Tuesday, March 31, 2009

Bent TIG electrode = trailing shield?

Do you think this looks messed up?

Check out the welds that I can make with the messed up electrode. This is 1/16" 304:
I purposefully bent the electrode in the direction that I was moving the TIG torch. That way, there was a lot more gas coverage behind the arc than in front. It worked wonderfully! Even near the edge, the heat buildup was much less of a problem. I think the next step will be to make a trailing shield for the torch. Trailing shields are available, but only for amazingly high amounts of money. One alternative might be the "Monster nozzle". It could be large enough to act as a trailing shield.

Monday, March 30, 2009

Improved stainless welds with large gas lens

My new TIG parts just arrived today, and I had to do a quick test. In short, the large gas lens makes a huge difference. Take a look at this beast: #12 cup with "large gas lens" and 1/16 tungsten

I am using the same exact 1/16" thick SS304 sheet metal that I have been practicing with all along:

Compare that weld bead to the pair of beads in my previous post. All settings are exactly the same except for the gas lens. Well, I guess I was using .040" tungsten in the previous post, but that should have helped if anything.

Here's a few more. I've heard that "salmon color" is the best thing a stainless welder can hope for. I changed the flow rate from 10 to 20 CFH going from top to bottom -- not much difference. The bottom bead had a longer post-flow, so the tail of the bead has less purple/blue.

The backsides of these welds are pretty messed up. I'll report about the Solar flux later.

Sunday, March 29, 2009

First attemps at TIG welding stainless steel

I've spent most of my TIG welding practice time on aluminum, but have recently started to experiment with stainless steel (all 304 for now). It's difficult! Most welders say that aluminum is the most difficult because it liquefies quickly and has oxide layer problems, but in my opinion, stainless is more difficult because of the shield gas requirements.
Here's my setup:
.040" tungsten -- my local welding shop convinced me to try this instead of 1/16" tungsten. They somehow thought I could weld with less heat while using .040". I didn't understand it when they explained it so me, and I still don't -- especially since it makes no difference that I can tell.

no. 8 cup with gas lens

less than 1/4" stickout

Here's a 1/16" thick 304 sheet. The upper bead was done with 10CFH argon, the lower bead was 20 CFH. The picture shows the front and back of a simple bead with 1/16" filler. I was using as absolutely little heat as possible, sometimes solidifying the weld pool as I moved, making for an irregular bead. These beads both have major problems. They are pretty gray except on the left side where I finshed the weld and the post-flow cooled off the bead. The rest of the weld cooled outside of the gas shield, turning it gray, which is bad because the structure of the stainless steel has been altered. This will likely lead to corrosion or stress cracks.

I prepped the left side of the top surface to see if it would be any different than the un-prepped right side. The metal has a smooth almost plastic-like feel, so I was unsure if this was normal. It didn't seem to make any difference.

The backside shows major problems too. The upper bead looks better because there was more sheet metal all around the weld to soak up excess heat. The lower bead is "sugared" because it got very hot in an oxygen atmosphere. The weld is close to the edge of the sheet metal, so the heat built up more quickly.

To attempt to fix the topside problems, I've ordered a "large gas lens" setup with some huge gas cups from an online welding store. I tried to order these parts at my local welding shop, but they didn't have them, and were somewhat hesitant to even order them for me. I have no idea if the large gas lens will work, but the parts are relatively cheap.

To attempt to fix the backside problems, I've ordered some Solar Flux B, which was originally made for gas welding stainless steel. The alternative to flux is to build an argon purge for the backside of welds. This purge could be a box, a nozzle, or some other device to make sure the backside is flooded with argon. The problem is that every weld situation (tubes, sheet metal, angle, etc, etc) requires a custom purge setup, and argon isn't exactly cheap either. I'll definitely be posting more information about the flux in the coming weeks.

Here's a weld made on thicker (about 1/8") stainless. The grade of stainless is unknown. Don't mind the soot. I was just too lazy to regrind my tungsten after I hit it with the filler rod. Notice the bead is NOT gray. The thick metal is able to pull heat out quickly enough to prevent problems. Unfortunately, most of my stainless welding will be on tanks and tubes that will never be 1/8" thick. I need to find a solution that will work down to .049" at least.

