How to join MDF boards edge to edge
Today I will show you how we join MDF boards edge to edge.
We needed this type of joint to build a white painted MDF bookshelf with a custom shape. The shape of the back panel had to be done, also out of MDF. For that, we needed to join small pieces of MDF boards and to joint them seamless.
After some online research, we found the right solution. First of all, we tested the method and then we improved it and used it in our project.
First test to see if the method for joining the MDF boards edge to edge works as expected
Our method for joining MDF boards consists in routing of channels in the edges of the boards. The idea is to glue in those channels thin strips of wood, MDF, plywood or other materials that are suitable for such joints. We first tried with using MDF thin strips.
1. We took two small MDF boards. The cut of the two boards must perfectly straight and square. In order to get a strong and perfect joint, both boards should be cut at 90 degrees. This way their edges will be very well connected.
Before routing the channel in the edge of the board, I secured it to the work table with a clamp, to make sure that there is no risk to move during the routing.
2. For these channels, I used a slotting cutter router bit with 31, 75 mm diameter, 4.76 mm cutting thickness, and 9.52 mm cutting width. I set the router so that I route the channels making two passes with the router bit (one on each face of the MDF board) to get an 8 mm channel. I made a first pass on the first face of the board.
3. I flipped the board upside down and I secured it again to the worktable.
4. I made the second pass with the router on the other face of the board. I’ve got an 8 mm thick slot
5. I cut an 8 mm wide strip of MDF from another 18 mm thick MDF board. I was going to glue it between the two panels, in the routed channels in the edges.
6. Before applying the glue, I checked if the cut strip fitted correctly in the routed channels. The MDF strip should not be forced into position (in this case there would be a high risk of cracking the boards), nor too easily (in this case, it would no longer have enough contact surfaces when gluing it, and it would not keep the boards aligned).
7. After I was sure that everything fitted, I applied the adhesive on the both sides of the MDF strip and in the routed channels.
8. I inserted the MDF strip into one of the channels by hitting it lightly with a rubber mallet.
9. Then I fitted the second MDF board, and I aligned it with the rubber hammer, until the two edges of the boards were joined together tight.
As you can see, the two MDF boards are glued and aligned very well.
The next day, when I was sure that the adhesive dried, I tested the strength of the joint. I put the new panel on the edge of the worktable with the joint hanging in the air and I hit the board with the hammer. After a few hits, the joint cracked. Actually, the MDF strip itself cracked, otherwise the two MDF boards were very well glued. I concluded that the joint could be very strong, but the material from which the strip was made had to be changed.
Improving the MDF joining method
I have improved the method to join MDF boards by replacing the MDF strip with an 8 mm thick plywood strip. The plywood is a stronger material because it consists of several alternating layers of wood glued together. That makes the strip and the joint much stronger.
1. So, I cut 2 cm wide strips from a piece of 8 mm thick piece of plywood.
I cut several plywood strips because our project needed a lot of such joints.
2. I started again the routing process. I used the same slotting cutter router bit.
3. I applied the adhesive on the plywood strip and on the walls of the routed slots and I adjusted the position of the MDF boards so that the joint aligned properly.
As you can see, the two MDF boards were correctly joined. What can’t be seen, but I can assure you, is that the connection is also very strong.