Tripod Housings

[Marc Martel]

We have been using CV-joints in the past but I want to switch to tripods this year. We are looking into buying tripod housings from Taylor-Race but they are too expensive for our budget. Besides, the housing seem to be really simple to machine but I want to know how you do it in case I'm missing something important. Is a reamer good enough for the three inside diameters surrounding the tripod rollers or should I use another technique to get the close tolerances and perfect surface finish?

Marc Martel
McGill Racing Team

[Marc Martel]

We have been using CV-joints in the past but I want to switch to tripods this year. We are looking into buying tripod housings from Taylor-Race but they are too expensive for our budget. Besides, the housing seem to be really simple to machine but I want to know how you do it in case I'm missing something important. Is a reamer good enough for the three inside diameters surrounding the tripod rollers or should I use another technique to get the close tolerances and perfect surface finish?

Marc Martel
McGill Racing Team

[Travis Garrison]

I wouldn't recomend using a reamer...as the bores aren't continious it wouldn't be a very fun job....you would probably want to bore them for the best results.

When I made our tripods, I actually just milled them, gives a nice fillet at the bottom of the bore, not to mention its just plain easy. The surface finish was pretty good, hopefully more than good enough. The reason for my gamble was that taylor actually specifies quite a loose fit (they were nice enough to send me engineering drawings) Of course this is assuming you have access to good CNC equipment

If I do have to remake ours I'll bore them this time around....and if I were going to do them manually I would DEFINETLY bore them...no reamer (I think a reamer would wander on you, pull towards the opening in the bore)

boring bar might actually wander too much as well now that I think of it...interupted cut and all...I guess I would do a few test peices with open sides on their bores, see what works with your equipment

Travis Garrison
WWU FSAE

[Marc Martel]

Could you send me the drawings Taylor sent you, I've been bothering them for a long time but they don't want to give me more detailed drawings then those on there web site. Send them to:
darmak21@msn.com

Marc
McGill Racing Team

[Mechanicaldan]

Travis,

Did you buy the Taylor tripods? Did you buy axles also, or make your axles?

Would you mind sending the information to me also? happydan @ iastate . edu

Thanks,

[clausen]

regarding boring or reaming the interupted cut,

Can't you drill and bore (or ream) the three holes first, and after they are finished, then machine the big clearance hole in the middle? That way the three important holes can be finished as full diameters.

Regards

Paul Clausen
Uni of Adelaide

[Travis Garrison]

Marc, I'll see what I can do about the drawings when I get back up to school...

Daniniowa, We bought the tripods, and made our own axles, like everything else we do most of our motivation was to save money...

Clausen, yup, you're right. I guess I wasn't thinking two clearly on that last post....if I was going to do it manually I would definetly be boring it, I'm not a fan of reams (gotta buy just the right one which is expensive)

We did ours in the mill becuase we were pretty sure we could get the surface finish to the "good enough" range alot faster with an endmill...


Travis Garrison
WWU FSAE

[Travis Garrison]

One other thing before I take off for a while, if you're going to bore you might want to start looking into some way to put a fillet on the bottom of your bores, unless you are doing through holes in which case it doesn't matter...

Just thought I would mention it since getting a boring bar with any kind of a radius might be a challenge, not to mention expensive...

Travis Garrison
WWU FSAE

[markocosic]

Digging up an old thread here!

I'm planning on using Taylor's shafts and tripods on an FSAE vehicle, but would like to use non-standard housings.

Taylor Bits (http://www.taylor-race.com/pdf/ACFC3D.pdf)


On the outboard side, this is the kind of thing I would like to emulate - a relatively large diameter combined "live spindle/tripod housing."

http://www.cosic.org.uk/misc/tripod%20housing%201.JPG
http://www.cosic.org.uk/misc/tripod%20housing%202.JPG

Manufacturing this:

1) Billet
Take a 125mm/5" billet and machine a piece in much the same style as Brookes. Ideal, but would have to be farmed-out.

2) Taylor&plate
Take a Taylor (http://www.taylor-race.com/images/products/02004131TULIPSTUB.jpg) "tulip style" joint, slice off the stub shaft and bolt on what would essentially be a short "wheel spacer/wheel adapter" plate:

http://www.cosic.org.uk/misc/tripod.jpg
(representative image only - you'd effectively have three 8/9mm HT steel bolts holding the rim on where Brookes have their driveshaft cover plate retaining screws - feasible, but ugly)


I've never made any bits like (1) before and am not sure what the best method would be. Can anybody recommend sites/books/resources - or vendors - that would help in working out how to/actually getting (1) made?

