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Resawing dry wood without causing stress movements

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Forum topic by TopamaxSurvivor posted 04-09-2011 10:38 AM 2015 views 0 times favorited 24 replies Add to Favorites Watch
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TopamaxSurvivor

14753 posts in 2333 days


04-09-2011 10:38 AM

Topic tags/keywords: resaw dry wood stress movement cup warp

I have followed a lot of issues here on LJ the last couple of years where fellow JLs have experienced various stress changes in wood they have sawn. I have a piece of dry 9/4×9 x 28 inch blackline spalted maple I want to resaw on of these days. I am thinking the best time to saw it will be in the hot, dry days of the August summer. I believe it was air dried in western Oregon. I am also thinking I will sand a 1/16 off the side opposite the saw cut. I am hoping this should receive the board of the propensity to cup, warp bow, curl or otherwise decide to change shape. Any comments, suggestions or criticism of the plan? Better ideas??

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence


24 replies so far

View patron's profile

patron

13034 posts in 1998 days


#1 posted 04-09-2011 01:21 PM

spell relieve

wish i knew more about the milling and drying end of things
done allot of felling
and allot of using
but not much knowledge about the sawmill side of wood

only one way to find out

keep us posted
always ready to learn something

the proof is in the
blackline spalted maple pudding

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

View ScottN's profile

ScottN

259 posts in 1337 days


#2 posted 04-09-2011 02:04 PM

All stressed wood is a result from the moisture in the wood, it will absorb or desorb moisture until it is in equilibrium with its surroundings. The biggest factor is in the drying process. When wood is kihln dried, they’ll dry the wood down
and shrink the cells in the wood and the condition the wood by slowly bring the moisture content back into the wood. Each wood species is different and needs to be done so accordingly. And if its not done correctly and rushed through the process you’ll get case hardening…which is “stressed wood”.

The same thing applies to your wood shops. Most woodshops and millworks keep there shops around 40-45% humidity to prevent adding stress to the wood.I keep my shop between 40-50%. So if you keep your windows open or exhaust your dust collector outside I don’t see how you you can control the humidity levels in your shop.If you don’t control the humidity level you’ll end up with more bowed, cupped and internal stressed boards…your call.

I was debating if I should post this or not. But I think its important.


-- New Auburn,WI

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ScottN

259 posts in 1337 days


#3 posted 04-09-2011 03:54 PM

I was searching for a video to further explain what I was getting at. http://youtu.be/HQGjDHtN3MQ

-- New Auburn,WI

View NBeener's profile

NBeener

4806 posts in 1831 days


#4 posted 04-09-2011 04:17 PM

ScottN:

Darn.

My shop DOES stay at between 41% and 43% RH.

Meaning …. I have to find yet another excuse for my crappy woodworking ;-)

Good info. Thanks !

-- -- Neil

View Bob Kollman's profile

Bob Kollman

1796 posts in 1848 days


#5 posted 04-09-2011 07:02 PM

I work with exotic plastics, basicly we anneal the plastic and then machine it.

in dealing with movement and stress the best approach is to cut rough, let

the material spring. With wood it is the same. You can also insure a good out come

by doing several rough operations by making several rough cuts pulling the twisting

and cupping out as you go along. We use a lot of double sided tape turning on the

lathe. This way we can remove the high points with out puting any external force on

the material, after out first side is flat and stress free, it’s just a matter of maching

the second side. My biggest problem is my jointer has only 6” of width, but I can

rely on the 6” and less boards to be dead flat. The big issue is removing the high

without stressing the material i.e. the rollers on your planer usually put to much

external force on the high spots…..Basicly it’s a matter of building jigs, using hand tools,

to think your way thru the stressed material problem…..I think i had to much coffee

already!!!! Blah blah blah…LOL

-- Bob Kenosha Wi.

