Re: Request for help with steel shaft deflection problem

• From: "Mike Young" <boat042-spam@xxxxxxxxx>
• Date: Fri, 07 Oct 2005 22:03:57 GMT

"John2005" <johnjmechanical@xxxxxxxxx> wrote in message
news:1128379660.115810.46370@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Hello everyone,

I have a 2mm OD hardened steel dowel pin used as a bushing shaft,

that

is 0.505" inches long. Each end of the dowel is supported by a small
Igus plastic bushing, i.e., www.igus.com Part # GSM-0203-03, which

are

each 3mm long. The bushings are located flush with the ends of the
dowel. The clearance between the shaft OD and the bushing ID will be
from .0006" Minimum to 0.003" Maximum.

The distance between the inside edges of the two bushings will be
0.269" inch.  In the center of this .269" span, a 3/16" OD X
3/16" long steel tube is pressed onto the 2mm OD dowel pin. The tube
acts as a small roller or cam-follower. When the roller rotates, the
2mm OD dowel "rotates with" the roller, since the roller is pressed
onto the dowel and is basically like one piece.

I have a .031" thick thrust washer located on each side of the
roller, within the 0.269" wide span.

If a shaft is simply supported at each end, and you put a load in

the

middle of the supports, not only does the shaft deflect down at the
center, but the ends of the shaft will tend to deflect & curl up as
well.

I can calculate the shaft deflections if the 3/16" OD X 3/16" long
tube were not pressed onto the shaft, but after the tube is pressed
onto the shaft, it's as if the center of the shaft has a 3/16" OD
and the two ends have a 2mm OD. The 3/16" OD tubing stiffens
everything up.

Can anyone please tell me how to calculate the deflection of the

shaft

after the 3/16" OD X 3/16" long steel tubing is pressed onto the
dowel ?

I will have a 200 pound load on the roller, the cam is 3/16" wide
just like the roller, so I suppose you would consider this to be a
distributed load.  I am not concerned with deflections inside of the
.269" span because I think they will be very small, probably less
than .0005". I am concerned with how far the very ends of the dowel
will curl up or deflect, since this could produce misalignment and

/or

binding of the dowel / shaft in the ID of the bushing.

I would appreciate any feedback anyone can offer.

Thanks for your help.
John

I don't know what the allowable shear stress is of the pin, but that
may be the limiting factor-or the bearing load on the plastic....

.

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    • From: Rick

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