Cheers,

[Scotty]

Marc,

I do not recall your request for any drawings.
Do you need detailed drawings of our tri-pod housing.?
If so..shoot me an e-mail.
scotty@taylor-race.com

[markocosic]

Sent them to the sales@ address rather than scotty@ mate - I've forward them to Soctty@ too now http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Scotty]

Yep.

They need to come to scotty@taylor-race.com.
I do not look at that other address very much

[murpia]

Just a thought about making tripod(e) housings, are the three bores required truly circular? And if so are the 'sphericals' truly spherical?

Just trying to understand how the contact points resolve once angularity occurs...

Regards, Ian

[markocosic]

The three bores in the housings are circular on the drawings Scotty sent. Bore tolerance is marked up as not insignificant, which fits with the freeplay you can feel on them in practice - my guess is spherical ends and 'three-point contact with freeplay' rather than 6-point contact.

[markocosic]

Ok,

Have been doing some calcs and looking at the available materials and am considering using En19 steel (roughly SAE 4140) as supplied in the 'T' condition.

Plenty strong enough as far as wheel/bearing loading go, fairly tough, machines ok, 80USD for all four wheels and overnight availability which is nice, available through the uni's existing suppliers thus potentially 'acquire-able' http://fsae.com/groupee_common/emoticons/icon_wink.gif which is even nicer.

'T' condition is 300 Brinell hadrness, or ~Rc30. Taylor's own outer tripod housings are 4340 hardened to Rc50. My question to you who've made your own outers: what materials did you use, and is Rc30 considered sufficiently hardwearing for FSAE use?

Everything I can see says Rc50 4340 is overkill, but I'd like to check there aren't any schoolboy errors or wandering decimal points involved! http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif http://fsae.com/groupee_common/emoticons/icon_eek.gif

[billywight]

http://img516.imageshack.us/img516/5887/rhubzl8.jpg

These are our hubs from last year - 4340 at HRC 38 with the tripod bores ion-nitrided to HRC 60. They've held up very well, with no wear or problems. As you can see the bores don't have to be circular. The tripod geometry came from a CMM of the Taylor tripods and modified to be less round. I cut the bores a little tight with a long 5/8" carbide endmill and just offest the cut a little at a time until the tripod bearing slid in easily without too much slop. The contour was done at full depth so there wouldn't be any ridges in the surface finish.

[Mechanicaldan]

That's a really great design Billy. I'm just wondering how you preload the bearings on the inside side? Do you have a picture? Are you using ball bearings or tapered roller bearings?

One last question. Do you put springs inside the hub to centralize the axles?

Thanks,

Dan http://fsae.com/groupee_common/emoticons/icon_smile.gif

[billywight]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">That's a really great design Billy. I'm just wondering how you preload the bearings on the inside? Are you using ball bearings or tapered roller bearings?

One last question. Do you put springs inside the hub to centralize the axles? </div></BLOCKQUOTE>

Thanks Dan. We used 2 deep groove ball bearings, not the best design, but it worked out OK for us and is still holding up really well now. We had to make some spacers to go between the bearings inner and outer races to ensure we didn't over preload anything. Yes, springs were used on the outboard side (taking all the tripod plunge) with the inboard tripod remaining stationary (not plunging). Kind of like the Taylor spring design, but the springs were external to the axles so there wern't any holes or other stress risers created in the axle.

[Marshall Grice]

They look pretty cool. Might I ask what they weigh?

[billywight]

A bit heavy at 2.6 lbs for the hub not including bearings or wheel studs. It was worth it to us though considering it increased the stiffness of the assembly, decreased angular displacement of the driveshafts (they're longer), increased service life, and it's one part instead of a few parts with a bunch of bolts. It could definately be made lighter with some Ti and probably would work just fine out of 7075 with the right coating at the loads FSAE sees. We just didn't have the testing time to risk the above two materials so we went with what we knew would work.

[Alastair Clarke]

Hi guys,

our current hubs are very similar to what Billy has shown. We made them from EN24T, so of a similar hardness to the EN19T which you're proposing marco - we've used these hubs on 2 cars now, with no signs of wear or increased clearance etc. In total these hubs have done 3 events, plus god knows how many days of testing, so I think you can have some confidence in using EN19T or EN24T for your hubs.

