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Advice on bowed/warped boards

Started by oakiemac, January 03, 2004, 05:46:43 AM

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oakiemac

I've noticed that a certain percentage of the boards that I saw come off of the mill where one end will bend up (bowed) or as you look down the length of the board, it will curve to the right or left (warped).
How, as a sawyer, can you prevent this? Or is this inherent in the log due to stress? I have a Mobile Dimension circular saw so I don't normally turn the log while sawing. The mill cuts very true-a 1X4 will be the same dimensions all along the board. I am wondering if this is something that I am doing wrong or if all logs yeild a certain percentage of these boards.
I would appreciate any input, especially from all the MD folks out there.

Oakie
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

Minnesota_boy

All logs have some stress in them.  Some have very little and the weight of the board will straighten them out.  Other logs, especially certain species, have much greater stress and the boards will bend or bow.  I turn the logs on my mill so that the boards will bow up or down instead of left/right because in normal usage you can straighten out a bow.  
I eat a high-fiber diet.  Lots of sawdust!

Frank_Pender

I do as Minn. Boy when I set the logs on the MD Mill bunks.  But, invariably you will find that even doing that you will end up with a board or two that bends edgewise.    If the warping is too bad and the board is of a longer type length, I may just trim it to a shorter length trying to remove the warpage as much a possible.  
Frank Pender

big_sid

 :) yes about all logs have some stress in them, i try not to take to heavy a slab off to start with, be sure to clean all the bark off all four sides,when you get the cant square, be sure to turn it often. :)
never been so happy to be so broke

Captain

Hey Oakie,

Being in the class of another "dimension" sawyer (swingblade mill)  I'll share with you one of my many lessons....

As you know, our mills can release boards in the vertical and horizontal directions.  My biggest mistake when starting out was starting to cut vertically in the log too early....and trying to get two or more vertical drops out of a log.  By doing this I was having trouble with boards bowing as they were released from the mill.  This was due to the fact that one side of the board was newer growth, and the other side of the board was old growth, juvenille wood from the pith.  They also may come off the mill straight, but crook when drying because of the differences in tension on the newer growth vs the juvenille wood in the pith.

Now when I am cutting, I refrain from doing a vertical drop too early.  I will take a clean face off the top of the log, and release boards horizontally (If I am not quartersawing) until I get to the point where I can make a vertical drop that will include the middle of the pith. (The pith is centered in this drop)  I then clean the face on the left, and proceed to make vertical boards across the pith to the right face.  Once this pass is done, I return to making horizontal boards in the bottom remainder of the log.

This method gives me less control of what comes out of the log, I'll give an example....
Lets say I have a large order of 2x6s to cut.  My old temptation was to take as many 6" vertical drops as possible in the log, and cut exclusively 2x6s out of it.  Now I take more 2" drops and cut horizontally, and may not get just 2x6s out of that horizontal face, I may cut a 2x4 or 2x8 to minimize waste.

I'm not sure if this helps or is clear enough, but it has sure helped me and the quality of the materials that I cut.   ;)

Captain

oakiemac

Captain, I think I understand your procedure. You're saying that the boards that you cut horizontally from the top of the log down until you can make a verticle drop that centers the pith, won't bow or warp because they don't include the pith?
What I have been doing is is cutting a pass off the top of the log to get it flat and recovering what ever small boards that I can in the verticle direction. Then I drop down 6-10"(depending on what customer wants for board width) then start cutting boards vertically until at end of log. Then I drop down and do the same thing until bottom of log is reached. This is basically a through and through method.
I'll try your method of cutting vertically only in center of log, but it seems that when cutting horizontally you will still end up with boards that contain new wood on one side, then as you move to the center portion of the log it will contain older wood.
Does species make a difference? I noticed most of my problems on Cherry.
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

Minnesota_boy

Wow, does species ever make a difference!  :o :o  I can cut a white pine about any old way and it will lay flat unless the tree had a serious lean when growing.  Quaking aspen is much more tricky, never growing straight and with all kinds of stress in it.  Tamarack (larch?) can be even worse.  I've sawed into a longer piece of it (16') and had the first slab start to arch away from the log behind the saw so strongly that it ripped out the last 2' before the saw could cut it!  :o :o :o
I eat a high-fiber diet.  Lots of sawdust!

Kirk_Allen

I cut some Hickory two days ago that was full of stress!  The log was 18 feet long and 24" diameter at the base.  

After the first cut the slab lifted almost 4 inches at the end.  I chose to relieve the stress with a technique demonstrated at WM.

I know you can keep turning the log but that is time consuming.  

After squaring the log I dropped down to 3" above the center of the log and then cut from end to end.  The starting end raised about 2 inches by the time I got to the other end.

I then take that cant and place in against the dogs with the bow up.  I find the lowest spot and set my blade height to match then make my cut into the cant.  Once that is done, I now have a flat side and I flip it 180.

Now I have a flat bottom and a top that is lower than the ends.  Again, find the lowest spot and set you blade height to match and then make another cut.

From that point I finished cutting 1" boards and not a single one of them bowed.  

Once that cant was done I did the same with the other portion of the log.

I know I lost a little of the wood by doing it this way but I found that it works better than flilpping the cant each time.

