First: I think you did something amazing and I probably want to go in a similar direction. I just wanted to add my personal views/perceptions on some points, maybe also for the benefit of people reading this in the future.
That is pretty neat! I think it might not be suitable for the big, heavy laser I'm using though.
That is a very valid argument. However, with more power you can also cut, engrave etc. I'm not sure, how much power is exactly required to remove the paint.
As far as I can tell, there is no proximity effect whatsoever for the spray paint method, where I would expect a small a proximity effect in the photo-resist solution (the resist is transparent, so reflections from the copper also develop nearby resist). So from theory, but also from the results I've achieved so far, I don't think there is much of a difference.
I think both techniques have their strong and weak sides. Since most (all) PCB design softwares use-defacto vector descriptions to begin with, I don't really see your point here to why it would yield higher resolutions. Also, there is a well-working plugin for eagle to produce nice gcode files already. For pictures with shading etc, I think you totally have a point.
Hmmm, it appears you have a very different beam geometry than I do. My beam is currently rectangular with one side about 3x longer than the other. As I said, I think it is much easier to compensate for weird dot geometries in the raster/pixel scheme. The only way to compensate is to use a pinhole (which especially for low power (150mW) should be no problem whatsoever (albeit extra work)). I don't really understand how rotation and defocus can make a gaussian profile out of a non-gaussian profile. Could you maybe explain this a bit further?
If you really have a gaussian profile you have a very valid point. However, in my case my beam is a pretty well defined rectangle, so this is not an issue. Also for PCBs you basically only want discrete paint removed/not removed. As my beam is currently smaller than the apparent step size of the UM2, this does not seem an issue to me. Again, if you want shadings etc, go pixel ?
I did a few test patterns and with speeds of ≤ 300mm/s, I see no residual ringing whatsoever. Also check the picture I appended: I think it is high-res enough, that you should be able to specifically point out any artifacts - and I don't see any oscillations.
I think this is advantage no 2 of the vector approach; its much faster and potentially uses less etchant. Advantage no 1 being, that you can implement is much easier for beginners/as a first test and cheapter (unplug fan, plug-in laser, extract gcode from eagle, replace a few commands, run).
That's super nice. I think I should also go with the exp-port and introducing the 'B1' command. Does this port also support PWM directly? I would like to set the laser power from the gcode directly for the vector mode (as you then only have to update the gcode on the SD card, nothing else).
Well, you could use the FAN output as sync. Otherwise, I totally agree. I would also go with an external controller. In the case of vector mode, I would just forward the PWM signal (either from the ext or the FAN) from the main board.
That's good to hear! I would definitely love to see a write-up and some pictures of your rig! I'll try and see if I can drill the holes by cutting them out with the laser, but I'm still a bit sceptical about that.