Mechanics question - force at end of screw...

[Chris D]

I am working on a new tool holder system for my bench top lathe. I am trying to get a handle on how much clamping force I need for the tool blocks. Currently, the tool bits are held in the block with three 1/4-20 set screws, so that is going to be my baseline.

I am wondering if someone can tell me how much force is applied to the tool bit using one 1/4-20 setscrew with a 4" long allen wrench.

If you have the formula, I would appreciate a walk through on it too so I don't have to bug everyone again as the design progresses.

Thanks!

Chris

[Chris D]

I guess it would also be helpful if I knew how much force is being applied to the 4" long allen wrench - frankly I don't know. I have not used that small of a torque wrench in many years, so I am not even sure of that anymore - it sucks getting old.

Let's guess at the force being 15 pounds as in 15 pound feet of torque if that seems reasonable.

CHris

[OCNC]

Originally Posted by Chris D I am working on a new tool holder system for my bench top lathe. I am trying to get a handle on how much clamping force I need for the tool blocks. Currently, the tool bits are held in the block with three 1/4-20 set screws, so that is going to be my baseline. I am wondering if someone can tell me how much force is applied to the tool bit using one 1/4-20 setscrew with a 4" long allen wrench. If you have the formula, I would appreciate a walk through on it too so I don't have to bug everyone again as the design progresses. Thanks! Chris

Check out this link or this one for a bolt torque calculator. Google bolt torque calculator for other hits.

[ViperTX]

Just looking at the Machinery & Metalworking hanbook....

T = KLD where T = Tightening torque in lb-in,
K = dynamic coefficient of friction (0.15 if dry and zinc plated)
L= clamp load, lb
D= nominal bolt diameter, in.

So, what you're looking for is the L (clamp load).

Paul

[fyffe555]

Originally Posted by ViperTX Just looking at the Machinery & Metalworking hanbook.... T = KLD where T = Tightening torque in lb-in, K = dynamic coefficient of friction (0.15 if dry and zinc plated) L= clamp load, lb D= nominal bolt diameter, in. So, what you're looking for is the L (clamp load). Paul

It's surprising the thread pitch isn't a factor..

[OCNC]

Originally Posted by fyffe555 It's surprising the thread pitch isn't a factor..

A more comprehensive formula and explanation that includes pitch can be found here . Also check out boltscience.com.

[ViperTX]

Actually L = Minimum Yield Strength of the Bolt x Stress Area of bolt

The stress area of the bolt is based on it's thread and the Min. Yield Strength is based on the bolts grade.

What OCNC refers to is the basic equation...what the Machinery Handbook does is work with an equation and Tables.

[Chris D]

Thanks guys!

Much appreciated.

Chris