Anyone else do it this way?

Kirk

Captain

Hey Oakie,

If the log is large enough, you can cut with as many vertical drops as you want.  Just be sure that your largest vertical drop in the middle of the log centers the pith.  Give it a shot and let us know!!!

Captain

SwampDonkey

Hi All

Juvenile (sap) wood is to the outside next to the cambium, where the tree is actively putting on wood and transporting food from the leaves. The hearwood and pith is dead wood which takes up all the water and minerals to the leaves. The
sap wood will cause the most sawing grief.

Why not quarter saw your timber? This will enable you to produce the best results with your lumber products. When using this method the growth rings are perpendicular to the most exposed surfaces. This sawing method gives timber seven times more resistance to water penetration than normal flat-sawing (with which the growth rings are at an angle of less than 30° to the surface).Further advantages are that your timber will be more wear-resistant, it retains its shape to a higher degree. Also the best lumber is sawn from the HEARTWOOD. Quarter-sawn timber is much more stable than plain-sawn, both with regard to its expansion and contraction with change in humidity, and its tendency to cup or twist.


This link shows the grain of quarter sawn lumber
http://www.jrsimpsonlumber.com/qsawn.htm


Consider the falling: Back Vs Quarter sawn lumber

*Quarter sawn timber is usually required for structural purposes.
* Quarter sawn timber is more stable than back sawn.
*Back sawing does produce at least one quarter sawn slab.
*Quarter sawn timber has a less attractive appearance compared to back sawn.


Check out this page for sawing methods with diagrams  8)

http://www.hardwoodcouncil.com/display_tip.asp?artID=146


regards
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

Tom

There is a place for each.  I don't necessarily agree that heartwood or quarter-sawing produces the best.  sapwwod is favored for handles as an example.

While wear resistance is good for the surface of vertical grained wood a beam with the vertical grain on the narrow side is stronger.  This type of dimensional lumber is gotten by flat sawing.

When you go after vertical grain, you sacrifice the wider stock to the effort.

Vertical grain boards will have more of a tendency to have spike knots than flat sawed and spike knots will ruin a board.

One of the most stable beams is boxed.  That exposes flat grain on all 4 sides.

Bastard grain is asked for in wood for table legs because all four sides look alike.

vertical grain/quarter-sawn is only more stable relative to the direction that is being examined.   While is is resistant to cup and bow, it is susceptible to crook.

The effort in producing vertical grain is more than flat sawn and the cost would show it.

Some woods that are sawn for figure are favored by flat-sawing.  Cherry is an example and so is Magnolia and pine.  Other woods favor quarter-sawing like the oaks and sycamore.

It is best, I think, to know what the product is to be used for and try to saw it for its intended purpose.  In a production atmosphere where that is unreasonable, flat-sawing produces the highest grade boards from sapwood with the least amount of time.  

Just an opinion.

(Oh, Juvenile wood as it's been explained to me is the first 5 to 10 years of wood layed down next to the pith.  It does cause difficulties in sawing because of the growth tensions and differences in cell structure between it and mature wood.  While the wood produced by the cambium is "young", it isn't "juvenile".)  :)

There are some articles in the knowledge base about sawing and the prevention of bowed and crooked boards. While they are in the band mill area they could apply to any mill. :)

Captain

Hey Tom,

Could you review (once more, I know...) the difference between BOW and CROOK?

Thanks,

Captain

SwampDonkey

Hi Tom:

Sapwood is used for handles mostly because its waste otherwise. And your only using small pieces. Try using sapwood for an axe handle and your going to be pawing thru the wood pile for the blade  :)

Yes I do agree its alot more effort to quarter saw lumber, but most wood workers here prefer it for  yellow birch and sugar maple for its stability. Flat sawn white ash and butternut make nice bowed lumber, and black cherry turns inside out if not dried soon aftern being flat sawn. Hardwood lumber here isn't cheep ;)

Black Cherry and red oak for instance are $6.50 - $15.00 / running foot, not a board foot. (kilned)

Beams have flattened grains since the sapwood is removed from the out side on smaller wood. If its a large piece of wood, the beams are quartered so the grains are 60-90 degrees on 2 sides and under 45 degrees on the other two surfaces. Beams would be made from heartwood in my barn, because its also most resistant to fungi because of natural extractives :)

Flat sawn birds eye figured sugar maple and tiger striped red maple would be best. But it has to be kilned soon after being sawn or your going to pull your hair out when your wood project starts to pull apart.

Yes I'de see where the lumber could crook from the quarter sawn method, because the flatter grain in on the edges.  ::)

Your right on the Juvenile wood, I was thinking sapwood. Sorry folks, terminology :)

regards

"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

Tom

Captain,

If you lay a 1x6 on the floor and it bends to the side, then you have crook :).

If it lifts off of the floor like a rocking chair rocker then you have Bow. :)

If it twists like a peppermint stick then you have ......Twist. :D

There are pictures on the forum but I can't find them right now.

Tom

Here!   I found one! :D



The Crook is standing on edge but you can see that it bends in the direction of the narrow side of the board while the Bow bends in the direction of the wide side of the board.

Captain

Thanks, Tom.  I think I use "bow" to classify "crook" also.  I will change that habit...

Captain

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