Monday, November 24, 2008

Electric etching pencil

Sorry about no posting, if anyone actually reads this blog. Which, I doubt.

After a day of frustrating work on my home-built plasma cutter, I decided to try a much smaller project to take my mind off of things. I got this idea from this article on vintageprojects.com - an electric arc etching pencil. I've been wanting to make this for years now so I can write my name on my tools or label control panels in projects.



I started with a small threaded bolt from my junk box and shrinkwrapped it to prevent the sharp threads from shorting the first layer of the coil as it has only enamel insulation.



The magnet wire is 20-something gauge salvaged from some old toroidal switching cores. I wound the thicker stuff on a larger bolt as an experiment. When I ran out of wire to wind I just scraped of the enamel, soldered on another piece, and kept on winding.



I wound two coils using this method and saturated them with some superglue to hold the windings in place.



The hardest part was finding some material to use for the spring. I ended up cutting some pieces out of a springy motherboard bezel (the part that mates your mobo to the PC case). I drilled a hole for the small bolt and bent the spring into a U shape. I tightened two screws on the core bolt to trap the other end, and attached a peice of 16 gauge copper wire to the small bolt to serve as the electrode.



I wired up the ground clamp and decided to give it a try. It took some fiddling with the gap between the solenoid and the small bolt but it worked! It definitly needed a handle though, as its too small to hold and gets hot. I used a 3/4" wooden dowel and drilled a hole in it lengthwise to press fit the coil.



I can write on pretty much anything conductive. The tip buzzes along as your write and it seems to work best on bare metal, stuff with mildly conductive coatings also works but its more difficult to get a smooth oscillation.

5 comments:

Pwag said...

I accidentally bought one of these. I was a yard sale and snagged an ammo can full of "stuff" for $10. The can was my original goal, but imagine my suprise when I found an electric etching pencil in there!

I just printed out the plans for this, we ran it pretty well off a car battery, Does your power supply leave the juice as household (ac?) current? How do you avoid being shocked?

I also have one that has a broader copper point. Maybe 1/4 an inch across, coming to a dull point. My father thought maybe it was a soldering iron. I thought maybe it was for much higher electrical current. Do you have any ideas?

(had to edit to get email follow ups, sorry!)

digitaltwilight said...

That makes sense, a car battery would give you 14 or so volts DC, and a wicked amount of current, cranking a car can suck like 500 amps. The power supply I used is a modified ATX (computer) supply so can use either 5 volt or 12v, so the current is fairly high too, especially the 5 volt line, it can source like 25 amps. For the second one I'd try and measure the leads to it with multimeter and check the resistance. If its a dead short or if it goes form zero to infinite impedance when you move it, then it would be an arc pencil. If the Ohms were something higher then I'd imagine it would be a soldering iron

Pwag said...

I'll give that a try, thank you. I've always shied away from AC because it scares the bejesus out of me. I'll have to see about modifying a power supply in the same way you did and give it a dance.

Kurt Wickman said...

You really should be MORE afraid of the DC ampers, those will kill you dead.

Pwag said...

I'll be honest... Electricity in general just scares the crap out of me.