[Machiner1]

We just installed a new Royal Collett chuck on our ST-20 and it is rated for a max drawtube force of 5,400 lbs. How does this translate to the reading on the Chuck PSI gauge on the front of the machine?

[txcncman]

First, an ST-20 is a lathe, not a mill.

Did you go with a 5C or 16C or some other type of collet?

In ideal conditions if everything is clean and well lubricated, you should get about 5.5 times of gripping pressure for the draw tube pressure.

If draw tube pressure is 100 PSI, this should give about 550 PSI of collet pressure. I do not think you will ever be able to max out your collet chuck. I do not know what the max draw tube pressure is. You would more likely strip the threads or snap a collet in two before this could happen.

[Geof]

All you need to know is the area of the hydraulic cylinder. If you can find a make and model number on it you should be able to find some info online.

[Machiner1]

I posted here because I couldnt find a Haas Lathe Forum.

The Gauge on the front of the machine reads hydraulic line pressure applied to the drawtube cylinder. It will go up to 600 psi, but the manual says the max psi for the 3 jaw Chuck the machine came with is 320. I guess Im a little nervous about going over that with collet chuck.

Geof is correct, I was just hoping somebody had run in to this question before, and had that data.

[manike]

There is a Haas Lathe forum slightly further down the forum list. Haas Lathes - CNCzone.com-The Largest Machinist Community on the net! I have no idea why it isn't right under this one? And I often miss it even when I am looking for it.

I am patiently waiting for my own ST20 to arrive, so I am curious about your question also.

I order a 16C collet chuck to go with it also.

[txcncman]

Not to get into a whole physical course here, but try to comprehend what is happening in the gripping of material. We are talking PSI here. Pounds per square inch. On solid stock, you can grip with more PSI and not damage or crush the material. With tubing, this will force needs to be quite a bit less. The contact area (square inches) of the collet against the material will help determine how much force can be applied without damaging the material. In practice, it is best to apply just enough force to hold the material securely against acting cutting forces. Applying too much force, crushes material, deforms collets, damages contact surfaces, and wears contact surfaces sooner.

[Geof]

Txcncman you are missing the point. The question is what is the relationship between hydraulic pressure and drawbar force. You are talking about the relationship between drawbar force and chuck grip force.

[txcncman]

You are correct and maybe I misunderstood the question. The exact answer can be given with a phone call to Haas. I will let the original poster know that they will never max out their collet nose with the pressure applied by the draw tube. The collet or the draw tube threads will fail before 5,400 pounds is reached, or the part or material will be crushed or damaged before 5,400 pounds is reached.