Wood cupped (bigly) after milling

[James Jayko]

Hi all, I'm building some doors out of African mahogany. I milled down the lumber for two doors...one set is perfectly fine, square, and stable, the other side cupped and/or warped so badly that its likely unusable for this project. It moved in both directions: it cupped along the wide front and also along the thin edge.

What causes this? Is there something intrinsic to the particular piece of lumber that caused it to 'release' when I started milling it, or did I screw up my milling process? Any advice on how to avoid this in the future?

[John TenEyck]

Cupped along the thin edge? Do you mean it bowed when you ripped it? Cupping across the face is likely due to non-uniform moisture content in the board. Bowing could be the same problem, or it could be internal stress. Do you have a moisture meter? If so, that would provide some info. with which to judge what happened.

Where did the lumber come from and how long was it your shop before you used it?

John

[Bob Vaughan]

Sometimes a single piece of wood does that. Its not predictable in most cases. I'll tend to agree than there was a 'release' of internal stresses. If it was your milling process, you'd be able to get that same effect on other pieces also and that's not likely. Its frustrating when a piece of good looking stock goes south after machining.

[James Jayko]

Cupped was the wrong word. It bowed both ways. IE if its sitting on my bench, at both ends the end is higher than the middle, and the ends are bowed out laterally.

I got it from a reputable lumber yard who I've never had a problem with. The other board, taken from exactly the same stock, was completely stable in all directions, so I assume moisture wasn't the problem but that it was likely either my technique or something unique to the particular piece of wood. It was in my shop for ~2 days before I used it.
Cupped along the thin edge? Do you mean it bowed when you ripped it? Cupping across the face is likely due to non-uniform moisture content in the board. Bowing could be the same problem, or it could be internal stress. Do you have a moisture meter? If so, that would provide some info. with which to judge what happened.

Where did the lumber come from and how long was it your shop before you used it?

John

[David Eisenhauer]

I have never had kiln-dried wood move as much as the one largish batch of African Mahogany did in 30 years+ of wood working. Beautiful stuff, not hard to work, finished nice, but oh did it move. Narrow rails and stiles, wider panels all. I have some of it left over, but have not touched it for a while. I do not have a moisture meter, but I did buy it from the same place I usually buy and have not had any other issues with the vendor. I think it is the nature of that species.

[Nick Decker]

"The other board, taken from exactly the same stock, was completely stable in all directions..."

I'd look to see if the grain runs the same in both boards. I've been working with some African Mahogany (or whatever they're selling as Mahogany these days) for a jewelry box, and the grain is pretty swirly in places. It's pretty, but probably confused about where it wants to be.

[Bill Space]

Someone posted this image here recently. Sounds like you ended up with a bow and a crook...

355685

[Art Mann]

Nice illustration!

[J.R. Rutter]

Khaya mahogany is one of the worst woods that I have used in terms of staying flat during and after milling. It has a lot of internal tension, and seems like it must have high initial water content when cut so that fast drying/kiln schedules almost ruin it.

Anyway, it probably isn't a big flaw in your process other than it takes a lot more patience than most other woods and needs even air circulation as it is milled. Don't try to save a board that starts out with any twist (a loose term here for pretty much any of the above non-flat states) because it is almost certain to return to that state...

[Mark Carlson]

When making doors, I always rough mill (slightly oversized) then let stabilize, and then final mill a day or two later. This gives me the best results. If some of the wood moves a lot after rough milling I dont use that wood for doors.

[Andrew Hughes]

I was going to post the same a Jr I stay away from African Mah.I also don't like sapele if you find a piece flat sawn with good figure forget about.
Now Honduras Mah is very nice to work and has a much better color.
Sorry for my negative post James.

[Mel Fulks]

Agree with JR .Its terrible stuff and I especially hate the occasional good piece of it that behaves and fools many into believing it can be trusted. I once had to make a few pieces of moulding about 4 feet long using "run and rip" method. Not only did each piece of the moulding twist ,bow,and warp; but the wide "mother " stock did too. And in different direction with each rip. But I got out enough wood to cover all that... So if you use more time and twice as much material as you would with Honduras ,it's fine!

[Chris Padilla]

Wood: a fickle medium! :)

[John C Cox]

Try pitching it outside to sit in the rain and weather to relieve some of its stress... Sometimes it works.

I have had several pieces of wood do that to me.... A few left me so frustrated that I pitched them out onto the deck in the fall and left them there all winter and the following spring. They lived the winter covered in ice, snow, and rain...

But when I found them the following early summer - they were dead flat and stayed that way...

I have since used that trick and it has worked more often than not.

Another trick I have used with thinner wood is to use the clothes iron and some water to flatten it back out. Get it good and hot/wet. HOT! You will feel it relax... Then stack about 300 lbs of junk on top of it and leave it for a few months... flat... This works well with oak and maple... Mahogany can be cranky when it comes to trying to bend it....

[Patrick Walsh]

I use african mahogany quite a bit because it is cheap works wellish other than the movement and mostly because its cheap and im learing still. I actually purchased exactly 14 bf just this afternoon to finish a project.

This is what i have found to combat the proboem. I only choose the flattest boards at the lumebr yard. When i say Flat i am talking near perfect boards in the rough. I also only choose boards with dead straight grain. If the grane takes a sharpe left or right i dont care how pretty it is or perfectly flat it goes back in the pile.

