anyone have experience making pcb on a cnc?

[mistermikev]

I have read on the subject quite a bit and am aware of folks who use some sort of touch probe and software to create a map of a specific circuit board and then the cnc code is modified for height when machining... I'd like to forego this alltogether. 

I can't help but think I'm missing something, but I use 2oz copper pcb and 1/8" thick fiberglass backing so have lots of height to spare and it just seems like it would be easier to cnc it like any other thing I might cut.  Just wondering if I'm missing anything?  I plan to do this in the near future as I'm tired of manually making pcb so as soon as I run out of etchant I'm switching over.

any/all input appreciated.

[curtisa]

I've done it a few times, but it's a fair bit of hassle to get it to work right. Unless there's a very specific reason why I need to get a one-off PCB made up I normally just get them done by one of the online Chinese PCB vendors like JLCPCB or PCBWay. It might cost more and you end up with multiple boards if you really only wanted one or two, but it takes away all the heartache and stress of trying to do it all yourself.

But if you're interested...

 

4 hours ago, mistermikev said:

I'd like to forego this alltogether.

For really small boards without much detail it can work OK without all the height probing. I've done a couple of pedal-sized boards like this that came out workable in the end, although not perfect. They were double-sided designs so the result was far better than I could have managed using things like Press 'N Peel or photo resist. The problem is that if the blank PCB isn't perfectly flat (and they never are) the routed traces will grow and shrink as the lumps and bumps in workpiece drift closer to or further away from the bit. To combat this try and limit yourself to small designs with generous trace widths so if the routing does get affected by a slightly warped PCB there's still be enough of the circuit left to work with. You may also be able to devise some kind of clamping system that squeezes the four edges of the board tight against your CNC bed which could help reducing any warp in the PCB.

For anything bigger than a couple of square inches, you really have no choice but to use height probing and surface mapping. The warp will be too great and you'll risk the artwork fading out completely in the low spots, the PCB traces shrink down to nothing in the high spots, or the tips of the bits get broken if they're pushed through too much high material. Again, I've done it but it's still been a bit hit and miss. Maybe if I did it regularly I'd get more consistent results, but it's such an infrequent thing for me I find I have to relearn everything pretty much from scratch, which invariably results in broken bits or a board that is unusable.

The software I've used to do the probing and surface mapping is AutoLeveller, and the PCB artwork I generate using FlatCAM. Both are free. When they work they do work well, but getting them to work in the first place can be a bit of struggle.

Note that if you do decide to explore this idea a height probe/tool setter is still an extremely useful addition to your CNC. I added one to mine a few years back and even without doing much PCB work it makes multiple tool changes within a single job soooooooo much easier. You can get away with touching off only once at the start of the job and then just wait as each stage completes to install the next tool, It does the rest automatically without losing tool height, even if the tool length is different each time. Beforehand I was having to split the job into multiple files, one for each tool, and touch off at the start of every file.

[mistermikev]

27 minutes ago, curtisa said:

I've done it a few times, but it's a fair bit of hassle to get it to work right. Unless there's a very specific reason why I need to get a one-off PCB made up I normally just get them done by one of the online Chinese PCB vendors like JLCPCB or PCBWay. It might cost more and you end up with multiple boards if you really only wanted one or two, but it takes away all the heartache and stress of trying to do it all yourself.

But if you're interested...

 

For really small boards without much detail it can work OK without all the height probing. I've done a couple of pedal-sized boards like this that came out workable in the end, although not perfect. They were double-sided designs so the result was far better than I could have managed using things like Press 'N Peel or photo resist. The problem is that if the blank PCB isn't perfectly flat (and they never are) the routed traces will grow and shrink as the lumps and bumps in workpiece drift closer to or further away from the bit. To combat this try and limit yourself to small designs with generous trace widths so if the routing does get affected by a slightly warped PCB there's still be enough of the circuit left to work with. You may also be able to devise some kind of clamping system that squeezes the four edges of the board tight against your CNC bed which could help reducing any warp in the PCB.

For anything bigger than a couple of square inches, you really have no choice but to use height probing and surface mapping. The warp will be too great and you'll risk the artwork fading out completely in the low spots, the PCB traces shrink down to nothing in the high spots, or the tips of the bits get broken if they're pushed through too much high material. Again, I've done it but it's still been a bit hit and miss. Maybe if I did it regularly I'd get more consistent results, but it's such an infrequent thing for me I find I have to relearn everything pretty much from scratch, which invariably results in broken bits or a board that is unusable.

The software I've used to do the probing and surface mapping is AutoLeveller, and the PCB artwork I generate using FlatCAM. Both are free. When they work they do work well, but getting them to work in the first place can be a bit of struggle.

