How do you create a pass-thru via on a double sided pcb? A milling domestic device and chemical etching is available.?
You can insert a small wire and solder both sides before calculation components.
If you don't own the ability to plate in the hole you could use a copper eyelet that make contact on both sided. A small rivet and washers could also be used.
Conductive vias are created by electroless plating process. This means no electrodes and electricity are used. Once all holes (both component and vias) are drilled, the pcb is next except for the holes. Then they are dipped into a super saturated copper depositing solution for hour or two. All exposed part of the pcb precipitates and deposits slender film of copper (inner walls of the holes). Unless you are making them in quantity, NRE cost is not justifiable for few boards. Unless you have the proper equipment (photo masking) and chemicals (you may find a supplier on the web) for more than one time use, it's cheaper surrounded by the long run to have a PCB manufacturer to breed you prototype quantities. Some small time operations are honestly inexpensive. If you are building a prototype, you might consider spot weld wiring. You just spot weld a rope from a pad on side A and the destination pad on side B.