The idea for the casting workshop was to get people into the metal shop that wouldn't have time for a full semester course, or who didn't know what facilities are available here. A friday night and an afternoon on Saturday is a much easier commitment. In fact we had four people in the class that had never taken any CCC class before. Even more amazing was that people found this class just by reading through the entire course catalog. Just imagine what would happen if someone advertised or put up posters somewhere, we'd be overwhelmed.
Friday night was boring lecture night. I went on and on about primitive people thousands of years ago putting shinny rocks near the fire and then having them melt into puddles, taking on the shapes in the sand/dirt. From there it was just a matter of making more interesting shapes in the sand, and figuring out more convenient ways to get the metal hot enough to melt. After about half the class is asleep, we move out into the shop where I connect with the visual based students by doing a demo. I pick one of the random shapes on the wall, pack sand around it, cut some gates from the shape to the pouring & air tunnels (call the sprue & risers), take the pattern out (don't want to leave that in there), put everything back together and then pour some metal in it.
Then comes the most important part.
I could do everything in a single day, but then we'd be stuck pouring more copies of the boring patterns we have in the shop. Its not that everyone doesn't need another metal picture frame, its just that most people can find something around their house that would be fun to cast in metal. So now I've lectured, I've demonstrated, and they all have an idea of how its done. Now I send them home for the night and tell them to bring in stuff of their own to pour.
The next day is easy. I really don't do anything. Of course ten people can't pack up sand projects all at once. Even with the new sand counter we built out, we're hard pressed to have five projects going at once. So I told people to pair up, and had the extras melting down cans so we had metal to pour. If you're going to do backyard metalcasting, better get used to skimming all the slag you get melting cans. Everyone did at least one aluminum project, a couple did two or more. Just about everyone melted scrap, and poured projects (which takes up to three people). By then we had done some pretty interesting things, including this casting of a plastic replica of a mayan calendar. In this first attempt the edges didn't come out because they were too thin, so the next go round we backed it up with a piece of cardboard and it came out quite well.
After lunch we switched to brass, and poured a bunch more projects, though everyone didn't get to do something because we ran out of brass. We did get a great replica of a dodge truck ram hood ornament (the brass version actually looks cooler than the chrome), and we did the calendar in brass as well which looked great. Everyone was totally thrilled with the results and several were considering taking the full class the following semester.
Thin Gauge Welding
My thin gauge welding class was a success by most measures as well. Sure we only started the semester with three students, and even after yelling and screaming and threatening the other classes I still didn't have a full class but that's ok. Yes, they docked my pay, but really, the $400 I get per month to teach a couple nights a week isn't a real budgetary make-or-break issue. What's important is that we did TIG welding for many weeks, used bottles and bottles of Argon gas, and a few students actually could turn out a good weld on thin metal.
One guy was just going to form up a box for a cover over his gas powered RC truck, but I made some suggestions, and pretty soon he had a mean looking metal body, complete with bumper and roll bar. Most excellent. Other guys welded up square tubing trays, pans and boxes, motorcycle ramps, abstract sculpture, and a couple even helped me with my project to weld together a couple of toolboxes for Christmas gifts. And unlike the other classes chewing up $40-60 a night in steel plate for welding coupons, these guys were just using 22 gauge sheetmetal scrap we have tons of (which helped me justify spending $800 on TIG parts).
Even better, we also got to do a bunch of experimentation. Besides making them spend more time with the gas torch filling large gaps, and patching holes; they also did some different joins with large gaps. One funny thing was that welding a T joint with a quarter inch gap is actually easier than welding one when they fit up. You can point the flame right under the vertical piece and weld a bead from the middle of the bottom piece to the edge of the top. Its like being able to reach both sides of the metal and weld it up. Doesn't take that much more filler either, as you're drawing it up right underneath instead of trying to push a puddle into a corner.
We spent a little time with wirefeed welders as well. Normally wirefeed welding on thin gauge is a source of constant burn through as I can attest to from prior experience, but I decided to try an experiment based on something you learn TIG welding. In TIG welding, when you're welding DC, its important to get the polarity right, as the negative side gets less heat than the positive side. Think of those electrons jumping from minus to plus and smacking the plus side with their kinetic energy. When the TIG torch is hooked up right the steel melts and the tungsten manages with its share of the heat. When its hooked up wrong, the steel just gets red and the tungsten is vaporized. One spec sheet lists the distribution in heat as 30/70. So I wondered if you hooked up MIG backwards, would you drastically reduce penetration?
