Ideas on how to measure this clamping pressure?

This post is related to the air closer post. Now that the air closer
project is started I realized that I need to figure out how much air
pressure to use. I could do this empirically but this approach may
show that my air closer isn't up to the job. After I have gone through
the the whole process of adapting it to the lathe in question. The max
air pressure I can use is 150 PSI which is dictated by the rotary
union. So, how would I measure the clamping pressure the collet puts
on the part? In production the part is clamped in the collet .050 from
the collet face. The dead length stop controls this distance. But I
think I can remove the stop and grip on something that is about .500
long and still get a good idea of the clamping capabilities of my air
closer. I have the gauges but I'm not sure what would be best to
squeeze on.
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How about locking the spindle and measuring the torque when the part starts to rotate?
Reply to
Jim Wilkins
Measure, or calculate? Assuming a standard collet, like maybe a 5C, and assuming the closer is an annular piston, it should be easy to calculate the linear force the piston applies to the collet. Computing the squeezing force on each third of the collet seems harder, and friction is going to be a major component. But, assuming half the pulling force is lost to friction, you ought to be able to compute the inward clamping force on each jaw. Of course, the pulling force is divided by 3 to each jaw. You just need to know the angle per side of the collet taper, which you ought to be able to look up.
Measuring the grip force of a collet seems like something pretty hard to do.
Reply to
Jon Elson
I really need to measure it. This is because right now I am using the hydraulic closer in the machine to grip the parts. This closer won't operate when the spindle is turning and I want to change parts while the spindle is turning. Furthemore, the hydraulic closer is slower to open and close the collet than the air closer. So I need to see how much pressure the collet is now squeezing the part. Then I can see if the air closer is up to the job. Eric
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