what's the idea behind PCB milling?
Can't speak for anyone else, but for me it is fast and clean. If I etch then I have to get the tank of ferric out of the garage, heat it up in the kitchen, print the film, etc. Always a possibility of spillage and consequent explaining to the missus, and while that's going on no-one can make coffee or anything.
With the mill there is no printing, exposing, or any of that stuff. All the holes are exactly aligned with the pads. An important factor is that the holes can be drilled
before the pads are produced, so there is less risk of the drill pulling off thing pads.
Chinese PCB houses are indeed cheap and quick, but even they can't beat a mill for really quick - I have had an idea at 1am on a Sunday morning and got a working PCB before 2am. For the price of the cheapest copper clad board - no photo resist to go off or get scratched or add to the cost.
I wouldn't sell the boards - they are for quick prototyping of ideas and one-off 'homers' that are suitable for the technology. Not all projects fit that scenario, but enough do to make the mill useful. Since I got the mill I've never etched a board - if it isn't suitable for milling it goes off to Itead and I wait 2-3 weeks for it to come back.
Your Mileage May Vary. But we don't have to do either/or, you know. You could use a mill to drill the holes accurately and then cut out the PCB. Do that before exposing and it should be reasonably easy to line up the artwork with the holes, then expose and etch as normal. Voila - you no longer spend an hour straining your eyesight to drill the holes off-centre, and no need to make an allowance in the pad diameter. Slots easily, er, slotted. What more could you ask for?
