[BeerFizz]

Hi,

I have a Mini Mill (X2) converted to CNC with servo motors and I am interested in cutting some copper clad PC circuit boards.

Does anyone have any experience with this and can recommend which router to use? I have a Bosch hand held router which will run up to about 30-35K and I could use that???. Any other ideas regarding a router?

Are there any good tutorials for doing this?

Thanks for all help
Phil

[Rhodan]

Well, I wouldn't recommend a router at all. Runout on routers, while great for wood, is HUGE when doing circuits.

For example, my PC892 router (which is excellent) has a smallest collet size of 1/4 inch and PCB sized bits are 1/8th. I bought a DA300 collet to fit 1/8th bits (needed for circuit cutting) which fits into a 1/2" collet and the combined runout is +-0.01. That means that the smallest cut I can make will be at least 0.02" wide + the width of the cutter. Using a 45 degree V bit and cutting 0.004" deep that means the minimum cut width is 0.024".

DIP legs are 0.01" apart and pads are typically 0.06" in diameter, that leaves you 0.04" of copper between the legs. Its kind of hard to get even a single trace between those legs when you need 0.048" of space for the two isolating cuts!

I also tried some 1/8th adapters from Lee Vally in my 1/4" collet and they work a lot better (which is odd since they are just single split bushings really). Runout is 0.005". Still not great but you can do some fairly simply circuits with them.

If you are OK with swapping spindles for different jobs then I'd recommend getting a Wolfgang Engineering spindle specifically for PCBs. It runs at 24K RPM and has a max runout of 0.0004" (typical 0.0001"). The one I bought has no detectable runout at all with a 0.001" graduated dial micrometer.

Here's a video of me checking my runout

http://www.youtube.com/watch?v=nzSjIV9tr3E

The achievable results are fantastic and I have a short video of PCB cutting with it as well

http://www.youtube.com/watch?v=VUDW5pQbxAY

I'm working on a PCB routing primer video to help folks get started (not an expert's video since I'm no expert - but at least it shows an achievable way to get going). Dunno when it'll be ready as I work full time etc.

The Wolfgang Engineering products are available from

http://stores.ebay.ca/Wolfgang-Engineering

I have the TB-440 which I don't see for sale now. Its the TB-350 with an AC motor & mounts and it cost around $200 - $250 (can't remember exactly)

Just remember these are not built for high-torque but for high speed and exceptionally high accuracy. I can route 1/16th FR4 at 10IPM with a 0.063" diamond shaped carbide rasp all day with it but a 1/8th drill bit is a pretty much the limit with my setup. If course, a larger motor and better drive system (just using an "O" ring) would be more capable but I really don't see the need. I drill up to 0.06" holes and route out anything larger with the diamond shaped rasp. Those are usually mounting holes so there aren't many of them. Besides, the bits are tiny and you really can't put much more force on them without snapping the things.

Oh, here's some photos of what I've cut recently. The first and third ones are an experiment in surface mount chips. The traces are 0.01" and 0.005" cut 0.002" deep. I goofed on my Z adjustment and I think they're closer to 0.003" deep. The 0.01" traces came out great but the 0.005" got wiped out.

The second image is 0.014" traces on a board I have since soldered up and have working (a 4-20ma transmitter for testing actuators).

[Jay C]

Rhodan ... very nice, thanks for taking the time to record and post videos. Looking forward to your primer video. It's fun to watch it move so fast yest so fluid. Are you using Mach4 Quantum?

I too have a X2 with a CNC kit. PCBs were just one of my interests when I bought/built it.

Jay

[BeerFizz]

Rhodan,

Thank you very much for your response.

Your setup is terrific and I am so glad you posted as I would have been off and running down the wrong track with absolutely terrible results. In my head, I knew that run out was going to be important, but not yet taken the time to sit down and do the calcs...

I need to look into this further, but I guess I will be able to mount the Wolfgang on the side of the head of the Mini Mill and take it off and on as needed. This will work just fine for me.

Your videos are great It looks as though you're running at about 200 IPS but I am sure that's an illusion due to the size.

Couple of additional questions:

What is the maximum speed you have tried cutting at?
Have you been successful with cutting the surface mount?
What software are you using?

Thanks again for the great info and the videos
All the best
Phil

[BeerFizz]

Rhodan,

What motor and belt/O Ring are you using to drive the spindle, or did this come with the model you purchased?

Thanks
Phil

[Rhodan]

Well, if folks are really interested then we should probably carry this on in an electronics forum. Or maybe a mod can move the thread?

[BeerFizz]

Hi Rhodan,

I am very interested and would like to chat more on this subject...

I am on the verge of ordering the Wolfgang, just need to get all the info re motors, belts, mounts etc.

So, if you want to have a mod move it that's fine, just as long as I know where it went

Best
Phil

[Rhodan]

I was thinking simply electronics general. There isn't a PCB making specific forum here that I see.

The belt and motor came with the spindle. The belt really is just an "O" ring that you can pick up at hardware stores and the motor looks like one from an RC model - but in AC. I don't think the motor is critical other than getting enough RPM out of it that you don't need a big difference in pulley sizes. If I remember correctly, the ratio on this is 1.2:1 to get 24k RPM.

