Lamination cupping?

[bdsmith1]

So I had some osage I cut lams out of for a bow I was going to work on tomorrow. I've got a full time job with a pretty irregular schedule, so I only get to work in the shop in spurts. Living in Georgia, humidity will get to thin cut lams pretty quick so I taped the stack together and put it in my dry box with a single indirect bulb that gets to about 100F to keep it from going limp until I could get back to work on it. . Unfortunately, the top lam cupped up on me. I'm debating on whether or not I can rely on the pressure hose to press this flat enough for good glue lines or if I should just toss this lam. I'm more concerned with preventing this in the future. I've never had this issue with ash, maple, or boo.  Have you guys had this problem and how do you prevent it.

[bdsmith1]

As an aside, This is the first time I'm using clear glass, which is why I'm working with Osage for these limbs. Any extra precautions or differences from using black glass? I've heard about letting it set in the form for 30 minutes prior to setting it in the hotbox, tho I don't know the reason.  I know I've got some sap wood on a few of these, but it's in the nock side and will get cut out. Will sap wood mess with clarity?

[simk]

I dont think you will have any problems. When I glue thinner lams with water based pva glue instead of epoxy the laminates quickly warp the same, while the endproduct is fine. The pressure of your airhose will flatten out everything, np.
Simon

[kennym]

Think it’ll be fine

I also air up in 10 lb increments roughly with a few minutes between

No idea if it helps lol

[garyschuler]

Have you thought about flipping the top lam and alternating in opposite grain configuration with #3 lam. Then putting those in the middle with the straight grained  pieces on top and bottom of stack. I like to alternate opposing grains to help even out twisting issues after glue up. Don’t know if this will help you, but good for thought.

[Kirkll]

Gary has a good point on those lams that have the grain running at 45 degrees. I think it would be wise to pay close attention to how those lay up and keep the opposing grains alternated in the center.  With osage i think it might make a difference on limb twist issues.

Good catch Gary....

[bdsmith1]

Thanks Gary, I wouldn't have thought about that!

[mmattockx]

No one has said anything about why that lam cupped in the first place. I would guess you taped the bundle together and then put in the box with that lam on top of the bundle. It was the only one exposed to air all along that one face, the rest were covered on both faces and only drying on the ends and edges. The exposed face dried more than the rest and it pulled in that direction.

Next time you put a bundle together like that put an extra piece of scrap on the top to cover that lam as well and you should minimize any cupping/warping problems.


Mark

[bdsmith1]

you know, that seems very common sense after having had it explained to me.. Almost as if I should've thought about it lol..

[Kirkll]

Another thing to think about is what your MC levels are before you rip your lams. If the MC level is too high, you can pretty much guarantee not only cupping, but cracks or checks when it dries out. especially if you are force drying them in  a hot box.

Think about how they mill green lumber. Those logs are at 25-30% MC levels,  and back in the old days they were left in the mill ponds, or large rafts in the river so they wouldn't split before sawing them. So old style milling operations still use this technique too.
Larger lumber mills keep water sprinklers on their log piles in warm weather....

check this out.... we used to fish off these log rafts clear up until 1980 . You dont see as many anymore...
   https://images.search.yahoo.com/search/images?p=log+rafts+in+Willamette+river+photos&fr=mcafee&type=E214US714G0&imgurl=https%3A%2F%2Fgoodnewstree.com%2Fwp-content%2Fuploads%2F2019%2F09%2F1200px-Log_driving_in_Vancouver.jpg#id=9&iurl=https%3A%2F%2Fc8.alamy.com%2Fcomp%2FD4XJJJ%2Ffishermen-on-a-commercial-log-raft-on-the-willamette-river-051973-D4XJJJ.jpg&action=click

But once they mill the green boards, they start out with rough cut  2"X 6" , then stack them with stickers between each layer until they get a full unit of lumber, then they band them together and stack them up dead flat in the yard to let the MC level come down below 20% before running them through the planer and ending up with 1.5" X 5.5" as the finished 2x6 dimension.

Now even though they are at 20% MC levels now...In Oregon and Washington we use green lumber a lot for rough framing. But If you leave that 2x6 out in the sun too long it's going to warp up or cup. I guarantee it.

 When doing rough framing jobs, you always keep your lumber stacked until you are ready to use it and nail it in place. And... The top pieces in those lumber units are typically not as straight as the pieces inside the stack, and get cut up for short stock or blocks.

[bdsmith1]

Kirk, I had the MC at around 14% before I sawed them up. That may have been a bit high. 

My grandaddy worked in timber in West Virginia back in the 50's.  He passed in the early 2000's, but I remember him telling us the stories.  My uncle has some pretty cool black and whites from it. Pictures with several guys standing on huge stumps and posed with crosscut saws a head taller than they were. 

My neighbor has a walk mill, so He's sawed some elm and hickory for me.  I have several slabs stickered and drying.  I paint the ends to try and keep them from checking, but they've checked and cracked anyways.  Stickering seems to have kept them flat-ish though.  I've even noticed in cutting lams from planed wood that they seem to warp some when they're released from the lumber even on straight grained stuff.

[Kirkll]

Kirk, I had the MC at around 14% before I sawed them up. That may have been a bit high. 

My grandaddy worked in timber in West Virginia back in the 50's.  He passed in the early 2000's, but I remember him telling us the stories.  My uncle has some pretty cool black and whites from it. Pictures with several guys standing on huge stumps and posed with crosscut saws a head taller than they were. 

My neighbor has a walk mill, so He's sawed some elm and hickory for me.  I have several slabs stickered and drying.  I paint the ends to try and keep them from checking, but they've checked and cracked anyways.  Stickering seems to have kept them flat-ish though.  I've even noticed in cutting lams from planed wood that they seem to warp some when they're released from the lumber even on straight grained stuff.

Yup.... Air drying rough cut lumber is half luck, half art form.  Some light colored woods like maple can even get a mold on them and stain them real bad if you don't have enough air blowing through the stack. Sometime it requires spraying the wood with an anti fungal spray. Fans and air flow are very important...... I've actually had better luck air drying lumber in the winter time with fans blowing, and cooler temps,  than in summer time... If it dries too quick it checks easier. If it starts getting too hot in the summer, you can help it by spraying it daily with a hose to help the surface checking. Alway keep it indoors if possible, or out of the sun in an open shed.

14% is not bad at all really.  Just use a cover lam on top and bottom before bundling them up. The critical time for air dried lumber is above 20% . once you get below 20% it's easier to control the checking....

Trying to force dry lumber above 12% by heating it is risky.... Trying to kiln dry lumber is a whole different ball game... You could spend days studying the different processes and techniques  they use. And.... the percentage of good stock you end up with is much lower than air dried material.

I've dried my own curly maple and black walnut a few times, both being native to Oregon. I did some english walnut too, but only got about 40% usable material on that batch...

Good luck on that....   Kirk

PS.... Talk to Gary about air drying lumber, and slabs. He has a lot of experience with myrtle wood and other woods too.