Set Screws
Set Screws
(OP)
I'm doing an analysis for an aluminum dock. The legs are square tubing inside square tubing. A 1/2 inch by 13 bolt is threaded through the outside tubing and pushes up against the inside tubing. In a set bolt kind of fashion. I need to calculate how much force can be applied to the inside (moveable) square tubing before it slips. I'm looking for a way to calculate how much torque applied to apply to the bolt.and the resorting force on the inside tubing. any ideas?
Cheers
Cheers





RE: Set Screws
By the way, if there is any chance for uplift, it would be a lot better to through bolt. Thermal expansion may be a game changer for you. Are your screws steel?
RE: Set Screws
RE: Set Screws
RE: Set Screws
RE: Set Screws
I have fired people for coming up with crap details like that.
You should, too.
Mike Halloran
Pembroke Pines, FL, USA
RE: Set Screws
You can estimate the axial force on the bolt from the formula:-
F = T/(0.2xd)
F= axial bolt force
T = torque applied to bolt
d = bolt diameter
O.2 is a friction coefficient.
All that said you need to check the strength of the threads in the aluminium which I doubt will be very good and liable to strip, also if you tighten the bolt to any degree you need to consider whether or not it will permanently dent the tube or not.
Desertfox
RE: Set Screws
If not, you can forget the whole idea of a set screw arrangement.
clamping (with a slitted outer tube) or cross bolting are the better options here, my .02$
RE: Set Screws
Because of the variables, I would agree to building a fixture (not a jig) and run some experiments for your analysis.
I would use the original tubing expected in the design, and remember to not use pieces you deformed.
It seems simple enough but will probably have to be two part.
First, use a torque wrench to measure torque, and measure the resulting force on a load cell.
Then, take that torque reading to another fixture where you have the tube assembly set up.
Apply the same torque, and then use an air cylinder to make the tube slip.
Measure the pressure that made it slip.
Run a sample lot and take an average.
Just an idea
Charlie
www.facsco.com
RE: Set Screws
http://www.boatliftanddock.com/images/PRODUCT/larg...
RE: Set Screws
RE: Set Screws
You would be hard pressed to find a stronger bad example to use as a baseline.
I will caution you about that.
In Real Life, your baseline for improvements will be someone else's best effort, and someone else's sacred cow. ... and it may in fact be better than your best effort. When you evaluate alternatives, be brutally honest with yourself, and/or get help from a neutral party.
... and be very persistent and pushy and neutral about finding all the bounds, limits, and parameters associated with the problem before you start solving it.
... and double check your results, again. Mostly, when you think you have a brilliant, simple, elegant solution, it only seems so because you are not seeing an important part of the problem space. Look again.
Mike Halloran
Pembroke Pines, FL, USA