CNC Slotting Gider Joint

Slotting Gider Joint is a quite interesting joint as the wood pieces are connected to each other with a “sticking in - sliding in” structure. It's not the most stable joint, but it is really flexible. In this post, I will share the making process as well as some reflections. Please follow this table of contents.

1. Sketching
2. 3D Modeling
3. Exporting the Toolpaths to Carbide Create
4. Manufacturing with the Shapeoko CNC Machine
5. Cutting Off the Tabs and Polishing With Sandpaper
6. Unexpected Situation & Reflection

I also uploaded the .dxf file of the design. Hope that helps if you are considering making a similar kind of structure.

• Shapeoko CNC Machine
• 18mm wood board
• a small saw
• sandpaper

According to the picture we received from the catalog 50 Digital Joints, I tried to figure out how the two pieces of wood boards are connected, as well as the dimensions of it. Although the size is not fully determined, which means I have some freedom to design, there are several important parameters we should bear in mind.

• the thickness of the wood is 18mm
• the radius of the end mill (toolsize) is 6.35mm

Finally, I calculated a seemingly realistic and achievable set of dimensions and 2D modeled it on Rhino7. The radius of the circle I left for the seams is 7mm, as I think it gives more space when I try to connect them together.

And for 3D simulation, I extruded the planar, and set the thickness of the "sliding part" as 12mm (6mm thinner than the thickness of the wood board), just as shown in Figure 1. I also translated the two parts to make them fit together. Figure 2 shows the process of how they are combined together, and figure 3 shows the side view of the joint.

Since CNC is a subtractive manufacturing process, I exported the .dxf file to the application Carbide Create and then set the parameters for the Contour and Pocket making. For the Contours, I set the depth to 18.3mm (0.3mm larger than the wood thickness), so that the wood will be completely removed without leaving a thin layer of wood. I also learned that it's unnecessary to reserve values for the pocket. We can just set the right amount.

And it's always better to start from the inside contours/pockets instead of the outside ones, or the manufacturing process will be more dangerous with vibrating woods and louder noises.

Also, for fixing the wood parts, we should set several tabs so that the cut wood will not affect other part of the manufacturing process. For example, if the small part is completely cut off and moved to other places, it may collide with the end mill and bring a lot of danger.

Finally, we set the metal pieces to fix the raw wood board, calibrated the Shapeoko CNC Machine, and set up Prof. Garcia's self-made cleaning system. Voila, the pieces are there! Cut out but quite fixed on the board with those tabs.

Then I used a small saw to cut out the wood boards and polished its edges with sandpaper. Prof. Garcia also helped me cut off some of the sponge (covered with sandpaper), so that I can do some more precise polishing to the inside of the pieces.

After I polished the two pieces, I tried to connect the two parts. But it turns out that, the smaller one is not the same as the design in .dxf file. The length of the upper piece shown in the picture should be 62mm, but it's only 57mm. Maybe there is something wrong with the manufacturing process, but I still don't know the exact reason. However, we manufactured another piece. And finally, the joint works!

Reflections:

1. During the whole process, we are always reminded of the safety issues. It is quite essential that we bear those tips in mind, especially when we are using this kind of large manufacturing machines.
2. Also, the manufacturing process does not always end up as how we designed it due to some limitation in the raw material or the machines. For example, we should set the depth as 18.3mm instead of 18mm to ensure the wood are totally removed.
3. When the pieces are manufactured, be sure to check if the dimension of the final product is the same as the design. Although the unexpected situation happens may not usually happen, it's important for us to compare every aspect of the design including dimensions and seams, to either try to find out the flaws in our design, or to decide whether to re-manufacture it.