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 <b>automatically</b>.
</p>
<h2>1. Securing the copper clad</h2>
<p>
The easiest way to secure the copper clad to the machine is to use clamps. When using clamps, <b>be mindful of two things</b>:
<ul>
<li>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.</li>
<li>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.</li>
</ul>
The easiest sacrifical layer is simply more copper clad. Use a total of <b>three layers</b> 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.
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".
</p>
<h2>2. Preparing the file with mods</h2>
<p>
For the purpose of PCB milling, we'll assume the machine has the following tools loaded:
<ul>
<li>Tool n°3: 1/32" (0.8mm) flat end mill</li>
<li>Tool n°5: 1/64" (0.4mm) flat end mill</li>
</ul>
The 1/64" flat end mill as tool n°5 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 <ahref=https://modsproject.org/>mods</a> in a web browser. Right-click, then go to programs->open program, and find the "Carvera mill 2D PCB" program under "machines":
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 <ahref=https://quentinbolsee.pages.cba.mit.edu/gerber2img/>gerber2img</a>.
</p>
<p>
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.
</p>
<p>
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 <b>autmatically be downloaded to your hard disk</b>. If in doubt, check your Downloads folder, or the browser's download history.
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":
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 <b>lower left corner</b> 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 <b>X and Y distances</b> 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.
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.
