Quick MIG Question

[poohbear]

Hi all,

I'm just about to buy a new cross-member (from these guys: http://blacksheepoffroad.co.uk/Site/Home.html) for the 110 and am wondering if my MIG set-up is up to the job.

The Crossmember itslef is in 6mm plate with the extensions supplied in kit form in 4mm. I've been doing some test pieces in the garage and with the wleder on it's max settting have successfully 'glued' 6mm to 2mm in various configurations using a couple of beads where necessary. Having cut the welds up they look to have made good penetration into the 6mm, so I'm pretty sure I can manage the 4mm to the chassis but I'm worried that my Migmate 130 wont manage the 4mm to 6mm needed at the other end. Is it acceptable to join the thicker pieces using multiple passes or should I be looking at getting hold of a more powerfull machine?

My other quesiton is can I maximise the output of my current machine at all - for example at the moment the welder is running off a standard 13A socket in the garage and then via an extension lead, which I'm guessing can only be 0.75mm cable at best. If I use a 2.5mm extension would that make any differnce to what the welder can put out at the tip?

Any enlightend views welcome.

Dave.

[Boris113]

I'm not sure about the capacity of your welder but this may be of use to you. Having just bought a welder I was looking into wiring a 32amp supply in my garage. http://forums.lr4x4.com/index.php?showtopic=75865

The MIG Welding Forum also contains some very useful advice.

Harry

[poohbear]

_{Hi Harry,}

_{Thanks for the reply - My set has a nominal max current of 130A, though I'd be surprised if it will actually achieve this in the real world. I am electrically proficient, unfortunately I don't have the time or funds to be re-wiring the garage at present, so I guess the real question is can I make a decent weld between 4mm & 6mm plate with 130A?}

_{If it's just a question of optimising the supply to the set or using a different technique then I'll give it a go, otherwise I need to arrnage access to a bigger welder!}

_Dave.

[Cliff Pountney]

Dave,

A 130A DIY mig set should be up to the job provided you prepare the joint properly. You'll need to V out any butt joints and weld external corners 'open', You may struggle a little with internal corners, What you will find is that the duty cycle of your set will only allow you to weld for a short period then the performance will drop off. At that stage stop and give it half an hour to recover.

Multiple passes are perfectly acceptable provided you get good penetration and don't include any carp into the joint. They just take longer and may give you more distortion.

What are you doing that requires a 6mm thick cross member? I've built some Land Rovers which have been used for 'team recovery', which is absolutely mental in terms of loading the crossmember (20' snatches on kinetic ropes), but we only ever used 100 x 50 x 3mm box with a bit of extra reinforcing here and there.

Cliff

[simonr]

Turn the power to max, the gas to the absolute minimum - you should JUST be able to hear the hiss as it comes out the torch in a quiet room, and turn the wire feed down to the minimum that will give you a decent weld.

The Wire and Gas cool down the weld, so if you are short on power, turn both down, move the torch more slowly so it deposits the same amount of wire into a given area. Conversely, if you want less heat, for example welding upside down, turn up the gas & wire and move the torch quicker.

130A is plenty for what you are trying to do. Don't worry about the mains wiring, it will only make a trivial difference to the output power.

If you want to increase the duty cycle, fit a fan in the welder casing to blow air on the Transformer.

I rarely turn my welder above 120A at which it gives the nicest weld. Then just adjust the wire feed a bit for the job.

Si

[fozsug]

If you use a 2.5 mm extension cable that too will help as well as the advice above.

[poohbear]

Thanks guys - speedy response, with great advice!

Cliff - I wouldn't have chosen 6mm but I wanted to stay clear of the cheap chinese parten parts and 6mm is what the guy makes them in and at a good price (delivered). At least it will take a while to rot out! Though if 3mm is perfectly adequate I might build my own - anybody got a pattern/dwg for a rear cross member with extensions?

Simon - Thanks for the tips, I'd already adjusted the power/wire speed but wasn't sure how little gas I could get away with without adversely affecting the weld. The welder is already fan cooled, but I appreciate it wont have the same duty cycle as a pro machine. NB.Good work on the pedal box by the way - already on the Christmas list!

foszug - I wasn't sure whether the welder could be 'throttled' by lack of supply or whether the limits were more down to the machine and it's internals. the mains lead on the welder certainly isn't 2.5mm

Dave.

