Like a banana

[Bonzo]

Originally Posted by fabbyglass

There is a knack to welding light gauge tubing so it doesn't twist but it takes years to master, I'm 45 and been faffing about welding stuff together since I left school.

Clamping doesn't work and cutting to dead on sizes cause problems as does cutting angles spot on....just because you cut two pieces of tube at 45 degrees doesn't mean you will end up with spotty dog 90 degree once welded.

By eck Mark, that's the most sense you have made for ages, are you having a sensible day

Only kidding mate, some darn fine comments there

The importance of a propper weld gap can never be under estimated in the war against distortion & knowing how any given joint being welded is likely to pull, is all part of a welders skill

It does happen, being sensible I mean but very rare as I find it very disturbing

[ayjay]

Well you learn something every day on here!!

There's me worrying because my angles and joints in the chassis tube are less than perfect to put it mildly - in fact a bit gappy. But in the end it may have done me a favour

Back on subject any thoughts please on my earlier post re packing up brackets to adjust wishbone positions.

Thanks

Adrian

[Wynand]

Originally Posted by ayjay

I've been reading too many of those posts that warn against distortion as the welds cool -- having nightmares ,waking up screaming!

Even when steel is tack welded to a solid steel base will have some distortion when cut loose, light steel moreso.
Here is what happens to steel when welded, regardless of type of welding such as Mig, Tig, stick etc.
Weld metal is deposited at a high temperature, above the melting point of material. For steel, this is around 2,500°F (1,370°C). As the weld cools to room temperature, it shrinks, but is restrained from doing so by the adjacent cold base metal, resulting in high-residual tensile stress. The weld is now like a stretched rubber band, with the workpiece holding the ends. This is the reason that the base metal moves, or springs back, when the clamps holding the workpiece are removed, distorting the part.

The only way to control this to minimize distortion is to keep welds as small as possible (read cool) and stagger welds to prevent heat buildup.
Also important not to weld on one side only as this will pull the frame into a banana shape. Take a piece of off cut plate, tube, angle iron etc and run a few welds on the same side and see what happens

[holdenchris]

hello all, been a fabricator for too many years now my advice is spend as much time getting fit and gap right,smaller gap,smaller weld,less distortion
hope this helps chris

[CTWV50]

So it's not just me then!

[jerkins]

If you hold down the back of my chassis the front is about 3 - 5 mm off the ground. I worried a bit, then someone suggested that I check the straightness of a production car...
...I felt a lot better after doing that!

I wouldn't worry about a bit of up-and-down bending from front to back, but I would be concerned if there was a significant twist, or if it was bent to one side.

[robo]

Thats why a lot of people have opted for yellow bodywork. Landrovers chassis can be 20mm twisted from the factory and thats apparently ok!

[baz-r]

Originally Posted by Wynand

Even when steel is tack welded to a solid steel base will have some distortion when cut loose, light steel moreso.
Here is what happens to steel when welded, regardless of type of welding such as Mig, Tig, stick etc.
Weld metal is deposited at a high temperature, above the melting point of material. For steel, this is around 2,500°F (1,370°C). As the weld cools to room temperature, it shrinks, but is restrained from doing so by the adjacent cold base metal, resulting in high-residual tensile stress. The weld is now like a stretched rubber band, with the workpiece holding the ends. This is the reason that the base metal moves, or springs back, when the clamps holding the workpiece are removed, distorting the part.

The only way to control this to minimize distortion is to keep welds as small as possible (read cool) and stagger welds to prevent heat buildup.
Also important not to weld on one side only as this will pull the frame into a banana shape. Take a piece of off cut plate, tube, angle iron etc and run a few welds on the same side and see what happens

there are other ways but none i can think are practical for home build on a roadster
like preheating, postheating in an oven to the point of destress
there is all sorts of stress and tension in the complex frame of the chassis when its fully welded. you try and cut a tube out and you will soon find out
if you had a problem area in your build of your chassis where the welded joint was problematic if you had a oxy/gas torch it could be heated

[MarkB]

Bananas and custard is quite nice but awkward to drive as your feet slip of the bits of banana and if you get custard in your eyes then well it's game over really. maybe safer to have a yoghurt and use a spoon