[ATM] (no subject)

[towens@shibumi-consulting.net]

Don, Jay

I've had success combating the contact stress and galling issue by using a
hard anodised surface on a hard temper (T6 or T9) alloy like 6061 or 6082.
It is important to control the load on the roller bearing to manage this
stress. There are several online resources to help calculate the stress for
different geometries of contacting parts. Unfortunately, there are no hard
and fast guidelines about what the limiting contact stress should be, due to
the simplifications and assumptions in this kind of analysis. But
understanding how to proportion and load rollers running on metal tracks is
a big help when engineering smooth-running scopes that use metal.

Tony

-----Original Message-----

From: Don Clement [ <mailto:don_clement at charter.net>
mailto:don_clement at charter.net]

Sent: 08 January 2007 17:05

To: atm at atmlist.net

Subject: Re: [ATM] flex rocker azimuth stickiness

Aluminum does not work as a bearing surface with roller bearings. Aluminum
is too soft and will easily gall. Unlike Teflon that distributes load over a
large area, roller bearings concentrate the load about a thin line and will
quickly damage soft material like aluminum. Hardened stainless steel strip
is a better choice. I use ½" diameter solid carbide end mills regularly on
the vertical mill running at 6K rpm to mill aluminum with excellent results.

Vortex air-cooling is used. YMMV.

Don Clement

Running Springs, California

 

Jay Kirkland wrote:

> On the re-build of the 20, I didn't even consider teflon - just 

> went straight to sealed ball bearings. I used 4 sets of three bearings 

> each, a bolt with it's head cut off for the axle. Instead of ebony 

> star, I used 1/16" aircraft grade aluminum. That was a mistake. It 

> works fine, but it was too hard to router into a ring w/o losing a 

> whole lot of weight (in sweat that was scared out of me). If you go to 

> an aluminum ring, use regular 6061, maybe a bit thicker, and cut it in 

> several passes with an upcut spiral bit, preferably with a 1/2" shank 

> to help with the heat, and - very important - NOT carbide tipped.