Frage Double-sided PCBs, Eagle and UCCNC

I've designed a circuit in Eagle, and have ended up needing to make it double-sided. This is my first significant project in Eagle, and the first circuit to mill on my Stepcraft 2/600.

I found a user-language program written by Kina Smith: www.instructables.com/id/How-to-Mill-a-circuit-board-with-a-Stepcraft-Mill-/
It looks quite simple and straight forward, and apparently produces quite clean & compatible g-code that works with the Stepcraft.
(An alternate, apparently older method, is the PCG-GCODE plugin for eagle - I haven't looked at this in any depth yet, and it doesn't seem to have much activity per a quick look at its' website/forum)

I haven't found a way of setting the home point in Eagle (seems quite different from setups in Fusion 360), and am trying to puzzle through how to make the home point match between the top and bottom layers.

Do you tend to have a hole drilled for the home point? Perhaps have the board cut out while the first side is being milled, providing an accurate corner? (this method would mean I can't use the stepcraft elevated workpiece holder as it would block off the bottom edge, and should use double-sided tape to a spoil board).

I'm eager to hear any advice any of you may have on this challenge.
Does anyone out there have experience with this with Stepcraft?

Thanks,
Ben

Hi Ben.

I've used Eagle and pcb-gcode extensively for both single and double sided boards and have found the results extremely good.

The zero reference point in an Eagle layout is always bottom left of the board, and is marked by a small "+" sign and has co-ordinates of (0,0). This maps to point X = 0, Y = 0 in the Gcode for both top and bottom layers. I always work looking down on the top layer - no need to "flip" to work on other layers.

Define the board outline with closed wires on the "dimension" layer 20, and a coincident "milling" outline on layer 46. Running the "board" file through pcb-gcode gives several completed gcode files (.txt) that requires no manual intervention whatsoever (amen to that!). These files cover both top and bottom "etching", drilling and milling operations - they are set up when configuring "pcb-gcode"

When making double sided boards, I place a couple of symmetrical reference holes outside the board outline - these act as location points when the board is flipped to mill the second side. They are drilled through into the spoil board when working the first side, and steel reference pins inserted before removing the board. You will have to edit a copy of the drill gcode file to make a file that just drills these reference holes

When milling the second side, having flipped the board onto the reference pins, the Stepcraft X or Y reference point must be adjusted manually by the exact board outline distance so that the Stepcraft (0,0) point is still at the same position on the now flipped board.

Once the tracks are milled, the penultimate operation is to drill all the required component holes and finally mill the board outline. Make sure the reference pins don't get in the way of the milling cutter - this will break the tool for certain!!

I use a home made vacuum table to hold the board - having milled the top surface flat in situ. Thousandths of an inch are critical here when milling narrow tracks, and it is vital to have backlash correction correctly set up as well.

Good luck - and persevere with the setup, it can produce boards to accommodate SMD's.

Look at some of my earlier posts to see examples of my set up and learning curve!!

Peter

Thanks Peter,
This will be quite helpful.
Now I only have to debug the skipped steps in my X and Y-axes that showed up yesterday in a laser job, then I'll work on testing out a PCB board.
Ben