Thermocouple Welder (Nov 2004, p24)

[tlinbeck]

Has anyone tried to weld a thermocouple per the instructions in the magazine. Using a 12V battery [in a portable jump-start rig] and reducing the resistor to 0.25 ohms seems to be going in the right direction, but I have not had a "bead" form in the process. The carbon rod was taken from a standard D-cell. Any suggestions?

[terri]

Where on earth did you find a carbon-zinc cell? <p>I used to do this a lot with a TIG welder. I have not read the article, so this may be redundant. You twist the wires together, establish the arc, and slowly bring the twisted wires together to the arc, with the ends of the wires pointing toward the arc. Note that you never actually get the TC wires in the arc itself. Just the proximity to the arc will do the trick.<p>You have to watch it. It takes a steady hand and a slow approach and careful observation while you're doing it and make sure the wires are "fixed" so they don't move out of position with respect to each other while they're melting, and again, while they're cooling.<p>One hint is to only melt up to the last twist, and untwist them that last turn when cool. Not as pretty, but still functional. <p>I wonder if you have a steady enough arc with just the portable battery --which would be putting out 50 amps on first strike -- will it hold up this long? I'd maybe try a fully-charged "real" car battery. (After all, I was doing this with a top-of-the-line TIG welder.)<p>As I was doing this years ago, I often thought I'd just build a specialized little spot welder with a charged cap for the energy source, but never got around to experimenting with it. Besides, I thought, if I went ahead and built a spot welder, then my specialized skill would be nullified since anyone in the plant could do it with the spot welder. Flatten and polish the ends of the wires, clamp them in the electrodes, and zot them with the cap, was the way I was going to do it. You might try this approach. <p>Again, maybe not as "pretty," but if you're handicapped by lack of proper welding stuff and using a portable starter, this might be the right thing to do.<p>[ January 02, 2005: Message edited by: terri ]</p>

[tlinbeck]

Thanks for the advice, Terri. I'll give it a try.
OBTW: Carbon-Zinc battery - go to the nearest "dollar store" and buy the cheapest battery you can find.
TOM

[terri]

OK re carbon-zinc "Le Clenche" cells. I'd have gone to my local welding shop and picked up one or two 1/4" - 3/16" carbon rods --used for brazing, etc. They usually have a copper jacket along their length which evaporates/melts as the rod is used up. The jacket also reinforces the rod. I hope you're using a welding mask with a dark filter --ND 9, as I recall. That arc is bright!<p>[ January 03, 2005: Message edited by: terri ]</p>

[Engineer1138]

Terri: are they called anything other than "carbon rods?" Couple weeks ago I was looking for some to use in my carbon arc experiments (I do have welding glass for safety).<p>I looked at Home Depot's welding/soldering section and someone there referred me to a local industrial supplier that he said carried them, but at that place they had a good welding department, but no idea what I meant by carbon rod. That lead me to think that they may be known by a different name.<p>I've been using motor brushes in the mean time, but they'll wear out soon.

[terri]

My memory fails on exactly what they were called... maybe "carbon torch rods" or "carbon arc torch rods," or some variant like that, but I'll check with my son. I think he bought a couple a few years ago --maybe there's a modern nomenclature for them. <p>I was referring to a "real" welding shop, not just a hardware store which happens to sell welders and sticks. <p>You might try a farm equipment/feed store in your area. As you know, farmers acquire an awful lot of mech skills, including probably every kind of welding and brazing and baling wire trick there is. I'll get back to you on it. <p>Clever, using motor brushes. I like that. Reminds me of the old New England adage:<p>"Buy it cheap.
Make it do.
Use it up.
Do without. Ayup."<p>[ January 05, 2005: Message edited by: terri ]</p>

[Engineer1138]

Thanks terri. Your comment made me realize that one of our mechanical engineers will probably know where to find them. We even have one who owns a farm! Best of both worlds

[terri]

Okay. My son said he just asked for carbon arc torch rods and they knew what he wanted.

[abare33]

For carbon rods. They are used in Movie Projectors
to produce the carbon arc for the movie anyone who sells projector parts can supply them or maybe you can talk the manager out of one they range in size and can be up to a foot long.