DIY aquarium chiller

See update here:

My nano reef aquarium is usually 2-3*F hotter than the ambient room temperature (after the heater setpoint has been reached). This is a problem, since the temperature in my living room is often higher than 82*F in the summer. This puts the tank water at an uncomfortably high temperature (84+), and I think that the corals suffer from the temperature swings as well as the overall high values.

So, how to lower the tank temperature? For a 5 gallon tank like mine, a peltier heat pump like the Coolworks Ice Probe would seemingly be a good choice. I tried building just such a device a few years ago, and it was a big failure. I learned that peltier heat pumps cannot be controlled by raw pulse width modulation (PWM) signals, and they don't do well in thermostatic (on/off) systems either. One reason is that the semiconductors inside the Peltier device do not like the thermal shock of the constant on/off switching. Also, Peltier heat pumps are already horribly inefficient, and using PWM or on/off control makes things even worse. During the "off" cycle of either the PWM pulse or the on/off cycle, the heat will flow backward though the device -- the same heat that the device just pumped during the "on" part of the cycle. Think of bailing out a sinking boat with a bucket that has a huge hole in the bottom. The best way to control the peltier modules is to generate high-frequency PWM, then smooth it out with an inductor/capacitor filter. There is still the problem of the peltier junction's inefficiency, and the hot-side heatsink must be massive with a massive fan to make the system viable. Anyway, I haven't heard anything great about the Ice Probe, nor any other Peltier cooling systems designed for any application that requires a good amount of cooling. I have a thermoelectric refrigerator that is just marginally good enough for its purpose.

So, today's design for a new aquarium chiller will NOT use Peltier junctions, as much as I love the idea. I bought a $99 water cooler that uses a conventional compressor and r-134a refrigerant.
I filled the cooler with tap water, and mounted a Rio pump with an outgoing hose and return line.

The two hoses connect to a stainless steel coil. I've had this thing laying around my shop for a long time. It came out of junked, expensive lab equipment. It is non-magnetic, which indicates 3-series stainless steel. I'm guessing it's 316, which is highly corrosion resistant. Of course, the aquarium purists would insist on titanium, but I don't have any, nor do I think it's really necessary. I'd love to hear from anyone who saw a stainless steel chiller coil corrode, or definitively caused tank poisoning.

I melted a couple slots in my hang-on cheapo protein skimmer (it's not a Skilter, but very similar). I would have used a dremel, but I didn't feel like taking the filter off the tank, and I also wanted to avoid getting plastic shavings in the water. The stainless coil sits down into the slots and is just held by gravity.

The cooler is plugged in all the time. It keeps its insulated water chamber around 47*F. The Rio pump in the cooler is turned on and off by the PID temperature controller that I mentioned in a previous blog post. The controller can be configured to use a longer cycle time (eg 30 seconds) since it is controlling a pump, and it would not make sense to turn a pump on and off once per second as it would be for a heater.

The cooler is rated 86 watts. If this is what the compressor draws while normally running (I didn't check it). I would estimate the cooler can pump about 170 watts of heat (about 580 btu/hr). The coefficient of performance is around 2 for small compressor systems. For comparison, a large peltier device can move around 70W under ideal conditions, at a very specific current/voltage. The coefficient of performance for Peltier devices usually tops out around 1, and is often about 0.5 for realistic situations. So, a peltier pump drawing 86 watts, would only pump about 43 to 86 watts of heat.

I just installed this chiller today, so I'll monitor it on hot days and make another post about its performance.

Thursday, March 26, 2009

Thirst extinguisher

This is an old, but good, project that I built a few years ago. I retrofitted a commercial fire extinguisher to hold and dispense beer. I brew my own beer at home, so it is fitting to have a homemade "keg" to hold homemade beer!

The extinguisher tank is stainless steel, and fairly easy to clean. The top unscrews, and leaves a 3" dia hole. The extinguisher was originally setup to dispense fluid (ie it has a downtube that connects the outlet to the bottom area of the tank, and a port on the top for adding pressurized gas). This is exactly what we want to dispense beer. The main modifications that I made were:

Replacing the original (nasty) downtube with a new clean one
Replacing all of the rubber seals with new ones
Lots of cleaning
Added a low pressure gauge and compressed air quick-connect system (not shown in the photos)
More cleaning

I got my CO2 cylinder and regulator at a local welding supply store. It was expensive, and I am not sure if it was worth it.