Your best bet is to email Richard (link in EBay store) and ask. He's had a lot more experience matching up motors etc than me. You might ask if the TB-440 is still available (or some version thereof) since AC was a lot simpler for me - just plug it into the wall!

As he said to me in email when I was looking to buy

Thank you for the interest. Yes, the DC motor I used was very difficult to find a power supply for (9.6VDC), so when I came across this motor, it was a match made in heaven. The AC motor, of course, simply plugs into the wall, and if you need to control the speed an inexpensive router rheostat will work just fine.

The belts are simple o'rings, but they last quite a long time. I can send a couple (no charge) and that should last you for quite some time. They can also be picked up at almost any hardware store. If you would still like me to send 10 it would be $.50 for each additional one.

Yes, it uses a 10-32 draw-bolt, and I have an idea etched in my head for a ATC design. It'll be sometime down the road, but is an item I'd like to get out to the public.

Please let me know if you have any other questions.

Thanks again,

WgE.

[BeerFizz]

Thanks Rhodan,

I have an email into Richard.

What software are you using?

Phil

[chuck99z28]

Rhodan,
Cool information, thanks.
I can't figure out what mill you are using. Is it commercial or DIY?

[Rhodan]

Its a K2 KT2514 but I replaced the Y rails with thomson supported rails and bearings. The 3/4 stainless rods were just too weak and would deflect pretty badly when I was V-carving and plunging the V-Bit. Even with a 1/2" V bit I couldn't plunge faster than about 5 IPM without leaving a divot and couldn't route faster than around 30 IPM (1/4 DOC) without tilting the V bit.

With those rails replaced I can plunge at 40 IPM to 1/4 DOC and route at 60 IPM. The route limit is mostly due to the unsupported rails holding up the gantry as the gantry starts to wobble and shake when doing more complicated moves. Depth of cut doesn't matter and in fact I can't route PCBs past 40-50 IPM or the gantry wobble messes up the traces.

Thats not really a critisism of K2 or the machine. I bought the unsupported rail version and I got the unsupported rail version. At the time they didn't have any smaller machines with blocks and rails but I could have gone larger and cut back on the software.

They now have a 14x14 model with blocks and rails (servo option too) all around and I bet that'd cut PCBs at a crazy speed!

Of course, even cutting at something like 10 IPM a circuit board doesn't take all that long to make. Its still much faster than photolithography.

[neilw20]

Hi Rhodan.

As previously requested by BeerFizz, what software are you using for the PCB routing?
Can it make G-Cde from Gerber files, or should I finish writing my own converter.

I have written my own 32 layer PCB (32bit) editor I have been using for 15 years. Exe file is still under 400K

Neil.

[Rhodan]

Sorry!

I use Diptrace to create the circuits and output DXF. Diptrace has an option to output the edges of the circuit (outline of traces etc) which is perfect for importing into a CAM program and applying MOPs to.


There's also QCad which outputs GCode directly. I don't know about the current version but the one I have (couple years old now) had horribly inefficient cutting strategy. Instead of simply following the outline of a trace it would look at each line segment seperately, plunge and cut, then retract before cutting the next segment. Its DXF/Gerber etc isn't (or wasn't) suitable either since the lines are very wide. When reduced to single point the segments no longer line up at the end points. Diptrace was cheaper than getting the most recent QCad and the demo showed me its near-perfect output so I went that route.

Oh, Diptrace does have one glitch with its output. There are usually a couple of redundant line segments in the DXF though its not hard to find and delete them. When I first tried there were LOTS of redundant lines but the author has calmed that down a lot. Now I usually find 2 extras in about 70% of the exports instead of 8-20 in every export.

Here's an example of the output (in Visual Mill) with two redundant lines highlighted in yellow.

P.S. They're easy to spot once you get used to looking for them. Each trace should have only one origin dot and the extra lines each have their own. At most I spend 1-2 minutes searching and deleting when they appear.

[Rhodan]

BTW: Since not everyone has Visual Mill, I was playing with VCarve Pro to see if I could use it for PCB milling. With one exception, I find it as good or better than VM for getting from DXF to Gcode.

VCP has layers which makes it easier to seperate the routing artwork from the drilling (equal to VM).

VCP has a preview so you can be sure the bit does what you think it should. VCPs preview is also very fast (VM wins due to flexible control over the preview though I usually only care about the end result when doing PCBs).

One clear VM advantage is in selecting holes for drilling. It has a tool that selects all holes of a supplied radius or min and max radiuses (radii?).

Oh, and I just remembered, VM inserts the tool diameter as a comment into the GCode while VCP does not. Not quite as convenient for those folks that don't have a tool table printed and handy.

So if you don't have VM and have VCP, you don't need another CAM package.

[CountZero]

GCAM is free and can import gerbers: http://gcam.js.cx/index.php/Main_Page

I have yet to cut a board with the output but it won't cost you much to find out if it works for you..