Warp Question

[trackman]

Made this sometime back an it had warped just a small amount, enough to see. I used eighth inch plywood for backer. Should I have used quarter inch instead?  Or is the problem using the two different types of wood?  Thanks 

[OCtoolguy]

39 minutes ago, trackman said:

Made this sometime back an it had warped just a small amount, enough to see. I used eighth inch plywood for backer. Should I have used quarter inch instead?  Or is the problem using the two different types of wood?  Thanks 

Not sure but it might have been the backer that warped. I've heard that strange things happen when gluing to only one side. Internal forces at work.

[jollyred]

Usually the problem is that the plywood doesn't expand or contract with changes in the relative humidity, and the wood does.  This causes the warping.  One way to prevent this is to not glue the entire surfaces together.  Just fasten at one point and the different expansions won't matter.  Another way is to use a flexible adhesive, which will give some give to the connection.  Another way is to ensure the relative humidity from the shop to the final resting place doesn't change. 

Nice looking plaque, by the way. 

Tom

[daveww1]

I don't know about the warping but it's very nice job

[teachnlearn]

Warping is a moisture absorption problem. Its also a grain 'problem'. As wood absorbs and releases moisture it moves in the direction of the grain. Good, hardwood furniture takes the seasonal movement into account. Many old pieces have been nailed and screwed for repairs and the wood splits cause of the movement. Hardwood flooring is opened on site and left to sit to adjust to the sites moisture. Different wood has different absorption.

Plywood has the different layers running different directions along with a lot of glue. There are grades of plywood that can take water better then other grades. Scrolling tends to create small pieces that can be combined with different wood species. The smaller piece is going to move less. The larger it gets the more the movement. Since many projects use plywood the craft doesn't have many articles on thinking about the wood type, what the cut is ie 'quarter sawn', and everything being completely finished to protect it from moisture.

The project looks like there is still unfinished wood. ANY exposed wood is going to continue to absorb and release moisture and will move. I haven't tried intrinsa. The use of different woods is common, so information on small pieces of different wood species is probably out there. RJF

[John B]

To prevent or minimise this I always try and make sure the whole item is sealed "Lacquered", including the back. This prevents the moisture fluctuations.

[trackman]

Thanks for the ideas. The cats have a finish on them. But I didn’t put any finish on the plywood backer. Thinking the plywood would be stable. What I get for thinking