MIG welding machine - copper-and-iron - consistency in time

Hello all
I'm thinking about calibrating welding conditions - MIG machine settings to the V, I and wire feed speed in which we think about
WPS's and welding conditions.
My instinct is that traditional solid heavy transformer MIG machine should be very consistent doing over time when doing an identical weld.
Reason for asking is - my gut feeling is it is very wrong to insist that small welding companies buy expensive electronic "inverter" machines so that they have meters and settable controls for V and I.
A traditional "copper-and-iron" MIG-welding machine with clicks for volts - typically two knobs - eg. 4 course settings and 6 fine trim settings - and a "pot" (potentiometer) controlling wire feed speed:
How constant are these machines in time if you are making the same weld (steel, thickness, welding wire, gas, etc, etc, way you weld, ...) at the same settings?
eg. if I went back to a 10mm h-v T-fillet on "2-3/9" a year after previously recording my V, I and wire feed speed, would my new V, I and wire feed speed be identically the same, give or take a random few percent of "random error"? Is there any tendency to "systematic error" - a drift in conditions - with copper-and-iron machines?
My instinct says these machines do not change in time unless they blatantly go wrong such as is obvious (where a complex power-electronic machine could "drift" in time and do unexpected things). I'd have thought Voltage has no systematic "drift" in time at all, as the "click settings" physically are discrete taps on the machine's transformer... Whereas I would have thought the wire feed speed could "drift" a bit in time, as the potentiometer would tend drift in its Ohmic resistance in time. But not by much - it's a simple robust device... So that's neglible and covered by an annual "calibration check"
??????
Thanks in advance
Rich S
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On Wednesday, November 12, 2014 11:42:28 AM UTC-5, Richard Smith wrote:

I would think it would be very easy to add a little voltmeter like this one on Ebay. 400705508624
It would probably take some simple filtering to have it readable while weld ing and it might be necessary to keep big spikes from damaging the voltmete r.
You could also put a voltmeter on the power to the wire feed. My instinct is that with the same voltage going to the wire feed motor, changes in the wire feed motor and gearing would make this a less accurate measurement. B ut it would still be useful information.
Maybe you could calibrate the wire feed speed to motor voltage using an opt ical tach on the wire drive to see if the wire feed changes during the yea r. Just changing the pinch tension on the wire feed might change the speed of the wire.
Dan
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On Wednesday, November 12, 2014 9:36:41 PM UTC-5, snipped-for-privacy@krl.org wrote:

ne on Ebay. 400705508624

lding and it might be necessary to keep big spikes from damaging the voltme ter.

t is that with the same voltage going to the wire feed motor, changes in th e wire feed motor and gearing would make this a less accurate measurement. But it would still be useful information.

ptical tach on the wire drive to see if the wire feed changes during the y ear. Just changing the pinch tension on the wire feed might change the spee d of the wire.

I agree with Dan on this. We were asked to make an automatic wire feed for a welder several years back. We found that we had to insert an encoder betw een the spool and the pinch roller to get repeatable readings. Tension and slippage were pretty big variables.
As far as V&I, I would expect that if the line voltage was repeatable, so w ould those settings.
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Hi again folk. Thanks for these inputs. Voltmeter is very very easy to add - no modification to machine beyond bridge Voltmeter between wire feed power pickup and Earth (???) Ammeter would be easy if cut into the Return lead, given "conservation of current" law means that's as good a place as any - no need to unhook and insert anything inside machine (???) Tacho - not worth it - easy to hold torch trigger for 12 seconds and multiply length fed by 5 (or 6 seconds and by 10, or whatever) ??? Have I got these right?
BTW - independent clamp-meter / tongues-tester been bril. for diagnosing welding conditions in a FabCo. Been good to know the Amps and Volts and match them to the welding conditions - helped with diagnosis as trying to improve welding conditions
PS "repeatable" - in spray transfer found had to adjust wire feed speed every few minutes when using transformer MIG welding machine. To keep the spray-cone just right... Line voltage varying? Machine "drifting". Effect of changing temperature? Never knew answer to that. Seemed to follow same general pattern through day of up-and-down on wire feed speed (maybe!)
Rich
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