Need from mechanical expert !

[Cavver]

Why a circular section is preferred over rectagular cross section for a Shaft ??? ???

[Sickscientist]

Force on inertia...

[Cavver]

care to elaborate ??

[Dynaway]

i believe the shaft is for rotational purpose usage....

 

if so, a circular would be better... lesser vibrations as well...

[Cavver]

Okay , for what i know is ; Solid vs Hollow Shaft,

 

Hollow ==> less Moment of Inertia = less twisting

 

Solid ==> more Moment of Inertia = more twisting

[Koren]

aerodynamic resistance be it in air or liquid.

 

something about counterbalance weight too? when spinning the weight distribution will be the same in all directions for the cylindrical shaft.

[Cavver]

So is it mean ? Rectangle cross section are more likely to twist much than a cylinder section shaft ??

[Cavver]

No. Not so chim to dynamic yet

[Sickscientist]

Ok.. But its only based on my physics knowledge..

 

If its rectangular, the effort to turn is much diff from a circle shaft..

 

The gravitational pull from a rectangular shaft is greater than circle shaft...

 

The rectangluar shaft have right-angle edges.. So when it turns, the distance from the centre to the edge varies unlike circular shafts where by the length is constant...

 

Turnability on a circular shaft is much easier than the former...

 

Not forgetting to counter balance it...

[Dynaway]

i think twisting of the shaft or bar... will still be very much determine by the material used to construct it...

[Jayq]

I think is because shaft is normal used for revolution so easily to calculate how much RPM, and circular shaft because of the weight distribution is dynamic balanced.

[Ah_liang]

1. The shear stress taken by a circular and square shaft of same width are different, circle is more.

 

2. Circle shaft easier to balance than square.

 

3. Fabrication???

[Jayq]

When spinning if your weight is not dynamic balanced centrifugal force will cause the shaft to vibrate worst case might even break your shaft.

Edited January 1, 2008 by Jayq

[Fondue]

There are 2 main considerations : bending moment and twisting.

 

To put it simply (cos I've forgotten all the correct terms ) :

For a square shaft, its easier to bend when the x-section is a square than when you rotate it 45 degress and it looks like a diamond. But for a circular shaft, the bending moment is the same at any orientation.

 

 

 

When twisting, the sharp corners on square shaft will shear at a lower stress that the iwider section due to a smaller x-section on the shear plane. But on round shaft, again, all surface are identical, so shearing will only occur at one pt and would be spread evenly.

 

Its just like when you over tighten a alu allen screw with a stainless steel allen key .... you end-up with a circular hole on the screw instead of a hexagon.

Edited January 1, 2008 by Fondue

[Bern2]

Other than convenient rotation, essentially better moment of inertia in torsion and bending.

[Efinity]

You pretty much got most of the reasons.

 

Another one would be edges of a square cross-section shaft will act as stress raisers, leading to easier crack initiation and propagation.

[Nkps]

  Quote

Why a circular section is preferred over rectagular cross section for a Shaft ??? ???

 

i dunno the answer but since is lite & Ez.... have u wonder why your shaft down there is circular and not rectangular?

 

 

JUZ Kidding

[Apollo]

my kachang puteh friend say is airlowdienehmic coEfeexionsi lor....