I’ve been having some issues with probing and automatic leveling while milling PCBs on the cnc - this is the work around I came up with to make sure I can still get usable boards while I work on solving the issue.
If you give the copper side of the PCB a light coat of spray paint before milling you can soak it in etchant to remove any copper that didn’t mill all the way through. The paint will come off with some acetone. If you are not going to solder the board straight away you can leave it on to help prevent the copper from tarnishing.
This helps avoid wasting perfectly good PCB blanks while testing and tuning and lets you produce usable boards earlier than you might be able to normally.
@Shane_Gough Thanks for sharing. Did you try Chillipeppr? There is very nice autolevelling function built in. Another option is Eagle import directly into Chillipeppr.
What is the tool you use to create the PCB milling gcode?
@Shane_Gough , @sszafran I agree … ChiliPeppr is very well supported, especially if you are using a TinyG. There is also GRBL support but I don’t know how many of the widgets such as Eagle support and leveling have been migrated ti that space.
@sszafran I’m using LineGrinder (http://www.ofitselfso.com/LineGrinder/LineGrinder.php) to generate gcode from gerber files and bCNC (https://github.com/vlachoudis/bCNC) to drive the CNC. I’m pretty happy with both tools and bCNC has autolevelling support - it’s just that my first probe always seems to be off resulting in the first quadrant (the front left corner) not cutting deep enough. I’m pretty sure that is related to my hardware setup rather than the software. Using a pressure foot during the probing process eliminated the problems with bowing in the board.
@Paul_Frederick It’s not the perfect way to make boards but it sure beats toner transfer in speed and reliability. I lay out multiple boards on a single panel so set up time and wastage are both reduced. If you were just milling a single arbitrary sized PCB each run it would get frustrating very quickly.
@Shane_Gough
The results people get using toner transfer vary. Once the toner is applied I can personally etch a board in under 2 minutes. Which is pretty quick. The tricks are to heat the vat, and aerate it while the etch is underway.
The best results are achieved through pressure spraying etchant. But setting that up is a bit more involved than I really want to get. That is how the pros do it though.
Commercial practices tend to be best methods.
Photoresist is also the best masking method available. With it the finest resolution can be achieved. Which is ultimately the deal breaker when routing boards with a CNC. You can only achieve a certain resolution with the process, and that is it.
Even toner can beat routing for resolution. Folks with laminators can pass traces between DIP pads. If that is possible to do with a CNC routed board I have never seen it.
@Paul_Frederick All good points, I’ve seen some very impressive toner transfer boards but I’ve never been able to replicate them myself As you point out there are limits to milling PCBs (I’m not sure I would want to try fine pitch SMT for example) but for the mostly THT prototype boards I’m doing it works pretty well. Having ready to solder boards that are routed, cut and drilled for me is the next best thing to sending them out for fabrication
As with everything, there are pros and cons. If you use toner transfer or UV photoresist, you still need to drill them somehow, make vias etc. Doing that manually is quite tedious. Friend just bought a PCB milling system from http://cirqoid.com. That machine can do some impressive stuff. He is doing smd layouts with it all the time, no problems. Sometimes doing 3-4 board iterations per day. Cirqoid guys themselves did a test with 0402 resistors and it worked fine.
Of course it is quite an investment if you do few boards a month. But I still think it proves that you can get very good results with milling.
@Viljo_Marrandi If you really find drilling circuit boards out so tedious that it is unbearable to you then perhaps you need to find something other than electronics to do.
@Paul_Frederick It’s not really about unbearable-ness. I just wanted to point out, that it is quite allright to mill out PCB’s, most likely it’s faster for prototyping than other methods.
I’ve used all 3 methods and so far I like milling the most. As always, YMMV. But I really do like the results that UV photoresist gives.
@Viljo_Marrandi
I would hope that you like photoresist. It is the best method commonly available. For the longest time I can’t be bothered even trying to etch boards. I just wire them up point, to point. I am not mass producing anything myself. I finished a board up yesterday that I need to test out now.
Looks good from that angle. But on the bottom it is just jumper wires
Sufficient for my purposes. I enjoy making the boards that way anyways. Drilling the holes manually does not trouble me either. I rather enjoy doing it in fact. If I didn’t I wouldn’t do it at all.
From my experience the photo etch worked the best. The hardest part there for me was keeping the film flat on the board. Unless a glass can be had that doesn’t block the UV it takes longer.
I have tried to carve up a board on my router table. Not for me. However I have found that using wood for my tabletop “skin” for leveling is great. It is easy to change when it gets carved up from use. To zero the surface after replacing I just run an x,y pattern around the surface with a large bit and it is perfectly parallel to x,y travel. I found this when engraving due to heavy engraving in one area and light in another.
As you point out there are limits to milling PCBs (I’m not sure I would want to try fine pitch SMT for example) but for the mostly THT prototype boards I’m doing it works pretty well. Having ready to solder boards that are routed, cut and drilled for me is the next best thing to sending them out for fabrication 
