Broken CSR Rear Upright - Any Experiences?

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aerobod
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Be careful in using heat on the upright, some aluminium alloys start to anneal at 340C, 6061 T6 will change mechanical properties when heated above 200C for any length of time (it is initially aged to T6 temper by heating at 205C for one hour) and will be annealed if heated to 400C.

James

MarkTheGoose
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5mm impact driver allen bit arrived this morning and one bolt came straight out. The other needed a quick tighten and then also came out. Didn't need heat, which was good.

Not sure if I can now get these two bits apart though ... Its a much bigger thread to be stuck together!

Looking at where it's cracked through, it's now apparent that one side had cracked through some time ago, as there's corrosion in the crack, so it's been surviving on just one side for a while

Mark, Orange CSR 200, Stack dash

Wrightpayne
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Good work.

I'd send a picture to Caterham after sales and see what they have to say - could have been a fault in the metal or it could be a design issue? 
 

That said they didn't take any notice of the dedion tube failures (of which there were many) or acknowledge there was a problem other than change the design of the tube (increase wall thickness and extra butress). 

MarkTheGoose
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I'm not a structural engineer, but the fact that the entire weight of the back end of the car, along with all the loads that it is subjected to with bumpy B roads, is supported by 2 pieces of metal 14mm x 4mm thick on each back corner, doesn't seem like it's massively over-engineered!

Mark, Orange CSR 200, Stack dash

Blue C7
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Would I be wrong in suggesting a careful cut either side down until close to the thread and then split the Ali from one side

MarkTheGoose
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You would not... although, current Plan A, is to put a pair of bolts through the slots and then a plate across those bolts, so that I can effectively attach a long bar to the bottom of the black bit. It's then going upside down in the bench vice, which will grip the flats on the bit that goes through the wishbone...

Suspect that I might be back in a bit to ask how to reattach a vice to a broken workbench!

Mark, Orange CSR 200, Stack dash

Blue C7
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Sounds like a good plan A

aerobod
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It looks to me like the failure was due to stress corrosion issues. If the boss area each side is 14x4mm, the total area taking the stress would be 224 square mm, which would have a yield strength of 6 tonnes for billet machined 6061 T6 aluminium (the most likely alloy used), which would be fine if the area is crack-free.

You can see two small cracks on the "good" side, which would be under severe bending stress due to the previous failure of the other side. Salt water corrosion mixed with stress could have caused the problems, always a problem in the aerospace industry.

I would say this is an area for annual inspection after cleaning away all surface corrosion and preferably spraying on a crack detection dye to reveal any cracks that corrosion could be penetrating into.

James

MarkTheGoose
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Gosh - 6 tonnes! Ok, agreed, with no cracks, that's plenty, especially as there's 4 of those 224mm2 areas in total. Assuming having the part made is not silly money (I'm waiting on answers on that currently), I'm going to replace both sides, just to be on the safe side and then agreed, it's something to keep a close eye during future servicing

Mark, Orange CSR 200, Stack dash

aerobod
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Each side of one boss is 56 square mm, so 224 in total.

It seems a straight forward piece to machine for a competent machine shop with a CNC machine. For a greater safety margin the boss could be increased in thickness. It shouldn't take a competent drafter more than 30 mins to measure and create a CAD file to be used in the CNC machine. Material should cost about £5 for the 6061 T6 billet stock and about 2 hours of labour for the drafting, setup and machining time for a pair of components. Hopefully less than about £150 for the pair.

Assuming you can carefully remove and reuse the four pressed-in steel bushes, otherwise a bit more cost if they need to be manufactured, too.

James