How to make strong rounded corner joints
When making MDF furniture, we want the joints at the corners to be as strong and stable as possible. Here are three methods we use:
- for the furniture boxes with simple straight corners we use screws. We hide them with putty, before applying the primer and the paint
- for the furniture boxes with rounded corners, we use two methods (because the screws can no longer be used): either wooden dowels or “box joint”
In this post, we will describe the method to reinforce the corners with wooden dowels. We will use an MDF nightstand box to which we already added the strips to the corners, to thicken them. This way rounding the inside and the outside of the corners becomes possible, without reducing the wall thickness.
The reinforcing method used, is part of a video on our YouTube channel. You can watch it to better understand the process:
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How to strengthen corner joints:
1. Depending on the length of the joint, we establish the number of dowels to use. We distribute them evenly along the length of the joint. We use two of the dowels on the ends. We place them at about 4 cm from the edges. We do not place them closer to the edge to avoid the risk for the boards to crack.
Sometimes it may not be necessary to use so many dowels, but an extra one to reinforce the joint does not harm, since the time required is almost the same. In this case, we used 4 dowels for a 35 cm length of the corner joint.
2. We usually use 8 mm diameter dowels. For such projects, we use a long 8 mm thick round rod, out of which we can cut pieces to any size we need. In fact, we cut them 2-3 cm longer than the project requires to handle them easier.
3. The next step is to drill the holes into the corner joints. For this diameter of dowels, we use an 8 mm diameter wooden drill bit. With the screwdriver tilted at about 45 degrees, the drill penetrates through the three boards. The hole is drilled so that the drill bit passes completely through the horizontal board (the one with the edge joined to the surface of the vertical one), goes through the added strip and stops close to the edge of the vertical board (there must remain 4-5 mm to the front of the board).
4. We apply class D3 adhesive inside the holes after we clean them in advance very well to remove the dust resulting from the drilling. The adhesive can be applied on one side (in our case inside the holes). It is not necessary to apply on dowels too. The adhesive can be applied at once inside all the holes because the hardening time of the glue is about 10 minutes (it can vary depending on temperature and humidity).
5. We insert the dowels into the holes and hammer them in place. You can also use a mallet not to appear any risk of damaging the MDF surface.
6. We remove the excess adhesive as well as possible with a dry cloth.
7. After removing the adhesive, we cut the dowels. For this, we use a hand saw. The hand saw must be handled parallel to the MDF surface to avoid scratching it. It is better to let the dowel a little popped out since it can be sanded easily after the glue dried.
8. After the glue dries, the surface can be sanded. We first use 80 grit sandpaper to remove material from the surface quickly. Then we use 150 grit sandpaper to get a smoother surface. After that, we apply a layer of primer for MDF and a layer of paint (sanding the surface with 320 grit sandpaper before applying the paint).
Following the steps described, we always get a piece of furniture with stable and strong corners over time.