Like a banana

[ayjay]

I am welding (sticking lumps of hot metal to) my chassis and watching it curl up as it cools . My rolling chassis only goes round in circles you need arms like a gorilla to wrench the steering wheel to hold it in a straight line:eek:

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

It didn't really end up like that or at least not as bad anyway. I got a slight curve ( I can see light between the bottom rails and the table top) but its good enough for me --I studied at the Bodgit & Rush Academy of Precision Engineering.:o

But wow isn't it great to stand back and look at it and say " I did that !" So if,like me, you feel a little less than confident, take heart , It will be all right on the night! (probably)

[minicountryman1961]

It didn't really end up like that or at least not as bad anyway. I got a slight curve ( I can see light between the bottom rails and the table top) but its good enough for me)

I choose to believe my build table has sagged.

[ayjay]

My thoughts exactly ( near enough is good enough!);)
Cheers

Adrian

[vetteman1355]

Ever look at a flat bed trailer when it's empty ? sit you ass in it and it will be straight !!!!

Nigel:D

[HandyAndy]

But wow isn't it great to stand back and look at it and say " I did that !" So if,like me, you feel a little less than confident, take heart , It will be all right on the night! (probably)

Yes indeed, that feeling is a very special moment :cool:

Just wait for when your car is finished & someone asks you where did you buy it from? & you can reply..." I didn,t buy it, I MADE it" :cool:

keep up the great work you are doing & keep the build photos coming, we all like photos :)

cheers
andy

[flyerncle]

Its the nature of the beast,it like's to twist.

Mine was fully welded tied to a car jig and still moved.:rolleyes:

[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.

[Talonmotorsport]

The chassis needs to be curved so you can run lower ground clearance but still get over speed humps! :D

[fabbyglass]

The chassis needs to be curved so you can run lower ground clearance but still get over speed humps! :D


Now that made I laugh...about right too.:D

The other thing is there seems to be enough tarmac to make speed bumps but none to fill the pot holes.....odd that!!!:mad:

[ayjay]

Thanks peeple for the positive comments:)

I'll post some pics soon when the swishbones are mounted . At present r/h rear is slightly toe in ,the other side is slightly toe out--guaranteed to go round in circles :o

What's the best way to adjust the mounting brackets? I'm thinking of shimming with bits of thin plate --is this approach the best way?

cheers

Adrian

[Bonzo]

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 :eek: :D

Only kidding mate, some darn fine comments there :cool:

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 ;)

[fabbyglass]

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

[ayjay]

Well you learn something every day on here!!:o

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:D

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

Thanks

Adrian

[Wynand]

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

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! :D

[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]

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 :eek:
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:confused:

[CTWV50]

So I've decided like many that if I tacked the whole frame together I'd end up with a badly distorted frame when it came to fully welding it, with my limited welding skills, experience, potential for the table sagging under the weight and build space, I've decided to get the basic bottom rail frame fully welded and work out the distortion in it before continuing any further, I've learnt a lot doing this and now have an appreciation of weld procedure and heat management.

One thing I have found is that if you do get distortion that needs sorting, a good method is grind back the weld on the high side of the frame put a small V groove over the old weld and reweld. The heat generated doing this pulls the frame back in to shape and I now how a frame sitting pretty much level with minimal distortion. I'm a bit of a perfectionist and struggle to leave things if they aren't right but I'm happy with it.

A few more welds and a bit of tidying up and I should be ready to continue!:)

[jerkins]

I think that managing distortion is a major skill in the craft of welding!

I was a total novice when I started. I was told by more experienced folk to tack everything up, check straightness and symmetry, then alternate my welds across the car. In other words, weld a joint on one side, then do the matching joint on the other side. This isn't a hard and fast rule - if I was welding up a T-joint in square tube I would do one side of the upright, then do its opposite side, so that it ended up at 90 degrees (ish), THEN I'd go to the other side of the car.

Basically though, don't go up one side and back down the other! :)

[CTWV50]

Basically though, don't go up one side and back down the other! :)

Can you imagine! Ahaha!