Remember to check you're nuts and bolts!

[Jeffz]

2 spindles in a week and a half, actually. I think the fact that I had them powdercoated may be part of the problem. I think they cook the PC on at 400-500F. I believe this may weaken the aluminum to some extent. Both times I seemed to be putting a lot of pressure on the side that broke, as in going around a corner. The second time was a really hard hit which threw me off the sled.

 

[OVR4D]

You may have hit the nail on the head regarding powdercoating ... Aluminum is very susceptible to heat, so much so that you may have lost the the temper (hardness) of the material. This is especially true when welding aluminum ... Welders call the area weakened from the heat of welding the heat affected zone or HAZ, and if you want to restore the temper, the material has to be heat treated again.

EDIT:
Wanted to correct some misinformation posted above - See: Yahoo answer regarding powdercoating aluminum

 

[BombaPolaYama]

Interesting. Note to self - "do not powder coat aluminum"

 

[OVR4D]

Interesting. Note to self - "do not powder coat aluminum"

Edit: See the link I posted above.

 

[Cubby]

I "lost" the lower ball joint bolt on one of my spindles last year while doing 60 kph. Ski turned completely around and sled tipped on its side. Luckily no damage to the sled. This summer I replaced all the ball joint bolts and locktited everything. I check the bolts each time and ride and during the ride. Hate to have that happen doing 130 kph across a lake.

 

[Jeffz]

I'm a little worried about my suspension rails that I had PC'd at the same time as my spindles. They've taken some very hard hits this year with the low snow conditions,so i think they'll be alright.

 

[OVR4D]

I want to clear up some comments I made earlier about heating aluminum. While true, it appears that powdercoating does not weaken aluminum parts. What is more important, is how the part is prepped for paint. Most parts are sandblasted, which is not good. See the link I posted above.

 

[Jeffz]

I want to clear up some comments I made earlier about heating aluminum. While true, it appears that powdercoating does not weaken aluminum parts. What is more important, is how the part is prepped for paint. Most parts are sandblasted, which is not good. See the link I posted above.

The first answer specifically mentions 7075 series aluminum. I'm going to assume that the spindles are 6061. If you read the longer answer down the page, he advises against any heating of 6061, unless you are able to temper it at specific temps after PCing or you know what the temper is before hand. It was mentioned earlier in this thread that broken spindles are almost non-existent on these forums, and the only two broken ones are mine which were powdercoated. I know correlation doesn't equal causation, but I'll err on the side of caution. I will admit that I blasted my parts before coating, but used aluminum oxide instead of glass beads. Not sure if it makes any difference, but I thought i'd mention it. Another thing to consider about the Yahoo! post, is that he's talking about a thin-wall MTB frame, while we are dealing with much much thicker aluminum extrusions. If blasting does do any sort of work-hardening, it won't be any deeper than a .005-.010", which I think would be negligible on a part this size. I think in the future I still won't be PCing any structural aluminum pieces and will stick to good old paint. And soda or walnut chip blasting.

 

[OVR4D]

JeffZ - I agree with everything you posted, and you obviously have a better understanding of metallurgy than I do ... so if we agree that the spindles are probably 6061 (I'll guess T6 hardness) and substantial enough not to be work hardened by blasting, in what way do you think the heat of PCing affected them?

Correct me if I'm wrong, but my understanding is that heat anneals (softens) aluminum, and that if you want to restore the temper, the material has to be cooled rapidly immediately afterward (which would probably be impossible after PCing), and sometimes re-heated and cooled again, depending on the temper you're trying to achieve.

 

[Jeffz]

I'm not very familiar with heat treatment of aluminum. I first heard of aluminum becoming brittle from PCing was on TY I think. I machine and weld with it at work, and it does seem to have a different "feel" to it if it's been heated.
It would be interesting to have the breaks looked at closely by someone that might know why they failed.

 

[cannondale27]

I think it is just fatigue that occurs at a slower rate for us trail riders than the racers and from your posts you ride pretty hard.I remember Yamaha 177 bending quite a few and ending up heavily reinforcing them.But he never mentioned breaking them just bending so maybe you have a point with powdercoating being harmful. I also dont think Yamaha177's mods went all the way down to where yours broke.