Your load will not be "double shear" since in actuality, you are
applying half the load to two places on the bolt. I'd focus more on
the hardness of the bolt in this application, rather than the shear
strength. 5/8 is a pretty strong grade 5, but if it is not case
hardened it will wear at the point where the two peices move.
Eventually this wear will compromise the bolt no matter what the
strength is. You could avoid this by clamping the assembly tight and
giving up the tilt capability. You definetly do not want the load to
ride on the threads, that would concentrate the wear on a vary small
area of the metal and accelerate the failure mode. I'm not sure what
the hardness of a hitch pin would be, but if you go that route, I
stringly suggest you use a small bolt or other captive locking pin.
THere may be more side load on this than you would guess.
On Mon, Jun 29, 2009 at 12:58 AM, Mark Andy<mark@sccaprepared.com> wrote:
> Howdy,
>
> I need a bolt recommendation...
>
> The tow dolly I'm rebuilding has a single bolt that carries the load from
> the tongue to the tilting dolly platform. This bolt gets all the weight of
> the car. It goes through an inverted U section on the tilting platform,
> with the boxed tongue in the middle. It doesn't clamp tight, the inverted
U
> section / tonque pivot around the bolt (it was kept in place with a
> locknut).
>
> The bolt that came out of it was a 5/8-11 grade 5 bolt. Even if I wanted
> to, I can't reuse it, because the reason I'm rebuilding this thing is
> because the inverted U on the frame frame the tongue bolts to cracked, and
> now its thicker after reinforcement. In addition, the bolt's shoulder
> didn't go all the way to the edge of the inverted U, so weight was being
> carried on one side by the threaded portion of the bolt, not the shank.
> There's wear on both sides, where the U/tongue loaded the bolt.
>
> First question... Stick with grade 5 or use grade 8? The mount is in
double
> sheer, but there's no clamping happening here, its a strict bending load
> with either end of the bolt supported. Essentially, the bolt is being used
> as a 5/8" hitch pin.
>
> Second... I assume I want a shoulder that goes all the way through, so that
> load isn't being applied to the threaded area, right?
>
> Third... Should I just use a hitch pin? Are there ratings on hitch pins
> that might tell me what'll be safe for sure? Only thing with a hitch pin
is
> that I'd need to make darn sure the cotter pin or whatever couldn't come
> out... If this thing fails, the tongue comes outta the dolly and havoc
> ensues.
>
> Outside to outside of the new reinforced U is 3.75". McMaster doesn't
quote
> the shoulder length exactly on the grade 5 & grade 8 hex bolts, they quote
> it to 1.5" to 2"... That makes a difference if I'm trying to minimize the
> extra shoulder sticking out past the load area.
>
> Appreciate any thoughts. I'll make the call on safety, but I'd love to get
> some opinions. At this point I'm leaning toward just using a hitch pin and
> wiring closed the cotter pin, since this seems to be the exact design
> criteria for them, though normally it'd be holding on tractor implements
> that aren't going 75mph on the highway...
>
> Mark
--
=================================
= Never offend people with style when you =
= can offend with substance --- Sam Brown =
=================================
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