Slotted Spring Pin Installed Orientation 1

[jimbod20]

Hello,

I have questions regarding the correct orientation of a slotted spring pin used as a torque transfer feature in a rotating drive shaft.

The attached picture illustrates the design;
- The shaft with the slotted spring pin installed.
- The shaft/pin assembly illustrates my understanding of the preferred orientation of the slot in the spring pin when installed in the drive shaft.
- Direction of shaft rotation is shown.

I install a slotted spring pin in a shaft to drive a permanent magnet rotor assembly. The magnet/rotor assembly has a slot on the ID which is engaged with the drive pin. The slotted pin is installed, the magnet/rotor assembly is then installed and a locking thread nut is then threaded on the shaft to retain the magnet assembly. The shaft rotates the magnet assembly via the slotted spring pin and the magnet assembly rotates within a wire wound stator assembly.

Two questions:
Do I have the slot in the preferred orientation given direction of magnet assembly rotation/torque transfer etc?
Are there any design/installation lessons learned regarding the use of slotted pins those who read can share with me.

Thanks.

 

[Sparweb]

I don't know why this should matter.
This would be difficult to control in production.
If your concern has something to do with torsion/shear strength of the spring pin, then you're probably overloading it, and then you need a different fastener.

STF

 

[Tmoose]

My concern with a keyed connection is that if the key is asked to do all the work, there will be micromotions that over ( not that much ) time will tear everything up. Pure torsional loading is bad even if assumed constant, one directional radial loading ( belt drives, gears, fat rotors on horizontal shaft) is murder.


The solution is diameteral interference fit, or powerful axial clamping, or both.

 

[Sparweb]

Images can be inserted in-line, rather than linked to the download manager.

STF

 

[WKTaylor]

Jimbod20...

When it comes to assembly intended for torque transmission, I would NEVER use slotted spring pins as a fastener: I only recommend use of coiled spring pins. I have seen too many slotted pins facture straight down the side [end-to-end] opposite the opening... in any orientation.

Also passivated CRES will survive much longer in a corrosive [IE: seacoast] atmosphere... with added corrosion protection on installation [wet with sealant or epoxy primer]. Carbon steel [Cd plated] works well when located in a low moisture/corrosion environment... and installed 'wet' with epoxy primer or sealant.

May consider following coiled spring-pins... NAS561 [heavy duty, HD] or NAS1407 [Medium/light duty, MD, LD] or MS39086 [HD] or MS51923 [MD] of MS51987 [LD].

DO NOT be fooled by the tables which imply 'common static strength' for slotted and coiled spring-pins... reversing shear on opposite sides of the pins [opposite orientations] due to shaft actuation, has a way of loosening then cracking the slotted pins. Coiled pins are far more tough in this load scenario.

NOTE. Use of lockwire or lock-cable, thru the core of the pin and around the shaft, helps secure it from shifting.


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[BrianE22]

You do have it installed per the manufacturer's recommendations. I think the reason is that bending strength of the pin is maximized in the orientation shown.

 

[WKTaylor]

FYI... may find these specs useful...

ASME B18.8.2 TAPER PINS, DOWEL PINS, STRAIGHT PINS, GROOVED PINS AND SPRING PINS (INCH SERIES)

NASM33547 [was MS33547] PINS, SPRING, FUNCTIONAL LIMITATIONS OF

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]