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Foil arc-cutter

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Marko

Thu May 18 2006, 09:54PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I think I just found another fun use for that mechabnic pencils.

I simply hooked one with metal head to small 18V DC supply (rectified and filtered small 20VA transformer).

Positive clip was connected to piece of aluminium foil.

I used as thin as possible cape (0,3mm). It showed to be thinner = better.

Graphite vaporises alluminium at contact in very small spot.
Using a ruler it can cut perfect lines with much more speed and accuracy than scissors or scalpel (scalpel also tears the foil every 3 cm).

It may spare a lot of time doing big lifters.

Only problem was That I would need to use piece of ceramic or glass for a ruler.
Due to spot-heating plastic one sticks to the foil edge (poorly, but still does) andI needed to tear it apart every time.

xcept that lines can be drawn almost ideally, in unlimited length and with speed you can draw with a normal pencil.
When graphite rod burns up I just use pencil's reloading system (actually it is used slower than in normal writing on paper)
Basic idea was actually to make something that could cut PCB copper to repairbadly-etched boards.

Copper seems much thicker and harder to blow apart than foil.
I tried to use a huge carbon rod and specialtechnic pencil but I just melted it, and left some black spots on the copper.

Here is some mess I wrote on the foil, and closeup.
Clip is hooked to metal head, if I wanted something more real I could maybe put a wire inside the pen.

Reaching

Thu May 18 2006, 09:59PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

hehe, thats interesting stuff, great idea

Maz

Thu May 18 2006, 10:00PM

Registered Member #111 Joined: Fri Feb 10 2006, 01:04AM
Location: Menasha,Wisconsin
Posts: 65

wow thats qualiy stuff you got there!
i would have never guessed. i only managed to use pencil lead as a resistor...

Marko

Thu May 18 2006, 11:08PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Small movie of cutting, note how fast it is.
Looks like some star-trek plamsa scalpel... (if there were no that aligator clip :P )

Michael W.

Thu May 18 2006, 11:10PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

Its actually pretty cool, until you touch the graphite to the foil too long, and it glows like a filiment and the explodes....

Marko

Thu May 18 2006, 11:15PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

This can't happen.

Only when I used huge 1,5 mm carbon rod it would 'weld' to the foil in short periods and heat up too much.

0,3mm can no way do this, it just 'eats' aluminium no matter how is it positioned or how fast it's moving.

Graphite is used mainly because it doesn't stick.

Only sometimes I don't leave enough graphite out and foil shorts to metal part of pencil, blowing a little bigger hole.

Michael W.

Thu May 18 2006, 11:45PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

well yes it can happen, i tried it with thin pencil lead and the lead glowed bright red and exploded....

Alex

Fri May 19 2006, 12:21AM

Geometrically Frustrated
Registered Member #6 Joined: Thu Feb 02 2006, 04:18AM
Location: Bowdoin, Maine
Posts: 373

Neat.

I wouldn't expect it to work well as a PCB etching tool, because there would be carbonized copper remains in the cut paths. Maybe it could be wire brushed or chemically cleaned reliably, I'm not sure. Even if it could, it might not be very good for making intricate boards, but it'd at least be handy for lashing up a quick prototype.

Bjørn

Fri May 19 2006, 01:45AM

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

Pencil lead can explode violently enough to cause damage to skin and eyes when heated. Heat it slowly, never cool it in a liquid and keep it away from your eyes.

...

Fri May 19 2006, 05:21AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Great idea!

I have been known to cut out Al foil by just dragging the alligator clip across it, but that gets messy and I can't use much current... I never though to use a pencil lead

I can vouch for the exploding thing... They will heat up to a certain point, the suddenly go bang shooting little carbon projectiles everywhere. I suppose if it is inside the pencil all should be fine though...

As to pcb etching... I wouldn't really recommend using this. There is the problem of the carbon left behind, but also you can only make thin lines, not obliterate a nice gap between traces to prevent solder bridges forming... I would recommend a dremel tool for that... I hear the cutoff wheel work well for strait lines and those little SiC masonry bits for the detail work...

But both of these can be surpassed by the sharpie/enchant if you know what you are doing...

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