Problem in rear shaft manufacture

[ketan]

We are most probably gonna take rear axle assembly from GKN but there is a slight problem...actually the shaft lengths are not accd. to our requirements so we need to cut it short and then weld it.

But i m not sure if its a good idea.Also let me know if any other team has done anything of this sort.
Ketan salhotra
FSAE-IITD
Drivetrain 2

[ketan]

We are most probably gonna take rear axle assembly from GKN but there is a slight problem...actually the shaft lengths are not accd. to our requirements so we need to cut it short and then weld it.

But i m not sure if its a good idea.Also let me know if any other team has done anything of this sort.
Ketan salhotra
FSAE-IITD
Drivetrain 2

[The Bunker]

Disassemble your GKN assembly and make a new center shaft, spline it and heat treat it. I'm not sure how well a welded shaft will hold up, But if thats your only option.....test it well before comp.

[John Valerio]

i am continually amazed at the ridiculous amounts of money alot teams shell out for custom made drive shafts because they don't want to make them in house. if you have a high temp oven available to you theres no reason to outsource. the only problems we have ever had with in house drive shafts is failure in the HAZ due to improper welding, which is a mistake you learn from quickly. it really doesn't take much to do some research into alloys, heat treatment, filler rods, and top it off with some hand calcs for torsional shear and safety factor and you're good to go.

i wouldn't suggest chopping and re-welding the GKNs without re-heat treating them. guaranteed failure in the heat affected zone.

[Chris Allbee]

I'll refer you to Caroll Smith's comment on people who do their own heat treating on critical components....

[billywight]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I'll refer you to Caroll Smith's comment on people who do their own heat treating on critical components.... </div></BLOCKQUOTE>

That's a pretty ignorant comment (by Carrol Smith). If you have the proper equiptment and the time to research and do it correctly, why not? Why didn't Carol have a comment about people machining critical components themselves? It takes time and research to learn how to fabricate things properly (good surface finish, knowledge of proper manufacturing techniques, etc.) Maybe we should all pay someone else to do the heat treatment and learn nothing about it ourselves. OK, begin bashing me because I called the great Caroll Smith's comment ignorant...

[Ehsan]

I think a number of Carrol Smith's comments about things like this are more a warning to those who don't know what they are doing. And its true. if you don't understand heat treating, then putting your welded part in your wife's oven and pretending its heat treated will cause you some trouble.

On the other hand, a properly trained mechanical engineer with correct tools and necessary experience should be able to build pretty much any part of a car with accuracy and adequate strength. Now what constitutes "properly trained", "correct tools", and " necessary experience" are a matter of trial and error and estimation.

[John Valerio]

i agree ehsan, somehow i don't think carroll smith had formula sae competitors in mind when he wrote that section.

[Chris Allbee]

You are retarded if you cut and weld on axles and then think that heat treating it will make it OK. Your drive axles are the most highly stressed part on your car outside of the engine, so why on earth would you risk having them fail during competition. How certain are you that the weld was perfect? How certain are you that your oven can control (maintain, ramp, etc.) the temperature as precisely as needed? And the higher hardness you aim to get on your axles the more precise you need to be to keep the damn thing from being too brittle (that doesn't end well). And even if you are one of the teams that gets your car done early enough for testing, just because it made it through 10 hours of track time doesn't mean its not going to hit that wonderful fatigue limit at competition. In a part like this crack initiation and failure are often separated by mere seconds, so a crack check before the race won't necessarily mean it will last. I'm all for learning through trial and error and please feel free to experiment with heat treating, but why make your first "oops" such a critical component. Its just not smart.

[Marlin]

I have a question about welding axles: I am building an A-mod car with a 140hp sled engine. I was planning to shorten miata axles by welding a sleeve over the cut and not heat treating. Are automotive axles heat treated? Am I asking for trouble?
Thanks

[Wes Johnson]

A few months ago an axle shaft on our '01 car snapped due to a poor design, just took about 5 years worth of beating on to finally do it in..

Not really worrying about keeping the car running, we welded the shaft back together right at the crack! Needless to say it broke after a nice bit of brake hop. Certainly this was an improper way to do it, but I still think re-welding axles can be pretty sketchy.

Perhaps with the proper calculations you could increase the amount of material in the axle to compensate, but you will be giving up a lot in weight.

