Date: Thu, 13 Jan 2011 13:17:12 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
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From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Stinkin' Audi Rims
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At 08:20 AM 1/13/2011, J Stewart wrote:
>"don't have the equipment". From what I read on this I assumed it
>was going to be no big deal, now I am ready to give up! Jeff
Jeff, if you've got time and patience, you already have a lathe, of
sorts. Get a dial test indicator with an adjustable base (something
like this
http://www.amazon.com/PREMIUM-PRECISION-JEWELS-INDICATOR-MAGNETIC/dp/B001DBZ5UK/ref=sr_1_15?ie=UTF8&qid=1294931853&sr=8-15
- not the plunger kind) and a set of dial/digital calipers. Harbor
Freight has six-inch digital calipers on sale for $10 down from $30,
tomorrow and the three following days. They're not Brown and Sharpe, but
Rig up a rest for your drill and the DTI - angle iron? Should bring
your tool somewhere around half-height on the mounted wheel. Mount
the wheel with some shims under it so there's room for the tool to
reach the back of the rim. Scribe out the desired diameter - you may
have to sneak up on it by scribing a circle, measuring it, scribing
another so much outside the first etc. A can of machinist's layout
dye can be a great convenience making the scribed lines stand out.
Rotate the wheel, using either your neighbor's kid or the van
engine. In either case suitable precautions apply. Spin up your bur
and ease it out toward the work, spinning against the wheel rotation,
until it just starts to clip the high spots of what you've already
done, then keep gradually working out to your scribed line. If you
have a straight bur, great, otherwise be sure to work the bur in and
out to get an even cut. Tap Magic for aluminum (or in a pinch almost
anything else) should help the cut and help keep stuff from sticking
to your bur. The Tap Magic smells rather like cinnamon, which is
kinda neat at first but gets tiresome. Use your third hand
(neighbor's kid) to apply a steady dribble -- I use a Jet-Dry bottle
with a 20-ga hypodermic needle pressed through the lid, but you can
do it from the can if need be - but it's thin stuff and comes out of
the can very easily.
If I'm understanding correctly exact diameter isn't critical, but
circularity and centering are. For circularity, once you're at
minimum diameter start using the DTI to check for high spots, and
using something like a flap wheel maybe? to blend them in. You need
to end up with something that very closely describes a circle, within
(wild guess here +/- .003). The occasional low spot won't matter
even if it's deep, but you mustn't have any high spots.
For centering, once it's round, pull the shims and remount the
wheel. Is it still concentric? If not, then measure and mark it,
and remount it with the shims as close to that as possible and make
that concentric again. Rinse and repeat.
If you haven't already messed up the indexing surface by
grinding/cutting on it, then mount it gently on the shims ahead of
time and use a big mallet to tap it gently into concentricity,
gradually taking up on the bolts (nuts? I forget which end is
which). That will be lots easier.
If you're not a patient person this won't work well for you. Given
the close tolerance needed to be able to balance the thing I'm not
sure I have the patience yet, and I for sure didn't twenty years
ago. What I also didn't have twenty-thirty years ago was the real
gut understanding that the universe didn't care whether I thought it
was too much trouble to clean *all* the dirt off before I opened up
the hydraulics, or {pick your example}. I somehow just assumed the
universe would make an exception for me, and I was remarkably
resistant to learning by experience that no, it wouldn't, and didn't.
Good luck,
David
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