Hello,
I was curious as to peoples methodology when dimensioning rough cut lumber. Specifically, how long do you let the pieces “settle” before continuing on to final dimensions. I find that when resawing thicker stock, there is obvious cupping, bowing, or twisting after initial cut. Is it beneficial to wait a period of time before flattening and planing or will subsequent removal of outer surfaces continue to release tension within the wood and call for several flattening sessions until the wood stabilizes?
I have found that if I wait a day after resawing and flatten and plane, the next day there is more twisting, etc. Would a longer waiting period allow for a single flattening and planing later or would the twisting, etc. still take place- considering that the wood is 6-8% moisture content.
Hope this makes sense,
Eric
Replies
Eric, deep resawing wood (if that's what you're asking about) can be a risky enterprise if an important test is not carried out prior to attempting it. By deep resawing I mean you intend to create two, say, bookmatched 3/4" boards out of one 2" thick board.
Before resawing like this it's best to do the fork or prong test to establish if the board, and by extrapolation, the whole batch of wood is case hardened or stressed in some other way.
Here's how to do the fork test. About 18" (or more from one end of a sample plank) cut a short length out across the grain about 1.5" to 2.5" long. Take this short length and lay the end grain down on the bandsaw table. Cut out the centre of the plank from one edge to within about 3/4" or 1" of the other edge leaving two forks of the original outer faces about 1/4" -- 3/8" thick. Sometimes three forks or more are cut, particularly in thicker stock.
If the plank (batch of wood) is under stress the forks will, either immediately or over an hour or three,
1. Close up indicating case hardening, or
2. Spring apart indicating reverse case hardening, or
3. Remain approximately parallel indicating unstressed or minimally stressed seasoned wood.
Only attempt deep resawing with wood from 3 above. Deep resawing attempts using wood that exhibits results as in 1 and 2 above are doomed to failure at some point in the project. Without doing the prong test your first indication that you have wood that is case hardened or reverse case hardened is cupping and or severe bowing/winding of the board as you deep resaw.
You as a user can do nothing to fix case hardening or reverse case hardening. You can often use the wood if equal amounts are planed from either face keeping the stresses approximately in balance, but you cannot resaw. You can only take the whole faulty batch back to the supplier for replacement if you must have stress free wood.
The prong test, although it might seem wasteful of wood in the first instance can save hundreds or even thousands of pounds or dollars depending on the project you're working on.
I can highly recommend you get a copy of R Bruce Hoadley's Understanding Wood. Worth every penny if you want to learn about trees, wood, its character, its strengths, and its problems and how to avoid them. Slainte.
Great advice, I never have encountered theis severe twisting with most of my resawn projects before. I will certainly look into the book and do some research. Thank you for your assistance.
Eric
Eric, I don't have an image handy to post. It's better perhaps to link you to an essay which is posted on the US based Woodweb site which discusses wood stresses and has a picture of the fork/prong test. Slainte.
http://www.woodweb.com/knowledge_base/Conditioning_Relieving_those_stresses.htmlRJFurniture
Very useful info, thanks. It is so dry here in Massachusetts that I think the inner core is drying out very quickly- I never had much trouble in the more humid months.
checked out your website- very cool and inspiring work!!
Eric
This is great info. Would you mind posting a pic of one of your "forks"?Thanks,
Mark
Measure it with a micrometer, mark it with chalk, cut it with an ax.
After you resaw a board, you should tape it back together and let it sit for 3 weeks. This lets the moisture even out a little slower and prevents some of the cupping. I read that trick out of a Tage Frid book, and it seems to help.
To answer your original question, I let the boards sit on stickers for four or five days after initial runs through the bandsaw, jointer and planer. These initial runs are to bring the board to within one eighth to 3 sixteenths of the finished dimension on three sides. At this point, the length is within one inch, maybe a little less. Then after the 3-4 day wait, I true up the boards to final thickness and length. Most of what I make are chairs and rockers, so I am dealing with blocks of wood that are bandsawed and otherwise shaped into the final chair part, be it a leg or arm, only after the blocks are stable. The goal of the two step process is to get to the point where I am working with stable, true blocks of wood.
When I have the time a I also follow CHATOBOB's process.
Mikeplease excuse my spelling.
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