[TR] Run out conclusion. -Related question

[pethier at comcast.net]

From: <cfisher at borgwarner.com>
> I checked my hubs because of the shimmy problem and found the right
> front to have over .055" runout. My question is how best to true it.
> 
> I asked a machinist at work about chucking on the inside of the hub bore
> where the inside bearing presses in. He didn't think it would work 

I believe he is correct.  You need more support and a longer axis for location.

If I had a large lathe and lots of time, I'd machine a fixture that would locate/hold the hub by the counterbores for both inner and outer bearings.  A couple of light facing cuts and you are done.

If I had only a small lathe and a milling machine, I'd make on the lathe a cylinder matching the inner bearing counterbore and bolt it to the mill table.  Walk it with an indicator.  Plunk on the hub and hold it down with clamps. Walk the outer bearing counterbore to make sure all was straight, then make very light end-mill cuts on the hub face.

If you could mount a spare axle stub vertically on a surface grinder (lock the table travel), you might be able to grind the face.  Don't try this without knowing what you are doing.  Since you are by-definition going to grind a total of .055" from the high spot it is imperative that you take a thousandth off the high spot first.  Accidently making your first touch anywhere else could make for entirely too much excitement in the shop!

There may be some sort of dedicated method to do this on brake machine.  There are lots of cars that have brake drums with integral bearing counterbores.  How do automotive machinists locate them?

>and
> suggested I mount it on the car and use a die grinder to even it out.

Either he was joking or that was the most astonishingly-bad advice I can imagine coming from a machinist.

> If I go to an automotive machine shop, will they know how to tackle
> this?

Maybe.

> Can someone tell me how to tell them to do it?

You could tell them of my suggestions, but I have to believe that if they don't have a system in place for this, following my methods could be expensive at shop rates.

Outfits that do brake disks on the car (I have never seen this done, but I am told that it sometimes is done) may be able to adapt their setup to face your hub.

> Should I just try the die grinder with the hub on the car?

No.  Unless the spindle is immobilized and you have a precision method of keeping the grinder on a straight path in a plane perpendicular to the axle axis, you have little hope of success.  Rotating the hub 180 degrees from the indicator to a spot where you could grind a little and then back to check might take you ten years.  It would take me a hundred years.

--
Phil Ethier   West Side  Saint Paul Minnesota  USA
1962 Triumph TR4 CT2846L, 1992 Saturn SL2, 1993 Suburban,
1994 Miata C package
pethier [at] comcast [dot] net    http://forum.mnautox.com/forums/
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I decry the textmessagization of the American-English language.