MIG Welding

[bmcecosse]

I'm going to need to revive my MIG machine. So planning on getting some spares in stock. I think I read somewhere that it's a good idea to use a slightly larger tip ie 1mm tip when using 0.8mm wire.... Can anyone comment on that ?? And if I want to try 'gasless' wire (never used it before) do I have to reverse the polarity of the machine???

[mogbob]

A larger tip is required for the thicker wire.Gasless operation normally just requires you to reverse the main power cables.
Machine disconnected !( For other readers, Roy ).Either check your instructions or download from Manufacturers website if lost.

The thicker wire will be in the larger groove, on the driving wheels, for wire feed.If the machine has been in hibernation for a while, disassembly and a light brush with a brass wire brush wouldn't do any harm.Check the torch liner operation in case it's got
a bit rusty with moisture during storage.
Generally give it a work out before welding in anger.
Bob

[kennatt]

allthougth you are supposed to reverse polarity with gassless,i've ,many times ,forgotten and to be honest haven't realy noticed any difference in the weld. I've also forgotten or couldn't be bothered to switch the drive wheel round for thicker wire,again havent seen any change in the wire feed,mind this was usually for just a quick tack or two ,for lengthy jobs would do it as a matter of course.The wider tip i'm told,is supposed to prevent the wire sticking at the tip,therefore preventing burn back,but I just use the 8.One thing you will notice with gassless is that it produces a fair bit of fumes from the shielding flux,and can make seeing the weld a bit difficult,but since it is normally used outside in windy conditions soon gets cleared by the wind,. But can be a nuisance if inside or in confined spaces.Other than that not much difference from gas.

[bmcecosse]

Thanks lads - I have used 0.6mm wire in the past - but the machine has terrible wire feed problems...perhaps due to the large /heavy drum of wire I stupidly bought So I am going to try thicker 0.8mm wire (on a small/light drum) and yes - since at least some of the work will be outdoors I'm going to order a roll of the 0.9 gasless - so I was thinking 1.0 mm tips would handle both sizes. Is there any great DISadvantage using a 1.0mm tip with 0.8 wire?? Additional question -is gasless wire ok for plug welds - and, what size of hole in the upper plate is normal for plug welding? I see 1/4" suggested in some places - seems a lot to me - I was thinking 3/16" ??

[katy]

Is there any great DISadvantage using a 1.0mm tip with 0.8 wire??

Yes, as the tip is where the power is fed to the wire, having too large a tip allows the wire to move around too much and not always make contact w/the tip causing an intermitent arc.

is gasless wire ok for plug welds

Yes, for normal autobody work IF the material being welded is not too thin.

what size of hole in the upper plate is normal for plug welding? I see 1/4" suggested in some places - seems a lot to me - I was thinking 3/16" ??

3/16" is adequate.

[MarkyB]

"adequate" suggests, not ideal, what would you suggest?

[bmcecosse]

Ohhh -thanks - hadn't considered the power transfer is through the tip contacting the wire. Maybe better get 0.8 and 1mm tips then. I'll be welding the main Xmember with plug welds down from above - through the main floor on to the nice thick new Xmember metal. I see special torch 'shields' available with a couple of longer prongs on the end - designed for plug welds - anyone know if these are worth having? This a job I have been 'dodging' for the last 10 years - but the time is NOW....

[mogbob]

The "prongs " are designed to give the optimum distance for spot mig welding ( Standard gas sheiled I guess ).
If you've done spot welding before, it's value is a matter of personal taste.On the other hand they don't cost a fortune.

Freehand.... catherine wheel swirls of weld, starting from the centre is just as effective.Practice on some scrap to get the hang of it and the correct penetration.

