Stress, Gangsaws, and my question.

Jeff · January 06, 2004, 06:36:56 PM

At our mill, much of our 4/4 lumber is generated through the use of a gang saw. We will cut a 3 sided dimensional cant, say 5.5 or 7.25 inches in thickness, and anywhere from 8 to 12 inches wide then send the whole thing through a gang saw ripping it into boards. Rarely do you ever see a board come out of the gangsaw twist or bow. I was watching today. I had some aspen logs with quite a bit of stress. Example: I would slab, take a 4/4 board and it would peel off like a ski. I would flip 180 and take a slab and then another board and that board would peel off like a rocking chair rocker. I would then flip the log down, take a slab, then a board to square the edge, yes another ski, then drop the cant to go to the gang saw.

They would push it through and all the boards come out nice and straight.. ??? ???

Whats the thoughts on why this might be?

VA-Sawyer · January 06, 2004, 07:08:43 PM

OK, Here's my WAG... The outer layers of the tree have dried more than the inner ones. The outer 'skin' wants to be shorter because it is drier. When you saw the slabs they turn onto skis. The inner part of the log is closer to it's normal moisture so it doesn't have the stress.... yielding straight boards.

Rick
VA-Sawyer

Kevin · January 06, 2004, 07:12:16 PM

Pilot error? :D

ARKANSAWYER · January 06, 2004, 07:15:40 PM

Jeff,
It is because most of the boards produced by the gang saw are qsawn. (well some what any way. most are rift for sure) The cant is sawn through and through and my guess is that the first board or two from the top of the cant that still has the slab on it will "rocker" as well. Also most of the stress in the log is relived by the time it gets to the gang saw and what it is sawing is more stable.
ARKANSAWYER

Jeff · January 06, 2004, 07:16:00 PM

QuotePilot error? :D

I'll ignore that. ;)

Well, these logs were trees just 3 or 4 days ago. There should not be any drying stresses involved, I would think.

Corley5 · January 06, 2004, 07:16:34 PM

Or the outside of the logs are frozen and the insides aren't. The frozen outer rings have more tension ???

Jeff · January 06, 2004, 07:18:32 PM

Could it be how the stess is released in the remaing boards? That it is kinda chopped up so to speak and it is released through out the log evenly? In my experiments today, I cut a couple on up into boards on the head rig and in the center cuts I had side warp.

Jeff · January 06, 2004, 07:21:10 PM

The logs seemed froze clear through. Half froze logs generally produce some tell-tail sawing problems.

East_West_Dan · January 06, 2004, 09:35:25 PM

I wonder if the fact that the tension/stress on both sides of the board are being released at once has anything to do with it. Maybe by releasing some of the stress one side at a time causes the board to take a certain set which makes it better for a ski than a piece of trim.Just a guess. I wonder if the gang saw manufacturer's would know something? Maybe Dr. Fred (Fred Lamb) would know something about it. He writes a regular column in Modern Woodworking magazine and is Professor and Extension Specialist at Brooks Forest Products Center at Virginia Tech in Blacksburg, VA. He deals mainly with boards after they leave the saw but he's one of the smartest and helpful guys I've run across. You can read his column at www.modernwoodworking.com.
Dan

Neil_B · January 07, 2004, 04:04:46 AM

Jeff, you could post this question over at WW and see what the good Dr. Wengert has to tell you. :D :D :D :D :D ;)

dan-l-b · January 07, 2004, 05:58:46 AM

What is WW? ;) Who is Dr. Gene? ;) FF forever!! 8) 8) 8)

Tom · January 07, 2004, 06:01:06 AM

I think it would have more to do with relieving the stress by cutting everything across the log at once. I'll bet if you had a 12 X 12 and put it through a gang saw with 5 blades that cut everything from one side of the log that the remaining cant would be bowed and probably the boards too.

MrMoo · January 07, 2004, 09:11:11 AM

Jeff,
Look at the bright side of things.
Yup its the right time of year to be making skis. Mill up a couple of poles & you're in business eh. :D

Jeff · January 07, 2004, 12:50:03 PM

QuoteJeff, you could post this question over at WW and see what the good Dr. Wengert has to tell you. :D :D :D :D :D ;)

Yea, I'd have to be the one to do it. I hear everything Tom posts over there gets deleted. :D

Ron Wenrich · January 07, 2004, 03:03:29 PM

I'd be kinda curious if a heavy slab could be resawn with straight boards. Something that doesn't have any heart.

I like Tom's idea

sawhead · January 07, 2004, 05:33:21 PM

My guess woul be that the stress is being relieved on both sides at the same time. At the mill I saw on we also run a gang but instead of all lumber we take a crosstie or pallet cant from the middle .There are hardly ever any warped or bowed boards from it.

OneWithWood · January 08, 2004, 06:14:20 AM

Jeff, a timely post for me. In the not too distant future (yeah I know I've used that term before and the not-to-distant future ends up being a long ways off :

) I will be actively milling my aspens for barn lumber. Very few of the trees are straight so I know there will be a lot of stress in them. Any suggestions on how I can best prevent the production of propellor blades instead of 2x6x12 dimension lumber will be appreciated.

Jeff · January 08, 2004, 12:59:53 PM

You could always sell it for pulp and then visit your local lumber yard. ;)

VA-Sawyer · January 08, 2004, 04:45:29 PM

It would seem that Mr. Jeff hasn't visited a retail lumber yard in this century. Sam's ( that's my dog ) hind leg is straighter than most retail lumber. ;D

Jeff, you wouldn't believe how bad they mangle those boards after you work so hard to saw them straight. ;)

VA-Sawyer

Ron Wenrich · January 08, 2004, 04:50:45 PM

Young trees or when you get down to the heart has a lot of juvenille wood. That stuff won't give as good of lumber, but the lumber yards will put it up for sale.

Crooked logs will give wild looking lumber. Of course, you could curve saw it.

Fla._Deadheader · January 09, 2004, 05:02:38 AM

STRESS ??? ??? I got a chance to get these logs fer free ;D
Any suggestions on how to get some usable boards would be greatly appreciated ;D :D :D :D

Maybe I should just cut them "Bridge beams" that are in high demand, EH ??? :D :D :D :D

OneWithWood · January 09, 2004, 08:39:33 AM

Jeff, that would take all the fun out of it plus VA has it right on the commercially available lumber unless you are willing to part with some serious cash.
Ron, a wild looking saw barn would fit right in around here :D

Tim · January 17, 2004, 02:34:55 AM

I've found that frozen poplar is far more stable than poplar that ain't frozen. If I were to hazzard a guess, I'd say luck of the draw on the way the tree grew. I'd imagine that it grew out of the side of a hill yet remained straight to some degree. This would tend to give an off centre heart and a log with a mess of stresses in it. If the heart was low and indie to the bunks, it would give you reaction wood on three sides like you described.
I've boxed hearts on one corner before. I had the same results.