[steve b]

I'd second using a good size ext lead , and also make it just long enough , having 30m coiled onto a drum will not help as I understand it .

Using 0.6mm wire will help with maximising the weld pool . Multiple runs or a series of short duration spot/puddle type welds will work fine

cheers

Steveb

[Hybrid_From_Hell]

Hmmmmm

Being the "Negative pessimist and bearer of Joy" I would actually urge a tad of caution ?

Rear Cross member is a Key part of the chassi, when your up to it in deep mud and a KERR is being used just how confient are you

of your welder / welding skills ?. If in ANY doubt, why not tack it all up and then someone who is known good with good kit to give it the full monty ?

Post up some of you 2mm to 6mm that will give a clue as to if OK or erm "Non"

Just not worth the risk, also there is a vast difference between nobbing up some new steel easily got at vs some nasty rusty pooh, at horrible angles and

positions etc ...

Sorry but sort of needs to be flagged ? If you were more local I would buzz it for you if all tacked up.....

Nige

[longlandy]

120amp is not good especially as the duty cycle will drop off quickly down to maybe 70amps. Remove all scale from the steel as with small migs this can cause cold lap.

Again with a small mig dont do vertical down as again this can result in cold lap.

Cap lap can be a problem on even heavy duty welder ,thats why critical parts are still speced as tig or arc only.

[poohbear]

Hi Nige -

you are obviously absolutely correct, hence why I am seeking advice before planning how to complete the project. If I don't think I can do the job properly then it will have to be done by some one that can.

But seeing as my bluff hs been well and truly called here are some work pieces I've knocked up tonight:

the little blob on the right is the original tack - the rest was done in two runs.

An below is a cut through the middle of the bead on the long side:

these wer both done in 'ideal' conditions - i.e. a warm garage in a comfortable position and using nearly new metal. I am well aware that in the field things are very different. I am hoping that i can tack up all the heavy gauge stuff on the truck and then bring it inside to weld up properly, just leaving the 4mm to chassis seams to be done on the truck.

All comments, good and/or bad, gratefully received.

Dave.

[Bowie69]

Looks good enough to me

[landroversforever]

Dave I can't see it on the photo, but has the weld melted right to the corner?

[simonr]

You can zoom in on the photo by pressing [Ctrl] + [+] on your keyboard. [Ctrl] + [-] to zoom out. At the max zoom - it still looks pretty good!

They reckon (though I've not tested it) that a Land Rover with a Kerr rope can develop 300,000N (30 Ton) of force. The bolts holding your tow ball on, will break somewhere between 16 & 32 Ton depending on the angle of the pull - and there is this rule of thumb that 1" of weld will support 1 Ton - though that does include a bit of a safety factor for sub standard welding etc.

On that basis, so long as you can get 30" of weld holding the corss member in place, and your welding is reasonable, something else will likely fail before your weld. The chassis rails are about 4.5" x 3" so 15" circumference, 30" between the two chassis rails (coincidence?). The upshot is you need to make sure you get a good quality weld all the way round the chassis.

Si

[landroversforever]

Still blurry so you can't see the edge though Si.

[Gazzar]

You can zoom in on the photo by pressing [Ctrl] + [+] on your keyboard. [Ctrl] + [-] to zoom out. At the max zoom - it still looks pretty good!

They reckon (though I've not tested it) that a Land Rover with a Kerr rope can develop 300,000N (30 Ton) of force. The bolts holding your tow ball on, will break somewhere between 16 & 32 Ton depending on the angle of the pull - and there is this rule of thumb that 1" of weld will support 1 Ton - though that does include a bit of a safety factor for sub standard welding etc.

On that basis, so long as you can get 30" of weld holding the corss member in place, and your welding is reasonable, something else will likely fail before your weld. The chassis rails are about 4.5" x 3" so 15" circumference, 30" between the two chassis rails (coincidence?). The upshot is you need to make sure you get a good quality weld all the way round the chassis.

Si

Last time I did a 110 crossmember I puddle welded where the extensions overlapped the chassis rail. I drilled some larger holes about 1 inch back from the weld seam, and filled them rossette style. It adds to the amount of weld, but also makes the repair more distributed, spreading the force and stress.

The guy used the 110 on some winch challenge thing, tree stumps and picking the worst trail, and the like, and it never shifted. Lots of recovery and other fancy stuff was applied to the poor 110, no panel survived the event intact, but the chassis took it.

