Q on CNC PCB Routing

[soundmotor]

I am sure this is an obvious question. I tried the FAQ & I tried searching this too but could not find an answer. Perhaps it is my search parameters or terms?



Basically, my question is this: If you have an exactly dimensioned PCB to be cnc routed (or any material stock of a specific and required external dimension), how do you accurately locate/position the stock on the work table so the rout starts exactly where it needs to?

I know, this is really entry level. As you can surmise, that is exactly where I am.

[ShayArnett]

You would position and square your workpiece on the table, then zero the router out to a known point in your drawing so they line up.

[soundmotor]

Originally Posted by ShayArnett You would position and square your workpiece on the table, then zero the router out to a known point in your drawing so they line up.

Thank you, that makes sense.

So for an item that you want to make more than one of, some sort of jigging that holds the correctly dimensioned stock in exactly the same place each time would be the likely solution?

Sorry for the lesson in CNC basics, but appreciate your answers very much.

[paulC]

Pegs and screw mounts are also useful. If there are mounting holes on the board you can pre drill these then use them to screw or peg the board in place.
The peg or screw holes having been drilled using cnc into your table so the locations are exact. These then relate directly to your drawing.
Paul

[jeffs555]

Haven't tried this, but it might work. If you are doing several with boards that are all precut to the same size, you might mount a piece of wood or plastic on the table, then mill a shallow depression the size of the boards. This would guarantee that your boards were all aligned the same. The sides of the depression would keep the board from moving horizontally.

[fyffe555]

When you come to mill the tracks you're going to be trying to maintain the Z height to cut the track to 1 or 2 thou to ensure correct cutting of the copper and to maintain cut width. By following Jeffs suggestion you'll be assuring the PCB is parallel to the movement of the Z. Not all base boards are ! Jeff's idea is a good one and is something I've done and it works well.

[spalm]

All the boards I design at work have tooling holes for locating. These are etched boards, but the tooling holes are used for precise positioning in the various jigs used for testing along the way. Drill rod pins in the fixtures allow repositioning.

If you are going to do multiples, either cut the outside dimensions and “drill” the tooling holes with your CNC, or just stack a bunch of blanks along with the base and use a drill press to drill tooling holes in three corners (placement does not matter as long as they are all the same). Disassemble. Insert three small pieces of drill rod in the base and mount this square on your bed. Now you can use these pins to install new blanks for routing.

As fyffe mentioned, getting your Z depth just right will be a PITA. Make sure to make several extra blanks, and don’t turn off the machine once you got it set the way you want it.

Steve

[soundmotor]

I very much appreciate your replies. The more I read on building a CNC machine, the more I realize that is about 1/3 the battle. Learning the programming and actually getting that to output something useful and accurately rendered via the electromechanics, the other 2/3.

I will start on a small CNC router build first to learn with. Making multiple & precise PCB's seemed to be the most intensive project you could do with one. I guess my goal would have to be being able to build several equivalent PCB's on this machine before I would reasonably confident in the processes to move onto a much larger machine; like a CNC plasma cutter.



Does this sound like a reasonable approach for a n00b to get involved with DIY CNC?

(As an aside, it was actually plamsacam's magazine ad that led me in the realm of all this. I really had no idea a community like this existed. It is quite humbling.)