Calculating a push up load
Calculating a push up load
(OP)
Hi Guys...I just registered on here after someone recommended the site to me. I need help with a calculation and as my name suggests, the ol' grey matter just aint doing it for me right now!
Okay, I got a taper shaft which is 2.88" dia at the large end and 2.715" at the other. I've also got a bush with an internal taper. The outside of the bush is 3.25". I need to force the shaft through the bush. The bush is a thin wall cylinder so will expand in diameter. I know how much I need to expand the bush (4 thou on dia) but don't know how to calculate the force required to achieve that expansion.
Can anyone point me in the right direction?
Thanks.
....maybe I shoulda posted something less difficult but it's important for work that I come up with a solution.
Okay, I got a taper shaft which is 2.88" dia at the large end and 2.715" at the other. I've also got a bush with an internal taper. The outside of the bush is 3.25". I need to force the shaft through the bush. The bush is a thin wall cylinder so will expand in diameter. I know how much I need to expand the bush (4 thou on dia) but don't know how to calculate the force required to achieve that expansion.
Can anyone point me in the right direction?
Thanks.
....maybe I shoulda posted something less difficult but it's important for work that I come up with a solution.





RE: Calculating a push up load
Mike Halloran
Pembroke Pines, FL, USA
RE: Calculating a push up load
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Calculating a push up load
Yeah, most definitely a textbook problem. Without the textbooks and seemingly no answers to be found anywhere on google, I thought I may benefit from the experience of the guys on here.
Hi Greg,
Thanks, I have worked out the taper angle to be 1:40 on diameter. I'll have a look under Lames equation. Thanks again.
RE: Calculating a push up load
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Calculating a push up load
RE: Calculating a push up load
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Calculating a push up load
In any case, to add more meat on the bones:-
The bush has an od of 3.25". Its internal diameter at the large end is 2.88" (i.e.its flush with the shaft) so t (being the thickness) is 0.185" radially. The bush inside diameter of the taper at the small end is 2.717" so sits slightly inside the shaft.
RE: Calculating a push up load
Patricia Lougheed
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Calculating a push up load
This is where I got to so far..
I calculated a circumferential stress in the bush based on the required expansion of 4 thou over the mean bush diameter
From that I looked at calculating an interface pressure based on the above stress, modulus of elasticity, poissons ratio, thicknes of the bush etc etc...this threw up a figure of 7832 psi (interface pressure)
So now i need to calculat the force required to achieve the required expansion...assomebody said way up there..its prob a textbook question but I'm certainly struggling to find it!!
RE: Calculating a push up load
RE: Calculating a push up load
If you have the interface pressure then this formula may help but it is for mating cylinders:-
Force = 2*pi*mu*Rb*L*p
where mu= coeff of friction
Rb = radius of outer diameter of inner cylinder
L = length of interference (engagement length)
p = interface pressure
Force= axial force req to assemble cylinders
not perfect by any means but might get you in the ballpark
regards
desertfox
RE: Calculating a push up load
I used the calc offered by desertfox....we applied the load using hydraulics and achieved the interference fit we were aiming for. As you say desertfox, it may not be perfect but ballpark it certainly appears to be. A note to chicopee...appreciate exactly where yr coming from but our H&S dept are crazy about dry ice (don't ask...much source of bemusement here too!)
So thanks to Greg and the above mentioned contributors...marvellous.
RE: Calculating a push up load
Your welome.
desertfox