7. Computer Controlled Machining - Collin Kanofsky and Evan Park¶
We used a genmitsu CNC machine that is talked about on Collin Kanofsky documentation to test the effects of different settings on the cut.
Speed Test / Feed Rate test¶
The first test we did was to see how speed impacts the accuracy of a cut or in the term Feed Rate, the amount of material cut in a period of time. To do so, we created the test file shown below in fusion 360 and adjusted the speed for each circle cut to find the difference.
After many hours of learning to collaborate fusion 360 with candle, the gcode>cutting software, we finally cut out the board as shown below.
The bottom circle was cut at 10in per minute. The bottom middle at 20, top middle at 30, and the top circle at 40in per minute. The video of them cutting tells us a lot about the effect of speed.(3.5 times speed on the video)
For starters, the 10in/min, though it was successful, didn’t have high accuracy and that could be seen by the circle having a bump in it on one of the sides.
Next, the 20in/min and 30in/min were around the same accuracy as the 10, but the noise they emitted made it evident that there was more and more strain on the bit as we got higher.
Finally, as seen in the video, during the 40in/min the piece of wood broke free from its clamps. This shows how much force was being put on the bit considering the piece was clamped tightly.
ChatGPT neatly organized this in the markdown code below
| Speed Rate (in/min) | Accuracy |
|---|---|
| 10 | High |
| 20 | Medium |
| 30 | Medium-High |
| 40 | Low |
Conclusion of Feed rate¶
Though 10in/min might seem reasonable, the accuracy of that and the speeds above it are low and it would be more practical to go with a low speed such as 2in/min in order to get the ideal results. For reference, this test was done with a 1/8 inch bit and with a genmitsu machine so take these variables into account when using these feed-rates.
Depth/Pass Test¶
The next test we did was seeing how the accuracy of the cut is affected by the depth of the cut.
Milling the Cut¶
To mill this this cut, I used the shotBot Desktop
Before I could even start the cut, I had to create a tool for the aspire file because the tool library wasn’t there and the Ethernet wasn’t working meaning I couldn’t download it.
After I created the tool, I created a simple 4 circle cut with :
3 passes on the bottom one
4 passes on top mid
5 passes on bottom mid
6 passes on bottom
Results¶
As expected, 6 passes went the smoothest but took the longest
5 passes was also pretty good but we could start to see a dink in the outer cut
4 passes was ok with a little bit bigger dink but still a solid and nice cut
3 passed was also ok which surprised me. I expected a much rougher cut but overall it still wasn’t that bad.
Fun Issues¶
This was my first time using this machine so I spent an hour figuring out where the zero was and why my air cut was also off.
Turns out that when you select 3D offset, the cut offsets by x, y, and z instead of just Z. Also, the zero was in the bottom right and the cut turned out well.
Runout Test¶
To test runout, we had to use a runout meter. Runout is how much the bit deviates from its original or intended origin. This video below shows the runout.
Results¶
The runout on our spindle is very low, like less that 1000 of an inch.
Fixing the material to the bed¶
To fix the material to the machine bed, we used 2 methods. The first method we used was a brad nailer. Brads are basically plastic nails that go through the material and secure themselves into the replaceable machine bed. The pros ot this method is that it is fast, easy, and its not a big deal if you hit a brad with the router. The cons of this method is that you need a brad nailer which requires compressed air. Also, removing brads can be difficult for big items.
The second method to attach material to the bed is using clamps. When we used the Genmitsu, we used clamps to hold down the small piece of wood. The pros of this method were that it was easy to remove and not terribly hard to clamp material down. The cons of clamps is that clamps cannot be in the middle of the material and you have to account for them in your cut.
Results¶
Both of these methods work fine. However, there are more upsides to using brads than clamps if you have access to a brad nailer.