Balls, sphericals in fact…

suspension_bushes_doneI’ve finally managed to finish all the Delrin bearings which is a great relief. Mind you, as I went around the car I rather refined the process. So much so that the last few were much better than the earlier.

“Like pancakes”, Anthea said. Indeed, something to do with the frying pan, methinks.

sphericalThis leaves me with the issue of the need for some sort of spherical bearing in the outer housing of the lower rear wishbones. Just to remind you, here’s the photo I included a couple of posts ago.

The problem with all this is the dimensions of things. I bought some spherical bearings with a ½” ID (as usual, they’re mostly Imperial, these things) and they’ve got an OD of 1″. That is, 25.4mm, or real money as it’s properly called. The housing here has an ID of 27mm, or thereabouts, which is probably some mysterious size derived from Standard Wire Gauge and Isaac Newton’s inside leg measurement. That is, the spherical bearing is just a wee bit too small to fit snugly in the housing. Even if it did so fit it would promptly fall out unless restrained in some manner.

ballsThe conventional way to retain a spherical bearing (centre left on the photo here) is with a circlip (top left). At first I thought that that wouldn’t take the axial load that’s present here. However, talking to the cam7 bods and it’s clear that a DIN 472 25mm circlip groove, which is pretty close to 1″, can take an axial load of  8kN. (The circlip itself can take rather more force.) If entire 500kg car was accelerated with that force it would accelerate at 16 ms-2; that is at about 1.6g. As there are in fact two circlip grooves and a collection of other rod ends and so on doing the accelerating there’s a decent safety margin in such a thing. In fact, if one single circlip transferred that force the tyre that was on that wheel would have given up a while ago, at least an A048 would have done anyway.

The problem is, as I mentioned before, it’s not clear how to machine a circlip groove here. Then it occurred to me that I didn’t have to, as the ID of the housing is pretty much the same as the diameter of the required circlip groove. That is, if I fitted a shoulder inside one side of the housing against which the spherical bearing could rest and sleeved the other side of the housing so that the sleeve stopped just short of the bearing then I’d automatically get the required groove. I could just weld, I reasoned, the sleeve and shoulder into the inside of the housing and it’d all just work. So, I set about making something and turned a significant quantity of a 40mm diameter solid lump of steel into a couple of parts. The one at the top right of the photo would make the sleeve, well a 9.7mm long bit of it would.

However, I’m still not convinced that it’d work. That sleeve has got a wall thickness of about 0.6mm and I reckon if I tried to weld it into the end of the housing it’d mostly disappear in a flash. So, that leaves me wondering what to do, although I could of course just try it anyway. The alternative is really to just cut the housing off the wishbone and arranged to weld a bush into there into which I could just screw a conventional rod end, as at the bottom of the photo.

Hmmm.

pedal_box_02In the meantime, I’ve been peering at the pedal box a bit more. Here’s a photo of it roughly in position in the chassis. Note that the brake pedal actually goes a long way forward without thumping into the front suspension. I need to fabricate some sort of test foot rest for this and see what it feels like to sit in the chassis with the pedals, roughly, in position.

7 thoughts on “Balls, sphericals in fact…”

  1. Hi, I’ve been reading you blog for a long time now (since the westfied I think), it’s always nice to see something being properly considered and engineered.

    I just thought I’d ask if the bracket on the wishbone next to your tricky spherical bearing is the damper mount? If it is I wouldn’t use a rod end there as you will be loading it in bending, and at some point it will break! A spherical bearing would work very well, and if you have to chop the end off anyway a proper housing could be made up and fitted.

    Hope you don’t mind the question.

    Nathan

  2. Nathan,

    No problem at all, thanks for the comment.

    You’re right, that is the damper mount. However, although I know that using rod-ends in bending is considered naff, especially in FSAE, they can work fine and many, many, race cars actually use them this way. They just need to be sturdy enough and properly lifed.

    Mind you, you’re right in that a proper housing for the spherical bearing could be made up and welded on instead of the current housing. To be honest, that’s another possibility that I’m looking at. The problem with that is machining the circlip groove accurately enough.

    Tim

  3. In order to mount the thin sleeve for the spherical bearing, could you leave a shoulder on the end of the sleeve (a bit like the threaded insert on the rose-joint) and then weld the shoulder onto the existing housing? If the housing can’t be made wider in one direction (where it butts up next to the upright) you could just take a couple of mm off the end of the housing.

  4. Hi Tim
    I was one of the many who came to chat to you about the Spectre at Silverstone. Thanks for your time! I too have issues with Jeremy’s 1/2″ & 12mm capers having converted two Furys to 1/2″. Were all the Delrin bushes identical or did you have to fit each individually? I replaced knackered front rocking arm bushes on a previous Fury with nylatron which worked well.
    Regards David (R1 powered Fury)

  5. David,

    They were pretty much all different. I did keep wondering whether I should have ground all the housings so that there was an equal space around them all, but never got round to it. I might do so in the future, to be honest, as I’m still not sure what’s the right thing to do. Apart, that is, from using metalastic bushes!

    Tim

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