Opinions sought on cheap desktop PCB milling machine

**leadinglights** · 09-06-2010

Hi Kevin,

I am not so much reticent as a bit choosy where I would use it; my main problem is that it takes quite a large investment in time. Boards to be milled have to be planned for in the layout stage and there is an extra step in converting Gerber files to G code (Coppercam or similar). The board then has to be milled - which normally has problems such as short circuits caused by copper swarf (not to mention operator error), as well as the extra steps of fitting shorting pins to replace the vias. The completed board has to be treated with extra care as there is no solder resist.

A simple PCB may take 4 hours of your time to make - compared with about £40 from PCB-Pool. Except for the time from dispatch to recieving the goods the commercial process is cheaper and better in every way.

Having said that, I routinely use PCB milling if it is for my hobby - and would at least consider using it if time is particularly critical.

Mike

**russell** · 11-03-2012

If you want really quick prototype PCBs why not use the Press-n-Peel / etching method. You can easily get 10 thou tracks and spaces. You can then use cnc to drill the holes from your Excellon files.

Russell.

**HankMcSpank** · 11-03-2012

Originally Posted by russell

If you want really quick prototype PCBs why not use the Press-n-Peel / etching method. You can easily get 10 thou tracks and spaces. You can then use cnc to drill the holes from your Excellon files.

Well I look at it like this ...I already have a CNC machine - and CNC machines can mill PCBs, so better to have it earns its keep than shell out for press n' peel (that stuff isn't particularly cheap!). But actually this is more about saving time and getting consistent results more than saving a couple of quid.

What I found with chemical etching...it was a real chore, massive time sump, got erratic results (unless you use fresh batches of developer & ferric chloride each time - but then that starts getting expensive) then there's the temperature variations....make a chemically etched PCB on a cold day...you'll get differing results vs a chemically etched pcb on a warm day (my point being lots of variables) & fraught with problem getting the alignment right (oh what joy to see 1.5 hours chemically ecthing wasted because the CNC machine wasn't aligned 'quite' right when drilling holes out or cutting the board outline) ...and wait there a minute, if we are going to use the CNC to drill out the holes, we may as well get it to isolate the tracks in the first place!

Your mileage may vary, but I need rather intricate shaped PCBs...and therefore for me at least it's better just to run the whole sequence on the machine...at least this way you can be assured of everything being aligned.

My next target now is - after the tracks have been milled on my CNC machine - to get my CNC machine to dispense solder paste on all the track pads (I have all the 'process elements' in place...I'm just waiting on some solder paste of the right viscousity to arrive) ....another huge time win (because for protos, it's not worth making a solder stencil, and it's a real chore dispensing solder paste by hand each time!)

**saxonhawthorn** · 11-03-2012

Hank, you're right on all counts. Fresh developer each day is a must (prepared the night before to stabilise), though I've found I can usually go on using ferric chloride until it's spent. But temperature control is very critical, and it took me a lot of experimentation to get it right. I was making boards for production then, not just prototyping, and scrap costs money.

Another nice thing about milling has just ocured to me: there's a big price difference between plain copper boards and pre-sprayed photo-sensitive boards (NB to anybody thinking of doing it: use Fotoboard 2. Don't even think about spraying your own photo-sensitive stuff on. You've got to spray it evenly with no missed bits, bake it dry at the right temperature, and never let it see daylight until you use it. You really don't want to go there).

A pick-and-place m/c for SMD is next on my list after PCB-making. Sounds as though you and I are travelling the same road. Are you using an "Archimedes Screw" device to dispense solder?

Ian

**HankMcSpank** · 11-03-2012

Originally Posted by saxonhawthorn

Another nice thing about milling has just ocured to me: there's a big price difference between plain copper boards and pre-sprayed photo-sensitive boards (NB to anybody thinking of doing it: use Fotoboard 2. Don't even think about spraying your own photo-sensitive stuff on. You've got to spray it evenly with no missed bits, bake it dry at the right temperature, and never let it see daylight until you use it. You really don't want to go there).