Marlin, the reason our axle snapped was due to a collar welded on the outside of the axle to act as a stop. Think about the stress concentration right where you weld the collar to the axle.

-Wes

[FryGuy]

I agree with chris on this one. It seems way too risky on such a critical component. But if you are feeling brave, knock yourself out.

[John Valerio]

chris, thanks for the retarded comment. really brings professionalism to this discussion. making driveshafts is not a mystery. you need the right shaft materials, a good oven, a good welder, a rockwell hardness tester, and some TTT curves. we have all of those, so we can build our own driveshafts for the cost of a few feet of steel tubing. enjoy spending whatever ridiculous amount you do on them.

[Chris Allbee]

steel tubing? how thin are your shafts?

"the only problems we have ever had with in house drive shafts is failure in the HAZ due to improper welding" -John Valerio (expert in drive shaft failure)

Again, I think its retarded to be making those learning mistakes on such a critical component when those mistakes are more than likely to happen during competition, especially if its your first time doing this process. Why would you risk your team's success and all their hard work because you wanted to save the problem of finding a couple sponsors or shelling out a few hundred dollars. I hope the look of disappointment on your teammate's faces haunts you for the rest of your life as you remember your lesson. Months of hard work, endless hours, the money, all the time smoozing the sponsors, the trip to competition...and your drive shaft fails after the first driver change. You end up in 80th place (again). Was it worth it to experiment with heat treating on such a critical part?

[Sooner_Electrical]

I am Going to have to side with chris on this one. Drive shafts are important. Seems like the investment of a few Dollars, might be worth it. Perhaps the Heat Treating and Weld-o-palooza could be used on a shifter lever or something.

[SNasello]

As far as i know, our 80th place finish last year was due to a problem completely unrelated to drive shafts. Y
es driveshafts are an important part of the drivetrain, but i do believe that this is an engineering competition and not a go out and buy stuff to bolt on to a car competition. Making a driveshaft, testing it, and having it fail is one way of learning. That being said, doing some research on how driveshafts are made, and making them properly, (which shouldnt be beyond the capabilities of most teams) is what i would call a better way of learning. And if you are not comfortable consulting only textbooks, im sure your school has a number of materials professors who could help you out and point you in the right direction.

Chris, there are better ways of contributing to a conversation than saying the crap you are about other teams. This forum is here for people to learn, not for peoples opinions to get shot down.

[JHarshbarger]

We've used quite a bit of shortened drive shafts on our two formula cars that we've built so far. Our first 2 sets failed, but we haven't had problems since. The first set failed at endurance in Detroit in 2005. Those were just cut, sleeved, and welded. They broke because of stress concentrations at the weld. The second set gave the sleeve a curved end to spread out the welds over a larger area. We also heat treated these afterwards. The heat treating made the shafts brittle and that set broke after about 10 minutes of driving. The last set we did the same, except for the heat treating. We haven't had problems with that set after running the car quite a bit.

That being said, we are getting custom drive shafts this year. Saves weight, the headache, and the risk.

[Chris Allbee]

There is more to engineering than running equations and learning by trial and error, blah, blah, blah. There is also risk management and another side that some universities have to look at which is pleasing the university and sponsors. Its hard to get funding for a project or sponsors if you never finish the race. Our team has been in such precarious positions in the not too distant past. Making a few concessions in the direction of stability in reliability at the price of being able to experiment with one aspect of the car can have pay-offs not even directly related to that part.

Again, that being such an important part of the vehicle and long fatigue life and welds not having such a happy relationship with each other on reversed rotating equipment, advising a team (who by their questions sounds to be a newer team) to try and make their own when by your own guy's admission will most likely end in failure for a first attempt is just mean. For many first year teams their continued existence could be dependent on their success at competition. Why risk all of that on wanting to experiment with heat treating just for the sake of experimenting with heat treating. Do that on a less critical part, like a battery bracket. Feel free to spec out the part to your heart's content, then try to find a sponsor to do the work for you or maybe even a nearby team that has made all the mistakes already and knows how to do it. I'm not saying it can't be done. I'm saying that its a damned high risk for a first year team when they could better spend their energy developing parts of the car that will make them faster, not making sure they won't finish endurance by experimenting on axles. Buy a set of axles or have them made and once you get back from competition feel free to experiment, but don't jeopardize your success at competition for want of simple curiosity. Their may be more at stake and you not even be aware of it.

