Re: Shear strength of 3/4" square steel?


"Tim Leech" <duttondock@xxxxxxxxxxxxxxxxxx> wrote in message
news:n21nd2tcb9s5oi0vv0h5grf9meu5bqd78l@xxxxxxxxxx
I've got to do the final tightening of some cylinder heads tomorrow.
I've been using a torque multiplier but for some of the bolts there's
no good way to secure the reaction arm & it's been getting damaged.
(it's the type designed for waggon wheel nuts which uses a second
socket on another nut)
My big torque wrench has lost the 3/4" square shaft which connects it
to the sockets, they're a special order item so I can't just buy one
off the shelf tomorrow.
If I square up a piece of mild steel bar, will it take the 500 lb-ft
torque, or just twist off? I could find a bit of stainless or EN8 if
that would do better.
I would just try it & see if the job was here, but it's 30 miles away,
it must be finished tomorrow, & I'd struggle to find something here to
test it on. OK, I could weld a big nut to the side of a boat on the
dry-dock and use that, but we've just finished painting it and the
owner is coming to collect tomorrow!

Here's my take on it if my calcs are correct. The amount of torque a bar can
take is hopefully proportional to the cube of the diameter. If I've got that
bit wrong we're stuffed.

The most I've seen listed for torque and impact wrenches is as follows.
3/8" 100 ft lbs
1/2" 250 ft lbs
3/4" 800 ft lbs
1" 2000 ft lbs

That pretty much ties in with the cube of the size. However these are going
to be made of high tensile steel with a tensile strength of (I'm guessing)
around 60 or 70 tons per square inch. At least twice that of mild steel.

On that basis you'll be lucky to get 400 ft lbs out of a 3/4" mild steel
square bar. If the professional wrenches have enough safety margin on their
design specs then maybe you'll just reach 500 but it'll be touch and go.
With something a bit higher tensile I think you'd be in business. EN8 might
just do the job.
--
Dave Baker
www.pumaracing.co.uk
Usenet - a collection of people who only open their mouth to change feet.


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