Re: SunRisers review (long)

Yeah, Jim, that's what I meant to say.

So really, it would be really tough to knock
Frankenstein's monster's head off!

V

----- Original Message -----
From: "Jim Stewart" <[email protected]>
To: <[email protected]>
Sent: Wednesday, March 08, 2006 3:27 PM
Subject: 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
>
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