Intro: Awesome CNC Table
I designed this little table in Fusion360 to practice modelling and adjusting non-square box-joints in CNC and it worked out so great in plywood that I had to share!
This was cut with an X-Carve and I made a video that includes all steps from calibration to finishing. Take a look if you like! But of course, you don't need a CNC to cut the parts, you can make this even with a scrollsaw!
In any case, these are a few options to adapt or adopt my design:
- Here is the model in Fusion 360 if you want to take a look or customize it!
- I also luploaded the drawings in svg format in the Inventables project page so you can modify or scale them. Keep in mind though that the box joints are adjusted for 8mm plywood and they might not line up properly if another material thickness is used.
- If you are planning on using an X-Carve to cut it, you can just open the project already set up and click carve!
So, list of materials:
- 8mm plywood, at least 75x75cm, but you can use scraps, the separate pieces are not big :)
- Cutting thingie: ideally a CNC, but of course a bandsaw, scrollsaw or even a coping saw will do!
- Hand files: A "triangle" one is recommended to adjust the fingers
- Others: Wood glue, sandpaper / orbital sander, x-acto knife, paint, varnish...
Step 1: Design!
I started playing with Fusion360 for the first time. It's so cool! So I made 3 main pieces, (top, leg and "apron") and put them together in the assembly.
As I mentioned I used 8mm plywood so I adjusted the box-joints to match that thickness. In this link you can access the project and modify it, or scale it if you have a different thickness board.
I wanted the edges of the table to be visually continuous from top to bottom so I designed the boxjoints so that the edges of the mating pieces would form those outlines eventhough the interlocking fingers at 45º leave some gaps in both faces. As a result, and because the faces are not square to eachother, there is a bit of interference in the back (or the inside of the table) and a little bit of material has to be filed down after cutting, but no worries! it works just fine :)
Another feature to keep in mind if you are gonna use a CNC is leaving some "Indents" or "undercuts" or "dogbones" in the inside corners of the pieces. The router bit will eat a bit more material in those places so assembly is straight forward. If these weren't there, you would have to file down every corner, since the router bit leaves a radious and not a straight edge. In my case these "dogbones" are meant to be cut with a 1/16 router bit
Step 2: Cut Your Pieces!
In my case, I used an X-Carve, but any kind of saw and some sanding would do the same work :)
I used a 1/16 downcut bit to make sure I didn't have any tearout. After cutting, I had to remove the pieces from the plywood sheet, cutting the tabs and then sand them flush. These tabs are meant to keep the pieces in place after they are cut, so they don't move around and are bit by the router again.
Step 3: Prepare the Mitered Box Joints
As I mentioned, after cutting you will still have to file down some small areas of the box joints since it is indeed a double bevel joint. No worries though, just a little bit here and there. The model is a good reference to visualize the interference but you can just position the legs using a square to keep them vertical, and file down the "aprons" until they fit. I recommend filing down the same amount of material in both the leg and the apron so they have more glue surface.
Don't worry, this is not complicated, it requires a bit of thinking and then all the joints in the project are the same!
Step 4: Glue Up!
I suggest you start glueing the legs using a square to keep them vertical and then, once they are dry, the aprons just fall into place easily.
There is a lot of glue surface so plan the glue up before applying the glue and have the clamps on hand! I used a box to make sure my legs were square.
Step 5: Sand Fingers Flush
The finger joint is designed so that after glue up the finges are a bit proud of the surface. Now it's time to sand them down so the faces look neat!
I glued a piece of sandpaper to a board and moved the joint areas along the sandpaper. This way flaness is 100% assured and the results are super neat. You can also use a file but you need to have a good eye so you don't sand more than needed or leave curvy edges, since you are sanding endgrain and it is not as stable as I'd like.
Step 6: Finishing Touches!
As you might have noticed, I painted the inside edges green before glue up, but that was just my personal touch. You can paint it or just apply some varnish.
My tip here! If you are going to paint the inside edges, just stack the pieces together. That way you just have to mask 2 faces instead of 8!
And that's all! Enjoy your table!!