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How to saw lumber that doesn't bow.

Started by grweldon, November 30, 2022, 05:38:07 PM

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grweldon

Good day y'all!

Before spring (in Alabama, that's about the end of Feburary ususally) I'm going to attempt to mill some 19' long 2x8 lumber from some fairly good-sized SYP logs.  In the range of 22-26" on the big end.  In the past when I've attempted to mill this type of board from SYP, they distort horribly in the drying process.  I've had issues with twist and bow.  I think my distortion issues were due to improper stacking, but I'm not really sure.

These boards are going to be used as rafters for a 16' lean-to that I'm going to add to my barn.  I really don't know where out of the logs these boards need to be cut from nor do I know how thick to cut them.  My 4/4 pine boards distort really bad.  My 6/4 boards are better but still have issues. 8/4 boards come out the best but they are extremely heavy (especially 19' long) and the yield isn't so great because they are so thick.

I hadn't intended to plane these if I can get away with it but I do have a 15" helix-head cast iron Powermatic planer that would be up to the task.  I'm not setup with roller tables so it would kill me, but the planer could handle it.

I guess I'm looking for those with much more sawing experience that I have (Only done about 1000 board feet or so over the years) to give me some pointers on how to succeed with the project I have in mind...stated above.

Thanks folks!
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scsmith42

i mill a lot 2" rafters from long, large SYP logs (commonly up to 25'), and don't have much of a problem with wood movement.

The most important thing is that the log grew straight and was not a leaner.  You can easily identify this by seeing how centered the pith is in each end of the log.  If it's within 10% or so of center, you're good to go.  

If I want 2x6's, I'll frequently mill 2x13's, dry them, and then run them through the edger after drying.  I've found that "at-risk" boards will dry straighter the wider that they are.

Unless the log has a significant amount of taper, I'll center the pith when milling.  This results in a slight slope of grain, but usually it is not a problem.  Tapered logs are milled parallel to the bark, which technically yields a higher grade of lumber due to the minimum slope of grain.  However, in my area most SYP logs don't have enough taper to worry about.

When squaring up the cant, I'll pay attention to which direction the slab offcuts are moving, and mill my structural lumber so that a 2x12 is bowing to the side, instead of crooking to the edge.  It's been my experience that it is easier to use side bowed lumber for rafters as opposed to edge crooked lumber (which I have to narrow up after drying in order to eliminate the crook).  Also, frequently side bowed lumber can be flattened out in the stickered stack, but there is not much that you can do about edge crooked lumber.

Typically stresses are greater towards the bark, so the first board or so off the cant may have some stresses but then they neutralize out after a board or two are removed.

Now oak hardwood logs can be a different story, and typically I'll see more stresses in them than SYP.
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SawyerTed

Improper stacking will ruin the whole stack.  The base needs to be flat, and unevenness will be transferred in to the lumber.  I like to place stickers at most 16" apart.  Often my stickers are 12" apart.  Don't forget a sticker with a couple of inches from the ends so boards don't droop.

This stack isn't perfectly stickered, I would have preferred the sticks straight on top on each other and slightly closer to the ends.   My helper that day wasn't hitting on all 8 cylinders. When she's the one who fixes your supper, you pick your battles 



 

In framing lumber bow is preferred over crook.  Bow is worked out with blocking and sheathing.

Crook on the other hand is a framer's nightmare.  It would need to be sawed out after drying.  

When sawing a log with sweep, boards are going to either crook or bow depending upon where sweep ends up in the cant.  Stress will do the same.  

Too much sapwood one the face of a board will cause bow.  Too much sapwood on the edge will cause crook.  Same for pith. 

If the original sweep is either up or down in the cant, typically boards will bow.  If the sweep is on its side in the cant, boards will tend to crook.
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alan gage

Another thing to keep in mind when stacking to air dry is to cover the stack with something to limit exposure of the top layer. If the top of the stack is left exposed the top of the top layer of boards will be fully exposed while the bottom of the same boards will have less exposure and be in close proximity to the wet wood below. This will result in the boards on top of the stack bowing as they dry. 

Alan
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fluidpowerpro

Change is hard....
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Magicman

First, welcome home Glen, it's been a while.  :)

I do not profess to be some kinda expert but I have sawn well over 100Mbf of framing lumber this year.  Your topic title said bow so first lets define what I term as bow and what I term as crook.  I define side bend as crook meaning that the board would lay flat but would have a crown.  A board with bow would have a belly up or down when laid on the floor but would show minimum crown.  Google "warped lumber" for pictures of examples.  For framing lumber I much prefer bow and avoid crook.  

Establish your cant within your logs so that the saw-thru will be from the hump or horn face will produce a majority of lumber that may bow but have minimum crook.  Note that the side lumber that was taken off to establish your cant will have a tendency to crook rather than bow.  If attention is not paid to the log to determine the hump and horn faces, you could very well get lumber that will twist like propellers. :-X

Sticker bowed lumber with the ends down so that the weight will flatten the bow.

Here is a long topic on sawing framing lumber:  Framing Lumber
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Don P

You know what it is, most of us I feel are simple working folk with our 10,000 hours in. The word expert makes anyone like that uncomfortable. That's just enough time to know there is a whole lot to learn  :D.

Anyway, everyone is talking about bow and crook.  Notice what the crook limits do as the boards get wider and shorter.



 




 

grweldon

Thank you everybody for your useful replies.  Good Day to you Magicman as well.  It HAS been a long time.  Life has been quite different since my fall 7 years ago!

I just serviced the sawmill: replaced fuel pump, lubed up the chains, unclogged a fuel fitting or two and replaced the battery.  She fired right up after sitting for at least a season.  I've never fed it anything but non-ethanol gas and it has proven to be a good decision.

I'm going to take all of the info above into consideration and hopefully start sawing some logs in the next few weeks.  It was 80 degrees here today in Central Alabama.  I won't be sawing when it's that hot...50-60 would be perfect!  That will be here soon enough as we have seen temps below 30 for a few nights in a row this month.

Thanks again all!
My three favorite documents: The Holy Bible, The Declaration of Independence and The Constitution of the United States.

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