Re: Rotary gaps -- machine work

I have turned two hubs from 2" round aluminum stock.  I faced the thing 
in the lathe, and will use a boring bar to create the hole.  This gives a 
hole that's perpendicular to the plane of the hub face.  The hubs are 
about 2" long, so there's plenty of engagement of the shaft too.
>From the sound of it, everyone (both who replied as I write this) has 
this problem.  Yeah, I already have the ball bearing blocks.  That was 
part of my design.  Maybe I'll even take pictures and post them when done.

Thanks for everyone's feedback.  I believe that I'll shim up the worst 
nuts and turn the tips of them down so they are all "true".


On Wed, 7 Aug 1996, Tesla List wrote:

> Hi Chip
> I faced this same problem when I made my first rotary. I was using some 
> filled plastic material of some kind. My disk was absolutely flat but it 
> would not run true with the large aluminum washers which were supplied 
> with the work arbor I wanted to use to mount it to the motor shaft. 
> Eventually I determined that the hole which I had drilled in the center 
> was 1. too big in diameter and 2. not perpendicular to the plane of the 
> rotor. I filled the hole with a mixture of epoxy and glass fiber and let 
> it set up well. I then made very sure that the drill press table was 
> absolutely perpendicular to the drill chuck. I then clamped the rotor to 
> the drill press table and cut a new hole of the exact required size using 
> a Forstner bit which cuts extremely smooth walled holes. I found that the 
> rotor could then be mounted to the arbor without the aluminum washers and 
> it runs true. By the way, if you are using work arbors to mount the rotor 
> you might consider running the threaded end of the arbor shaft in a ball 
> bearing mounted in a pillow block. This really helps if you have any 
> imbalance in the rotor itself. Actually you will probably have to 
> dynamically balance the rotor but I like the added safety of the extra 
> support.
> I have built 4 more rotors since #1 and they all work fine.
> Skip