To get as much leeway as I could, I bought some superfine 0.023 wire, and put it on the portable 110V machine with C25 gas. One of the curious things about this combination is that the wire is so small, that you can get spray arc transfer going with that low power machine. But we weren't here to sprayarc. With this setup, the specs for the machine said it was just within the realm of the possibility to weld 22 gauge with the power set to 1 (lowest) and feeder speed set to 30. However, flip the polarity around and its a whole different ballgame. At power setting 1 (of 4), I don't think the weld was even stuck the metal that much. Looked like a caterpillar. Turned it up to 2, still not much penetration. Turned it up to 3. Now things were looking better, but even lingering around didn't burn through. Turned it up to 4 and got it laying in pretty seriously and after hanging around in one spot long enough, I finally got it to burn through.
Well, if it takes that kind of power on 22 gauge, maybe it can handle something even thinner. Turns out we had some other scrap in the back that seemed to be pretty flimsy. My little dollar thickness gauge only goes down to 28, and this stuff was thinner than that. MIG weld it? Impossible most people would tell you, but my students didn't know any better, so they had at it. Now I'm not saying it was easy to weld—heck, 30 gauge is almost impossible to TIG weld—but they laid the torch way down, let the wire stick far out, and managed to lay some lines on that thing that didn't melt through. Even did a few lap joints. The most important thing there is not that they might try to weld 30 gauge again, but that it makes going back to 24 or 22 gauge seem like a walk in the park, cause you have the skills to lighten up if things get a little hot.
The second big experiment was being planned when it happened by accident. With wirefeed welding you have a variety of shielding options, from none (self shielding flux core), to expensive (argon + co2 mix). While C25 is a fun gas to weld with, I don't bother at home, I have the cheap CO2 tank which is just fine. TIG welding on the other hand is always done with straight argon, which has the double downside of being more expensive, and not very dense (argon is just a pressurized gas in the cylinder while CO2, like propane, is actually a liquid under a certain amount of pressure). So wouldn't it be great if you could TIG weld with CO2.
My first concern was the behavior of tungsten in the presence of CO2, but it turns out that CO with enough heat can be used to turn tungsten oxides into tungsten, so the pure tungsten should be ok. The second was how the metal would behave. The answer turns out to be that it does ok.
We came into the lab one night, and started TIG welding and things were looking a little strange. The arc was the wrong color (more yellow), and was behaving a little different with steel; but not enough that I would dig deeper. It was the one guy who was trying TIG weld aluminum that brought the problem to light. Unlike tungsten and other common metals, aluminum is one of those metals that will rip any oxygen around it off whatever it happens to be attached to and grab it for itself. (Another metal like this is Magnesium, which happens to burn just fine when surrounded by dry ice.) So while our steel welding was going ok, the poor aluminum welder was ending up with massive holes in his metal and little flecks of black.
With a trip to the gas closet, we realized that the high school students had hooked up a bottle of C25 (argon & carbon dioxide) to the TIG feed line, which is supposed to be pure argon, and so the aluminum was reacting with the CO2, generating additional oxide (which is smacked out of the way in AC TIG welding), and leaving a residue of pure carbon. We switched the bottle to pure argon so the aluminum welder could go back to welding properly, but have made plans to dedicate a couple of DC TIG stations to CO2 only (to save money for the shop as all that argon gets expensive).
Now if I had a real project, where the quality of the weld mattered, I'd still use Argon, as I have no idea how good a weld this shielding is making; but for the most part in the classroom we're just welding thin squares together or making some sheetmetal art, so we'll keep experimenting with CO2 and keep our costs down somewhat.
Basic metalworking and Machining
This was the third time for me teaching this class, and things didn't go as well as I hoped. I had hoped to focus more on the machining aspect of the lab, only to find out that three of our lathes were hopelessly damaged, leaving only one working machine. Worse, was having several students sign up with more machining experience and knowledge than myself, wondering what I was going to teach them. Definitely a little uncomfortable.
The final nail was the non-working CNC plasma machine. While I won the auction for a hypertherm Max 200 last August, the machine didn't ship until October, then it sat down in Phoenix for several weeks getting checked out, and finally arrived at the shop right around Halloween. At least the power supply arrived. There was no torch head or leads. Yet another call to the seller and I got some weak sounding explanation about the torch head being tied on in the back, but no such luck. Price for replacements? About $600 for the torch and another $500 for leads. Well, as much as I like to think of myself as a man with no financial bounds, the $4,000 for the power supply had already put a pretty good strain on my resources; and November is a killer month for finances, as the property taxes, homeowners insurance and the bill for the winter propane all hit at exactly this time. So no plasma torch this semester.
I have high hopes for next semester though. I'd better get the darn plasma machine working, cause I've scheduled a weekend workshop just in Plasma arts & parts.