On our inboard tripode housings/output flanges, we used EN36C and case hardened them (different designers, different ideas) and have had no problems there either, but it obviously complicated the manufacturing process somewhat.

Hope this helps

Alastair

[markocosic]

The presentation on those axles/tripod outers are second only to the presentation of their chassis/wishbones...

http://www.cosic.org.uk/galleryv2/main.php?g2_itemId=1034
http://www.cosic.org.uk/galleryv2/main.php?g2_itemId=1028

Very nicely turned out machine.


2.5/63.5mm ODis about as small as I'd like to push outers based on (non-round) bores and the gkn-taylor internals - going on the shape of their "tulip style" tripod outers and a 5mm minimum wall thickness.


I'm revising "Everything I can see says Rc50 4340 is overkill, but I'd like to check there aren't any schoolboy errors or wandering decimal points involved!" by the way - in light of a schoolboy error... http://fsae.com/groupee_common/emoticons/icon_razz.gif


Rc50 hardness (~50 brinell) is nothing to do with "wear" resistance and more to do with the stresses created by the point-contact loadings. You can "work out" (or guestimate with academic pretenses at least) the contact point stresses using "Elliptical Hertzian Contact" models (ask a lecturer, and there's a handy calculator tool here too http://www.tribology-abc.com/sub10.htm) - these models will tell you that you need the Rc50 or 500 brinell to avoid plastic deformation at the point of contact - and not merely for wear resistance as I had previously assumed.

Thank you to the man from gkn who listened then smiled knowingly and suggested I might want to learn about Hertzian contact - you know who you are and sharing that titbit has probably just traded me some egg on face now for less in future, heh! http://fsae.com/groupee_common/emoticons/icon_smile.gif


Easiest way to Rc50/500 brinell is through-harden and temper some 817 M40 (EN24, approx 4340) 709 M40 (EN19) or even case-hardening a boggo 1040/1050 might be made to work, but on the back of a run of one and minimal change in component cost due to the material to hell with taking the chance...


Were your hubs heat-treated away from the 'T' condition Alistair, or were they left as-is? Did you drive through them only or did you drive and brake through them? (should clear up how conservative the hertzian contact and loading scenario data is)


Cheers,

[billywight]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The presentation on those axles/tripod outers are second only to the presentation of their chassis/wishbones...

http://www.cosic.org.uk/galleryv2/main.php?g2_itemId=1034
http://www.cosic.org.uk/galleryv2/main.php?g2_itemId=1028

Very nicely turned out machine. </div></BLOCKQUOTE>


Thanks. It's the result of many hours staring at a computer and then many more staring at a CNC machine and welder...

[Alastair Clarke]

Marko,

The hubs were left in the T condition. We only drove through them - we use outboard brakes on the rear.

Your comment that the hardness is nothing to do with wear depends on whether you count plastic deformation due to high Hertzian contact stresses as a wear mechanism or not. I'd argue it is, as permanent plastic deformation can lead to two things - one, permanent change of shape, and two, material removal due to asperity tips getting broken off.

Anyway, hope that helps

Alastair

[markocosic]

Cheers Alistair.

Craig Taylor emailed this morning and reckons we'll see plastic deformation at Rc30, Rc38 plus being vastly preferable.

What are people's thoughts on the UQ paper here:
http://www.mech.uq.edu.au/ugthesis/2002/FENNING_Mark.pdf
in particular page 56 with the driveshaft torque data - a 'rotating mass inertia' torque spike seems feasible under braking where you can be more aggressive than with the clutch that slips, but 2500Nm? Unfortunately there isn't more data there to say whether it's instrumentation issues or really happening.

[Boston]

Others have been able to run bare aluminum CVs without problems.

[Thrainer]

I'm a bit confused. Here, people are recommending Brinell hardness of 500, while 300 is supposed to be "too soft".
While in the topic about aluminium housings, most people wrote they didn't do hard anodizing and some deformation was there, but not a problem for one season.
Bare 7075-T6 has HB 150 (Rockwell A 54), while "usable" steel has around HB 250.

So, if you believe the aluminium guys, bare steel should not break a sweat, even without hardening.

What is other's experience with this? Has anybody actually used non-hardened steel?