View stefang's profile

stefang

13054 posts in 1991 days


#6 posted 04-09-2011 07:04 PM

Scott knows what he is talking about. I live in a climate with high humidity as you yourself do. This climate is pretty ideal for woodworking as opposed to other areas which are much less humid and where there are big differences between summer and winter humidity. It’s the differences that get you. However, I don’t obsess on this. I just try to use my materials before they begin to warp, and I rarely have any warping problems once they are incorporated into my projects. So I guess I’m saying ignorance is bliss, but only because you live in a wet area like myself. I know my advice sounds a little stupid, but if you build with the warp problem in mind, you shouldn’t have a lot of problems. Ok now I am in for it. Shoot away folks!

-- Mike, an American living in Norway.

View tenontim's profile

tenontim

2131 posts in 2402 days


#7 posted 04-09-2011 07:16 PM

I will usually mill the board to a thickness more than I need. Let them acclimate to the shop for about a week, so I can see what they’re going to do, then do the final milling to size. This will head off many of the problems.

View TopamaxSurvivor's profile

TopamaxSurvivor

14753 posts in 2333 days


#8 posted 04-09-2011 11:22 PM

Thanks guys, The board is flat now without any obvious signs of trouble. i have had it for about 6 months. i guess my concern is finding trouble a day or two after I resaw it. My thought was to expose new surface on both sides to reduce the risk of loss of equilibrium. ???? ;-)) Who knows until I do it eh? The shop is a garage with a double door that is opened frequently. Humidity control is out of the question. But, we never go to less than 30% and are usually in the 50 to 70% range. I’m not 10 % what I will do with it, but I have some ideas.

I’m afraid to resaw it thinner than an inch. Do you think I will be better off keeping it thicker than 3/8 to 1/2 inch?

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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TopamaxSurvivor

14753 posts in 2333 days


#9 posted 04-09-2011 11:26 PM

Guess I’m trying to be proactive rather than sorry ;-)

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Jack_T's profile

Jack_T

621 posts in 1688 days


#10 posted 04-10-2011 01:46 AM

You could cut it into veneers and really stretch the spalt.

-- Jack T, John 3:16 "For God so loved the world that he gave his only Son, so that everyone who believes in him might not perish but might have eternal life."

View rance's profile

rance

4132 posts in 1818 days


#11 posted 04-10-2011 02:17 AM

I mostly agree with tennontim. I might only extend the acclimation period. Imagine your board as a big sponge. The outer layers are drier than the inner layers because the inner layers are insulated by the outer layers. When you cut down the middle, you are exposing those moist inner layers. When they dry, they will likely affect the board because it is unbalanced.

If you resaw a board into thirds, then let the pieces dry, the middle third is mostly likely to remain straight since you have exposed equal parts on two opposite surfaces. The outer two boards are not quite as likely to remain straight since they now have a dry side and a moist side. They are unbalanced, moisture-wise, and as they reach equilibrium, they are likely to move.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

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TopamaxSurvivor

14753 posts in 2333 days


#12 posted 04-10-2011 05:13 AM

That is why I was thinking of doing an aggressive sanding on the out side before the resaw. Will that make much difference or just stir up a lot of dust?

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View John Ormsby's profile

John Ormsby

1280 posts in 2394 days


#13 posted 04-10-2011 05:36 AM

I would suggest you also plan your project to re-saw the spalted wood and work it and glue it in place the same day. This will insure that it stays straight. I have never had a problem with a board once it is in place. Most woods that tend to warp or move should be worked at once and secured. You will have much more movement if the processed board is left to “acclimate”. Just my 2 cents worth.

-- Oldworld, Fair Oaks, Ca

View rance's profile

rance

4132 posts in 1818 days


#14 posted 04-10-2011 05:54 AM

Topo, 1/16” off one side and 1/2” or more on the other? Only doing it will really tell. I’m just telling you you have a better chance with equal on both sides. Sorry, I’m just not that much of a wood whisperer.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View Bob Kollman's profile

Bob Kollman

1796 posts in 1848 days


#15 posted 04-10-2011 06:51 AM

Resaw….be happy!!!! :) Good luck, and may the warp be without you!!!!

-- Bob Kenosha Wi.

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