I use from SRBP copper boards (not so much nasty glass fibre dust in the air, they're easier on the tools & they're fine for protos)...

http://www.rapidonline.com/Tools-Equ...f-e2e6ffd711d1

....for 100pcs it works out about 36p inc vat & delivery for a 6" x 4 board" (cheapest I know of but I'm happy to be corrected!) ....the cheapest fotoboard of the same size I was ever able to source worked out at about £2.00 delivered per board, so yes a lot cheaper! (and the board I'm milling with are so cheap that it doesn't ruin your day if you screw up!)

re your comment...

2. Don't even think about spraying your own photo-sensitive stuff on. You've got to spray it evenly with no missed bits, bake it dry at the right temperature, and never let it see daylight until you use it. You really don't want to go there).

been there done that...bought some foto spray from Farnell & was appalled that they could even sell this stuff - complained to Farnell "This stuff truly sucks & you should remove it from your product range asap" ...they re-credited me for it!

Still got the can - doub't I'll ever use it....it's twatful stuff.

**saxonhawthorn** · 11-03-2012

Originally Posted by HankMcSpank

Still got the can - doub't I'll ever use it....it's twatful stuff.

Maybe it works as fly spray?

I'd be interested in details of your solder paste dispenser (apologies if you have already posted them somewhere - I've been away from this site for quite a while). What air pressure do you use? Is the amount dispensed repeatably accurate? I admit to a prejudice against pneumatic control of such small amounts of thick and gooey (and expensive if lead-free) stuff, but I'd be very happy to be proved wrong.

Ian

**saxonhawthorn** · 11-03-2012

Russel, thanks for the suggestion. I have admittedly never tried Press-n-Peel, but as far as I can see it goes most of the way back to chemical etching. It still needs ferric chloride (which has ruined more pairs of jeans than I care to remember) and still needs the intermediate stage of plotting/printing artwork. The only process it seems to avoid is UV exposure, which is actually the least messy part of what I do now, and not a problem anyway.

And I'm not sure that double-sided image location would not be tricky with Press-n-Peel. Double-sided is admittedly tricky with any system, but at least with both UV and milling it's possible to get precision - with care!

Milling appeals to me on two counts (well, three if you include having a new toy to play with) - (1) Not having to worry about slippage in a laser printer, or less-than-black inkjet printing, and of course (2) No messy bubble tanks. Not to mention the accumulated guilt of years pouring spent ferric chloride down the drain ("What me, gov? Nah, it's ketchup.").

Ian

**saxonhawthorn** · 12-03-2012

Grateful thanks to Mike for steering me towards a Proxxon mill. Their new KT150 compound table is the perfect size for milling my PCBs, and looks sturdy enough to hold the work properly. I have settled on:- a KT150 table, BFB 2000 Mill/Drill Stand, and BFW 40/E Mill/Drill Motor and Controller, all at http://www.proxxon-direct.com/index.html .

And to Hank for advice about leveling, calibration, cutters, and warping. All greatly appreciated.

I'll do the CNC conversion myself, and I should be able to machine the stepper motor mounting plates on the mill. Then I'll make a cabinet with extractor to keep the dust under control. So I now have an enjoyable summer ahead, and I'll post the results here when I have something to show.

Thanks again to all for your very helpful advice.

Ian

**HankMcSpank** · 12-03-2012

Originally Posted by saxonhawthorn

Grateful thanks to Mike for steering me towards a Proxxon mill. Their new KT150 compound table is the perfect size for milling my PCBs, and looks sturdy enough to hold the work properly. I have settled on:- a KT150 table, BFB 2000 Mill/Drill Stand, and BFW 40/E Mill/Drill Motor and Controller, all at http://www.proxxon-direct.com/index.html .

And to Hank for advice about leveling, calibration, cutters, and warping. All greatly appreciated.

I'll do the CNC conversion myself, and I should be able to machine the stepper motor mounting plates on the mill. Then I'll make a cabinet with extractor to keep the dust under control. So I now have an enjoyable summer ahead, and I'll post the results here when I have something to show.

Thanks again to all for your very helpful advice.

Ian

As it goes it's the Proxxon BFW/40E that I useas a spindle a nice solid quietish spindle (albeit a bit chunky & low RPMishh) ...I trialled AudioAndy's before buying it....in facr I think Andy had it up for sale a few weeks ago on here for a good price (though probably too late for you now!)