Subject: Re: Shaft Wear Problem

From: [email-masked] (Tony Jucewicz)
Date: 22 Jul 1996 05:54:22 GMT

Neil Poersch ([email-masked]) wrote:
: I have a problem with excessive shaft wear inside the inner race of a
: bearing. The bearing inner race is carving a deep channel into the shaft. 
: The shaft is initially a light press fit into the inner race.  However it
: is, after some use, obviously turning inside the race and eventually
: chewing up the shaft.  I am hoping that someone on this newsgroup can
: suggest a solution.

  Can you find a bearing which has set-screws on the inter-race. They
come in many sizes. We use them on many machines, but not at that speed.

: HereÕs the background facts:  
: This past winter I adapted an automotive alternator to my Moto Guzzi
: motorcycle. 
: The alternator sits on top of and behind the engine. I extend the
: alternator
: shaft to the front of the engine to a pulley and v-belt drive which runs
: off the
: crankshaft. 

: Configuration Details:
: The alternator rotor shaft ( which is threaded) is screwed into a 3Ó long
: threaded sleeve. 
: The other end of the threaded sleeve accepts a threaded end of a shaft.
: The shafts and sleeve are screwed together until their shoulders are tight
: against each other.
: This shaft is 15mm diam. by about 12Ó long. The shaft extends to the front
: of the engine where it is supported by a bearing. 
: (This is where the shaft-chewing problem is.)
: The shaft projects through the bearing about 2Ó where a 2.5Ó v-belt pulley
: is mounted.
: This pulley is driven by an ÔAÕ- section belt which in turn is driven by an
: adjustable pitch  5Ó pulley which runs on the crankshaft. This pulley is
: adjusted to produce about 1/2Ó free play midway in the belt. The
: center-to-center distance of the pulleys is about 15Ó.
: The shaft & alternator typically turn at 8000 rpm.

: I assume that there is some flexing somewhere in this set-up which causes
: the shaft to move inside the inner race and eventually allow the inner race
: to carve the channel in the shaft.

: My questions:

: 1.Is the concept of a threaded sleeve/threaded shaft coupling rigid enough?

: 2. I made the shaft from 12L14. Is this too soft and perhaps allowing the
: v-belt drive to slightly bend the shaft in front of the bearing initiating
: the
: wear problem? If so, should I use 1045 or even 4340?

: 3. At 8000 rpm balance may be critical. I made no special attempts to
: balance the components. Even if I did, the best that I could do would be a
: static balance. Any comments?

: 4. Is an ÔAÕ-section v-belt drive the wrong type for this rpm range?
: Should I use a lighter 4L type or a flat automotive type or even a toothed
: type
: of belt?

: 5. The support bearing that I originally used was a 3202-2RS double row
: ball
: bearing to provide extreme rigidity.  This carved up the shaft very quickly
: due to some slight mis-alignment.  I switched to a 2202-2RS self-aligning
: double 
: row ball bearing to compensate for the mis-alignment but still experienced
: the shaft wear problem. Comments?

: 6. Can anyone recommend any reading material on designing shafts, drives
: etc.
: relating to practical applications? MachineryÕs Handbook and bearing
: catalogues
: donÕt seem to cover this.

: If you have read this far you have lots of patience.  I would appreciate
: hearing
: from you if you have any suggestions for me.
: Thanks,

: Neil

--
Tony Jucewicz   [email-masked]         Stone is forever ########
http://www.voicenet.com/~tonyspg             And EVER ################
BBS (610)346-9047    Stonework "HOW-TO"      And YES, EVER ###########

---

From: [email-masked] (Carl)
Date: Mon, 22 Jul 1996 14:45:37 GMT

On 22 Jul 1996 05:54:22 GMT, [email-masked] (Tony Jucewicz)

>: chewing up the shaft.  I am hoping that someone on this newsgroup can

   It sounds to me like your problem is caused largely by the small
diameter of your shaft.  The load on the shaft is exceeding the
compressive strength of the metal.

   Possible solutions include:

    A larger diameter shaft. This will spread the load out over a
larger area.

    A wider bearing.  Same reason.

   A harder shaft.  A harder shaft will have a greater load carrying
capability.

    An outboard bearing.  Same effect as a wider bearing, plus less
bending of the shaft,

    Any combination of the above.

   I hope this helps you.

					Carl Grinnell
					[email-masked]