Structural equations, fatigue numbers, heat treatments, etc. are only a part of engineering. Engineering is about solving problems and implementing solutions. Sometimes those problems are not just limited to metal bits and pieces.

[John Valerio]

i really dont think you know much about this competition if you attribute our final result placement to one component of our car. i bet you feel proud that you beat us, but most teams did last year so don't feel too special.
and by the way, when we started making shafts the way we currently do we had a couple choices of filler rod, we chose one, it failed in the HAZ, we remade them with the other rod, and then they outlived the car. all you got to do was watch your bank account drain some and then tighten some bolts.
and with much less manpower than you have (see i can look stuff up too), we earn the luxury of being able to test and find problems like the one i mentioned because we have our car built before the snow is off the ground, partially thanks to our ability to do most things in house. so which is the better route is up to each team. but hey, the more people that buy drive shafts and other parts like that the better we look, so spend away good buddy!

[John Valerio]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Allbee:
Again, that being such an important part of the vehicle and long fatigue life and welds not having such a happy relationship with each other on reversed rotating equipment, advising a team (who by their questions sounds to be a newer team) to try and make their own when by your own guy's admission will most likely end in failure for a first attempt is just mean. For many first year teams their continued existence could be dependent on their success at competition. Why risk all of that on wanting to experiment with heat treating just for the sake of experimenting with heat treating. Do that on a less critical part, like a battery bracket. Feel free to spec out the part to your heart's content, then try to find a sponsor to do the work for you or maybe even a nearby team that has made all the mistakes already and knows how to do it. I'm not saying it can't be done. I'm saying that its a damned high risk for a first year team when they could better spend their energy developing parts of the car that will make them faster, not making sure they won't finish endurance by experimenting on axles. Buy a set of axles or have them made and once you get back from competition feel free to experiment, but don't jeopardize your success at competition for want of simple curiosity. Their may be more at stake and you not even be aware of it.
</div></BLOCKQUOTE>

you posted while i was writing my previous post, so allow me to comment.

first, we've been around this competition since 93.
second, what kind of series do you think this is where with doing better at competition comes amazing rewards and endless sponsorship? sponsors know what they are getting for their money in any series, they're not stupid or naive. for example, our baja guys won overall last year (total points over 3 comps) and they actually lost sponsorship from last year to this year from a company who just didnt feel like supporting them again. simple as that. think about what do sponsors get if you do well. not necessarily more exposure and advertising, except to other students who will just end up calling them up and asking for money or parts. the real exposure and advertising comes from doing local events, shows, autocrosses, all things unrelated to competition.
third, you keep referring to heat treating as "experimenting". it's not an experiment, its a published and verified process. those materials classes can come in handy sometimes, you know.
and just so we're clear i am definately NOT talking about just chopping and rewelding stock driveshafts with collars or inserts. i agree that's haggard.

[Chris Allbee]

After some gentle reminders from an associate of mine I tried to redirect the conversation back to the original point, sorry for the previous slight, but i still think it was irresponsible to advise a new team to fail. And if you think that making everything yourself makes you look better in the judges eyes...I highly doubt it. They are looking for engineering solutions...that involves using your resources to your advantage. If that works out that you make your own axles then fine. As previously stated I don't doubt that it will work once you have figured out the process. But that doesn't make your vehicle better than the next one. Its about how all those parts work together. I think a new team would be better served by figuring out that bit of the puzzle before fiddling with individual parts.

[Chris Allbee]

wow...i was not referring to "heat treating" as "experimenting", but a team experimenting with heat treating. A HUGE difference. Huge difference. Yes, not that winning equals more sponsors yadda yadda, but i know that with our own univerisity and surrounding sponsors that more often than not a good record won't hurt you and may even help you. Welding and heat treating axles together is not a "simple" process and the understanding of the mechanisms invlovled is quite complicated. Kudos to you and your team if you have that in the bag. How long did it take to learn? Does this new team have that time or that luxury? You started off by scoffing at other teams and looking down your nose from atop your high horse at others for purchasing axle components. A sweeping generalization based entirely on your ignorance of those teams' decision making process. There is more than one way to do this right, and that way will be different for each team. I still stand in my belief that it would be irresponsible for a new team to risk failure on a part that doesn't need to fail. Get a reliable car built based mainly from off the shelf components and overbuilt parts and get it running early, test, tune, learn about vehicle dynamics and engine tuning which will earn you better lap times than dropping the pounds will. once you have a good understanding of that then look at individual parts. The judges can't fault you for good engineering, but they can fault you for slapping things on your car for not knowing why it was done that way (and no John, that wasn't directed at you, don't get your feelings hurt.)

