The new cutting mechanism
The CNC currently in development is a TwoTrees CNC that has to be modified to fit in the freezer.
Modifying the new cutting mechanism
Y-Axis:
The width of the internal freezer space is measured to be 39,5 cm.
We remove 0,5 cm due to the lead-screw bearing attachment, which is 0,5 cm thick.
We remove an extra 0,5 cm as a safety margin.
When cutting the y-axis to size we have decided to cut at 38,5 cm.
The steppermotor with its plate is 5,23 cm.
If you measure with the stepper motor detached, the cut appears at 33.23 ~= 33,3 cm.
The lead screw is 0,5 cm longer than the profile because of its mounting, and will thus need to be cut separately.
The material that will be have to be removed from each section of the profile is: 27,2 cm.
Cutting will be performed on the opposite side of the stepper motor, due to it being easier to accurately measure, as well we avoid the need to machine new notches on the profile.
Add image.
X-Axis:
The width of the internal freezer space is measured to be 39,5 cm.
We remove 0,65 cm from each side due to the y-axis-attachments.
We remove an extra 0,5 cm as a safety margin.
We remove an additional cm due to the stepper motor 4,74 cm.
We remove 0,53 cm due to screws on the y-axis attachment on the opposite side of the stepper motor.
When cutting the x-axis to size we have decided to cut at 32,43 cm, rounded down to 32,4 cm.
The lead screw is approximately the same length, but not quite, so it should be cut separately.
The CNC x-axis is 59,4 cm. Thus we remove 27 cm from the axis.
27 cm will be removed from the lead screw as well.
The current cutting mechanism
Currently, a CNC machine is used to mill out the samples.
The CNC currently in use is a ..., and it is controlled with a GRBL and with Lightburn software.
Make sure to over-engineer the CNC frame. A partially poorly made CNC will cause new problems with vibrations, inaccuracy etc.
Possible improvements
Upgrading to a better CNC
One could improve the CNC in a few ways that would be beneficial for the end-product.
Longer axes/Bigger Bed: A bigger work area would provide more space for bigger samples and would give more space for manual interaction with the samples. One disadvantage with this upgrade is that the entire product would have to increase in size and would therefore be more difficult to move/relocate.
Stronger Stepper Motors: We encountered some accidents when testing last semester that we believe could be the result of step-skipping in the positive z direction (due to increased resistance from gravity). If that was the reason, stronger stepper motors could solve that.
Inductance auto calibrating z axis
To sufficiently calibrate the length of the tool, as well as the z-axis, It should be possible to auto-calibrate the z-axis to the cnc bed.
Utilizing a CNC router z-axis touch probe tool could solve this relativly easily and cheap. They can be attached to the tool, and Gcode could be implemented to sufficiently calibrate the tip of the mill.
The following links are relevant for further exploration of this concept:
Youtube Short showing t a CNC calibration procedure
Amazon link to one such Z axis tool
Tests
Test 1: Electrical components in cold environment
Extraction popping has been tested over 5 days. The freezer has been on the entire time. There have been no signs of malfunction in the electrical components, like we saw last semester.
Test 2: Electrical components in cold environment
We are running a very long program on the mill and studying if we see any shifts in the z axis. We will also be recording the heat generation from the motors. The height will be measured visually using a soft foam piece that will not harm the mill bit should the z axis shift.
The camera had significant ice buildup and did not work during this test. Whether the malfunction was caused by cooled moisture or by prolonged exposure to heat is unsure.
Heat generation test 1: Many small circles.
In this test the z motor runs quite a bit, but the x, y motors runs a little less.
| Time (min) | Temperature (*C) |
|---|---|
| 0 | -9.9 |
| 1 | -11.4 |
| 2 | -12.4 |
| 3 | -13.2 |
| 4 | -13.7 |
| 5 | -13.7 |
| 6 | -13.9 |
| 7 | -13.9 |
| 8 | -14.1 |
| 9 | -14.4 |
| 10 | -14.4 |
| 11 | -15.0 |
| 12 | -15.2 |
| 13 | -15.0 |
| 14 | -14.7 |
| 15 | -14.9 |
| 16 | -14.9 |
| 17 | -14.8 |
| 18 | -14.7 |
| 19 | -14.5 |
| 20 | -14.7 |
| 21 | -14.8 |
| 22 | -14.7 |
| 23 | -14.6 |
| 24 | -14.6 |
| 25 | -13.7 |
| 26 | -14.0 |
| 27 | -14.4 |
| 28 | -14.4 |
| 29 | -14.5 |
| 30 | -14.5 |
Heat generation test 2: Many big circles.
In this test the z motor runs less, but the x, y motors runs quite a bit.
| Time (min) | Temperature (*C) |
|---|---|
| 0 | -13.4 |
| 1 | -14.2 |
| 2 | -14.4 |
| 3 | -14.5 |
| 4 | -14.5 |
| 5 | -14.5 |
| 6 | -14.5 |
| 7 | -13.9 |
| 8 | -14.1 |
| 9 | -14.3 |
| 10 | -14.3 |
| 11 | -14.4 |
| 12 | -14.4 |
| 13 | -14.4 |
| 14 | -14.4 |
| 15 | -14.4 |
| 16 | -14.4 |
| 17 | -14.3(Speed x2) |
| 18 | -14.2 |
| 19 | -14.1 |
| 20 | -13.9 |
| 21 | -13.8 |
| 22 | -13.9 |
| 23 | -14.0 |
| 24 | -13.9 |
| 25 | -13.8 |
| 26 | -13.6 |
| 27 | -13.6 |
| 28 | -13.7 |
| 29 | -13.7 |
| 30 | -13.7 |
| 31 | -13.7 |
| 32 | -13.7 |
| 33 | -13.7 |
| 34 | -13.7 |
| 35 | -13.7 |
| 36 | -13.7 |
| 37 | -13.7 |
| 38 | -13.7 |
| 39 | -13.7 |
| 40 | -13.7 |