El-Cheapo TIG pedal

This is made entirely from scrap. Only costs are the potentiometer and the connector:


Here's a detail of the pot connection:



Basically, a cord is wrapped around the pot shaft. A hole is drilled through the shaft. You can just see the end of the return spring.

It seems to work well. I need to add a stop so I don't risk breaking the string. I do want to try and find dial cord. Don't know if anyone even makes it anymore

Still need to figure a switch for the contactor. May just include a circuit to sense the pot is not at 0 and run a relay.

The pot turns slowly when you release the pedal. Will probably need a tighter return spring. I was tempted to have the cord return to the upper pedal for a pull/pull setup. But then I have to deal with adjusting both ends.

The pedal is made from L-channel from some big shelves. Probably 2.5mm.

Total spent, about $5.

Brilliant! I love home made tools. I don't know what dial cord is but have you thought of stainless steel rope? Yachting places sell various thicknesses & grades, you can get a very thin flexible one (3mm is the smallest I've found). Yacht shops usually have the tools to put in stop ends/ eyelets whatever and have nice mini shackles. You'll never break that!

Remember the old radios with a tuning knob and a pointer that slid across a window (straight window with all the bands?) The dial cord ran all over in those things connecting the dial pointer, knob and tuning cap. Real strong stuff. I think it was waxed also.

Steel would probably break with the tight radius around the shaft. It is not the tension that breaks it, it is the tight bending/unbending.

Now the hard part: Getting the Airco to use a standard pot instead of the 150 watt, 15 ohm rheostat it wants.

shenion said:

Remember the old radios with a tuning knob and a pointer that slid across a window (straight window with all the bands?) The dial cord ran all over in those things connecting the dial pointer, knob and tuning cap. Real strong stuff. I think it was waxed also.

Steel would probably break with the tight radius around the shaft. It is not the tension that breaks it, it is the tight bending/unbending.

Now the hard part: Getting the Airco to use a standard pot instead of the 150 watt, 15 ohm rheostat it wants.

Click to expand...

Ah yes! I remember it well! I think they probably used lacing cord, it's very similar.

One thing I would do is to fit a supporting bearing to the end of the shaft, or maybe fit two bearings to the shaft with the cord between them and allow the pot to float slightly to remove mechanical stresses. Could you use a pot with a built-in switch?

I would like a pot with a switch, but all I can find is audio taper (log curve,) or they are real tiny. Also, not sure if the spring would pull hard enough to close the switch. A pull/pull setup would probably be needed.

I may put a bearing on the end of the shaft. Probably would be needed long term.

shenion said:

I would like a pot with a switch, but all I can find is audio taper (log curve,) or they are real tiny. Also, not sure if the spring would pull hard enough to close the switch. A pull/pull setup would probably be needed.

I may put a bearing on the end of the shaft. Probably would be needed long term.

Click to expand...

A microswitch should be easy to incorporate somewhere. Did you consider using a slider pot rather than rotary? Run the string round a pulley where the pot shaft is now and fasten the slider to the spring eye.

Yes, I have found sliders, but i would have to order them. With the $25 minimum order and shipping, not worth it.

I could have sworn i had a microswitch in my junk pile. Finally gave up. I will add voltage sensing to the welder on the remote input. Will make it easier when I modify the wire feeder to have a local current control (and possibly constant voltage control), less wires to run.

Might not be any help but I have a potentiometer at work that looks and works very much like a tape measure. The wire is on a reel inside and pulls back in on a spring. Can't be expensive as I found it at work! Though it didn't have a on-off at the start which would be useful.

Re dial cord:- I reckon rigging twine would be similar, almost unbreakable and very thin.. No idea how far from the sea you are Shenion, but any chandlers would have some.

I reckon you could adapt a crybaby guitar effects pedal if you come across a dead one cheap. They use a pot, diecast housing, and have a diecast metal rack, and a tiny pinion on the pot itself. In fact, I think I may have a old one with no internals...

what about fishing line? that comes in some very strong flavours.

Tried ebay? dial cord

Not cheap but if you really must have some...
Nice work on the pedal too.

I ordered some dial cord off ebay. Cost me $3 US for 25'.

Have everything working, until my driver board toasted itself. Need some higher voltage transistors, then should be good to go.

Tried the pedal and it worked. (after adding higher V transistor/MOSFET.)

I did a current sense to trigger the contactor. Did not work with the type of solid-state relay I used. So added a microswitch from an old PC mouse as a on/off switch on the pedal. Works good, but the switch is so tiny it is hard to adjust. Will pick up decent switch.

I knew the current would be different, but did not realize how much. The font panel is a big rheostat (15 ohm, 150watt). I designed a remote control with a standard 1/2 watt pot and an voltage follower. When switched to remote, the front panel sets the MAX current.

Turns out the internal control has large voltage drops across the rheostat. With my amp/pot I could get almost full power with the max setting at about 1/2.

Seems to work reliably. I did a few small welds and once reducing the max control was comfortable with the pedal.

I'm almost clueless on the currents involved in the control circuit except I know it has a 10 amp fuse (one of those ancient screw-in types) and 30V pulsed DC. So, used a big f-ing heat sink (MOSFET is rated at 40A). Gets a bit warm, but once I mount the control board inside the fan should keep it cool.

I built the pedal in an hour or so (steel cut/weld/drill). Probably another 1 hour working on the linkage, adding connector and making cables (has 40' cable.)

The real time was designing and testing the amplifier. That makes the machine have a modern remote control. Next, I can add a pot to the front of the MIG wire feeder. That will be nice and a few minute job.

You could always adapt a radio controlled remote controller, use the servos to turn the controls on the welder front panel. That would look cool, the knobs turning in respnse to the foot control !

MrFluffy said:

I reckon you could adapt a crybaby guitar effects pedal if you come across a dead one cheap. They use a pot, diecast housing, and have a diecast metal rack, and a tiny pinion on the pot itself. In fact, I think I may have a old one with no internals...

Click to expand...

You can buy the parts as a service kit for the complete Jim Dunlop range.

Tig pedal

Heh Shennion, I saw your Airco welder on your homepage, and it looks seriously like a Miller 330 a/p. I heard that it is suuposed to weigh close to 800 lbs! I just picked up an old Dialarc 250, and it has the same 15 ohm 150 watt rheostat with reactor circuitry your Airco has. I would like to build a foot control or fingertip control with a small wattage pot. Did you know that Miller sells a power transistor board for $50 that will allow you to use a smaller wattage pot? Id surely appreciate if you could send a schematic of your design, so I could turn my dialarc into Tig. thanks

Did some searching, the interface is a MIC-2.

Interesting, it looks like it uses pulse-width control to vary the output. I may try that.

Mine was basically an amplifier. So, it needed a big heatsink. It has burned up 3 times. Took me a while to figure out the HF signal bleeds back through the control transformer. On the 30V control signals, I was getting 180V AC. Have not tried the latest, should work better.

Here's the schematic: Airco Ctl Board. Note: Q2 is wrong, it needs to be at least a 60V MOSFET.

I will probably redesign it as PWM. I am also working on a constant voltage controller to run the MIG properly.

HF feeding back

I remember when I built my homebrew tig 2 years ago, I kept blowing out my DC bridge diodes, and couldnt figure out why. The HF was getting into the diodes and blowing them so, i reduced the gap to .007, adn put capacitors across from dc output to work, and so far I havent blown a diode.... at $30 a diode it was getting to be a pain!

Thanks for posting schematic!