warping and hewing question

[NCEric]

A year ago a pretty big white oak blew down in a storm on a neighbor's place, and he let me have it.  My son and I marked out a roughly 12" x 16" heartwood beam and hewed three sides.  Then I freehand ripped the beam with chainsaw in half so that I have two roughly 12"x8" beams, except that one of the two beams isn't hewed on the outside 12" yet.  What I wasn't expecting was how much the beams would warp when I ripped them.  The half I haven't hewed yet is sitting with the ripped face (what was the middle of the tree) down now, and both ends are curving up about 1-1/2".  My main question is how I should now hew the last face.  If I hew to a straight line like I've been doing, the beam will be about 1-1/2" thicker in the middle than on the ends.  Alternatively, I could just measure 8" up from the opposite face and hew to that mark all the way down my log so that the beam would be a uniform 8" thick the full length.  I'm wondering if I did that if I might release some tension and the beam might straighten back out again, at least partially.  I've been hewing almost all of the sapwood away, so there are several inches of wood I'm planning to hew away.  I dropped my original plan for these beams, but I want to go ahead and finish hewing them just to have for a future project.  Any thoughts on how I should proceed?  Thanks!

[Brad_bb]

Unfortunately, many here would have advised against what you did, knowing that it would bow just as you describe.  Oak is especially notorious for this and has an incredible ability to bow as it shrinks and must pull with incredible force as it shrinks. Wood will always shrink more on the sapwood side, even if there's no sapwood, the outside of a flat sawn board will bow towards the outside of the tree.  The outer face will tend to shrink more.  

How you want to use it has some affect on what you do at this point.  Whether you're looking for a post, a rafter or a tie beam?  How long are these two pieces?  Do you need to have 8" Thickness, or 7.5" thickness?  If it's in the ballpark of the size it needs to be, a general rectangle with warp, let it air dry for a year or more to make sure it's done doing most of it's movement.  You may need to way 2-3 years.  I'd prefer to keep it inside my pole barn so it's not getting wet/dry, wet/dry.

So once you're confident that it's stable, hew it to a size you can use.  If you can snap lines and hew out most of the bow, do that.  You might be able to take some off so most of your beam is 7.5"?  Again, it all depends on what you need.

Did you take any video of your hewing?  I have some videos, not sure if you've seen, but maybe could pick up a tip or two?  falfas55bgas - YouTube

I'd watch your vid if you have one.  How did you learn?  What axes are you using?

[NCEric]

Thanks very much for the reply!

Unfortunately, many here would have advised against what you did, knowing that it would bow just as you describe.

What alternatives might you have considered?

Whether you're looking for a post, a rafter or a tie beam? How long are these two pieces? Do you need to have 8" Thickness, or 7.5" thickness?

I was originally thinking sills, including a small cantilevered porch, and the size may have been overkill even for that, but I don't know how to calculate such things.  But my original plans got scrapped, so I don't have any particular plans for these beams any more or need any particular size.  The beams are about 16'6" long.  My son and I went ahead and hewed the last side straight, so that beam is now wider than 8" in the middle due to the bow.  I guess we can hew that flat after it finishes drying if we need to, although I don't know what it would be like to hew dry oak (or any other species of dry wood.)  The beams are in my barn drying now.

Did you take any video of your hewing?

Not of these oak beams, but my son has been hewing a smaller cherry beam recently, and he started making a video of his process.  I'll try to share that video with you when he's done.  What we've mostly done has been to run strings for our line, then saw close to our line with the chainsaw and then finish with a big frame saw (I think that's the right name for it.)  Then my son has done practically all the axe work just using a regular felling axe.  With this smaller cherry log he's been doing everything by himself, without the chainsaw.

[Brad_bb]

Generally, you'd want to box the heart so that timber is symmetric about the center which makes the stress as it's drying more or less even on each side.

You can cut a large log Free of heart (FOH).  So this is without the pith and no sapwood.  If doing that it may bow with each end bending towards the outside of the tree.  If the piece is small like 4x6 or 4x8 it's going to tend to bow more.  If the piece is large like 8x10, it will likely bow less. and it may even be very minimal.  One option is the let it sit for a year or more and see what it does.  And then recut it as needed to make it straight again.  Remember that there is going to be more drying stress in the outside 1" of the timber, so as you cut one side, it may be pulled in the other direction somewhat.  The smaller the piece the more pronounced this will be.  But you could always let them air dry long enough to get most movement out of them and then re-hew to straighten, albeit smaller.

[NCEric]

Thanks again!

One option is the let it sit for a year or more and see what it does. And then recut it as needed to make it straight again.

You mean after ripping it, right?

Have you hewed any dry wood?  How does it compare to hewing green wood?  I guess the answer varies according to species.

In this case, I hewed almost all the sap wood away and still had about a 12"x16" beam afterwards, so I definitely needed to reduce it in size somehow, because even after ripping it in half (at 12"x8") it's still probably generously large for anything I'd need it for.

[Brad_bb]

Green or dry, doesn't make a difference. I thought dry would be more labor intensive, but not the case.

[Brad_bb]

Hewing difficulty has little to do with how green or dry it is.  Straightness of the grain and defects far for affect hewing difficulty.  When choosing logs or timber to hew, look for straight grain, avoid knots as much as possible, especially large ones.  Even small knots will take extra care to hew around.  Avoid crotch grain as the changing grain direction will be difficult and tear out will also occur.