Note that if you do decide to explore this idea a height probe/tool setter is still an extremely useful addition to your CNC. I added one to mine a few years back and even without doing much PCB work it makes multiple tool changes within a single job soooooooo much easier. You can get away with touching off only once at the start of the job and then just wait as each stage completes to install the next tool, It does the rest automatically without losing tool height, even if the tool length is different each time. Beforehand I was having to split the job into multiple files, one for each tool, and touch off at the start of every file.

awesome info... I am very grateful.  yes... unfortunately everything I do is a a 1-3 off.  I usually do up a board of 3-5 designs at one time... but I'm always trying new designs or improving/changing my old ones... so a pcb fab house is a nice fallback... but I'd rather at least pursue this route.  

for me this would only be single sided so that keeps it a little bit simple.  I haven't checked yet... but was planning on using my .0177 bits to cut.  idk if that will be small enough... and I know it will take forever... but I have success with those for wood so hoping that level of detail would be ok... or I'll have to start re-designing my stuff.  

perfectly flat... well... my plan was to use a perfectly flattened piece of baltic birch and use the tape/crazy glue method to secure.  I was thinking I'd mill a whole 6" x 8" pcb board... but perhaps that's crazy talk. is fiberglass really that hard to cut?

also... I'm not planning on using a tapered bit... but a straight shank .0177 bit.  I figure this way... all I have to worry about is getting low enough to cut the copper completely.

I cut .06 depth with the .0177 bits through ebony w/o issue... so I guess I'll just have to find out how hard fiberglass is by compare.

touch probe... that does sound nice.  I know I should def get one.   currently I just pick a zero spot and mark it... and I'm really good at driving a bit right up to the wood fairly fast.  I've figured out the quick keys to help me move rapid to the spot and then once I'm within 1/16" of the zero point I just use the slow keys while watching carefully... really doesn't seem like too much of an inconvenience but I will keep your words in mind.

thank you very much for the input... I will reread and digest!

 

[curtisa]

10 hours ago, mistermikev said:

planning on using my .0177 bits to cut.  idk if that will be small enough...

Then the narrowest spacing between any two traces you can achieve is .o177". You'd have to check if that would be acceptable for things like DIP packages, where the pads sit on 0.1" centres.

10 hours ago, mistermikev said:

my plan was to use a perfectly flattened piece of baltic birch and use the tape/crazy glue method to secure.

Might work? I never had much success with my usual doublesided tape method in the past; if the board was warped it tended to have enough spring to pull itself off the bed partway through the job, which would naturally ruin the PCB. Haven't tried the tape/CA method though.

10 hours ago, mistermikev said:

is fiberglass really that hard to cut?

It's hard on the tools. Typically you'd use solid carbide bits which will go the distance in fibreglass but they're more brittle than HSS or steel alloys, so they can break easily.

A straight bit will avoid the issue with the PCB artwork growing/shrinking if the board is warped, but they will snap as soon as you look at them if they're asked to go through a high spot in a warped board. That's why most people recommend a vee bit with a shallow tip angle for PCB work. They're much more forgiving to unexpected changes in cutting depth and you can move them faster in the material. 

[mistermikev]

2 hours ago, curtisa said:

Then the narrowest spacing between any two traces you can achieve is .o177". You'd have to check if that would be acceptable for things like DIP packages, where the pads sit on 0.1" centres.

Might work? I never had much success with my usual doublesided tape method in the past; if the board was warped it tended to have enough spring to pull itself off the bed partway through the job, which would naturally ruin the PCB. Haven't tried the tape/CA method though.

It's hard on the tools. Typically you'd use solid carbide bits which will go the distance in fibreglass but they're more brittle than HSS or steel alloys, so they can break easily.

A straight bit will avoid the issue with the PCB artwork growing/shrinking if the board is warped, but they will snap as soon as you look at them if they're asked to go through a high spot in a warped board. That's why most people recommend a vee bit with a shallow tip angle for PCB work. They're much more forgiving to unexpected changes in cutting depth and you can move them faster in the material. 

dip... well just tested by adding a .0177 circle to my diylayout creator and moved it around the board... yes good call the dip is where it is going to be the most problematic but should work ok.  

tape/ca - well perhaps I'll have to set my level for each 2" x 2" section to mitigate. 

that said... I could simply zero a hair above the board, and cut deeper... forcing the bit to cut a bit of 'air' before cutting the pcb.  it's gonna take that much longer but would mitigate potential issues of cutting too deep and breaking a bit.  the end mills I use are carbide but I imagine at the least it's going to dull them up pretty fast.

with all this in mind I think I might do a clearing pass with a .0625 bit and then just use the .0177 bit to clean up the really tight spots.  this is all good info and is going to give me a lot better chance at success so - thank you very much for the help!!