I bring it home and let it sit 2-3 weeks minimum in my shop. I cut to lenght for my project then joint two sides only till flat. I then plane only as much as needed to get get a perfectly dimensioned board i can sticker. The boards get stickered on a dead flat surface with a weight applied on the top of the last board. It then sits another 1-2 weeks and i take it down to .125 or .25 of final dimension depending on what i started with for stock. Then right before i am going to say make athe carcass or door rail and styles i bring only those parts to final dimension. Once build i again weight my doors for a numebr of weeks or clamo them to a flat surface. If the carcass is not being glued together i stack all four pieces and clamp them to my bench and weight the middle.

Seems crazy but it has been working so far.

[Mark Blatter]

I did a pretty big job about 8 years ago using A.M. We bought about 500 bdft for the job and it had some wide boards. I am talking about 22" - 24" wide boards. I remember ripping some of them down, cutting off 2" strips for face frame stock. As I ripped it, you could see the small end move to the left as much as 6" then move back then up 4-5" then back down. It was incredible how much it moved from releasing the internal stresses. The wood had sat for 2 - 3 weeks to acclimate, but didn't help at all. We got the job done and it turned out beautiful, but as noted above, I wouldn't take anything that didn't have straight grain.

[James Jayko]

I'm thinking about just getting two pieces of 4/4 and gluing them up to get some additional stability on the second door, given the concerns and issues raised above. Would you do that so the bark side would be out on both pieces? To avoid a future cup?

[James Jayko]

Yes, definitely a bow and a crook.
Someone posted this image here recently. Sounds like you ended up with a bow and a crook...

355685

[J.R. Rutter]

Just remembered I snapped this during the last khaya job that we did. Each half moved in opposite directions in two planes.

http://i.imgur.com/hbFR8bD.jpg

[David Eisenhauer]

That's the AM I remember so well trying to make a kitchen's worth of raised panel doors.

[Peter Quinn]

355821This is me, last weekend, turning a 2K BF pack of 8/8 African mahogany to get enough material for 1 exterior door. Problem with african mahogany (https://en.wikipedia.org/wiki/Khaya), its not one tree, its a marketing name for seven different species of trees if I understand it correctly. There is gross variation of quality between species and between individual boards or trees in a given species. There is little sorting or QA at any stage. The issue is not moisture, it dries easily, its internal tension. I spent a lot of time with it over the years, and have learned to identify and choose carefully, some if it is beautiful, nearly the most stable stuff Ive ever worked with, other is absolutely basket case interlocked grain that cannot be subdivided and is suitable for little more than paint grade trim. On large jobs where we have gotten a whole pack and have to utilize it all I'm careful about sorting as best I can to make the most practical use of the material. Some boards I know will be crazy from the grain, other times I get surprised by movement in what I thought would be stable. So don't give up on it, but choose carefully. The stuff with the ribbons, the "chatoyance" or "bee's wings" grain may make a beautiful top, but cannot be successfully broken into small parts. The medium brown vertical grade, very flat colored boring grained stuff of medium weight and density seems to work best for milling into delicate parts and sash bars. When ever possible I want to go to a yard and choose my material with african mahogany, spend some time and really look at what I'm buying, I won't even consider mail ordering that one. Otherwise, total crap shoot.

[Robert Engel]

Wood: a fickle medium! :)

There's your answer!!

Any species can misbehave.

I've heard a theory that tension ultimately results from how windy where tree grew up. This tends to result in a twisty trunk? Kinda makes sense.

[peter gagliardi]

African Mahogany- AKA in my shop as African Firewood! I won't even look at a job if it is hard spec'ed out in it. Nasty wood all the way around. Good Honduras substitutes would be either Sapele, or my choice if I have one, Sipo, also known as Utile.
Both of which are comparable from my experience in price only with African Mahogany.
If wood can't behave in the shop, it sure as heck shouldn't be used on doors.

[James Jayko]

FWIW:

I went back to the lumber yard I purchased the mahogany from. Talked to the owner (who's a helluva cabinet maker) about the problem. I'm sure this is fairly obvious to most of you with a lot of experience, but he pointed out that A. african mahogany is generally very stable, and B. if I was having problems, it was likely from the way the grain was oriented in the boards I was using; on a flat-sawn board, you want any of that 'cathedral look' centered across the width of the board as the straight grained sections are the most stable parts, while the cathedral windows (the "V"s) tend to be the cause of most of the instability. He spent 20 minutes or so with me out in the yard pulling boards, didn't like what was out there for my project, and cut down a 16" board to get me two very straight grained pieces perfect for my application.

If you happen to be in the PA/Del/MA/VA area, Hearne Hardwoods in Oxford did a really nice job for me.

[John Seybold]

Many years ago I used to go to a shared membership shop in California in which there was a large variety of experience levels. One day I saw a guy trying to resaw some AM boards on the tablesaw. I think they were about 7" wide, so he was running them through on one edge, then trying to flip them over to complete the cut. I had ear protection on and was concentrating on what I was doing at the router table, so I only noticed when a thick cloud of smoke drifted over from the saw, which was grinding to a halt as the boards twisted and closed up the kerf. I could see him wrestling the board down onto the table as the rising teeth tried to toss it across the room. At that point in my career I generally didn't feel in a position to offer other people advice, but in this case it seemed appropriate, so when there came a break in the action I mildly suggested that a) the bandsaw would be a more appropriate tool, and b) in any case, it didn't look like resawing those pieces was going to result in usable lumber, no matter how he did it.