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Bowed box lid

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Forum topic by grumpeegramps posted 05-25-2017 04:15 PM 1255 views 0 times favorited 8 replies Add to Favorites Watch
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grumpeegramps

13 posts in 1152 days


05-25-2017 04:15 PM

8 days after completing this box the lid started to bow. 8 days!! The first week dead straight. I have tried cauls holding it bent the other way for 5 days, still bowed. I can get it straight after using a heat gun, but not while the heat gun is heating it up. It straightens as the wood cools off to room temperature, but after an hour it bows again. ?! 175F degree oven for a few hours which does the same thing as the heat gun, as it cools, it’s straight, a few hours later, bowed again?! Sprayed water on the concave side to increase swelling put on the cauls ,let it dry, no effect. All the boxes I have made and never happened before. I have 12 days to correct this problem before presentation to a HS grad.
The lid and box are oak, and the grain pattern flows around the box, ( so I don’t really want to redo the lid) and that oak was flat and straight AND dry when I cut it. The lid insert is book matched Zebrawood 3/8” thick. I believe the problem is in the Zwood. It was a very tight fit inserting the Zwood into the rabbeted top of the box, before I ran it through the tablesaw to separate the lid from the box. But why 8 days to show up!?
HELP PLEASE!! If you want to contact me directly
gras53@earthlink.net
Thank you .


8 replies so far

View Loren's profile

Loren

9627 posts in 3485 days


#1 posted 05-25-2017 05:12 PM

You can hand plane the box rim to follow
the curve of the lid. A flat board with
coarse sandpaper glued to it will also
work.

Otherwise, remake the lid.

If there’s no room for the zebrawood to
expand and contract across the grain,
that is a recipe for problems.

View mahdee's profile

mahdee

3828 posts in 1604 days


#2 posted 05-25-2017 05:50 PM

If you didn’t glue the top to the edges, you can take the lid off, trim the border on the table saw to level it with the top. Remove the top, expand the space, replace the top and glue strips to match the border.

-- earthartandfoods.com

View jerryminer's profile

jerryminer

805 posts in 1278 days


#3 posted 05-25-2017 06:09 PM

As Loren said above, if you glued the Zwood panel tight to the mitered frame, with no room for expansion, you created a problem.

The Zwood is fighting the cross-grain oak frame. Real fix is cut the Zwood loose from the frame and re-work the top to allow for wood movement.

(Even if you are able to force it flat for now, it will move again when humidity changes)

-- Jerry, making sawdust professionally since 1976

View Carloz's profile

Carloz

973 posts in 428 days


#4 posted 05-25-2017 06:20 PM

You learned hard way to leave room for expansion. Frame on the lid does not expand as it is narrow long along the grain. The wide boards do expand across the grain and since it has nowhere to go it pushes the frame and bends.
Remove the frame and redesign the lid to not have tight fit across grains.

View grumpeegramps's profile

grumpeegramps

13 posts in 1152 days


#5 posted 05-25-2017 06:21 PM

THANK YOU, THANK YOU, THANK YOU, ALL FOR THE VALUABLE ANSWERS. Yes the Zwood is the problem. TOOOOOOO tight in the oak frame. Paid $$$$$$$$$$$$$$$$$$$ at Woodcraft for that 8BF of Zwood. Still have 6BF left. Wanna buy it? A noted box maker just told me that he doesn’t use it anymore because of the expansion/contraction issues.
I have been told by a few that heating up a Titebond PVA joint can loosen the glue.
What do you all think about a 350F ( or Hotter) degree oven for the lid, for 15 minutes at a time, over the course of hours to see if I can push the lid free from the glued rabbet? Worth a try?
Any of you tried to loosen PVA with heat? This lid has been together about a month.
I’d really like to save the lid and just re-work it after the Zwood is out.
Opinions please.
And thanks again.

View Aj2's profile

Aj2

1176 posts in 1635 days


#6 posted 05-25-2017 07:36 PM

I would just leave it be. It really doesn’t look bad to me.
Use your time to do the next one with improvement.

-- Aj

View Kirk650's profile

Kirk650

514 posts in 585 days


#7 posted 05-26-2017 01:35 AM

If that’s as bad as it gets, I agree with just leaving it alone and move on to the next project.

View JBrow's profile

JBrow

1274 posts in 757 days


#8 posted 05-26-2017 04:32 PM

grumpeegramps,

I have not tried heating PVA glue to un-do the glue bond so I cannot say whether it will work. But I have soaked a joint with water to release the glue bond. Of course the obvious problem with this method is the introduction of moisture into the zebra wood as well as some surface discoloration of the wood. This method only works with glue that is not water resistant. I use Elmer’s yellow PVA wood glue.

A dripping water-wet rag can be placed over the glue joint after a little water is introduced to joint. The rag can then be pressed into the joint in an effort to squeeze some water from the rag and into the joint. The water must be in contact with the glue. After about 30 minutes, an effort to pull the joint apart could be attempted. If the water does not have an easy path to the glue, it could take longer.

A method that is faster and fraught with fewer problems than the water method could be to rout the frame away from the zebra wood. A straight bit could be used. Limiting the depth of cut so that the straight bit does not contact the zebrawood would leave a thin strip from the frame which could be sanded, planed and/or scraped away. I suppose a dado blade in the table saw could also work if a carry board were used to support the lid. This method would destroy the frame but would save the zebrawood panel.

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