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Thread: Wood cupped (bigly) after milling

  1. #1
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    Wood cupped (bigly) after milling

    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?

  2. #2
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    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

  3. #3
    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.

  4. #4
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    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.
    Quote Originally Posted by John TenEyck View Post
    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

  5. #5
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    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.
    David

  6. #6
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    "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.

  7. #7
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    Someone posted this image here recently. Sounds like you ended up with a bow and a crook...

    IMG_6546.JPG
    Too much to do...Not enough time...life is too short!

  8. #8
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    Nice illustration!

  9. #9
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    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...
    JR

  10. #10
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    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.

  11. #11
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    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.
    Aj

  12. #12
    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!

  13. #13
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    Wood: a fickle medium!
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  14. #14
    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....

  15. #15
    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.

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