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Forum topic by maraziukas | posted 05-17-2011 07:39 PM | 10076 views | 0 times favorited | 19 replies | ![]() |
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05-17-2011 07:39 PM |
Topic tags/keywords: question Hello fellows, I faced with a problem when resawing a blank of oak – it bows. Why is it happening? Help me guys with that, please! Thanks! -- Maraziukas, Lithuania, https://www.marius.morazas.com |
19 replies so far
#1 posted 05-17-2011 07:47 PM |
Grain and moisture can have a lot to do with it. Other things that cause bowing and twisting is internal stress in how the tree grew and later cut. -- David in Damascus, MD |
#2 posted 05-17-2011 08:08 PM |
Internal stress and/or moisture. That’s milling for you. Cut your |
#3 posted 05-17-2011 08:48 PM |
Thanks. As I understand, there’s nothing to do with this. -- Maraziukas, Lithuania, https://www.marius.morazas.com |
#4 posted 05-17-2011 09:48 PM |
After milling, stack the pieces up on a level surface, using sticks (approx 3/4” x 3/4” and long enough to go across the boards) across the grain to provide room for air flow. Weight it down. Let it sit for a few days and frequently the moisture content will equalize and the part will straighten out. Not a guarunteed fix but worth trying. Be Careful! Herb -- Herb, Florida - Here's why I close most messages with "Be Careful!" http://lumberjocks.com/HerbC/blog/17090 |
#5 posted 05-17-2011 10:18 PM |
Wood bows because the internal stress that is contained in the piece. These stresses usually run along and radiate from the grain. The direction of cut either relieves them or focuses them to some portion of the board….When wood bows like yours…the best bet is to use short pieces of the wood so that the stresses are reduced….otherwise it will continue to move…thus making your joints weak and possibly destroying a well made project. Here is some technical explanation from : Woodweb.com -- Woodworking.....My small slice of heaven! |
#6 posted 05-18-2011 07:07 AM |
The only material I’ve that doesn’t change shape when resawn is MDF. Wood has natural internal stresses and pockets of MC higher then other parts of the wood. You can test for MC with a meter and I’ve had it vary over different parts of the wood. One thing I’ve found that can help straighten a board (warp or cup) is your lawn and the sun. Place the board on the grass crown up. This way the underside will absorb some moisture from grass and the sun will remove some moisture from the other side at the same time. I’ve had pretty good success with this method for many, many years. Not all boards will respond and flatten out but many will. -- Don, Diamond Lake Custom Woodworks - http://www.dlwoodworks.com - "If you make something idiot proof, all they do is make a better idiot" |
#7 posted 05-18-2011 09:28 AM |
Thanks a lot for the explanation and suggested methods. The boards already lay on the grass :) -- Maraziukas, Lithuania, https://www.marius.morazas.com |
#8 posted 05-18-2011 01:45 PM |
Reg – There is more to this. When kiln dried, I forget the actual temperature, the sugars in the wood will change. If the wood is dried too quickly, the moisture inside is trapped until the wood is cut or milled. In wood like white oak, this gets even more touchy because the pores of the grain have a membrane that makes the wood basically waterproof. Air dying does not crystalize the sugars so the movement of moisture is not impeded. This is why kiln dried lumber splinters and is more brittle than air dried lumber. The main problem with air drying is that it does not kill any critters that might be in the wood where kiln drying over 125 degrees (F) kills them or drives them out. -- David in Damascus, MD |
#9 posted 05-18-2011 05:51 PM |
DLCW – isn’t that a pretty temporary fix, until the moisture re-stabilizes? |
#10 posted 05-18-2011 06:31 PM |
MrWoodworker – I’ve not had a board spring back when using this method. The drying and absorbing does stabilize the wood a lot. But, like I indicated, this method works for most boards but not all. Like David says, there is a lot more going on inside the wood during the kiln drying process. If not done correctly (I.E. – most dimensional construction lumber kiln drying) you can have a real mess on your hands. -- Don, Diamond Lake Custom Woodworks - http://www.dlwoodworks.com - "If you make something idiot proof, all they do is make a better idiot" |
#11 posted 05-23-2011 01:45 AM |
I have had this problem when resawing oak to 1/4” thickness. In order to minimize this, I keep the wood inside my workshop a few days to allow it to acclimate before resawing. Works for me. -- Website is https://craftingcouple.com/ |
#12 posted 05-23-2011 05:24 AM |
Maraziukas, Besides the above mention reasons for wood to bow another one is the knot density and the size of the knots. Another reason for bowing is the time between when the lumber you cut for use and when you actually use it. I’ve seen a good example of this when cutting stair stringers for multifamily projects. I’ll get a bundle of #1 2×12s usually pine or douglas fir. These boards don’t have a knot in them, they’re “butt cuts” meaning the wood taken between the tree stump and the first tree limb. If I cut the stringers for the stairs from them, they will be ok to use as long as I use them inside of a few hours. I can pick the straightest prettiest board from the bundle for a pattern and by the end of the day the bow in the board is already going the other direction from the way it was when I started. On the other hand. I can use a #2 2×12, this one has a few knots and they are small. I pick the best looking one, make a pattern and can cut with it all day and sometimes even another day or two and it will maintain the same side bowed as when I started. -- Darrell, making more sawdust than I know what to do with |
#13 posted 05-23-2011 02:50 PM |
One word: Lointer -- A TOOL JUNKIE- There, I just admited it to myself... |
#14 posted 05-23-2011 08:37 PM |
WoodRMe: Lointer, what dictionary does one find that word in? How does it apply to this topic? -- Darrell, making more sawdust than I know what to do with |
#15 posted 05-24-2011 04:28 PM |
A rose is a rose etc I don’t need an English lesson, stop wasting bandwidth. -- A TOOL JUNKIE- There, I just admited it to myself... |
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