In order to carbonate the freshly brewed beer, I keep the extinguisher in the refrigerator with the CO2 tank set for about 12 psi. I give the beer a vigorous shake once or twice a day, and after a few days or a week, it is ready.

The extinguisher is always a hit at parties, and has become a tradition.

Monday, March 23, 2009

Aluminum welding progress

I ordered a bunch of aluminum parts from eBay and McMaster. I've spent a few afternoons just cutting the metal into random parts and TIG welding it back together

I've made a few coupons to test the five basic weld types:

* Butt
* T-joint
* Open corner
* Lap joint
* Edge

The above picture only shows a T-joint and open corner, since those are my best types.

This pipe doesn't do anything useful, unfortunately. I just made random cuts on my miter saw, rotated the two pieces 180*, then welded them.

I'm still working on getting nice, consistent beads, but they have good penetration, and I'm getting a lot more confident with aluminum.

DIY wave-maker plans

I have provided a basic schematic and parts list for the aquarium wave maker circuit. Here is what you will need:

*Blue plastic "double" electrical box (for household wiring) $1
*Standard electrical outlet and outlet/switch faceplate $2
*12 volt transformer and full-wave bridge (cut up an old one that you are not using. $6 for Jameco #100095)
*Power cord (cut up an old one)
*558 timer chip (Jameco #27457) $1.20
*Solid state relay Kyotto KB20C02A (Jameco #175214) $6.55
*7808 or 7809 voltage regulator (Jameco #876352) $0.56
*two 100K pots (Jameco #29103) $2.18
*two 3,300 uF capacitors (Jameco #93666) $1.22
*PN2222 transistor (Jameco #178511) $0.12
*perf board, wire, maybe a 16-pin DIP socket, misc caps and resistors $2.00

Total parts cost is about $23. Here's a link to Jameco

Notes: My circuit provided times of about 1 to 6 minutes for the on and off periods. You may want to put a 10K resistor in-line with the 100K pots. If either pot is turned too far down, the circuit will stop oscillating, so the additional fixed resistance will prevent this from happening.

This circuit does not provide the "soft start" that many commercial wavemakers tout. These motors likely use shaded poles for starting, and a soft-start controller would have to control the frequency of the AC power, not just the voltage. I find it pretty unlikely that this is what any wavemaker does, and for the price they charge, it's probably cheaper to buy a new powerhead every year! I haven't used my wavemaker long enough to know if it will kill the powerhead. I'm using an Aquaclear powerhead, and it clicks loudly upon startup, but there is no chatter. I may make another post about modifying the impeller to cope with the repeated startups.

I've experimented with using dimmers, current-limiters, etc, to control the speed of powerheads. The speed can only be reduced %10 or %20 before the motor stalls. It's not really practical without control over the frequency of the AC waveform.

The Solid-state relay in this circuit has a current limit of 2A. This mean it can control up to about 200W of powerhead.

Saturday, March 21, 2009

Aquarium wave maker

Here's a really simple project that turns an aquarium pump on and off at a specific rate. This is supposed to simulate ocean currents which periodically vary instead of blowing constantly like a mechanical pump does.

The project is built within an electrical box and uses a 558 quad-timer chip as the timing device. I used a monster capacitor and resistor to get time values of 1 to 6 minutes (variable with a pot). The on and off times are independently variable. I used another part of the 558 chip to flash an obnoxiously bright LED. There is also an override switch. The output of the 558 chip drives a transistor, which triggers a solid-state relay. The relay controls power to the outlets.

I added some plans here: http://benkrasnow.blogspot.com/2009/03/diy-wave-maker-plans.html

Aquarium temperature controller (PID loop)

Store-bought aquarium heaters suck. It's just that simple. They're cheap too, so maybe the suckage-to-price ratio is correct, but I felt that the temperature in my tank could be a whole lot more stable than it was a with a standard submersible heater. The main problem with the glass-tube heaters is that the temperature sensing device (a bi-metallic strip) is located inside the heater itself! How does the heater know what the tank water's temperature is? It doesn't. These submersible heaters are setup to maintain a relatively constant temperature inside the heater tube. The assumption is that the heat load on the aquarium is approximately constant, therefore the water temperature will be fairly steady. In my house, the ambient temperature changes quite a bit, so the heat load on the aquarium changes, and the submersible heater does a poor job of temperature regulation.

