PCB routing on any CNC

[PW2008]

Hi,

I have made PCB's at home using etchants, but now at work I want to make PCB's using a CNC machine. I can use an engraver or one of two EasyCut/Many machines. They all have enough accuracy.

I've tried routing a few times using the engraver and a conical bit with a 0.3mm-wide flat tip, but I've found it difficult to get the ideal depth of cut, i.e. enough to clear the copper but not too far into the substrate. The best result (using the engraver) was achieved by having the stationary collar around the cutting bit press against the PCB and relying on the compressability of the collar to set the depth of cut, but I doubt the consistancy of that method.

Put simply, I want the machine to cut a constant depth (from about 0.03mm to 0.1mm) relative to the surface of the copper even if the PCB isn't quite flat or level, and do the same repeatedly without test runs.

(Hope that makes sense.)

Does anyone know of ways to get good results from a typical engraver or a general purpose CNC machine?

For sake of argument assume a resolution of 0.02mm. Almost anything goes, as long as it works reliably.

Cheers, Pete.

[kn6za]

Pete,

I use a vacuum chuck to hold my circuit boards flat. With the vacuum system I can maintain .03mm very repeatably.

Check out my website www.drewtronics.net to see the vacuum system.

I have seen that other folks are able to get good results with super glue, and acetone to release the board. Superglue the pcb to a flat piece of aluminum, then cut your traces. Use the acetone to remove the pcb from the aluminum plate.

Another option is carpet tape. 2 sided tape the board to the table, and cut away. Without anything to prevent the board from moving around it can shift under cutting forces, but with a few board stops setup this could be a fine way to cut.

hope that helps

[PW2008]

Thanks,
A vacuum system isn't justifyable for my purposes.

At present I use low-tack masking tape and double-sided sticky tape - as has been done for engraving brass signs.

The aluminium sheet and superglue idea is worth trying, though I might want to change from aluminium to something easier on drill bits.

Pete.

[kn6za]

Pete,


I think the superglue trick is about the best low budget solution I have seen, but I have not gotten around to trying it yet. Next time I mill a small board that doesnt justify the vacuum system I think I will hold it down with the glue.

check out www.millpcbs.com for lots of good info.

[PW2008]

Hi,
I've often looked for PCB-related web pages, but I've not seen www.millpcbs.com before; they're now in my favorites. Eagle CAD's "ULP" may prove useful.

I would be interested to know if anyone has used a CNC to do PCBs reliably without routing too far into the substrate even if the PCB can't be made absolutely flat.

For the present, the machines available to me are quite accurate enough but PCBs are a sideline so I can't spend too much time on them.

I'm still a novice at CNC, but if I find a working solution I will post it here.

Thanks again, Pete (England)

[ivan_j]

I strongly recommend Accurate 360 (www.accuratecnc.com/A360.html).
I have got one, equipped with camera 6 months ago. It is excellent.

[PW2008]

ivan_j,

It does look impressive.

At my work there are three very capable CNCs, we don't need another one. For other situations I would be looking for low cost (hobby) CNCs.

I'm trying to learn how to use CNCs and looking for ways of getting the most out of what I have already.

Thanks anyway, Pete

P.S. I'm intrigued as to what the camera on the CNC is for.

[keebler303]

I use a 90 degree carbide half-round similar to what is pictured on Drew's site. I have found the best way to get accurate depth is to make sure your surface is accurate to start with. I always throw in a piece of aluminum and face it quick to make sure its flat to the machine. Then I clean everything good with acetone and stick it down with some double stick tape. The paper kind, not the foamy stuff. I had a couple crappy boards starting out but have gotten better in the last couple, mainly due to making sure everything was flat before putting down the board. I used to have problems with not getting all the copper or being too deep as well. I think this is mainly due to the type of cutter you are using. Speed may also play a factor. I don't know what is best, I use 3000 RPM on my mill when I'm milling traces and it does fine for me.

Matt

[kn6za]

Matt,

Good idea to cut a flat surface before you start. It is amazing how precise you can mill a circuit board when you start with a dead flat board setup. So much better results than I could ever get with toner transfer method.

Before I started using the vacuum setup I had trouble getting all the copper, and cutting too deep as well, now it always comes out very nice, except when I trip on the vacuum pump power cord


I have been cutting with a spindle speed of 10000rpm I would go higher, but I did not build the machine to go any higher.

[ivan_j]

Originally Posted by PW2008 ivan_j, It does look impressive. At my work there are three very capable CNCs, we don't need another one. For other situations I would be looking for low cost (hobby) CNCs. I'm trying to learn how to use CNCs and looking for ways of getting the most out of what I have already. Thanks anyway, Pete P.S. I'm intrigued as to what the camera on the CNC is for.

Hi Pete,

The camera is used for:
- Feducial Registration (for bottom layer aligment - 0.2 mil)
- Tool Test (very usefull to check the condition and the setup of the tool prior to start operating)
- Measurement (resolution 0.2mil)
- Quality control (visual check - very easy way to check the final result by clicking on different areas and monitoring them with zoom)

check the manual (there are a lot of pictures ):
http://www.accuratecnc.com/PhCNC_download_files/PhCNC%20User's%20Manual%20EN.pdf

For PCBs, the special Z axis design is very important (depth limiter, presure foot).
The software is very important too! PhCNC is really good (check the demo version)!

brgds,
Ivan

edit: the link is fixed

[PW2008]

Originally Posted by keebler303 I use a 90 degree carbide half-round....

Originally Posted by kn6za Matt, Good idea to cut a flat surface before you start....

Thanks. I'll try your ideas, they seem quite sound. If I get it to work well, or if I find out something useful, I'll certainly post it here.

Incidently, I've used an "Epson Stylus Color 600" inkjet printer and DOS-based PCB software (Ranger1) at home to do PCB artwork with some success. It needed genuine Epson inks & transparencies to work properly, and I got a decent contrast, but it doesn't do tracks between IC pins that well due to slightly fuzzy edges. I've tried the same within windows but it hasn't worked. The resulting PCBs look quite good if the designs are within its resolution.

Originally Posted by ivan_j Hi Pete, The camera is used for....

The PDF link doesn't work, but I will visit the site.

I tried twice to get my machine to scan an object, each scan taking about 5 hours, only to find out at the end that it wont save the data. My software has other problems too. So fast and reliable software would be most welcome, but I have no control over the budget!

My boss may be interested in reliable software or a camera if it can do quick scanning (a map of surface heights), but not a new CNC machine.

Regards, Peter

[PW2008]

Correction to my previous post regaring the PDF link given by ivan_j:

...check the manual (there are a lot of pictures ): http://www.accuratecnc.com/PhCNC_dow...anual%20EN.pdf For PCBs, the special Z axis design is very important (depth limiter, presure foot). The software is very important too! PhCNC is really good (check the demo version)!...

The link does now work, and you get a 45MByte file.