Any tips for TIG Welding Fish mouth joints?

nickp500 · Nov 18, 2011

Hi there,
My current college project is making an off road buggy.
Currently welding up the chassis and was wondering if anyone had any usefull tips.
Im using a decent TIG wlder and the material is 32mm O/D with quite a thick wall (2-3mm) Done a few tacks and running at about 110Amps (seems ok).
All of the joints are 90 deg fishmouths and a couple of 45 deg ones.
I haven't got allot of experience with tig, done allot of mig, mma and oxygen/acytelene.
Cheers, Nick

german8rcoupe · Nov 18, 2011

On the steeper angles access can be an issue. Sometimes it helps to pull the tungsten out a bit further. Also, I always drill a small hole(1/8") in the tube being covered by the other tube so that hot air can escape and not mess up the last bit of weld.

hotrodder · Nov 18, 2011

Doing a 'dry run' can be helpful in that it's better to find out what other tubes etc will get in your way (catch the end of the filler wire, knock your mask etc) or block your view before striking up.

If you're not already then knock back the 2 feathered edges of the fishmouths. Am probably reading to much into it but from "Done a few tacks and running at about 110Amps (seems ok)" i'm thinking knocking up a couple of test joints would be a good idea if you haven't already- set 'em up to weld in position and then cut 'em open to check for LOF (lack of fusion) etc

tommy dunlop · Nov 22, 2011

tig

hi, watch the whole lot dont move when you weld it

PhillipM · Nov 22, 2011

tommy dunlop said:
hi, watch the whole lot dont move when you weld it

This, tack the entire thing in well and spread you welds and heat evenly around the chassis, they can and will move otherwise, keep moving around, even if it means not finishing a full fish-mouth in one.

An assistant with a diagram to mark off the welds is handy so you don't miss one though.

nickp500 · Nov 22, 2011

Cheers guys,
Went ok managed to keep distortion down to a minimum

NTwoO · Nov 24, 2011

With a 3mm side wall, what does that bit weigh? If you get yourself a chair, it is easier to get your flight height nice and tight. Try and support as much as possible including your fore arms if possible.

PhillipM · Nov 24, 2011

Seems a bit of a strange design, small, thick wall tubes and no triangulation across the floor at all?

nickp500 · Nov 25, 2011

Have now welded on a roll over bar and tubing going from the rollover bar to the front bumper and to the back.
All seems very strong and ridgid.
I can pick the whole thing up myself so its not that heavy.
Aiming for it to be lighter than the 250 donor bike (135kg).
Its based on the haynes manuall "build a buggy for under £100".
Nick

PhillipM · Nov 25, 2011

One more thing Haynes has to answer for then

Wedg1e · Nov 26, 2011

nickp500 said:
Its based on the haynes manuall "build a buggy for under £100".
Nick

Must be getting more difficult with the price of steel lately :rolleyes:

PhillipM · Nov 26, 2011

Not kidding, I've just spent that on a bit of tube just for front suspension

tommy dunlop · Nov 27, 2011

project

looks like you are doing a nice job there,are you going to powder coat it,keep the picture comming,tom

nickp500 · Nov 27, 2011

Yep we are going to powder coat it.
Were only spending about £10 for 3m lengths steel.
We have got allot of stuff for free inc wheel, tyres, engine seat etc because its a college project and my local scrappy wants some PR and his place in the paper haha.
But yes, the prices and other things are very out dated!

PhillipM · Nov 27, 2011

Well, whilst I'm not trying to knock your work - the tube fit ups and welds look fine - the actual design of the frame from the Haynes book is terrible tbh.

nickp500 · Nov 27, 2011

I would agree!

Woody.v8 · Nov 27, 2011

As long as you brace and triangulate the down bars from the roll hoop it will be pretty stiff as a chassis

JWB · Feb 4, 2012

NTwoO said:
With a 3mm side wall, what does that bit weigh? If you get yourself a chair, it is easier to get your flight height nice and tight. Try and support as much as possible including your fore arms if possible.

Agree, I like to support my wrists and often take quite a bit of effort rigging up supports with blocks of wood on the bench or blocks clamped to the work.

tommy dunlop · Feb 5, 2012

project buggy

hi hows the project coming on,any more pictures please,tom

nickp500 · Feb 5, 2012

tommy dunlop said:
hi hows the project coming on,any more pictures please,tom

Heres the thread, http://www.mig-welding.co.uk/forum/showthread.php?t=30258
Steering is almost done apart from the track rods, just need to thread them for the rose joints.
Nick

Any tips for TIG Welding Fish mouth joints?

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