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How do you deal with internal stress relief when resawing?

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Forum topic by Jim Graham posted 11-05-2011 02:33 AM 1675 views 0 times favorited 15 replies Add to Favorites Watch
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Jim Graham

5 posts in 1092 days


11-05-2011 02:33 AM

Hello, I am fairly new to woodworking and as you can see, a new member here as well.

I am building a tv table using hard maple and ran into an unanticipated issue tonight while resawing. I purchased some hard maple from a local lumber yard two weeks ago. It is 2.5” thick hard maple in various widths and lengths. The pieces I had trouble with tonight were approx 5-7.5 inches in width and 6 feet in length. Using the bandsaw, I removed a piece from the width using the bandsaw, this provided a reasonably flat surface to use when resawing the piece in half. The first piece I had trouble with bowed outwards as I was resawing, the pieces were bowing away from eachother. The second piece I cut, the pieces bowed inwards squeezing the blade as it cut. I actually had to stop and wedge a square in behind the blade in order to relieve the pressure and continue cutting. Now I am left with four pieces I had intended to use for the top but are now fairly bowed. I do not think there is enough material left to plane the bow out on the jointer.

My first question is, Is there any way to know that there are significant internal stresses which will result in such bowing when resawn?

My second questions is, What do I do now?? I spent a fair amount of money on these boards and if possible I would like to use them. I could save them for a future project which requires lengths short enough that I can plane the bow out, but I would rather (if possible) use them in this project. If I cant, thats life and I will find something to use them on. I just dont want to spend more money on material if I dont have to.

When I got the boards home, I checked the MC and found a range of 6%-9%. The boards got slightly damp on the trip home from a light mist/rain. They were not soaked. The lumber yard I bought them from stores them in an unconditioned warehouse but it is dry in there. I brought the boards into my basement (shop is there) and sticked them up for two weeks. I run a dehumidifier at 50% humidity and the temp is roughly 55-60 degrees usually. I checked the MC every few days to monitor changes. For the past three days the MC has been stable between 6% and 7%. I did resaw one piece before these two and it was great. No bowing at all.

I am using a JET 14” bandsaw with riser blocks, carter bearing guides and tires, a woodslicer 1/2” blade. I also used a bit of blade wax before each board. It seemed to cut very nicely and did not produce any burn marks or smell.

Thanks for any input you may have!

Jim


15 replies so far

View Jim Finn's profile

Jim Finn

1706 posts in 1619 days


#1 posted 11-05-2011 03:32 AM

I have had similar experiance while resawing oak. I found, in my case, that if I kept the wood in my shop a few days before attempting to resaw it this problem dissapeared. I guess it had to adjust to the heat and humidity of my shop.

-- In God We Trust

View Jacob Lucas's profile

Jacob Lucas

100 posts in 1129 days


#2 posted 11-05-2011 06:23 AM

After the pieces have been cut and the bow appears, maybe you can wet them down with water and stack some heavy stuff (5 gal buckets of sand/water works well) on the piece to hopefully correct the bow.

View PurpLev's profile

PurpLev

8476 posts in 2345 days


#3 posted 11-05-2011 06:31 AM

Welcome to Lumberjocks!

And welcome to woodworking – wood moves – get used to it and plan ahead with the possibility it will move against your will.

Looking at the grain direction in a board you can guess which way the parts will bow if you cut them a certain way – my recommendation so some research on wood growth, milling, and moisture in the wood which in some texts can explain how the wood will move based on its grain orientation and flow.

My suggestion for these current pieces is to hold on to them and try to use them for another project. you should always mill parts oversized so that if the initial milling produces bowed or crooked boards you can still joint and thickness the parts to your specifications.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View EPJartisan's profile

EPJartisan

1079 posts in 1822 days


#4 posted 11-05-2011 09:28 PM

Hello :) I agree with PurpLev … I suggest that you try to learn less by the tools and learn to the woods. Most woodworking mags and books teach tool usage, but that only does half the job. Each wood species is unique and each board will do something different. Follow the grain patterns, avoid knots and tight grain areas as these are high stress areas. Also you should always re-saw lumber to a generous rough size you need and let stablize first. Moisture content has it’s place, but honestly a board can have different MC in different areas, depending on the species. Tension and compression in wood is an elaborate thing to try to explain, but know that wood moves with the growth rings and tension is what keeps the hardwood tree growing upwards and not out and down like confiers. There are cell structures (fibers, parenchyma, tracheids) to consider, hidden defects in growth or damage, not to mention some woods hold tylosis and other chemicals/metals/crystals in their cells and yes.. moisture to consider. Some woods even heat up and twist a bit just from friction with a cutting tool, and some can come back to shape later. Some woods burn at a slight touch of a dull blade. All this come with time and dedication. At first I was horribly intimidated, but now I can read a board like a billboard sign.. and yes.. I still get surprised. It is part of the fun.

Be warned with one question on here you will get a wide variety of backgrounds and opinions, but all that makes this one amazing website. Welcome.

