What is an AutolevelerIn this context, an autoleveler is a bit of softeare that reads your G-Code file – the one output by PCB-GCode – and adds a bit of clever math to it. To prepare “autoleveled” G-code is quite easy, just open the autoleveler, point it to the G-Code of interest, and hit “go”. Out the other end comes your G-Code with the autoleveler magic included.
Why use an AutolevelerUnless you have an amazing milling machine (I don’t – mine is made out of plywood. Nice plywood, but plywood nonetheless) – you will have challenges getting the work surface perfectly flat. How flat is ‘good enough’? I don’t know for sure, but I do know that the best I can manually level my PCB + the natural ‘waves’ in the surface of the PCB conspire to make the milling experience very frustrating. Some parts milled too deeply, others just a scratch in the copper, other parts nothing at all. Remember, the copper layer on a one ounce PCB is only 1.34 mils thick (2oz = 2.68 mils). And if you are trying to do 50 mill on center SMD pads, you will really need an autoleveler
How it worksThis is really a two part process. The “magic” code inserted into your G-Code will ‘probe’ the surface of the PC board, making a “topographical map” in memory of the variations around your Z axis 0.0 point, keeping track of the high and low points. Here is a video of my system probing a PCB. Probing Process. Notice a few things:
- I already manually leveled the PCB to within 1 or 2 thousandths of flat (still not good enough)
- You can see a probe in the background that is connected to the “probe in” port of my milling system. This is a mandatory part of the probing process. This probe is a sewing pin rigged through some plastic pipe in which is a bolt for some weight to ensure good contact to the PCB.
- I homed all axis before starting
- I use the same tool for probing as for milling – and I don’t touch the tool between probing and milling
Autoleveling SoftwareI have tried at least 4 or 5 different versions, and some work, some don’t. The one I settled on is easy to use, flexible and it works. Based on my experience I can recommend it. I have even used it on G-Code generated from CAM-BAM for engraving brass plaques, and it worked great. The software is from www.autoleveller.co.uk/. Older versions of the software are no charge. Pay the man the 20 pounds for all his hard work and you get access to the latest versions (which I recommend). The interface is very simple, easy to use and the results are spot-on. Consult the website for more information. NOTES FOR INCORPORATION
Lesson 2: Set up the ‘probe in’ signal on your CNC machine
To avoid punching holes in your PCB, you need to wire-up and configure the “Probe In” line using the StepConfig Wizard (EMC). I already had all my inputs brought to an opto isolation board so wiring up and configuring this line took only a few minutes. For my installation, I needed to check the “invert signal” checkbox for the Probe In line. For the actual probe, I use the same bit I will be using to mill. I do not move the bit at all between probing and milling, I just disconnect the wire and turn on the spindle.
Lesson 3: Calibrate your setup.
The copper on a 1oz PCB is 35 µm or about 1.4 mils (.0014″) thick. That isn’t much if the surface of the PCB is ‘waving around’ by 3-4 thousandths or more! I recommend playing around with this calibration board and ‘futzing’ with your settings until you have the best results possible.