The solution is to use a sensor that is mounted some distance away from the heater. The sensor will accurately measure the water's temperature -- not the heater's. Systems of this type are available to aquarists, but they are overpriced, and offer only on/off control. Instead, I bought a PID (proportional, integral, derivative) controller with a platinum resistance temperature device (fancy thermometer). The whole thing with a solid-state relay was $70 on eBay! I mounted the controller in an electrical box and wired the solid-state relay to control the outlet. I am still using the tank's original submersible heater, but I set its temperature control wheel all the way up, so that it is on whenever it receives power. It is switched on and off via the relay.

The controller is a Eurotherm 2132. This is a very complicated piece of equipment. It has numerous settings, menus and modes of operation. It's definitely overkill for controlling an aquarium's temperature, but I really enjoy tinkering. My favorite feature is the auto-tuning of the PID loop parameters. I set the controller up, and let the tank's temperature drop to about 78*F. I programmed the controller to bring the temperature up to 80* and to initiate its "learning process". It switches the heater on and off and records how quickly the tank rises and falls in temperature. This way, it knows the time constant of the system, and how to best choose the PID parameters. The learning process took an hour or two since the system has an inherently slow response. For those that are really curious, here are the parameters that the controller calculated:

proportional band: 1.45 *F
integral time: 3923 sec
derivative time: 655 sec

This means that the controller uses proportional control when the tank temperature is within .725*F of the setpoint (half of the total 1.45*F band). Below the band, the heater is constantly on. Above the band, the heater is constantly off. Proportional control means the heater is switched on/off rapidly to generate a percentage of its full output power.

The integral time is very large, which means the system reacts very slowly, and the integral action should be very gentle. Specifically, the controller will modify the proportional output up or down at a rate of one full proportional band per 3925 seconds of 1*F error. So, if the tank is constantly 1* too cold, after 3925 seconds, the controller will boost the output by %100

The derivative time indicates how much the controller responds to rapidly changing tank temperatures. 655 seconds means that if the tank temperature were changing at a rate of 1*F per second, the output would be adjusted by 655%. If the tank temperature were changing at a rate of 1*F per hour, the output would be adjusted by 18%.

I also added a chiller to my tank, and have it controlled by the same PID controller. Check it out here:

DIY automatic water top-off system for home aquariums

Please see my post about the improved level sensor here.

One of the daily chores of aquarium keepers is adding water to the tank to compensate for evaporation. For reef aquariums with intense lighting, the amount of evaporation can be substantial. In my 5 gallon nano-reef, I add 1-2 cups every day. This task is not only boring and repetitive, it is also stressful for the aquarium. The sudden change in salinity of adding 1-2 cups (or 2-4 cups, if I forgot a day) is bad for the tank inhabitants. The solution is to design an automatic top-off system. Here's how I did it:

I built a non-metallic water level sensor from two plastic fiberoptic cables and some spare plastic parts. The ends of the fiberoptics are directed towards each other at about a 60* total angle. The imaginary point of intersection is a few mm in front of the sensor head. The sensor works by sending light out one fiberoptic and sensing how much light returns via the other. When the water level is within 1cm of the sensor head, the amount of light returned is very high since the surface of the water is a good reflector. As soon as the water rises above the sensor head, the amount of returned light drops to near-zero.

This sensor works very well with only one problem: bubbles. If air bubbles start to collect on the fiberoptic ends, they can reflect enough light to cause a false-positive even when the sensor is underwater. I modfied the sensor after taking this photo by cutting away excess material, and making the fiber ends more flush with the sensor's plastic. So far, these modifications seemed to have worked very well.

The sensor is mounted on the aquarium's rim. The white plastic adjustment screw locks the sensor in place after moving it to the desired water level.

The light sending/receiving is accomplished with an off-the-shelf part. It's a Keyence FS-V11. These are used in factories to sense the status of parts on a conveyor belt, etc. It's a very cool little device, and is adjustable to have a custom light/dark threshold. The Keyence's output drives a solid-state relay, which controls power to the outlet. The outlet supplies power to a small water pump (Aqua-lifter AW20) that draws water out of a store-bought container, and drips it into the aquarium. The pump is slow, which is good, since it will affect the tank's salinity gradually.

Interestingly, the sensor has a sort of built-in hysteresis. The water forms a meniscus with the sensor head, and as the level drops, the meniscus keeps the sensor submerged as the level drops below the sensor head. Finally, the meniscus breaks, and the sensor "sees" the water surface. The pump is activated, and the level rises until it meets the sensor head. This provides a nice on/off cycle action.

