Carvera PCB tutorial

Quentin Bolsée, 2024

This tutorial will guide you through PCB milling using the Carvera machine, which is an impressive low-cost milling machine with automatic tool changing. In the context of PCB milling, this means that the machine can cut the traces with a fine tool, then swap it for a larger one to cut the board's edge, all automatically.

1. Securing the copper clad

The easiest way to secure the copper clad to the machine is to use clamps. When using clamps, be mindful of two things:

The machine has no knowledge of where the clamps are, and will happily mill into it if you tell it to. That would damage the tool, and possibly the machine itself.
You need a sacrifical layer under the clad you're planning to cut, or your program will reach the machine's bed when cutting the edge of your board.

The easiest sacrifical layer is simply more copper clad. Use a total of three layers to reach a good height for the clamps:

Next, secure this stack using the clamps. Make sure the lower left corner of your copper clads is pushed against the L bracket present on the machine's bed, with no gap. Use the side of the clamp with a lip, and check that the lip has good engagement with the top of the clad.

Use the bracket's two screws to secure the lower-left corner. Make sure they're effectively compressing the top of the clad stack:

Finish off with two more clamps in the back of the machine:

Congratulations! You now won't have to touch the machine until the end of the process. We basically just have to load the file and hit "play".

2. Preparing the file with mods

For the purpose of PCB milling, we'll assume the machine has the following tools loaded:

Tool n°3: 1/32" (0.8mm) flat end mill
Tool n°4: 1/64" (0.4mm) flat end mill

The 1/64" flat end mill as tool n°4 is not what the machine comes with out of the box. Instead, you can use the 30° 0.2mm V bit the machine has as tool n°2 by default, but V bits tend to leave a lot of burs on milled PCBs. A thin flat end mill is more delicate but worth it for milling quality.

To produce the g-code to mill your PCB, first open mods in a web browser. Right-click, then go to programs->open program, and find the "Carvera mill 2D PCB" program under "machines":

The program looks very daunting, but your input is only needed on the left side:

To continue, you'll need a png image of your board's traces, and another png image of your board's edge. You can obtain those files in many ways, for example by converting your gerber files to images using gerber2img.

Load the two images by clicking "select png file" in the respective nodes, on the left of the program. Double check the DPI value of those images, as it can sometimes fail to be automatically detected, in which case you can change it manually.

Next, check the "Tabs" node. Make sure a thin line is connecting the side of the image to your board. If needed, adjust the length of the tabs. If your board has a special shape, you might need to add them manually using some image editing software; just make sure they reach the every last pixels on the left and right sides of the image.

To obtain your g-code file, simply click on "Calculate" on the central node, marked by a note. The program will become slow or freeze for a few seconds. At the end, you will get a preview and time estimate in the lower right side of the program. The g-code file will autmatically be downloaded to your hard disk. If in doubt, check your Downloads folder, or the browser's download history.

3. Loading the file into CarveraController

Launch CarveraController, and make sure the machine is connected through USB:

Next, load the file by clicking the icon in the lower-left corner. The Carvera needs the file to be loaded into its internal memory, so you'll need to upload the file first, by clicking on "upload":

Navigate to the file produced by mods, and click on "Upload". Don't click on "Open", as that won't upload the file to the machine.

Next, click on "Close" to go back to the machine's locally stored files. Select the one you just uploaded, and click on "Select".

The toolpath is displayed:

Make sure it looks correct, then click on the gear icon in the lower left corner. A new dialog box opens, letting you configure your program before launching it:

First, you'll need to set the lower left corner of your program. If your PCB clad has already been used before (as should be the case most of the time), you'll need to measure the X and Y offsets needed to not run into it. Using calipers and a ruler, measure the X and Y distances from the L bracket at which you'd like to mill your board. Make sure to leave some margin, and check that your board will fit in the spot you've picked. If you want to mill close to the bracket, use at least 5mm of offset.

Click on "Config" under "Set Work Origin". Configure the following:

Tick Anchor1 as the reference
X Offset: the X offset you measured (in mm), >=5mm
Y Offset: the Y offset you measured (in mm), >=5mm

Click on "Ok" to confirm. Next, let's configure auto-leveling with the probe. Tick both "Scan Margin" and "Auto Leveling", and click on "Config" under Auto Leveling.

In the new dialog box, use the following settings:

Clearance height: 2mm
X points: 3
Y points: 3

If your board is large, you can use 5 points instead of 3.

Click on "Ok" to confirm, then click on "Run" to launch the job. The machine will pick up the probe first, and use a laser pointer to show you the margin of your program. If those margins go beyond the copper clad or overlap with the clamps, STOP the machine by clicking on the red stop icon. Go back to the configuration, and correct the X and Y offsets so that your program does not crash the machine in anything.

If everything looks right, the machine will probe, then start milling the traces with the fine tool:

If you see the machine failing to mill through copper in some parts of the copper clad, the most common cause is a bowing copper clad. As the machine is trying to mill, the stock just bends away from the tool. To fix this, you can pick a more flat copper clad, use better clamping, or use double sided tape to tape it to the sacrifical layer (which should also be flat).

Here is the result of a successful trace milling:

The machine then picks up the larger tool, and mills the outline of your board. Afterward, the machine will drop the tool and bring the working area toward you. Here is the final result:

4. Removing your board and cleaning up

Although the machine has a built-in vacuum, there will be a small amount of dust left after milling. To keep the machine tidy for the next user, please use a shop vac to extract all the remaining powder:

To break off the tabs, you can use a chisel to gently push the board. If the tabs don't break off immediately, use the sharp side of the chisel to gently lift the board, but don't scratch the sacrifical layer too much, as that might make it non-flat for future uses.

If you want the tabs to fully disappear, you can use a file on the edges of your board.

The milling process sometimes leaves burrs on the traces, as the copper gets lifted during cutting. To have a cleaner board, and reduce the odds of short circuits, you can use a light abrasive to deburr the surface of your board. Scotch brite or high grit sand paper is perfect for that use case.

Another perfect board. Pat yourself on the back, and move on to soldering. You can optionally use dish soap and water to clean off the last few impurities, but make sure to get rid of all the soap and water before soldering.

Last tip: if you want to quickly look for short circuits, you can shine a light from the back of the board to enhance contrast.