Computer-Controlled Machining¶
Group assignment requirements¶
The group assignment for this week is the following:
- Complete your lab’s safety training
- Test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine
- Document your work to the group work page and reflect on your individual page what you learned
Large format CNC router machine specs¶
Describe/list the available features and key settings of your large format CNC router machine.
Machine name: ShopBot (PRSalpha 120-60) ATC
Spindle max speed in RPM: (24,000 RPM)
Machine bed size (work area): (3.28m x 1.55m x .2m)
Toolpath generation software used: (Aspire)
Safety¶
- As for working on this machine safety is crucial part as when the machine is working it has to be monitored all the time at least 2 persons one of them has access to the Emergency Switch in his hand or at least near his hand.
- If the machine is working the door should be closed to prevent sound noises , Also everyone in the room should have their eye and ear protection on in addition to face mask.
- No one is allowed to wear cloves near the machine specially when its working, girls should have their hair tight and protected with hat.
Materials¶
At the lab we use the machine to cut different materials such as:
- [MDF] up to a thickness of [18] mm.
- [Plywood] up to a thickness of [17.5mm] mm.
For this assignment and this week we will be using [MDF] with a thickness of [18]mm. All the testing is done on this material.
Fixturing and machine setup¶
The machine In the lab comes with a vacuum bed but at the meantime its not working, so they are currently using screws to fix material on the bed.
After making sure the material is securely in place, we continue the machine setup process.
The machine firstly has to be switched on and it has its own calibration routine they call it C3 where the machine automatically calibrate its X-Y axis using its proximity sensors, Then we need to warm up the spindle for 9 min over different speed machine comes with its own routine C5, Then we can zero the x-y axis if needed (depends on the place of your work piece) after this we can Zero (Z-axis) through the plate comes with the machine which is automatic zeroing for the z-axis.
For changing the bit it has to be done before zeroing the (Z-axis).
Let’s go through the steps one by one
1- Switching the machine on.
2- Open the computer and shop-bot app.
To detect the machine we have to make sure the emergency stop is deactivated and to press the Reset button.
3- C3 Routine –> To re-set the machine using proximity sensors.
4- Then changing the bit if needed.
5- Placing the bet in the spindle.
6- Now we can Zero The Z-Axis.
7- After this we need to warm up the spindle if needed C5 Routine.
Its needed to press Start every time you want to start the spindle (Safety option)
Note : This is the required Routine every morning before the machine start operating.
Toolpath generation¶
For the Toolpath software we are using Aspire from Vectric
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We will Draw 8 Squares.
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Then we will Place the Squares.
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Then we will generate the toolpath for every square.
Each square will have its own feed rate and sindle speed.
We will be fluctuating around the optimal values for the cut because any mistake will cause the bit to break.
- I will also try the tab settings (which keeps the part attached to the sheet after the cut)
- Toolpath Preview.
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Then we will generate the G-Code.
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Finally we are ready to cut the parts.
Speeds, feeds¶
To find the best speeds and feeds for the material being used, we tested multiple speeds and feeds for cutting and engraving to see which gave us the best results.
write on each piece the speed/feed setting used
By completing this test, we found that for cutting [MDF], with a thickness of [18]mm, using a [6]mm bit, the best settings are the following:
Feed rate: (90mm \ sec)
Spindle speed: (15000 RPM)
Plunge rate: (4mm \ sec)
Pass depth: (3mm)
Runout & Alignment¶
Runout is the deviation in the tool/spindle from it’s true circular rotation. Where it will no longer rotate on its intended axis. This can be measured with a dial test indicator.
Axis alignment ensuring that the machine’s axes (X, Y, and Z) are properly aligned and in parallel with each other. Misalignment can result in inaccuracies, poor surface finish, and other issues in the machined parts.
cut a ~large square on the machine
To test this, we cut a simple square and measured the square at multiple ends. If the machine has perfect alignment, the square should be the same dimension if measured from any side. We measured the square from multiple areas and found the difference to be [0.1]mm But this is not accurate because we used a flexible Meter Roll which is not an accurate tool like the caliper.
I think this result is perfect but I hope this difference is not accumulated along the machine axes.
