Planed board strange behavior.
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Tagged: Board cup again
- This topic has 15 replies, 9 voices, and was last updated 6 years, 11 months ago by kevinjames.
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29 May 2017 at 3:12 pm #312409
I have a board of pine that is cup a lot. When I plane the board for the first time it took a lot of effort to do so with my planes. I first started with my scrub plane the I finished with my jack. The board was very nice when I finished planning.
You can imagine my surprise when I get to it on the next mourning, the board was cup again, a little bit but its noticeable.What have gone wrong?
29 May 2017 at 4:51 pm #312413I think that’s just the nature of wood unfortunately. Especially depending on what the original moisture content was, what the humidity of your working environment is, etc. I’ve gotten in the habit of wrapping my boards in plastic wrap when I’m done for the day to keep them from absorbing or letting go of any more moisture. I got the idea from Paul. He wrapped the panels for his drawer carcass to keep them that way. It worked for me.
Kevin
29 May 2017 at 5:40 pm #312415That can have alot oft causes, sapwood, defects in the wood vor the Tree itself, wrong storage, uneben moisture and so in.
Never leave a board flat in a table vor benchtop, always make sure air and moisture can get evenly at both sides.
Next thing is by far not every piece oft wood be it boards, slabs etc. is suitable for furniture making. Id look for a proper suplier or sawmill, and dont get the cheapest wood trust me quality lumber saves you alot oft cursing and problems.
I’ve had the same thing, particularly if I’ve reduced the thickness a lot. From doing some research, I found that it’s likely due to 1) the wood wasn’t dried all the way through, so when you expose the internal wood with the higher moisture content it starts drying and cups again, and 2) planing off a lot relieves internal stresses which allow it to move again (similar to when ripping.)
What I usually do is 6-square it and leave it a bit thicker than needed (just enough so if it cups/twists I can take it out again), then sticker it until I get around to actually using it, then I bring it down to final thickness and take out any cup if it came back.Tom
30 May 2017 at 7:14 am #312420Thank you all for your answers.
The moisture content of that particular board was under 6%(measured), the humidity in my shop is about 50%(measured). The wrapping of the boards with plastic wrap is a good idea, thank you Kevin. Philipp I am not sure about the quality of that piece but it seams of a good stock, but as I remember I indeed left the board on the bench top for the night. Unfortunately the wood quality is all the same here no meter where I buy it from, all the lumber is dried outside under shed. Tom thank you for your advices about the planning, that board has a cup and a twist so I had to remove a lot of material from the cup side, more than other side.Thank you all very much. I will take all your advices into consideration for my next project.
30 May 2017 at 4:22 pm #312429thats a big difference in humidity from the board to the shop it would take in a lot trying to balance for sure .
you may have to plan ahead and let your wood acclimate to your shop before starting a project for a few days to a week or so, I live in a desert and when I bring wood inside it sets for a week minimum before I do anything to it. seems to help a lot,
30 May 2017 at 5:10 pm #312431@dragomir are you absolutely certain that the board had under 6% moisture? because thats firstly too dry and secondly should not be achievable without kiln-drying.
With Airdrying you can get down to maybe ~ 15% give or take, keeping it near an stove will get it down further, ideally for furniture making you want between 8 – 12 % indoor and 15 – 18% outdoors (Gardenfurniture etc).
Only the Industries go down to 6 – 8% for making Plywood or sheetgoods.
The equilibrium moisture content at 70 degrees F and 50% relative humidity is 9%. See a calculator like http://www.csgnetwork.com/emctablecalc.html, which is the first one I found with Google (hope it’s right). Below 6% is low. A dry, forced air home at 40% relative humidity and 70F would give wood at almost 8%.
In any case, I think the answer is what @tom-r said. Don’t thickness directly to the final dimension. Stay fat, let things sit a bit, then get to dimension so that you can plane out any movement that happens.
30 May 2017 at 6:42 pm #312434No clue then maybe you have some different way of measureing the moisture, because the numbers i used above are more or less directly from the Textbooks we use and what my master told me and i do think a textbook and someone with over 30 years experience in the trade would know.
What i forgot earlier was that it may be down to local climates.
31 May 2017 at 8:31 am #312441Thank you all. For the environment humidity I am absolutely sure, but for wood I am not so sure ( I will check again) because my moisture meter is not very accurate (Chinese garbage). The measuring scale starts from 6% and there is a calibration procedure that I don’t do every time. The board was siting in my atelier for about a month before I get to it so it has a plenty of time to acclimate. I have the same problem with other wood species(walnut) from that supplier. I have checked and for my region the equilibrium moisture content for pine should be around 7 to 15% depending on relative environment humidity. So I think that this board is definitely kiln dry, and if so there is 90% chance to have a problem with internal stress of the board because the rapid change in the moisture content will shrink the wood intensively and when I plane there is going to be some stress accumulated because of the change of the dimension(smaller dimension will lead to increase the stress in the board). But it all depend on the kiln-dry process.
How long it will take acclimated before I get to it for furniture making? if the environment humidity is 50%Random tip I came across for dealing with thick stock that is going to recut or heavily reduced is to drop it a few times on your bench or shop floor to shock the the structure before you set it to acclimate to your shop. While a bit voodoo, it does seem to help.
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How long it will take acclimated before I get to it for furniture making? if the environment humidity is 50%
[/quote]I don’t know the answer to your question, and I’m not sure anyone else does, either. However, if you get a reliable moisture meter, you can test wood that has been in your shop for a very long time, and is therefore acclimated to your shop. That will tell you the equilibrium moisture level.
Then you can test the new stock, and note the result. After a few days (if it’s relatively thin, S4S stock) or a few months (if the bark is still on, it’s 16/4 stock from highly refractory species, ends are sealed in wax, etc) you can test it again, and after a few data points, you can estimate when your new stock will reach equilibrium. -
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