Snap rings (circlips)

I'd refer to the snap ring manufacturer....but...

I'd have thought a slight preload would be ok as it may be usefull to stop movement/vibration wear.

Del, I believe you're correct. In most applications that I run into the snap ring is generally snug. But as you say is there's any criticality, check w/ mfg.

Nice word 'snug'...

I like descriptive terms..let's have more!

There should be clearance on the width and tight fit on diameter, I use mfg specs when machining.

The Machinery's Handbook lists them as 'retaining rings' and gives both ring and groove dimensions for standard rings both internal and external.

Go to: http://www.smalley.com/

They have an online design guide and calculators that are very good for groove design, edge margin etc., etc.

I believe they should be tight and not able to rotate freely in the grove. Grove width would be larger then the ring.

If you look at Spaenaur catalog, they have grove size for the rings.

Pineapple

The general retaining ring, or "snap" ring as most of call them are designed to have a predetermined preload when assembled in a machined groove. The groove is designed and machined to produce a clearance for the thickness of the ring so it can have a predetermined side play-which also allows some variance in the flatness and thickness of the ring. The minor diameter of the groove (for external rings) is larger than the inner "free" diameter of a new retaining ring, as the major diameter of the groove (for external retaining rings) is smaller than the "free" diameter of a new ring in order to produce a preload.

There is of course a slight variance in the aforementioned scheme, and that occurs when a special type of retaining ring is used for the elimination of side (axial) play. This type of ring (commonly called a "bevelled" retaining ring) has a draft on the outer side, and the machined groove has an identical draft machined on its outer side. During the assembly of this type of ring with a shaft and retained component the inner diameter of the ring never contacts the minor diameter of the groove. The interference occurs at the point of the draft.

Without preload, the rings are free to rotate in the groove and wear themselves thin and wear the groove wider-hence the predetermined interference. For a reference you can consult the Machinery's Handbook, or a website of a retaining ring manufacturer such as Rotorclip.

Regards,

Ing. Robert Forbus