Aluminum welding progress: T-joint

I ordered a bunch of aluminum bars and cut them into 6" pieces to practice basic welding joints. It's going pretty well. Here's a list of quick tips that I have learned:

1/16" electrods seem good enough to handle almost any task at 150A or less. I'm not yet sure why anyone would use anything bigger or smaller for less than 150A.

The filler rod must be forcibly pushed into the puddle, then quickly retracted. It cannot be brought near the arc slowly, as it will melt before it gets to the puddle! I have found that I move the torch in the direction of the weld to get the base metal molten, then move it backwards slightly while I add filler, then move forwards again. I use this one-step-back, two-steps-forward approach for the entire weld.

The AC balance control can be pretty heavily shifted to DC EN. I usually keep mine at %70 to %80.

It helps to have the part propped up off the table. For the first T-joint that I welded, I had the plat laying flat on my metal table. This makes the angle of the torch more difficult, but worse, it sucks a lot of heat out of the aluminum that is touching the table. This is really a pain, because it makes the weld asymmetric in terms of heat required, and finding the magic torch angle to melt both sides evenly becomes more difficult.

Harbor Freight welding auto-darkening hood

Harbor Freight sells an auto-darkening welding hood (Item# 46092) for about $50 -- depending on the current sale. It is cheaply made (of course), but not ridiculously so, and has proved to be worthwhile to me. However, I had a very unusual problem that I could not find documented anywhere else on the 'net. Hopefully my blog post will help others in my situation.

For the first month I owned my TIG welder, I only welded aluminum. That is the main reason I bought the machine, and I was practicing quite a bit. Eventually I got curious about stainless steel, and switched the machine over to DC and tried some welds. I'll write more about welding stainless in another post, but the first thing that I noticed was that my welding hood flickered badly during the welds. Strangely, at low power arcs (10-20 amps), it was dark all of the time, but when I cranked it up to 150A, the lens would be become clear, and only ocassionally flicker into the dark mode. At the time, I didn't make the connection between using DC mode on the machine and the hood flickering. It had been a week since I last used the machine, and there seemed to be no reason why DC would cause the hood to fail. I also noticed that aiming the hood at a normal fluorescent light would cause it to darken. I thought the thing must be broken.

I took the hood apart and looked at its circuit board: 3 opamp ICs, 2 logic gate ICs, an oscillator, and two ICs that had their numbers scratched off. The board itself is multi-layered with an apparent ground plane on the bottom, so determining the wiring between chips is damn near impossible. I was expecting to find a soldering problem, dead battery, dead solar cell, etc, but all testable components were good. After connecting my oscilloscope and learning a little about how auto-darkening hoods work, I decided to return the thing. I figured one of those unmarked ICs might have fried. Harbor Freight gave me a new hood and tried to sell me a 2-year warranty. When I politely declined, the saleperson smirked and said "I'll sell you another one in 6 months." Gotta love Harbor Freight.

I really expected the new hood to work properly, but alas it flickered in exactly the same manner as the first hood. By this time, I had noticed that the hood worked flawlesly for AC welding, was darkened by fluorescent lights, and even was darkened by me waving my fingers in front of the sensor. It was NOT darkened by pointing it at the sun, or a DC welding arc. So, my conclusion was that the hood only responds to high-frequency changes in light -- not high-intensity changes. Apparently, the DC arc on my inverter welder is so stable, it does not have enough ripple to cause the hood to trigger. The solution: I set the machine to "pulse" at 200 Hz, with the background current %90 of the peak current. The current pulsing is so slight, that it doesn't really affect the weld, but it is enough to reliably trigger the hood.

Sunday, March 1, 2009

Reparing a worn-out pivot hole in steel

These pictures show how I repaired a clutch pedal with a worn-out pivot hole.

The hole is oval-shaped, which causes the whole clutch linkage to feel very sloppy. Eventually, the clutch would not fully disengage even with the pedal pushed to the floor.

The first step was to bore out the hole to .500" with an end mill.

I cut a piece of 1/2" steel rod to fit the depth of the clutch pedal plate, and brazed it into the hole. I used a grinding wheel to make the edges flush.

Now it is easy to drill a new hole that is the proper diameter

The repair is invisible under a new coat of paint.

The completed pedal assembly is ready to be replaced in the car.