moment calculation for chucking a hollow cylinder?

[Thunderbird336]

Please forgive me if my terminology is not correct, I'm here on this forum precisely because I am not well versed in this topic...

What I am looking for is - if I chuck a hollow cylinder in chuck mounted to the spindle of a horizontal lathe, how much force is required for a chuck jaw (that is at the 'top', that is 12:00 if viewed from either end of the cylinder's axis) to retain the cylinder? I know that coefficient of friction factors in to this, and I think I can handle that part... the part that I do not have a handle on is how to I calculate the force that the weight of the cylinder is applying to the 'top' jaw of the chuck? In other words... if the cylinder were allowed to 'fall', provided that there is also a jaw at the bottom of the chuck, the top-most point at the chuck-end of the cylinder would describe an arc with a radius equal to the cylinder's diameter. There is force that the cylinder is applying to the top-jaw, along this arc, as it wants to pull itself out of the chuck - how much is it?

Now, one caveat - what about if it is a 3-jaw chuck? That means that the bottom-most point of constraint, the point that the part wants to rotate about, is only .86603 (sine of 60°) times the cylinder's diameter. It seems like that would increase the pull against the top jaw.

I will know the ID, OD, length and density of the cylinder so I should be able to calculate this - that is, if I were smart enough!

A typical scenario for me would be something like a 22" OD, 11" ID, 26" length - so with a density of .283 pounds per cubic inch for steel that is like 2,097 lbs. These parts are not actually hollow cylinders, they are flanged and I know for this particular size the weight is actually 1,094 lbs. but I am calculating it is a hollow cylinder for a factor of safety of around 2.

and by the way, is this a moment arm calculation? moment of inertia? I'd like to know what it really is called.

Thanks in advance,
Gary

 

[IRstuff]

Chucking seems a bit complex for simply lifting an object. Usually, some sort of rotational torque is imposed on the object, i.e., like a drill, is it not? Doesn't that usually dominate?

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[IRstuff]

btw. This is the general FEA forum. Are you really trying to do FEA on this? If not you might want to red flag this and post in forum404 or forum281

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[Thunderbird336]

"Chucking seems a bit complex for simply lifting an object. Usually, some sort of rotational torque is imposed on the object, i.e., like a drill, is it not? Doesn't that usually dominate?"

Thanks for the reply...

There are two places that I can get information on the forces applied by the machining operation, Harding and Kitagawa, they're chuck manufacturers... but they completely ignore the force applied by the part itself, and that scares the heck out of me. The chuck force required to counteract the machining looks to be around 91.5kN, if I did the calculation properly. This is within the capability of most power chucks, but it may not be safe if the weight of the part adds much to it.

Also, I might add, all of the calculations that I have seen are for front-turret lathes, so the machining force applied, at least in the case of the turning operation would actually serve to support the part and offset the force that I am concerned about. However, my machines are slant-bed lathes, so the turrets are in the rear, with the tools upside down as is the usual arrangement for slant-beds. So the weight of the part and the machining forces are added.

And I know I am not very knowledgeable about all of this, I really though FEA was the right place to post this but i will repost it elsewhere if that is the right thing to do. I thought FEA was for like bending, pulling, twisting forces, etc. and this seemed to fit in.

Thanks again,
Gary

 

[IRstuff]

Finite element analysis is primarily a computer-based, quasilinear, approach to solving differential and integral equations that occur in engineering. While this forum tends to be predominantly ME, this isn't necessarily the best forum for asking about chucking forces.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529