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Stitch/Spot welding questions

So, after looking at the SP 125 Plus welder wiring diagram and corresponding with folks here I have come up with most of the parts necessary to build my own timing option. Using a kit from Velleman (PMK 111) will provide the timing. It has two adjustments: Pause and Pulse. The kit comes with pots that allow for a .5 to 5 second Pulse and a .5 to 60 second Pause. The Pause time pot is a 10 megohm and the Pulse is a 50k ohm device. Since the Pause pot has so much more resistance it is very hard to finely adjust. I will be replacing it with a 50k pot. In fact, I am going to replace both pots because the ones in the kit are trimmer pots and I want the adjustment knobs on the front of the welder. Whenever the the timer is powered up it pulses first so I'm going to wire the timer power to the trigger switch. The timer power comes from a 12 volt 200 ma wall wart. By using a double pole/double throw switch the timer can be totally isolated from the welder even though the trigger in the handle will be the on switch for it. So the welder will have a switch on the front that can be set to either CONTINUOUS or STITCH. Manually stitch welding a few minutes ago I discovered that the Pause time should be independent of the Pulse time. What I can't tell easily is how long either should be and what would be the minimum and maximum times. The timer should be made such that it has enough range without having too much so that it is easiest to adjust. I think the Spot timer is for plug welding. By Plug welding I mean that one piece of metal has a hole in it. This piece of metal is clamped onto another piece of metal such that the hole is blocked at one end. Then the hole is filled by welding. I hope I'm using the correct nomenclature. Please feel free to correct me. Since the Velleman timer uses higher resistance to increase the Pause time, and since it resets every time the power is removed, a switch which disconnects the pause pot will allow it to weld for a set time and then turn off until the power is toggled. Anyway, here are the questions:

1) What is the minimum Pulse time. 2) What is the maximum Pulse time. 3) What is the minimum Pause time. 4) What is the minimum Pause time. 5) What exactly is the Spot timer meant to be used for when the timer is the one provided by Lincoln. I called Central Welding, where I buy most of my welding supplies, and they hadn't even heard of the Spot/Stitch timer kit for the SP125, or the SP135. So they couldn't tell me what the Spot setting was for. And Lincoln doesn't sell it anymore. There must be someone there who knows the answer but that someone wasn't at the Lynnwood store today.

If anybody wants me to I can post a parts list and wiring diagram when I'm done and it's working correctly.

Thanks for reading and responding, Eric R Snow

Reply to
Eric R Snow
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Another name for "plug" or "spot" welding is rosette welding.

Ya don't need any electronic stuff to do this, said the congenital EE. The timer in your trigger finger works just fine.

I've done a fair amount of both stitch and rosette welding with an SP125+. For body work (rust work, not competition-class restoration) I used a pneumatic punch 'n flange tool (50 bux HF) that flanges one part and punches the other so they assemble to present a flat surface. Stick the repair panel in place with kleeco's or sheetmetal screws, fill the holes with MIG weld. It only takes a couple of seconds. With a bit of practice you don't even need a mask: just aim the gun, shut your eyes and fill the hole. One hole per inch, takes about 5 minutes to stick in a rear fender skirt. Another two minutes with the angle grinder to grind the weld flat, then about a plum-sized gob of Bondo to fill the crease and it's ready for sanding and primer. It's only a 10-year repair, but rust work isn't often done with expectation of another decade of service.

Ya do need a mask to stitch, but the trigger finger works just fine to accomplish the timing. A key part of the art and skill of welding is in managing the puddle regardless of what process makes the puddle. Gadgets work well in automated setups, but they need to be set up right for a particular job. OK in production, but operator skill works better in one-off or to make just a few welds in a given sit -- and the same operator skill would be required to get the production setup working right.

Gadgets don't make good welds unless set up by a weldor, and weldors don't need gadgets to make a few good welds.

I make no pretence of being a journeyman-class weldor, I'm an EE and research puke by trade and training, but I weld well enough to do what I wanna do most days.

Reply to
Don Foreman

I hope you're not replacing a 10 megohm potentiometer with a

50K ohm one and no series resistance.

While extend> The Pause time pot is a 10 megohm and the

Reply to
Mike Berger

I am gonna replace the 10M with a 50K. I will have a trimmer pot is series though. The way the timer works is that with a 10M pot the max delay is 60 seconds plus. With a 50K it's about 5 seconds. ERS

Reply to
Eric R Snow

The only knowledge I have of stitch/spot mig, is from an aqaintence that had those features on a Sears (Century I think) welder. He thought the sticher was neat until his shield gas consumption hit the roof. Apparently the gas was on all the time instead of switching on/off during the welding cycle.

That could probablly fixed with another valve and relay.

Reply to
John Miller

That is probably the value of a stitch timer. Constant gas flow provides more cooling between welds. If just pulsing the trigger, you have to wait longer for the metal to cool a bit.

Reply to
Don Foreman

I wondered what I was going to do about that. The way the lincoln worked, as near as I can tell fgrom the wiring diagram, is that the gas pulsed with the wire. But it may have kept the gas on all the time. I might put in another valve that allows the gas to flow all the time but at a reduced rate when paused. ERS

Reply to
Eric R Snow

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