On 6 May 2006 09:54:32 -0700, "Jeremy Samuels"
wrote:


Don Foreman wrote:
On 5 May 2006 19:52:52 -0700, "Jeremy Samuels"
wrote:

I'm working on a go cart as a school project with a friend. Our budget
is extremely limited, so we're leaning towards machining our own wheel
hubs. I have a HF minilathe, 1/2" drill press, and a 120v lincoln mig
with c25 and straight argon, so welding aluminum is possible. I'm
wondering what kind of accuracies would be required. Bolts will be at
a 4" circle, tire diameter of 6-8" at a speed of up to 25 mph, I'm
calculating 120 rpm (is that right?). Although this is kind of low,
I'm affraid the heavy radial loads may damage the bearings, especially
with no suspension. I'm confident I can hold 20 thou tolerances with
the setup I have now, but is there anything else I should consider?
I'm using the stock three jaw chuck, with HSS. I have a few boring
bars for the bearing. I don't have a rotary head or cross slide vise,
but have a wiggler.

An example can be found at
http://www.mfgsupply.com/m/c/53-681.html?id=XGPPnfW9

Forget about aluminum with the welder you have.

You'll want a lot better than 20 thou tolerance on a bearing housing.
You should be able to hold 1 thou with your minilathe over a short
distance like the depth of a bearing. Just take it slow, don't get in
a hurry, measure often, take more than one pass at a given setting
when boring because the bar (and the small lathe) will flex a little
until it's only skinning a thou or less.

I've welded aluminum before, 6XXX extrusions. It was difficult, but
not impossible. A spool gun would really help, all the problems were
wire feed related.

Turning the hub, I could probably get close to 1 thou accuracy.
Drilling the bolt pattern is where my inaccuracy will be. I expect it
to be 20 or more thou off. This is for a live axle, so no bearing, but
a keyway or a few strong set screws.
With a careful layout you should be able to get within .005" That's
you, not someone else with more experience. I see you have welded
aluminum before with your welder. Did you test your welds? If so, how?
Did you pre-heat the aluminum? Did you notice how soft it was after
welding? Remember, just because a weld looks good doesn't mean it is.
I've seen plenty of "good" welds separate at the weld/partent metal
interface. I personally would not use a welded aluminum hub for this,
unless it was heat treated after welding because the aluminum is so
soft after welding.
ERS