Post date: Apr 20, 2013 3:56:10 AM
Another weekend, another CNC upgrade and PCB attempt. It seems like there's always something stopping me from getting a decent PCB made...
This time around, the upgrade is to the mill's table. The previous incarnation was a pair of 2x4s with the workpiece (read: PCB) suspended between them. This allowed the workpiece to flex during milling. That, and it was hard to secure anything properly. Neither of these was conducive to precision work.
The table upgrade is pretty substantial- a slotted table of oak with an MDF topping. The MDF makes it easy to [re]level the table, while the oak provides rigidity and support. The T-channels allow the workpiece to be secured to the table- either directly, or via crossbeams/toggle clamps.
The PCB attempt this week went OK. It started out very promising, then died relatively catastrophically: the Z axis bound up while going up, and then proceeded to go too far on the next plunge, scoring the PCB. The rest of the traces were overall quite nice, with a possible exception being the ultra-fine pads of for the microcontroller. Some of those showed some rough edges, though nowhere else did. Maybe doubling over the isolation paths (once for each pad) has something to do with it?
What's next? Probably preventing the Z axis from binding again. I've been using a shim between the Z axis assembly and the spindle mount (the gold-colored part and the angle aluminum holding the spindle, respectively), since otherwise the torque applied during changes in direction cause the spindle to wobble (which only really matters for drilling, but still). Long story short, the shim caught, and caused the axis to bind up. A more refined shim with a lower coefficient of friction is being made to replace it.
After that, another PCB attempt perhaps, or maybe just some testing to see if I can reproduce the ragged edges and solve that issue. I'd really like to have a nice enough PCB made to try soldering the parts on it, but one can only go so fast (as infuriating as that is).
Long term, I'm thinking about re-engineering the Z axis to push right in the center, instead of cantilevered out. That would take significant effort, but I don't like the the idea of just using a shim to mitigate torques that shouldn't exist in the first place.
Enough talking... go look at the new Pictures!