Re: SunRisers review (long)

Robert Meador wrote:
> However, I like your screw idea. I wonder how much shear strength a
> screw adds. Suppose it depends on the diameter. Don't want to go too
> big though, or you eat away too much of the bar stub material.
>
and Vince Lok wrote:
 > Most bolts have some kind of shear rating, don't they?
 > I'm not a machinist, so I don't know really. And by
 > Not sure about screws vs bolts in terms of shear
 > strength, but it seems to me that most bolts seem to
 > be made for shear forces, and screws are made
 > for tension forces?



"A bolt is an externally threaded fastener designed for insertion through holes
in assembled parts, and is normally intended to be tightened or released by
torquing a nut.
A screw is an externally threaded fastener capable of being inserted into holes
in assembled parts, of mating with a preformed internal thread or forming its
own thread and of being tightened or released by torquing the head." (From
Machinery's Handbook.)

So the primary difference is that a bolt doesn't need to have a head you can get
a wrench on, like a carriage bolt.  We generally use hex head cap screws or
socket head cap screws (Allen screws). Obviously wood screws are -yes- screws.

Screws/bolts are used in tension (the stretching of the screw is what gives its
clamping force (tension)).  They're often used in shear, of course, and the
shear strength is about 1/2 the ultimate tensile strength (UTS).

----------------

So let's take the example of an 8mm grade 8.8 metric screw, about the same as an
SAE 5/16" grade 5.  The UTS of an 8.8 screw is 113.8KSI, or 113,800
pounds/square inch.

The weakest spot of the screw is at the root of the threads, with a diameter of
approximately 7.2mm or .28 inches, so the cross-sectional area of the screw at
the thread root is pi X R^2, or 0.06 square inch.  From above, the tensile
strength of the screw will be .06 X 113,800 or 6828 pounds.

Using the approximation of 1/2 UTS for shear strength, it'll take about 3400
pounds to shear an 8mm 8.8 screw.  A 6mm 8.8 screw, with 75% the diameter, will
have a shear strength of about 1900 pounds.

--------------

I'd use 6mm or 5mm in this application...

-js


--
Jim Stewart
http://www.strappe.com

-------------------------------------------------
For all your SV needs: http://www.svrider.com

To change your list settings or leave SV650-L, please visit http://www.hawkgt.com/sv650/lists.asp