6. Large format CNC (computer controlled Machining)¶
This week I learned how to cut sheets using a Computer Numerical Control or a CNC machine.
We had two main assignments 1. A group project where we did a joint fitting test to figure out the best dimensions to for the joints depending on the desired tightness of the joints. For example things meant to be assembled and disassembled frequently such as toys or puzzles should not have very tight joints, while things meant to stay fixed need tight joints that do not come off with time.
- To design and build a big object with press-fitted joints using the CNC machine.
Group Work¶
We used the CNC machine to cut and engrave on a wooden piece to learn how to use it, and what the results look like. We also had many joint holes with different widths on the piece, in order to try to press fit a some joints and see how different sizes give different results. More on the work can be found in Salman’s page
CNC Project¶
The individual work was to design and cut a big object and assemble it using press-fit joints.
My design¶
I designed a medium sized cupboard with shelves. I chose this design for two reasons:
- I can use it at home
- It is simple and neat
I designed the parts using Fusion 360 in a two-dimensional setting. I designed joints that had a difference of 0.2mm in both ways to guarantee a strong fit that won’t come off and can withstand time and use.
We tested the joint tightness by cutting a some parts and fitting them. The results were very good and the fit was tight.
This is my design in Fusion 360
This is the top of the cupboard
This is a flower I designed to be engraved on top of the cupboard
These are all the pieces
Setting up¶
I then exported the design in .dxf format and sent it to the computer connected to the CNC machine.
This is the CNC software VCarve Pro, where we set up the design for cutting, and we adjusted the machine settings. The drill bit used had a 6mm diameter.
This is my design in the software right before cutting
Here at the joint openings, we added dog-bone patterns. This is because the machine cuts using a drill bit that is rotating, therefore it cannot do inside angles unless the drill bit is extremely small. Due to that, we must adjust the design a bit to accommodate for that limitation. The other option is a T-bone pattern or to not have inside angles.
After that, we set up the machine.
We first changed the plywood sheet and fixed it using screws.
After that, we turned on the machine from a button on the side and adjusted the machine’s drill bit Z-height and origin from the machine’s operating software.
Finally we started the cutting by pressing this green button
Cutting¶
This is the CNC machine cutting my design.
This is my design after being cut
This is the engraved part
After cutting, comes the difficult part which is cleaning the wood and making the cut parts smooth.
Cleaning up¶
First I used this file tool to remove excess wood pieces from the cut areas
Then I smoothed them even further using this orbital sander
And finally, I smoothed them even more using sand paper to remove any remaining wood pieces.
These are the pieces after sanding
Final results¶
What remains now is to assemble the pieces together, and possibly add a finish to it.
I tried to assemble the pieces, but I found out that I had a design error that caused some mismatch.
Here are some photos to show that
You can clearly see the gap in the side
The top piece couldn’t fit properly as well
Luckily, I was able to flip the shelves the other way and get a good fit where the gap was no longer there. This however made the shelves at the same plane as the outer walls, which is different from the original design, but not a problem at all.
However, that made the top piece too big which we solved by cutting it using a saw. After that, we were able to fit it in and hammer some small wooden pieces to fill some gaps. In the end, we added some nails to the things that were too loose to make sure they do not come out.
This is the final result
