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Foil arc-cutter

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Marko

Fri May 19 2006, 06:11AM

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

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

Not inside the pencil, I tried it.

When etching foil spark is on microscopic level and can interestingly never generate enough heat to do it.

After tons of etching temp of pencil tip increases by just few degrees.

If I touch something too thick to etch (aligaor clip) then it does glow, and very brightly but it doesn't explode. I guess it's because if it's too short.

Only problem is that then I melt sensitive parts of pencil in very short time.

Touching to foil 'too long' does nothing, just etches anywhere you drag it.
Cutting is based on constant 'bad contact' between electrode and foil because foil constantly melts in it's way.

If you use few cm of lead and hook it directly to power supply it is normal for it to overheat and blow up.

If it is thicker there is even more risk of explosion and sharpnels are much bigger and dangerous.

Electroholic

Fri May 19 2006, 09:57AM

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

I was using 0.5 lead in my foam cutter,
it worked perfectly, but when i crank current up,
the middle part of it glow white hot.
It oxidized itself, and got two "extremely" sharp carbon needle.
so I guess only thick lead, like >1mm, would explode.

Marko

Fri May 19 2006, 10:45AM

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

guess only thick lead, like >1mm, would explode.

Good guess.

When I tried something similar with a 1,5mm carbon rod it used to explode violently, especially if I leave too much of it free.

I had to take cover when doing this.

To reduce heating electrical contact must be as close top the tip of lead, because of high ohmic resistance of graphite.

Also one important thing is to use negative pole of power supply on the electrode, I didn't belive it's important untill I tried.

With positive pole on the pen it sticks to foil and creates some garbled, wide cut.

Psyko

Fri May 19 2006, 08:03PM

Registered Member #81 Joined: Thu Feb 09 2006, 11:57AM
Location: Paris, France
Posts: 43

I just tried it with a 0,7 mm pencil. Incredibly powerfull. Nicest find man

But why is carbon so powerfull, compared with metal ( I tried with steel ) ?
I have tried to melt some solder wire with the pencil and the system could nearly solder. Nearly .

Coyote Wilde

Fri May 19 2006, 11:14PM

Registered Member #175 Joined: Tue Feb 14 2006, 09:32PM
Location: Sudbury, ON
Posts: 111

Psyko wrote ...

But why is carbon so powerfull, compared with metal ( I tried with steel ) ?

Because the carbon is burning; steel doesn't react nearly as much in air.

Marko

Fri May 19 2006, 11:34PM

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

Nope, It's not burning at all in foil-cutting operation.Carbon lead gets just warm a bit.
It can cut for very long getting just a bit wasted.

It does the job well because graphite doesn't tend to weld to metals like a sell tip would do.
This makes 'everlasting point of bad contact' anywhere it goes, and the spark occuring at the spot blasts the alluminium into vapour.

I also tried it for solder wire and it works, but I don't know for the boards.

I suppose that 'soldering' ability is just from ohmic heating of the carbon rod (graphite has a quite high ohmic resistance) and transferring it to solder, as it's too massive to get vapourised like alluminium foil.

You can distinguish these two events by occuring temperature andwasting of carbon lead.
If it's just filamenting it will be burned in series of small explosions and get consumed pretty fast.

ragnar

Sat May 20 2006, 01:06AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Much like a lightbulb, the current running through your carbon/graphite electrode is also self-limiting as the graphite heats up. This reduces sputtering and welding. Similarly you can vary the current by using a longer length of graphite between your supply and target.

Marko

Sat May 20 2006, 10:03AM

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

Much like a lightbulb, the current running through your carbon/graphite electrode is also self-limiting as the graphite heats up. This reduces sputtering and welding. Similarly you can vary the current by using a longer length of graphite between your supply and target.

Current drawn in the cutting is much lower than short-circuit current possible.
Length of graphite interestingly makes no difference at all, as the spark limits the current (It draws something like small 'bangs' from the filter cap but overall current is quite low).

Your self-limiting effect probably occurs only on microscopic scale on point of contact and this prevents welding.

'Electron wind' from the electrode also seems to help blowing the vapour away.

cbfull

Sat May 20 2006, 06:07PM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

I love all of the creative ideas on this board! This method of cutting foil sounds like killing a fly with a bazooka. I use a cutting mat and a wheel blade/straight edge when I need to cut a straight line in a hurry. I'm not sure how it could get any faster.

On the other hand, pencil lead is much cheaper than those round blades. I'm waiting to see how long it takes for aluminum to dull a steel blade.

Marko

Sat May 20 2006, 06:35PM

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

cbfull wrote ...

I love all of the creative ideas on this board! This method of cutting foil sounds like killing a fly with a bazooka. I use a cutting mat and a wheel blade/straight edge when I need to cut a straight line in a hurry. I'm not sure how it could get any faster.

On the other hand, pencil lead is much cheaper than those round blades. I'm waiting to see how long it takes for aluminum to dull a steel blade.

It was actually intended to etch and repair PCB's, but it didn't work there too well.

And how about writing letters, circles and very small shapes with a blade (I just needed two small circles to cover small sphere, I just drew them around solder wire roll...).

Pizza blade is also good idea but I have only a wavy one

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