Bob

[kennatt]

yes I tried those pronged tips,found they were next to useless,best to just do as above , when I tried them you got a nice round spot weld but the majority had not penetrated through to the lower sheet,it just tended to fill up the drilled hole,I think those tips were designed for industrial migs where you can set it to spot weld,where the machine is timed and you get a blast of high power to burn through the centre then the power drops and switches off after a second or two and the weld is completed. A friend of mine had one (pro coachbuilder) he used to weld panels together with this machine didn;'t even need to drill holes,just put the two edges together pushed the prongs down to hold them,pulled the trigger and hey presto,perfect welds in no time.Mind the machine was about £2.000,so no good for your job BMC,worth more than the car

[bmcecosse]

Worth more than the car?? I hope not....... But yes I agree - what I read about the prongs was for 'spot' welds with no initial hole. Just wondered - with my somewhat shaky hand - if it would be worth a go. Thanks for all the tips - much appreciated. Roy

[moggiethouable]

There was a song for welding, hummed all over the shipyard, sung to the tune of "hey diddly dee an actors life for me"
and it went
"hey diddly dee,
A welders life for me.
A packet of rods a protective screen,
A pair of gloves to keep me clean.
Hey diddly dee, a welders life for me"
Be warned, once sung its an absolute earworm and refuses to leave you be,
And not quite as popular, was the Elvis favourite, "see you later by the shaper,in a while with a file".

[IslipMinor]

Roy,

Definitely use the same size tip as the wire you are feeding to get best electrical conductivity. Feeding problems are almost never the tip (rather like coils!), and often are the feed roller pressure (more is better than less) or the state of the liner. I have a SIP 130A and had wire feed problems that turned out to be a sticking pressure roller - cleaned up roller and spindle and all good again. The inside of the liner needs to be near perfect or it will create hesitancy in the wire feed.

The smaller the hole you have for plug welding the trickier it is the get proper penetration. You are trying to get at the cross-member material and join it to the floor, you don't want to risk just filling up the hole in the floor.

A rule commonly used is 5/16" or 8mm, plus the thickness of the top material. Too big in this case is much better than too small, as once you start it is difficult to open up the holes with the cross-member in place. You need to see clear evidence of the weld in the cross-member face the opposite side to where you are welding from (not just a heat circle) - a small physical disturbance looking from underneath the car is usually a confirmation of good penetration.

Also this is one to practice first, using the same gauge materials, if you haven't done so already?

Couple of other things:

Make sure that the x-mbr is clamped up tightly to the floor to avoid gaps between floor and x-mbr and what gas are you using? Argoshield will give much better welds than pure CO2, which can be very porous.

[MarkyB]

http://www.uktool.co.uk/WeldingProductD ... oductID=50
A days hire of a spot welder wouldn't break the bank.

[bmcecosse]

Thanks Richard, I have already modified the feed roller arrangement with an extra meccano bracket, and it seems to feed well enough.....except that I had large drum of wire which unwinds and then snatches.. Just arrived some small drums of wire, larger diameter, and larger tips to match. I have a cylinder of argon (sadly not argoshield) but beggars can't be choosers.... I will be testing it all before I start.

[irmscher]

Roy don't forget the fire extinguisher

[Alec]

Hello BMCE,

this link may be of use, http://www.mig-welding.co.uk/forum/show ... php?t=2398 and the site in general is very good; friendly advice on all aspects of welding. I think also the consensus is that gasless is not very good for bodywork, better to shield if welding out doors with gas.

Alec

[katy]

I had large drum of wire which unwinds and then snatches.

Sounds like it needs a little braking action on it.

[bmcecosse]

Thanks Alec... And yes -I have braced up the drive spindles as shown on some websites, and I did try a simple 'brake' on the drum. It feeds fine for a while - and then away it goes again. I can SEE the wire tip coming and going unevenly as I'm welding. Heavier wire on small drum has arrived - just need to set it all up and get some practice in..... Thanks to all for input - keep it coming!

[chickenjohn]

I'm going to need to revive my MIG machine. So planning on getting some spares in stock. I think I read somewhere that it's a good idea to use a slightly larger tip ie 1mm tip when using 0.8mm wire.... Can anyone comment on that ?? And if I want to try 'gasless' wire (never used it before) do I have to reverse the polarity of the machine???

Don't do either!

Use a 0.6mm tip, 0.6mm mig copper coated wire and use gas (CO2), gassless welding is a bit like trying to arc weld your car, too hot and very untidy. Unless very experienced, you are likely to blow holed in your car. Best to use normal wire and gas (CO2 or Argoshield).

[les]

I've made no comment so far on this matter, mainly because I've not tried welding without gas but will say, 'quality wise' I can't fault using a mig with gas. Rightly or wrongly I feel gasless is just a half measure with mig, in fact the g stands for gas. Arc welding springs to mind!