i was going to buy the wishbones for my haynes roadster but as im skint i thought i would make my own. i sourced the steel and plates and have them all but one front upper made up and tacked waiting to fully weld. then the nerves set in ie is my welding up to it so tonight i welded some spare cds tube to a bush tube and tried to break it. i had to put a bar through the bush tube and put the bar under my tool box and then put a long piece of tube over the cds tube to get enough leverage and the tube snapped just above the weld. is this what i should be looking for in the welds

cheers Davie



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Well the welds certainly didn't break

Looks OK. Just make sure you don't get too much undercut at the edge of the welds.

quote:

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Originally posted by owelly
Looks OK. Just make sure you don't get too much undercut at the edge of the welds.

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Undercut is kind of where he heat of the weld burns into the parent metal and weakens the area just after the weld.

There is probs a more techy explanation somewhere but that is the jist of it.

Welds not failing is great - but weakening the surrounding area is not.

if you welded two bits of flat steel together, under cut would be at the edge of the weld where the parent metal appears to have a little bit missing and is slightly thiner than it should be.

eg (poor asci art)

---_/---_-----

The --- is the parent bit of metal, the /-- is the blob of weld. the under cut is the little bit either side of the weld in the parent metal.

cheers guys

i think the reason it snapped where it did was because i tried to bend by forcing the cds tube on its own but it just started to bendin the middle so i put a long bar over it right down to the weld and then levered it so all the force was at the weld (if that makes sense)


Davie

For reference.



Daniel

Your welding is a lot better than mine.
I'm still practising on garden gates and fish tank stands etc. Take it your using a mig? From what little I know about welding though there might be something to this undercutting thing. I'd be slightly alarmed that they both broke so close to the weld. When I tried this on one inch box section I knackered my arm in and managed to break the joint in a similar way to yours with four feet of box section to lever on.
I bought my wishbones and will get a mate who is a coded welder to put my brackets on and do the not so important bits myself. Tbh i think my welds would be strong enough, they just look like pigeon pooh. Anyone got a cheapish mig welder for sale?

Your welds look good, reason it snapped there is cos it has heated up past red heat and then cooled down rapidly making the crystals in the metal small and brittle. Try playing a small pre-lit propane torch over the weld immediately after finishing it to make it cool down more slowly (I’d let it take about 30 sec’s), this will cause larger crystals to form and therefore it will be more ductile and less prone to snap like that, infact if you do it properly it won’t snap at all but just bend. Never quench any welds as they will shatter in use.

Ive been doing a bit of testing myself.
It was 1mm shorter than the other 3

I bent it over with a bar then stood and smaked it with the hammer for 10 mins.

I got bored and its still in one bit so it must be ok

Cut through the weld with a hacksaw and inspect the penetration . Should give you some idea how good the weld is.

naaah - on my city and guilds course we had to hack saw along the weld till we'd taken about (eek, can't remember if it was 30, 50 or 60%) out.

You then used the hammer and looked what happened.

If it broke and left the parent metal nice and clean .... you've got no penetration. If on the other hand the parent metal was rough with little bits on the weld - you've got a good weld.