steering collar on shaft- theory

Joa38 · Sep 2, 2005

We're in a raging debate regarding the "best" way to clock a steering collar on a shaft (for a gear assy). The collar slides up and down as the shaft rotates.

The argument being which is better- more small contact points (such as a spline) or simpler geometry such as a flat on a cylinder. Other options include a tang or multiple tangs.

Assume any design we come up with can handle the load so strength is less of an issue. Arguments center around longevity (wear causing sloppiness over time) and manufacturability (tolerance stacking causing problems). Note- the shaft is custom so we won't use a commercially available spline therefore it needs to be able to be made affordably by a competent machine shop. The ID of the collar will most likely be EDM machined.

What is typically favored in industry practice? Useful resources specific to this subject?

Joa

MikeHalloran · Sep 2, 2005

EDM is going to leave the ID of the collar pretty rough, relative to what a broach would do, so I'd expect a high initial wear rate and high friction until it's been worn enough to have some actual bearing area. It may be perfectly fine for your application, or not.

There's one more option to consider. Take a look at Kerk and similar high-lead leadscrews with plastic nuts. The nuts are split like a collet, and equipped with a taper and spring- loaded collar that takes up any slack developed in service. There's no reason the same idea couldn't work with a spline or a tang, if you need to minimize backlash. There may be patent protection to consider.

Flats and polygonal stock can work for light torques, but consider the extra stress induced in the collar by the radial force components.

You need to evaluate the design in light of the torque to be transmitted and the friction that's allowable to slide the collar.

Mike Halloran
Pembroke Pines, FL, USA

berkshire · Sep 3, 2005

Have you considered a keyway using a key secured with screws,thereby making a tang. This would enable you to turn and broach your collar thereby giving you a better surface finish. It also allows you to replace the tang when it wears.
Is this for a nose gear application?
B.E.