LumberJocks

Advice about wood movement

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Blog entry by Pith posted 11-26-2015 05:00 PM 570 reads 0 times favorited 1 comment Add to Favorites Watch

Young woodworker here looking for some advice. I’m working on a 34” x 34” frame for squeegeeing film photographs after they have been developed in a darkroom. The design is fairly simple I’m using 5/4 white oak for the frame connected with finger joints and then cutting a dado in the middle of the pieces to allow for a piece of plywood and plexiglass to rest in. This will be inside a school and will be exposed (not submerged) to water for about half of the year. I am making this to replace a smaller version of the same thing that the teacher had but that was 30 years old and was starting to fail. In designing a new one I wanted to try to fix some of the things that plagued the last one. The last one was joined with miters on the ends and simply screwed into the plywood. The over the years the bottom middle piece has started to bow and sag and the miters connecting it have disconnected allowing water to sneak under the plexiglass and discolor the plywood. Instead of miters I chose finger joints because I figured that they would be stronger and keep the piece perpendicular to the plywood and plexiglass. Here is my question should I glue and or screw the frame pieces to the plywood? I know the when making frame and panel doors you are supposed to let the panel float but should you only do that when the panel is solid? The dado is nice and tight fitting and there was no racking of the plywood and plexiglass in the dado when did a test fit. and I plan to run a bead of silicone around the top of the dado (where the frame meets the plexiglass). Is this enough? Any advice would be much appreciated!



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92 posts in 2979 days


#1 posted 11-30-2015 10:37 PM

It sounds like you are going in the right direction. I would glue the assembly together. Expansion and contraction should not be a problem with the plywood. Finally, I would finish it with Spar varnish to protect the wood from the water.

Good luck.

map

-- measure once, cut once, swear, start over

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