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Circuit Board Plotting and a PP Magnetometer

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LAN_403

Dave Marshall

Mon Jun 04 2007, 03:16PM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

For those of you that don't receive Circuit Cellar magazine, the May issue (unfortunately probably off the news stands by now) has an awesome article on using an old HP plotter (a 7470 I believe) modified to plot with a Sharpie Ultra Fine Point marker for printing directly on circuit boards with a .025" tolerance. That should provide plenty of resolution for some SMD work.

I did some shopping around, and the whole setup will cost about $75, as the article suggests. You can purchase a copy of the article for $1.50 or so on the archives. Its titled Circuit Board Plotting, in issue #202. It looks like a heck of a project, and I'll definitely be trying it when I get home.

The issue also has a very interesting article on a proton precession magnetometer, which will also be going on my list of projects when I get home. I think it could present some interesting ideas for robotics, if it can be scaled down a bit.

Dave

Dr. Shark

Tue Jun 05 2007, 10:05AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I shouln't argue with the head admin, but I am not terribly impressed with this plotter. The resolution seems to be worse than what can be achived with toner transfer, and it seems like a lot of work just to save yourself the ironing stage. I'd be a lot more impressed if that plotter could be converted to a CNC-router that directly cuts the traces for you. I am not sure about the power / rigidity of that plotter, but people have used components from printers like

combined with a dremel tool to CNC route PCBs. Heck, this even saves you from drilling the holes by hand!
Andrew did something similar with a harbour freight mill, maybe he can comment if he ever got it to work properly?

Dave Marshall

Tue Jun 05 2007, 12:20PM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

An interesting point. I tried the toner transfer method with a couple different types of photo paper and transparencies and had a mother of a time getting it to work with very thin traces or fairly dense patterns. That probably speaks more to my methods than to the idea as a whole though.

The dremel idea is really interesting, though I really really doubt that plotter would be heavy enough to handly anything that bulky. If you could mount the dremel itself in some stationary position and just move the cutting bit with one of those snake attachements, it might be doable. Something to think about, anyway.

Dave

Bjørn

Tue Jun 05 2007, 02:33PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Getting a relatively small plotter to move a dremel would not work well. There are some lightweight engraving/cutting devices that are powered by compressed air that might work. The extremely high RPM would make sure the forces would be manageable.

The temptation would be there to add a lot of features to the cutting head so I would probably assume it would be too heavy and move the work piece instead.

Electroholic

Tue Jun 05 2007, 03:20PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

for toner transfer, try cheap magazine paper instead of photo paper

Carbon_Rod

Wed Jun 06 2007, 04:26AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Direct cutting with a laser system ($10g) or CNC system ($3g) are often less hassle in the long run.

I tried g-code based plotters (i.e. used the old Win98 driver trick to auto rasterise and print line art) and HP HPIB systems (requiring g-code interpreters and LabView.)

Laser transfers work well, as long as you use weak acid to clean the copper prior to the heat transfer.

More CNC tricks here (

)

Dr. Shark

Sat Jun 09 2007, 07:46AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Two more things to add: Most CNC machines seem to move the workpiece and not the tool, even the big ones used to mill out V8 motor blocks (remember that youtube video?

). I imagine it would be hard to mount a PCB in place of the pen though.

Regarding the toner transfer, it has a learning curve like anything someone does for the first time. It took me quite a lot of experimenting to find that HP Photo Paper works excellent and magazine paper does not work at all, but YMMV. Slightly etching the copper prior to ironing is a good idea, presumably it creates a rough surface for the toner to stick, rather than just cleaning. After some playing around it got it to work very well for SMD circuits with 32 pin TQPFs, plenty resolution for me.

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