How to build and reinforce thin wooden frames
Building frames out of very thin profiles requires a secure reinforcement of the corners because the gluing surface is very small. We had to fix this problem in a previous project: our small floating bookshelves with a “check box” design.
We really wanted to replace the black tape (used for the project we discovered on Pinterest) with a wooden frame, so we could paint it with matte black paint. We decided to build them out of as thin as possible oak boards to be sure the frames won’t be a problem when arranging the books on the shelves. That’s how we got to use 8 mm thick pieces. For such a thickness, we had to find a solution to reinforce the frames, so they wouldn’t break when installed on the wall.
The whole building and strengthening process is part of a video you can watch on our YouTube channel:
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Making the simple thin wooden frame
Building wooden frames is a very easy process. We usually start our projects with unedged timber. We plane them until we get a squared board with all the faces straightened. In this project, because we needed very small boards, we started from a few scrap pieces from older projects. We cut them with the bandsaw to a thickness of 1.5 cm and a width of 2.5 cm. We kept a margin large enough to be able to straighten all the faces.
We planed them with the thicknesser machine until we got the needed thickness of 0.8 cm and the width of 2 cm.
We set the 45-degree angle of the sliding circular saw. Then we cut one end of the boards. We cut two profiles at the same time. Why? To be sure that the boards that will be fitted face to face to form a frame would have exactly the same length. We turned the two boards, without moving them from each other, and we cut the second end at 45 degrees.
We did the same thing with the other thin boards. To make sure that the frame will close perfectly at the corners (that means the cutting angle of 45 degrees is correct), we matched the planks and checked the 90 degrees angle. If the angles were not 90 degrees, we would make small adjustments to the angle of the blade and then we would redo the cuts.
We put a strip of painter tape (as narrow as possible) and we placed four thin strips inline, aligning them on one side. Then we applied the adhesive on the cut ends and closed them nicely forming the frame. The tape kept them in the right position and also tightened them at the corners (it didn’t allow them to move until the adhesive dried).
These are the thin square frames we needed for our project. Without reinforcing them, the corner joints would certainly not have been strong enough.
Reinforcing the thin frames
The next step was to strengthen the corners, so we picked the simplest and fastest solution. Routing the corners and gluing narrow strips in the slots.
For this, we used a T-type slot cutting router bit (3.17 mm high, 10.17 mm diameter) that we found in our workshop (we don’t use it often, but sometimes it is very useful).
We cut a 3.17 mm thick oak strip (the height of the router bit). We wanted to glue small pieces cut from this strip into the routed slots of the frames.
We used a piece of plywood as a guide for routing the slots. We secured it with clamps, to make sure it didn’t move while routing the slots.
We set the routing height so that we could get the slot in the middle of the corner. In this way, the routed slot would have had the walls thick enough and resistant to be reinforced: (8 mm thickness of the frame – 3.17 mm width of the cutter router bit): 2 mm
We glued the small pieces of wood, and after the glue dried, we cut the excess on the bandsaw.
We sanded the outside edges of the frames using the belt sander secured to the work table.
We sanded the faces with the orbital sander with 120 grit sandpaper, and we rounded the sharp edges by hand.
At the end we applied two coats of matte black paint RAL 9011, sanding the surfaces with 320 grit sandpaper after the first coat dried. This is the way the thin oak frames looks after painting them: