My Clarke 140E Mk II mig welder is being a bit iffy. sometimes when welding it will stop welding smoothly, the weld starts going "bang bang bang" instead, spatter goes everywhere, and I can feel the gun pushing back against my hand. this happens every now and again, for less than a second to several seconds. Comes and goes.

This isn't too much of a problem for tack welding but I'd like to get it sorted out before fully welding things. Tried changing the tip, didn't help. I'd guess it's some kind of electrical contact problem. The reel of wire that's in there has been in since before I bought it, I've used a fair bit now but possibly corrosion? tried a bit of wd40 on the reel, made no difference.

any suggestions before I try buying a new reel of wire?

Sounds like the liner needs replaced

Turn the wire speed down a bit. It usually cures the pushing you described. I had a 130 sip years ago with similar problem and it was the circuit board controlling the wire speed, replaced under warranty.

Any rust on the wire, or any other insulator like say WD40 will result in a lack of continuity between the contact tip and the wire or a high resistance. Clean rust free wire is a must dont forget that what ever is on the wire will end up in the weld pool and either cause gassing or contaminate the weld. Clealiness is very important the cleaner the better. Poor contact between the tip and the wir due to wesr in the tip is also not good. But as you have replaced the Tip the problem will only be helped by clean wire. Also try not to use C02 use an Argon mix this will help as C02 is "cold" and gives deeper penatration. If you have to grind post welding Argon mix is much nicer. All this is basic stuff but not widely published. The other thing that will have a huge affect is the duty cycle of the power source used if the machine has a low duty cycle the voltage / current will change a lot as the machine heats up during use. Some of the cheap majchines only have a 20% duty cycle! So you have to let it rest for 48 seconds in every minute to maintain good levels. They would have you believe that you can use the machine for 12 minutes in an hour but think about it! After 12 minutes continuious welding the machine needs a rest what wa it like after 10 minutes? Good luck.

A little trick I learnt is to cut a piece out of your tip and bend the very end over slightly. Gives the effect of continuous electrical contact during wire feed.

See attached scribble (if it works!)

Ta all. I don't think it's the wire speed as it acts up on high power, high speed and also low power, low speed (and any other combination). I might get someone (mackie) to watch the reel while I weld, see if it's going faster-slower.

As for the wd40 being a bad idea - bother. I might try spooling off a couple of layers of wire off the reel, see if the stuff underneath is better before I spring for a new reel.

A thought (just the one...) - have you tried playing with the feed roller tension?

Your symptoms sound like what you get when your feed rate is too low (to my limited knowledge, I hasten to add!) -> "bang, bang, spit, pop, splatter". If the wire in the rollers decided to slip a bit then you would get low speed issues. Are the rollers clean and dry? Have you tested the tension lately?

If this sounds like a load of old cobblers, then feel free to ignore me!

David

This problem is usually down to the weld circuit being intermittantly broken - usual cause is poor/dirty earth connection or dirty/oily weld surface or wire.
Cleanliness and good conduct is essential.

On this note - one other known cause is using large magnets to hold your work pieces - they are great but can effect the welding wire feed.

We do use magnets, but pretty sure the symptoms have shown up when nowhere near them. certainly not with the gun lead trailing past one.

I will check the tension, I did set it up initially but haven't fiddled for a while.

I think the earth should be good, but I might go over the clamp with some coarse sandpaper.

Blueshift, U2U answered