[KU_Racing]

I am all with John on this one, for two reasons.
First, our 03 car broke a driveshaft. The shaft was fixed by welding in a patch sleeve cut at a 45 degree angle on both ends. SIDENOTE: if you are welding onto a driveshaft, DO NOT make welds at perpendicular angles. Look up some scenarious in your static book if need be, but a bevel cut sleeve is much stronger and relies much less on weld quality. (ok, this is me stepping off the soapbox). That driveshaft lasted through probably 40 hours of testing, (much longer than competition) all of this on a car that was well above 500 lbs without a driver.

Second, heat treating is not a black art. It is not an experiment. It is a valid, well researched engineering process, probably up there with the most researched and analysed manufacturing processes of any kind. And it isnt like some company is doing all the work and witholding their proprietary research. For reference, I looked in our school library for books on or related to heat treating. There are over 120, 80 of which were published later than 2000. This is a library at a school of less than 1500. I cant imagine how many books of that kind would be at a library like that one (or ones) at OU or Michigan or Texas or for that matter, any school that the real world has actually heard of.

[John Valerio]

one final word then i'm done arguing. you pointed out that im "looking down my nose", and perhaps you're right, i should have rephrased what i was saying. i am, however, still amazed at the lack of respect you are demostrating here. throwing our overall placing in our face? saying we sound like a first year team? i don't care who you are, don't ever think that i or anyone else who really cares about their team won't take personal offence when you insult their or my team, even in the slightest way.
this has gone on way too long.
see you at mpg.

[Sooner_Electrical]

So I am surprised that people are still talking about this. I don't quite see the point, I am sure we can all agree should someone have a good oven, good welder, and magical rod type mentioned before, ability to tell time and adjust temperatures, and a gung-ho attitude; drive shafts can be made reliable in house. Why they need to be done in house when they are only $136 is the question. You save no weight, you save roughly 80$ a side in money but spend umpteen house making (testing) and remaking the part. There are a lot of other parts on the car to make better and can save a lot more money (like make your own steering wheel and quick disconnect save you tons). Sounds to me that a team with a few resources as you have claiming would be better suited buying a drive shaft and then doing a good redesign on the part that kept you from finishing endurance. Perhaps a little less time testing and making a part that is bought by roughly 90% of the top teams is a good idea. And since heat treating is such a well documented and researched discipline I don't think the judges will be too impressed that you should read a book.

- Edit -

I think chris said that that the team that asked the original question sounded like a new team, not your team. And i would like to add if you are welding back together an axel that broke on a old car (as in KU Racing's) it is a great idea because who wants to waste money on the 05 car when you have a shiny new one.

[KU_Racing]

saving tons on your wheel and quick disconnect??

we spent less than 150 combined... less than 1 axle.. what the hell wheel and disconnect are you using???

[Sooner_Electrical]

We use the SPA and the Alpha Steering wheel which together usally are not seen for less than $365 alot of money to be saved there :-). We have found this to be a good set-up for compliance reduction.

[Nitesh]

ketan, you seem from India, probably the RV team. you can get the shafts machined, like we did. You can get them splined and mated to CV joints available locally, which probably you'll find suitable for your rear hubs

[major_ashwa]

i suggest go ahead with gkn driveshafts and cut it to required length .you can weld them and make special splined adapters for mating which needs to be induction hardened.

[Parker]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> SIDENOTE: if you are welding onto a driveshaft, DO NOT make welds at perpendicular angles. Look up some scenarious in your static book if need be, but a bevel cut sleeve is much stronger and relies much less on weld quality. </div></BLOCKQUOTE>

I would say, that if you ARE going to weld your driveshafts anyways, listen to this advice. If you can, I would even weld the shafts at angles as well.