together. Essentially they are flatsawn been and quartersawn white ash glueups 1" long x 48 or 60" wide by 3/4" thick. I've been wanting to mount them on a nice piece of leftover ply, fix at the top, and chart how they move during the year to show customers. With your suggestion I'll try to record every day or two the rel humidity in the workshop to see how that correlates with the movement. Then I'll be able to answer my own question.
(Edit) I'll have to try to record for the same days the rel humidity at home, too, won't I.
Thanks!
Edited 12/13/2009 6:31 pm ET by DonStephan
"Sgian/Richard helpfully suggested planning on an average summer relative humidity of 60%, and an average winter relative humidity of 40%."
I did suggest that Don. It's based on readings I took in our house in Houston when we lived in Texas. It's also based on the the RH readings I've gathered here in the UK since I moved back home to Blighty in 2003.
Whilst I can't say these numbers apply to all inhabited residential properties around the world they do cover a good range of RH values at temperatures comfortable to live in, ie about 20-21ºC (68- 70ºF). Slainte.
richardjonesfurniture.com
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