Geometric Turtle Stamp

Hello again to the next installment of assignments from Computational Fabrication! This week we were tasked to create a 3D design or convert a previous design and manufacture it with CAM programming so that a machine performing subtraction fabrication could create it.

Subtractive fabrication is different from additive fabrication as you start with some block of material (called a stock) and perform drilling and milling operations on it to create the final shape. Additive fabrication (common for 3D printers) creates the shape in layers that are based on each other. With additive fabrication we have slicers like Cura that can automatically create gcode toolpaths

I decided to create a stamp to make geometric turtle shapes. I saw a geometric pattern online and replicated it into Fusion 360 in 2.5D to make the stamp.

• Fusion 360

At first, I tried to replicate the design I saw online by hand, but it looked very off. I then found the import image feature in Fusion 360 and placed the image into the project and traced over it - I feel like I cheated but I'm sure all great artists start with tracing :^) You can see the difference between the image version and the version I tried to replicate by hand. It was much better when I could trace :-)

Each line has a corresponding line made with the offset command. I drew half of the design and then used the mirror sketch command to create the entire turtle shape. However when I did this it caused undesired profiles (or faces) that were created. This is because the lines and offset lines were not perfectly aligned and Fusion 360 interpreted these as different profile boundaries.

I had to manually fix these issues by hand and made sure all points touched together to create the desired profiles. It took me a while but one that that really helped was to only perform the mirror command on the lines of the sketch and not the points.

I then extruded the turtle sketch profiles outwards for the stamp and created a basic cylinder with a chamfered edge that the turtle rests on.

Now onto the CAM part! As from the professor's guidance, I set the coordinate system for the stock. I think by default Fusion 360 designs with the Y axis as the "upward" axis but all the tools we used from the Autodesk Pier 9 CNC tool library used the Z access as the "upward" axis. I first had to adjust that to fit the model.

When viewing the simulation performing adaptive clearing operations on the model, I noticed that the tool itself was actually colliding with the turtle. So if this object was actually milled, it would fail and possibly break the machine. I also noticed that most of the tools were a bit too large for the model. I had originally designed it to be about 2in by 2in seeing as the smallest tool in the tool library has a diameter of .125in it would be basically impossible for the machine to create such fine details as I have made in my model. So I scaled the model up by 2 so that the tool would be able to actually mill the product accurately. I also extruded the face of the turtle downwards so that it wasn't so tall that it would collide with the tool.

First I flattened the top of the model using the face operation and then did a series of adaptive and pocket operations to get the outline of the turtle.

I ran into some issues when doing the CAM programming because I did not know the best way to mill something is to make sure all unnecessary parts are milled by the machine and not just "cut" off. I originally though that you could use the tool to make some sort of cut and then the rest of the material could just be discarded, but the professor said this was a bad idea as the sliced part could go flying off and potentially break the machine. This also caused Fusion 360 to also throw some red errors at me that the tool was touching the stock when it shouldn't be.

I took her advice and continued on will the milling, making sure to keep in mind the order of the paths to make sure the best path was created.

The back was pretty simple. I had to rezero the machine for the flipped side. I had some trouble trying to figure out how to cut out the circular shape but eventually got it by adjusting the adaptive clearing to leave no stock and to use the outer edge of the stamp as a reference. If I didn't do this some stock would be left (2nd picture) and this is definitely not intended. I then performed a circular toolpath for good measure to make sure the stamp was cut out cleanly.

Here is the final simulation of the CAM Programming. In the class we weren't able to actually try fabricating the model out, but here is what it would look like if we could. As you can see, some of the edges were not able to be milled out because the angle was too sharp for the tool. But overall the design looks pretty nice!

I have also included the .stl file.