Making Lobster Back Piping

[Proximity Motorsport]

Hey guys..

I have been using a top of the line Kempi MasterTig 3 phase welder at work over the last 2 years we had it, just doing odd little jobs on it, and I really enjoyed welding things, there is so much satisfaction in making something yourself. So recently I purchased a 200amp 240v ac/dc pulse tig off ebay, brand is ProWeld, and its got a reasonable amount of adjustment in it.

There is however, a very large difference in welding with a $800 chinese welder and a $6k+ Kemppi welder. There is a few things I need help on getting right. Now I haven't had any professional welding advice. Im a fitter and turner so its not in basic welding we do at tafe.

First off.. The most annoying thing is, with the Kemppi welder I found that fusing aluminium with pulse at around 1.8 frequency was really easy.. but my pro weld tig set on 0.5 frequency and its still going at about 10!!! :@ so that makes pulse reasonably useless for me. So I have been welding with no pulse at around 50amps welding 2mm thick pipe 60mm diameter. And correct me if I'm wrong but you can't buy aluminium bends off the shelf and they have to be pressed from sheet?

Well I'm building an r33 daily out of parts laying around the house and just making it a stocko pretty much, but it needed new cooler pipes so the most cost effective way for me was to buy a lengh of 6mx60mm pipe for $80 and make lobster back piping. And the welds arent that crash hot, and I'm not blaming the welder but more so my lack of experience. Although if I had a decent pulse I could turn the amps up a little and run over it and make it look good.

The thing that is stuffing up most of my welds is the filler rod melting before I dip it in the pool, or when removing from the pool, and I would assume thats from not having enough heat in the material, but if I go any hotter it melts through! Any ideas?

And the other thing is can you guys post up any pics of little jigs or anything you have made to help hold piping on the bench. I don't have anyone to help me so getting things to sit nicely on the bench its so hard, I have been using the earth clamp, grinding discs and files stacking them under everywhere trying to level it out.

And as for the pipe, I set my saw at around 7.5 degrees, and welded a flat piece of aluminium onto the end of the pipe, and sit level on it, then clamp and cut, then spin pipe 180 degrees and get level again and take another cut and so on and just weld on as many pieces as I need. Is this the best way?

Thanks guys, let the discussion begin

[scotty nm35]

I love lobster bends. Your welds look fine, more than strong enough.

I set the saw to around 6 degrees, seems to be the nicest angle without too much welding, Go for some thicker wall for best results.

The great part with lobster bends is being able to spiral the pipe around and vary the radius to suit the job. A machine vice is the best thing I have found to hold the work but its not easy.

Heres a gt35 dump for a 370kw Aristo I fabricated and also custom cooler piping for the Stagea.

[Craved]

haha i use 7 degrees for 2mm stainless so its in that area

as for the filler rod, are you angling the torch like steel/stainless welding? if so get it more towards perpendicular this should help with the wire melting too early.

[jiffo]

In the olden days it was 15 degree segments. (so there's your 7.5 degree cuts)

Do the end in a half segment though, so you get more bolt room if you're squaring up to a bolted flange.

[ISL33P]

the lower half of the first weld in the last pic seems to have the right amount of heat and filler rod.

this stuff is a lot easier with stainless, but even then i would prefer to use something a bit thinner like 1.6mm in either s/s or alu. The best thing about stainless is that you only need to fuse it and therefore no filler which you can learn your tig control at the same time and not have to worry about filler.....and yes, always pulse thin stuff, esepcially stainless.

I wish I had some pics of stainless piping I did for a customers gtr (see my thread for some bits 'n pieces) they turned out quite well for it being one of the few stainless jobs I have ever done.

[Proximity Motorsport]

Scotty, thats a pretty nice dump. I just wish I had my motor in my car so I could practice re-doing my own exhaust haha.

Chris you know as silly as it sounds, I didnt even think of that.. but its probably my problem. I do hold the torch on an angle, so I'll try standing it up a bit more.

CPC that alloy I was welding was 2mm wall, I'm pretty sure that was the thinnest the supplier had and the next size up was 6mm wall. I have some 1.6mm stainless 2.5" pipe ill try some practice lobster backs. Is there any sort of rule of thumb for size of filler rod to use? Such as amps to mm or electrode size to rod size. One pretty handy tip I've found on the net that might help out some beginners is approx 30 amps per mm for alloy.

Do any of you guys purge pipes with argon or any other gas to help reduce that slaggy crap under the weld, especially on stainless? I think I'll invest in a die grinder and do one weld at a time, then clean the inside of pipe with grinder, then next weld and so on.

Any other tips please post.

[ISL33P]

My aluminium supplier gets majority of his stuff in 1.6mm thickness.

For aluminium, basically, filler and tungsten size should be the same tickness of the material you are welding, give or take. As for stainless, you can always going a little smaller in those items compared to material thickness.

Best guide is to buy one of those millers welding charts which tell you exactly what you are after...they are a good start and if you are not within those parameters, you may be doing something wrong.

No real need to purge pipes if the welding procedure is right. Try to get the pipe joins as close to absolute perfect as possible and there will be no need for filler.

[scotty nm35]

I back purge all my stainless, the black eruptions on the back are a bitch to grind back so I feel its worth the gas so I don't have to.

I haven't used the pulse function much, perhaps I should play around with it. What would be a good setting?

[mr 32]

whats everyone using to cut there angles?

[Craved]

i use a small bandsaw Norm

[mr 32]

Chris did you modify it to keep the pipe set while cutting or just the standard guides/table tilt?

[scotty nm35]

I use a cheap S/H Brobo cold cut saw, it has paid itself off many times over. Perfect cuts every time.

[Craved]

on the one i used i went with the std guides but ran the degrees off an external angle finder.

cold saw would normally be better, but anything can be used if you spend the time to set it up- ie most cheap drop saws will work once you get them cutting square

[mr 32]

thanks guys

i think ill look at getting a bandsaw a little more versatile for what i need

now just to find one that can do 100mm

[Yeedogga]

Can I ask a dumb question...

What is the advantage of creating lobster back bends as opposed to using mandrel bends?

[ezy_09s]

Can I ask a dumb question...

What is the advantage of creating lobster back bends as opposed to using mandrel bends?

Its usually done to titanium as it does not like being drawn in a mandrel..it wrinkles .

Some people just like the look of the lobster back pipes ,when done in stainless..or you could get a tighter radius if you dont mind welding 300 pie cut segments together..

No advantage doing it over a regular mandrel bend unless it's titanium.

[ISL33P]

There is no real reason to do it with aluminium because there are plenty of options for tight radius stuff....so this is where it comes in for the stainless and titanium because they dont have the same options

[ARTZ]

Can I ask a dumb question...

What is the advantage of creating lobster back bends as opposed to using mandrel bends?

I priced getting a 1.5 metre length of 60mm aluminium mandrel bent in 3 places....i forget the exact number but it was well over 300$

[ISL33P]

sounds like you are ringing the wrong people. just buy individual bends and all you need is 2 welds. custom made mandrel bent pipes cost a fortune and very very few people would make use of them

jnt performance.com.au or 02 4257 1000

Edited October 19, 2010 by ISL33P

[samstain]

donuts are the other option... can buy them in halves, or as two halves already welded together. I think it cost me about $50 for enough to do my invertd FMIC setup - 360deg of 3" bends in total.