Week 07 - Computer-Controlled Machining

This week we have the following tasks to complete:

• do your lab's safety training
• test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine
• make (design+mill+assemble) something big (~meter-scale)
• optional: don't use fasteners or glue
• optional: include curved surfaces

Group Assignment

The weekly group assignment can be accessed here.

Design Ideas and Requirements

The core idea is to create two shelves—one for the Prusa XL and another for all other 3D printers in our lab—featuring ample storage space for Euro boxes, potentially with drawer slides for easier access. We already use boxes from Auer Packaging, so a key design requirement is ensuring that these boxes fit perfectly, both with and without drawers. The drawers are currently optional and may be added later. To better visualize the concept, I used 3D models of potential boxes found on GrabCAD, designed by Gergely DEGI.
Another essential requirement is a dedicated SLA workspace to contain any mess associated with resin printing. In a future iteration, adding a door and ventilation system to this area would be beneficial.
Due to the limited space in the room, standard doors are not an option. A vertical sliding door would be ideal, as a regular sliding door would not work—the SLA workspace is significantly larger than the FFF printer area, meaning the door wouldn't have enough space to slide completely. Fold-up and flap doors are also impractical due to their large size. A rolling door would be an alternative but is considerably more expensive than a vertical sliding door.
The base material for the shelves will be 2500 x 1500 x 18 mm beech plywood, which is currently more affordable than birch plywood. Previously, birch was imported cheaply from Russia, but due to the war, its availability in Central Europe has decreased, making it even more expensive than beech plywood. The Prusa XL shelf will be made entirely from this material, while the second shelf will use 2500 x 1500 x 9 mm plywood for the back panels.
Some integrated lighting and power management would be beneficial. I plan to use Neopixel strips for illumination and additional UV LEDs in the SLA area to cure any unwanted resin spills.
For the Prusa XL shelf, I need to consider the height of my final project so it can be directly integrated underneath the Prusa XL. While it would be possible to build the project into the shelf itself, I aim to keep it as autonomous as possible.

Joints

For selecting suitable joints, our local instructor Ferdi recommended the overview from Winterdienst, which provides an excellent introduction with examples of nearly every joint type imaginable—and even more.
To ensure a perfect fit, a comb test, similar to the one used in Week 03, is necessary. It is highly recommended to test the chosen joints before milling everything, as sanding down imperfect fits would take an excessive amount of time, and time is limited. A small laser-cut model can also be useful to verify that everything aligns correctly. Parametric design is essential—otherwise, adjusting dimensions later would be extremely tedious.
Initially, I decided to use visible joints, as they are easier to mill, even though they may not look as clean as hidden joints. To validate the design, I also created a small test joint that includes all the joints used in the Prusa XL shelf for testing purposes.

Nesting

I manually nested my parts in an assembly in Inventor and then imported the .iam file into Fusion 360 to program the G-code for the CNC.

First Interaction with the Machine

The machine has a work area of 1500 mm × 2400 mm. Most of our base material consists of 1500 mm × 2400 mm × 18 mm sheets, so we needed to cut 100 mm from each sheet using the plunge saw.
Since our sheets were not stored perfectly, they were slightly bent. On our first attempt, the vacuum table was not strong enough to pull them down and straighten them. We decided to flip the sheet over so that gravity would assist the vacuum table in flattening it—this worked perfectly.

We also "tested" the vacuum bed, with the conclusion that the sheet was completely immobilized. Even without the vacuum, the friction between the MDF waste board and the plywood sheet made it difficult to move.

The vacuum table pulls air through the MDF waste board, requiring a vacuum pump. At the moment, the correctly dimensioned pump was in use by a customer, so we used a smaller 7.5 kW pump instead. Next to it, you can see a larger 5.5 kW pump (twice) with a silencer, which was connected to another machine at CNC Multitool.

For milling, we used a 6 mm crosscut/compression end mill, which needed to be inserted into the collet using the corresponding wrench.

The machine features a 9 kW spindle and can switch between the spindle and an oscillating knife. A unique feature of this machine is its automated dust shoe, which can move up and down automatically.

To start the machine:
1. Switch the big red main switch to "ON."
2. Start the PC using the small push button next to the emergency switch.
3. Open UCCNC, a highly customizable control software, which CNC Multitool adapted for their machine.

After starting UCCNC, it is critical to not close the small pop-up window. Just minimize it and then hit RESET in the bottom right.

