wisardd1
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Post by wisardd1 on Apr 4, 2010 23:21:37 GMT -6
Got me a bow on my table top. Dang, dang, damn. Good 1/8 inch, been sanding all day. Guess I might need to go to the millstore. Arrrgh! Cupped in the middle right down the seam. I hate glue ups.
Not to mention I only have a 1/2 inch front overhang (should be an inch). Oh well.
dale
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Post by fredbelknap on Apr 5, 2010 8:31:38 GMT -6
When I do glue up I found if I leave it overnight laying flat on the workbench I get a small cup in it. I try always to remember to put strips under them. Just an idea.
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Post by Ruffnek on Apr 5, 2010 9:50:17 GMT -6
When I do glue up I found if I leave it overnight laying flat on the workbench I get a small cup in it. I try always to remember to put strips under them. Just an idea. BTDT too. |
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Joe Lyddon
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Post by Joe Lyddon on Apr 5, 2010 12:02:48 GMT -6
Dang... Well, you're getting a little more exercise!  Did you alternate the board grains? (cup up, cup down, cup up, etc.) You could add a strip to each side... |
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wisardd1
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Post by wisardd1 on Apr 5, 2010 12:26:22 GMT -6
What do you mean strip on each end? I am pretty sure it is from the glue up, I tried to to do cup up then down, but I am not that good at recognizing which is always which. 6 different boards and all.
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Post by Ruffnek on Apr 5, 2010 13:04:52 GMT -6
I don't do the grain up/down thing. I just select the best arrangement of boards based on appearance. Even Norm no longer advocates that up/down sequence. ;D
I had a Mesquite tabletop warp when I clamped it down to my assembly table to hold it "flat" while I was gone offshore for two weeks. Boy, did I learn a lesson.
I ended up ripping it apart along the glue lines, re-jointing and then re-gluing the top. This time, I made sure it had adequate air flow on both sides of the panel.
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Joe Lyddon
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Post by Joe Lyddon on Apr 5, 2010 13:11:56 GMT -6
What do you mean strip on each end? Oh, I pictured it a 1/2" over hang on the sides... not the ends... Just let the breadboards do the extending... (  ) |
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Beamer
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Post by Beamer on Apr 5, 2010 13:41:12 GMT -6
They're talkin' about stickers .... Instead of leaving the panel lay flat on something solid, put it on a couple strips of wood to keep it up off the table. That lets air flow nicely around the whole thing. Panel cupping is more about keeping all sides equalized - do unto one face as you do unto the other. |
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Post by Ruffnek on Apr 5, 2010 14:46:22 GMT -6
- do unto one face as you do unto the other. Jason! Are you quoting from scripture now? KJV, no less!  |
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Post by imahic on Apr 5, 2010 16:40:16 GMT -6
Maybe Stretch will jump in here and verify this, but I think he had a good idea about this subject a good while back. I might be wrong but I did the same thing on a lid for a box I made for my dad and it seems Stretch had a good idea but I forget now exactly how he said to do it.
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rrich
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Post by rrich on Apr 5, 2010 16:40:52 GMT -6
I had one with about a 1" bow over 30 inches. I had left it in the back of the truck in the summer. (Shell + Carpet kit) An instructor at school suggested flip the desk top over and leave it for another day.
It did the trick. That removed the bow to the point that it wasn't noticable.
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Stretch
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Post by Stretch on Apr 5, 2010 18:03:48 GMT -6
As the others said, the bow was most likely caused by the side facing up drying out a bit while the side against the table did not. In the future this can be prevented by placing some stickers under the top so air can get to both sides. The good news is that the cupping can usually be reversed very easily. Simply mist a little water from a spray bottle on the cupped side and it should go back to flat. If not, you can get a little more extreme by misting the cupped side and placing it down on the grass outside so the other side is in the sun. You have to check on things periodically and it can take a few tries to get it right. After it is flat again, sticker it on a workbench to make sure it stays that way.
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wisardd1
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Post by wisardd1 on Apr 5, 2010 22:22:40 GMT -6
Actually, it went something like this. I glued her up on bessey clamps off the ground with titebond 3. Undid the clamps after 90 minutes and place it on the desk (opened due to not having a top!) After a while I noticed I got a bow. I placed it on my work table, clamped down the edges and put some various weight to flatten it out. The next day I took the weights off and put it back on the opened desk. I thought it was flat, but must have bowed again. I will try the cupped side up and mist? IF not, I will try the more extreme method. Thanks everyone, this is really helpful.
dale
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Post by imahic on Apr 6, 2010 7:49:10 GMT -6
As the others said, the bow was most likely caused by the side facing up drying out a bit while the side against the table did not. In the future this can be prevented by placing some stickers under the top so air can get to both sides. The good news is that the cupping can usually be reversed very easily. Simply mist a little water from a spray bottle on the cupped side and it should go back to flat. If not, you can get a little more extreme by misting the cupped side and placing it down on the grass outside so the other side is in the sun. You have to check on things periodically and it can take a few tries to get it right. After it is flat again, sticker it on a workbench to make sure it stays that way. That's the one I was thinking about, Stretch. I knew it had something to do with grass but just couldn't remember the details. Thanks for the other solutions as well. I hope it never happens to me but if it does, maybe I can remember all these ideas.  |
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Post by art3427 on Apr 6, 2010 9:12:56 GMT -6
I've had this same problem at various times. Did you square the board edges with the jointer before glue up? If the edges are not parallel the clamps will force them closed by pushing the resulting gaps closed. I now true one face and both edges before glue up. Keep the joined faces either all up or all down. BUT make sure your jointer fence is square to the table before you start.
art
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wisardd1
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Post by wisardd1 on Apr 6, 2010 11:43:24 GMT -6
I just want to make sure, mist the cup side and leave it up? or turn it over.
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Stretch
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Post by Stretch on Apr 6, 2010 18:46:50 GMT -6
I just want to make sure, mist the cup side and leave it up? or turn it over. Yes, you mist the cupped side. It doesn't really matter if you leave it up or down so long as you have stickers under it so air can reach both sides. If you have a lot of cup, you can mist it and lay the misted side down in the grass on a sunny day. The grass will give off water which will keep the misted side wet, and the sun will dry out the opposite side, which will bring the side into balance faster. Incidentally, I found out today that the same method can be used to straighten out warped chinese plywood. ;D |
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wisardd1
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Post by wisardd1 on Apr 6, 2010 19:00:57 GMT -6
Yippee! The method got me into an acceptable range, at least for me! Thanks Mark! Thanks a bunch!
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Stretch
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Post by Stretch on Apr 6, 2010 19:05:22 GMT -6
Yippee! The method got me into an acceptable range, at least for me! Thanks Mark! Thanks a bunch! You're very welcome. I'm glad it worked for you. It's saved my bacon a time or two. ;D |
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Joe Lyddon
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Post by Joe Lyddon on Apr 7, 2010 11:44:12 GMT -6
WOW! That saved you a BUNCH of grief didn't it?! |
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