-- " 'Truth' is like a beautiful flower, unique to each plant and to the season it blossoms ... 'Fact' is the root and leaf, allowing the plant grow and bloom again."

View richgreer's profile

richgreer

4524 posts in 1771 days


#5 posted 11-05-2011 10:09 PM

I find that when I am suffering from internal stress, a glass of wine works wonders.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View tnwood's profile

tnwood

204 posts in 1783 days


#6 posted 11-05-2011 10:46 PM

It is likely the problem is due to improper kiln operation if it is kiln dried material. I bought some maple several years ago at a relatively high cost and as soon as I cut into it, it started to twist. There was no way to use it so it sat in the corner until a project requiring thin stock came along and I could surface it flat. Although the outlet didn’t do the drying, I never went back there again as they weren’t doing their due diligence in buying the stock.

View Jim Graham's profile

Jim Graham

5 posts in 1092 days


#7 posted 11-06-2011 03:32 PM

Thank you everyone for your input. It doesn’t sound like there is much I can do aside from use them in a later project. Im going to give them a few more days and see how bad they are.

I allowed for a half inch of thickness to use for planing which I do not think will be enough. I may try to go down to 3/4 on the top, I think I can squeeze that out of the boards. The table top is 22×60 and its for a tv stand. I plan on having a stringer run through the center of the top along its length for additional support, so I think I can get away with 3/4” thick.

Any suggestions for books on the nature of wood and how to read wood when selecting?

Does anyone have suggestions for lumberyards in the New Hampshire area?

View StumpyNubs's profile

StumpyNubs

6249 posts in 1497 days


#8 posted 11-06-2011 03:38 PM

Rich beat me to my joke!

Do me a favor though, click over to the Charles Niel vs Stumpy Nubs contest thread and help judge the boxes! Then come back here and continue your discussion with the warm inner feeling of having done another good deed…

-- It's the best woodworking show since the invention of wood... New episodes at: http://www.stumpynubs.com

View PurpLev's profile

PurpLev

8476 posts in 2345 days


#9 posted 11-06-2011 03:40 PM

you can get a copy of the book in PDF version posted here:
http://lumberjocks.com/topics/9692

I also find “Tage Frid Teaches Woodworking” a good explanatory for this as well as everything else from tool usage , joinery, finishing, shaping and everything woodworking related.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View PurpLev's profile

PurpLev

8476 posts in 2345 days


#10 posted 11-06-2011 03:43 PM

FYI, depending on where in NH you are located, you might be close enough to Rowly, MA which has a nice lumberyard called Yankee Pine Lumber.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View MOJOE's profile

MOJOE

547 posts in 1966 days


#11 posted 11-08-2011 05:06 AM

Sorry to hear about your bowed lumber….I just went through a similar issue with a lid for a box. I picked up the lumber from the local BORG, and after removing about 1/2 the thickness from the center of the lid, it twisted bad…..bad enough that I didn’t think I could use it. I got busy with other things, and it sat on my tablesaw for about 3 days….I picked it up then, and it was flat again (not perfectly, but I could at least work with it). Not really sure what happened, but you might let the pieces site a bit longer….also, since you top is fairly long, you may be able to flatten the bow as you edge join the pieces together (assuming that is what you’re doing)....biscuits might be a good option here.

-- Measuring twice and cutting once only works if you read the tape correctly!

View Jim Graham's profile

Jim Graham

5 posts in 1092 days


#12 posted 11-13-2011 04:33 PM

Thank you everyone for your thoughts on this. I have let them sit since the original post. Heading down soon to see what has happened. They looked a little bettre, maybe I will luck out and be able to work with it!

View WDHLT15's profile

WDHLT15

1176 posts in 1173 days


#13 posted 11-14-2011 04:43 AM

Wood can have internal stress that the sawyer cannot see. However, most times, this type of bowing occurs because the moisture of the shell (outside) and the moisture of the core (center) are different, setting up the stress that bows the board. Remember, if you get wood hot with steam, bend it, clamp it, and let it dry, it will stay bent.

I suggest that you sticker your stock with sufficient weight to get the boards reasonably flat again, and let them come to full equilibrium between the shell and the core. That way, you may end up having less bow such that you can plane the boards flat and meet the requirements for your top.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT15 Sawmill. Nyle L53 Dehumidification Kiln

View Jim Graham's profile

Jim Graham

5 posts in 1092 days


#14 posted 11-16-2011 05:02 PM

I checked the boards and they improved significantly with time. Thank you everyone for your help and sharing your knowledge!

View buckles's profile

buckles

24 posts in 1239 days


#15 posted 11-21-2011 04:38 AM

Jim
When dealing with rough sawn or when resawing lumber it is always a good idea to do to each side what you do to any other side. When you cut one side, the stress is relieved and the moisture is now different so movement happens.
When you cut all four (or six) sides, movement is minimized. It is not always eliminated.

Storing lumber in a shop helps but only if it is stickered so air can move around it. The ends should be sealed also.
Regards
Joe

-- Politicians are like diapers. They need to be changed for the same reasons.

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