The program interface looks like this:

To ensure that the soft limits are correct, we need to perform a reference run for all axes by pressing the big button to the right of the coordinates. This process occurs at the XY machine origin, located at the rear left corner of the machine bed.

On the left side, hovering over the blue area with white arrows opens the jog menu, which is used to move the machine manually—for example, when setting the work origin. This menu has two modes:
- Static → Moves the machine while holding the button.
- Steps → Moves the machine incrementally (0.001 mm, 0.01 mm, 0.1 mm, and 1 mm).
The Jog Feed setting adjusts the manual movement speed of the machine.

Next, we set the work origin by moving to the desired position and zeroing the X and Y coordinates using the small buttons next to them.

After this, we let the machine automatically measure the tool for Z = 0.

If no fancy sensor is available, the same process can be done manually using a piece of paper. Lower the end mill slowly until the paper just barely stops moving.

For demonstration purposes, we moved the machine manually.

The MDI line allows for manual G-code input while the machine is idle. When attempting to move the tool manually, the machine automatically starts the spindle, dust collector, and vacuum. This prevents damage when switching between the spindle and the oscillating knife.

Next, we inserted a USB stick with our G-code and opened it using the "Open File" button. A pop-up window appeared, requesting the removal of the "carpet" (the underlay for the oscillating knife).

With the "Edit File" button, the G-code can be directly edited in the newly opened window.

Before running the G-code, we ensured that our post-processor was configured correctly. G28 (home) commands were removed to prevent the dust shoe from crashing into the tool holder, since it does not automatically retract when homing.

Then we started...

...and completely messed up. The end mill plunged straight into the material, through the waste board, and scratched the rubber mat of the vacuum table.

Luckily, nothing more than an ugly hole happened. The tool remained in perfect condition.

The machine detected an issue with the Z-axis, triggering an error mode on the corresponding control card. To reset this, we had to turn off and restart the machine, which was fastest by pressing the emergency stop and then resetting it.

To prevent future issues, we set Z = 0 manually. Most likely, the machine was programmed for Tool 1 with a much longer flute length. After restarting the G-code, everything worked perfectly.

We adjusted the feed rate to 800 mm/s and the RPM to 7000, with a step-down of 6 mm. The machine is robust and fast, but we were cautious to avoid damage and were not under heavy time pressure.

The process looks like that:

Additional Milling

I milled some parts for a master's thesis experiment using our small CNC mill, the Carvera from Makera. Different probes made from various materials and thicknesses were required. I started with the largest parts, which were made from 10 mm acrylic. Milling acrylic with a 1/8" end mill was slightly challenging because the preset for plastic in Makera didn’t work at all. By the second hole, signs of melting were already visible. To fix this, I adjusted the settings, primarily reducing the RPM to 5600 and setting a feed rate of 400 mm/min, which worked reasonably well with occasional cooling. I added a small amount of WD40 to aid cooling, but a slower feed rate of 250 mm/min proved to be more effective. Even then, some cooling was necessary. It was much easier to apply coolant from an open container, such as a glass, using a brush or pipette, rather than using a spray can, which created a mess and required extensive cleaning afterward. For the step-down, I opted for a small increment of 0.5 mm, which is suitable for soft materials.
In preparation for the upcoming electronics production assignment, Ferdi and I collaborated to design a small vacuum table for our Carvera, making PCB milling significantly easier. We also integrated dowel pins to ensure perfect alignment with the machine bed each time, as well as for precise positioning of the copper board. This setup allows for easy two-sided PCB milling.

What went wrong this week

I used a not suiting post processor for our machine, which results in the crashing issues I described before.

What I learn this week

• Turning a machine off, waiting a day, and turning it back on can solve almost any problem. Initially, I encountered connection issues with the Carvera—it would enter an auto-connection loop, followed by extended idling, and then repeat the process indefinitely. Turning the machine off for a short while didn’t help, but leaving it off overnight resolved the issue. I’m not sure why this happened, and I couldn't reproduce the error, but in the end, it worked, which is what matters most to me.
• Spraying a very small amount of lubricant from a spray can is quite difficult.
• In Inventor, you can use the rectangular selection tool to choose all the profiles you want to extrude. Using construction lines for elements you don’t want to include in the extrusion process is extremely helpful and can save a lot of time.
• Sleeping on a problem often leads to better solutions than overthinking it repeatedly.
• How much unnecessary code is add it to "universal" post processors.

What I want to improve next week

Design Files

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Copyright 2025 < Benedikt Feit > - Creative Commons Attribution Non Commercial

Source code hosted at gitlab.fabcloud.org