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Author Topic: Releasing stress  (Read 4372 times)

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Offline Tom

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Releasing stress
« on: January 28, 2002, 12:22:36 PM »
Sawing will release stresses in a cant and cause the cant to bend and the boards to be  thick ends/thick middles or thin ends/thick middles.

When sawing on a horizontal bandmill, the log is laying on a bed.  The saw removes wood from the top side of the log.  Since the tree made adjustments as it grew to try to remain straight,  the removal of this wood allows there to be more stress on one side than the other and, depending on the shape of the log, will causes the log to lift from the bed.  

Usually the log or cant will lift in the middle causing it to rest on the two ends as boards are removed from the top.  

You can see a board move as it is removed from the cant, the cant is moving in the opposite direction, maybe at a lesser degree, but it is moving.

When you cut a board from a cant and the ends of the board lift, then the ends of the cant are going down.  The cant is rising in the middle and your next board will have a thick middle and thin ends.  

The only way to keep the cant down is with the clamp, but a cant can soon overcome that pressure.  When the cant is held down you will notice that the boards removed will reflect the tension in the log increasingly and will not lay flat.

The resolution:  When you see air developing under the cant (as it arches) turn the cant over and make a tension releasing cut from the other side. Many times a cant will have to be turned every board or two in order to keep the stresses to a minimum.

If there is a sweep in the tree then the movement will be quite noticeable and generally the ends lift rather than the middle, but the solution is the same.

If the blade rises as it enters the cut and drops off of the cant at the end of the cut, then there are other problems that will cause the boards to be uneven.  These are to be found in the set of blade or the adjustment of the blade guides.

Cutting sweeps:

A log with a sweep(bend) will provide more usable lumber if the boards are removed in the direction of the sweep, either off of the hump or the saddle.

Turn the log on its ears and take a slab off of the hump.
Turn it 1800 onto its flattened hump and remove the ears
Turn it on its  side and take a slab
Turn it on its last side and cut a slab
Turn the cant again onto its ears and cut boards from the hump side and the ears side.alternately.

You will notice that the boards will come off with the tension lifting them.  Nails will hold them down.

If you cut from the sides of the cant, then the boards will bend to the side causing a tremendous amount of "crown" and a board that can't be easily pulled into place.
This phenomenon is experienced in quarter sawing and must be delt with there.

A good rule of thumb when judging a log is:  Boards tend to bend toward the bark, center the heart.  (if the center of the board is an equal distance from the bark on both sides, then the tension will keep the board straight.



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Re: Releasing stress
« Reply #1 on: January 28, 2002, 01:45:21 PM »
By Jove I remember you showing me that when I was trying to offload for you.  As you cut boards from one side of the log it would start rising in the middle. Now, what I thought you did was when the middle rose about an inch, you'd flip the log over and cut some boards from the other side to even out the tension. Whatever it was that you did....I decided it was safer for me to offload the 2" X 12" X 16' boards you were cutting.:o    DanG good thing I like peas.... ::)
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

Offline woodmills1

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Re: Releasing stress
« Reply #2 on: January 28, 2002, 05:07:25 PM »
James Mills,Lovely wife,collect old tools,vacuuming fool,36 bdft/hr,oak paper cutter,ebonic yooper rapper nauga seller, Blue Ox? its not fast, 2 cat family, LT70,edger, 375 bd ft/hr, we like Bob,free heat,no oil 12 years,big splitter, baked stuffed lobster, still cuttin the logs dere IAM

Offline Gordon

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Re: Releasing stress
« Reply #3 on: January 28, 2002, 05:51:57 PM »
That post deserves to go in the knowledge base Tom. Some great info there. ;)


Offline Bibbyman

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Re: Releasing stress
« Reply #4 on: January 29, 2002, 12:52:40 PM »
Hay Tom,

What's going on?  Why are you just giving away all this knowledge and experience?  Why not let the new guys struggle,  make mistakes and study and learn this stuff or fail trying the ol'-fashion hard way like the rest of us?  Is this something to do with having gray whiskers?  Hummm?

BTW,  I release stress by giving my sawyer a little hug and a kiss.  :-*  I just wish she'd take that helmet off when she comes into the house. ::)
Wood-Mizer LT40HDE25 Super 25hp 3ph with Command Control and Accuset.
Sawing since '94

Offline Papa Dave

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Re: Releasing stress
« Reply #5 on: January 29, 2002, 02:28:44 PM »
Thanks Tom, I needed that. It is real helpful. ::)

Offline Larry

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Re: Releasing stress
« Reply #6 on: January 29, 2002, 02:46:33 PM »

Great set of three posts.  I had the heart check down,  half way understand the stress in a cant but was completly lost on the reaction wood.  Your posts were just in time as I have a 10'  long cherry log that has a way off-set pith at the butt end and a centered pith at the small end.  I didn't have a clue on how to saw it but I will try to do it just like your picture shows and see what happens.  I was going to saw today but the skys kept dumping frozen rain on me so I decided it was a better day to work inside.

Thanks again for those three posts.  Got them archived in the PC for future reference.

Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

Offline Don P

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Re: Releasing stress
« Reply #7 on: January 29, 2002, 04:44:04 PM »
I felt the same way. The Red Oak I cut yesterday was a real ole lena  ;D. I mean a sweeping sidehill that I lacked a foot of being able to reach around. At the critical time I was wishing I had a big saw . Couldn't keep up and as the fall slowed with all the downhill weight it started to try to high chair. With the sweep I bucked it to 8'ers and the bottom 2 are cracked, happily the right way.
They sure make you wish for hydraulics when its time to turn a rocker.
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Offline TnAndy

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Re: Releasing stress
« Reply #8 on: January 29, 2002, 04:57:54 PM »
SO THAT'S HOW YOU DO IT.....i've been running around in front of the sawhead and walking down the cant to keep it down on the bedrails....and if I keep doing that, I MAY even have to start putting the covers on the wheels. :D
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Offline L. Wakefield

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Re: Releasing stress
« Reply #9 on: February 02, 2002, 12:19:25 PM »
   Tom, I have to add in- great information. I had posted a while back in some thread or other about how you deal with laying the log down to saw if it's not straight (and usually it's not. Your post goes way further- I hadn't heard those terms 'saddle' and 'hump' (not in this context anyway)- but i can see it. I had only thought as far as getting the most # of high-quality boards- you go past that to why they do, what they do, as they peel off- and how to compensate. It makes more sense but I hope I'll be able to retrieve this again if/when I am practicing as you preach :). That is the bad thing about the web- things go away as times change. :-[  lw
L. Wakefield, owner and operator of the beastly truck Heretik, that refuses to stay between the lines when parking

Offline Jeff

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Re: Releasing stress
« Reply #10 on: February 02, 2002, 06:54:20 PM »
What makes you think we're going anywhere??  L., we will be here long after the other guys. You see, if they lose money, their gone.
We never had any money, so we got nothing to lose. It'll be here. ;D
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Re: Releasing stress
« Reply #11 on: February 05, 2002, 07:07:31 AM »
Great articles Tom. You've saved me much trial and error. I just finished sawing my first red oak logs and was scratching my head a bit. I'll be looking forward to more of your posts.

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