Got a small one and need bigger.

[irondarren]

Got a small one have you, need a larger one to get that extra penetration. Well it isnt true. All these welds were done using 80amps on a 2.5mm 6013 BOC everyday rod, on 8mm plate. normally the pro's would run a nice 4mm rod and get 6mm fillet. So what happends if you have got a cheap and cheerful welder that only runs at 80amps.

its relatively simple, you start by doing a root run (tight into the corner), then you do a second run, half on the root weld and half on the flat of the bar, then another run against the root but this time on the vertical side of the bar. you keep repeating until you get the desired size fillet.

The last pic shows the end result with around an 8mm fillet built up in layers. Although the photo isnt that clear, it is one solid weld. it was cut through the middle of the weld there are no visable layers or joins (xray might tell a different story ).

Its a slow method of doing it, but if your stuck with a smaller machine it works, perfectly well.

 

[Paul.]

Yes, multi run stringers, a common technique, its one of the reasons we get students to weld a pad when learning, so that runs can be overlapped without inclusions, if the cut through sample is polished and macro etched you'll see the inter run fusion, and the depth of root penetration of the first run.

 

[irondarren]

yep the art i guess for the learn is to not get slag inclusions in the weld. (something i admit to getting occasionally normally at the beggining of the weld,)

 

[andypocock]

Here's the cross section with a bit more light on the subject

 

[scarecrow]

I would use the same method for 10mm plate but would use 3.2 Root and 4mm fillet until I get the desired size weld same technique and like everything you build from the ground up. A few old bail handlers the I used to have had just to single vertical plate for the arms Dz were about 10 or 12 millimetres plate 3 inches wide manufacturers only put one big weld in their and they tended to break off after a few years I have never broken one after a layer weld as far as I'm concerned they are stronger than the big single weld

 

[matt1978]

Got a small one have you, need a larger one to get that extra penetration. Well it isnt true.

Mind if I show that to my mrs mate? I have been telling her that for ages

 

[scarecrow]

Mind if I show that to my mrs mate? I have been telling her that for ages

 

[Sid]

How does a multi pass compare to a single run equivalent in terms of heat distortion or built in stresses in the final part?

 

[irondarren]

if your doing multi runs quickly, like i did the example. 3 inches of weld, camera shot, slag chipped, camera shot, and start the next run. Then yes it does get much hotter than with a single run or root run and then a larger rod over the top. Its a much slower process because of the multiple runs.
For my part it was a fun 10 minute exercise, to show some of the novice members of the forum, that even if you have gone out an bought a cheap and cheerful arc welder with a low output, you can weld thicker material, than you perhaps thought. The same apllies for Tig and Mig. when im in the mood i might do a similar thing using Mig and Tig for novice forum members

 

[snowcat]

How does a multi pass compare to a single run equivalent in terms of heat distortion or built in stresses in the final part?

Stringers are generally less inclined to crack and distort less than a root and fill, much of what I weld is either recommended or WPS to be welded with stringers, theres something called inter pass temps, which is the maximum temperature the work should be before laying in the next bead, strength wise and I'm hugely generalizing here as theres never a one fit all solution, a set of stringers is stronger

 

[Sid]

So it's not just the number of runs, but the temperatures and manner they are layed down. Interesting info, thanks.

 

[Drains]

Hey Sid. Weaves, or very hot welds, are more likely to contract and crack - Weaves because you have a shallow, wide area of hot, expended metal which as it cools, has to shrink. A stringer bead is rounder so shrinks less in terms of width, as it's also doing height too.

An overheated weld area has lots of shrinkage to do in all directions; it also will develop a greater HAZ (heat affected zone), which will have a brittle, hard crystalline structure, liable to cracking.

 

[Archie]

Talking of weaving I've a couple of questions. I was having a play earlier and after running a couple of fillets without weaving I went back and went over them again with a bit of a weave. The first time I ran over I did as I would have with the MIG, moving forward in a semi-circular motion pushing the pool forward from the 10 and 2 o'clock positions (I've never really thought about how I do it before so I hope that description makes sense) which worked a treat. Second time round the pool didn't reach across the whole of the fillet so I moved in an 'S'. The question is, is this a bad idea. Afterwards I assumed it was as I would have been moving the pool back over already cooling slag so probably leading to loads of inclusions. Am I on the right lines? Would I have been better off with the above technique? I'm assuming so. Second thing, when welding a fillet, apart from weaving the tip of the rod from one side of the join to the other, should I also move the electrode holder so that the rod is closer to perpendicular to the side the tip is aimed at? Christ. That makes even less sense! Sorry!!!

 

[Drains]

First, archie - you should be pulling from 10/2, not pushing (if i'm interpreting your description correctly). If the pool doesn't reach across the fillet, don't worry, just weave and move slow. The weld will penetrate through the slag if you're doing it right. Use any weave you like, that works.
I've got you with the electrode holder. Don't bother moving it if you don't have to, although it can be a useful skill to be able to move your hand whilst keepiing the tip of the rod in the same place.
Re weaving - reccomended width is no more than 2.5x the width of the rod (so 6.25mm for a 2.5mm rod) Doesn't quite apply to a cap though.

 

[Archie]

Doh! I have been pulling not pushing. I'm getting me MIG and stick confused. For a small weave it's easy to keep nice straight edges to the weld but if I get ambitious and go for a larger one I end up with a regular wavy edge. TBH, I was playing around really but it got me thinking. I was using a 3mm rod but I was probably attempting a weave of 15mm so sounds like I was over-stretching myself!

That's a relief to hear on the holder side of things! I can see why that would be a good skill but it sounds like it requires mega hand-eye coordination!!!

 

[irondarren]

archie when i do a root weld i never weave, i just drag the rod tight in the corner, if i go over the top with say a 4mm rod i really dont weave that much either, just enough to get a 6mm fillet.

 

[Archie]

I didn't weave the on the first run but thought I'd give it a go. Really I was playing, welding bits of 80x80x3 together just to get a feel for things. The smaller weave felt quite natural as I did it in the same way as I would with the MIG (though pulling as Si's already reminded me!). I have got some 4mm rods but they're ancient and damp and last time I tried them they simply meltedi nto a big blob on the plate. I'll get some more in the new year and have a play.

 

[irondarren]

archie if the 4mm rods are damp put them in the oven at 150 degs for about 1/2 that should sort them.