[CwazyWabbit]

......and there is this rule of thumb that 1" of weld will support 1 Ton - though that does include a bit of a safety factor for sub standard welding etc.

......

I've heard that rule of thumb before however surely this would differ considerably depending on the type of weld and welding rod?

[poohbear]

Thanks for the repsonses - didn't mean to start a debate!

I've had a play trying to lap two 6mm bars together which has shown that my technique needs some refining - mainly torch angle and bead pattern I think, though it may be the limitations of the welder. I'm not at home at the moment but will post the results tonight.

In summary:

1. I'm confident that using both lap and puddle joints the 4mm to chassis will be no problem.
   
2. I'm also confident that I can join the 4mm plates as required, hopefully mostly off the vehicle but there will be some faffing around the tub mountings.
   
3. The 4mm to 6mm at the crossmember will be the tricky bit, with my set-up:
   

• lots of short runs with plenty of time between for the welder to recover
  
• Multiple passes as required
  
• Welding bottom to top on vertical seams
  
• high current, low wire speed and little gas
  

Sound reasonable?

Dave.

[Gazzar]

Nought wrong with good, rancour free, debate, without entrenched views.

Oh, and remember to get some waxoil/similar onto the whole area as soon as possible, including the inside bits.

G.

[Cliff Pountney]

Good design is just as important as good welding, maybe better put as bad design or bad welding can cause failure.

Try and think about how the forces are being generated and moved from one part of the structure to another. I don't know what your cross member looks like or what you are doing with it but if I were adding a simple box member to the back of a chassis for extreme recovery I would consider-

Adding diagonal bars from near the recovery point to somewhere on the chassis rails up by the bump stops.

Adding a horzontal triangular plate on top of the box to chassis rail joint. You can put one on the bottom but it's a crud trap.

Plating the full height of the box at the recovery point.

That said I still wouldn't make it out of 6mm !

Good luck. That welding looks fine to me.

My old Unimog had a spring built ino the rear hitch to try and absorb the shock loading. Wouldn't help with a KERR but is probably usefull when towing with a bar or if some pyscho uses a chain.

Cliff

[simonr]

I've heard that rule of thumb before however surely this would differ considerably depending on the type of weld and welding rod?

I think that's why it's a rule of thumb, not something you would use if you were building skyscrapers! However, it is something I tested - in fact the first thing I tested when I bought a 25 ton Avery Load cell. I tested 2 pieces of 6mm plate prepped and butt welded together with MIG and Argoshield Universal. I found that (roughly, because it's difficult to measure) 8mm length of weld with good penetration was enough to hold 1 ton - but only just. 1" thus gives up to 3x margin so the absolute minimum for what you could consider 'safe'. Thus, I consider it a useful rule of thumb!

Si

P.S. I agree with Cliff!

[Daan]

My crossmember is 2mm box section folded up from sheet, reinforced where it matters ( a v from the towhitch point back to the chassis). It is a bit pointless to weld 6mm box onto a 2mm chassis in my humble opinion. I have done ridiculous offroading, kerr snatch recoverys you name it.

Daan

[poohbear]

Not planning any 'crazy' recoveries - it's a daily driver not an off road toy, just need to repair a rotten rear end and this seems the best quality vs. cost option. I don't have the time/resources to source the materials and build one myself, let alone a big enough or well equipped workspace. As it is I have to move the vegetables in the garage when I want to use the bench!

The actual construction can be seen here:

http://www.ebay.co.u...=item20c4d23578

Dave.

[CwazyWabbit]

Looks good value and should defeat the tin worm on thickness alone.... even without bothering to paint it!

[CwazyWabbit]

I think that's why it's a rule of thumb, not something you would use if you were building skyscrapers! However, it is something I tested - in fact the first thing I tested when I bought a 25 ton Avery Load cell. I tested 2 pieces of 6mm plate prepped and butt welded together with MIG and Argoshield Universal. I found that (roughly, because it's difficult to measure) 8mm length of weld with good penetration was enough to hold 1 ton - but only just. 1" thus gives up to 3x margin so the absolute minimum for what you could consider 'safe'. Thus, I consider it a useful rule of thumb!

Si

P.S. I agree with Cliff!

Would be an interesting test if you ever get bored to repeat but without welding. ie just narrow a bit of 6mm plate to 8mm in the middle and see how much it takes to break it. I could probably spend all day breaking things if I had a 25 ton load cell