Lathe chuck pressure (Mazak QT15)

Hi Guys,

I have a Mazak QT15 that we use to make parts for our products. I'm not experienced with CNC lathes, so I'm missing some fundamentals, I am sure.

I am preparing to bore my first set of soft jaws. While reading up on this, I've seen a lot of references to chuck pressure. My lathe has a chuck pressure indicator and valve on the front panel. It came set to about 1500 lbs and that is mostly where I have left it. I had an experienced Mazak guy come in and show my how to run the machine and he mentioned "don't turn it up too high", but didn't turn it down from where it was. On some thin wall parts I have gotten distortion, so I have turned it down some.


Now that I am reading about boring soft jaws, I see references to much lower pressures. But I really have no idea what my chuck pressure actually is. Do I need some magic multiplier to take gauge pressure and convert to chuck pressure? It seems that the draw bar cylinder should factor in there. It's a Kitagawa S1875.







Auto-Strong N-210 chuck:
N-2 Model Power Chuck | Di Chun Iron Work

Kitagawa S1875:
Kitagawa S1875 Open Centre Hydraulic Cylinder | Kitagawa

So how to I determine what my chuck pressure is? Or do I even care? The S1875 says it has a relief valve. Presumably whenever I have been above its relief valve pressure it has been regulated down to an acceptable pressure?

Very confused. Just trying to get some soft jaws made and now I'm down deep in a rabbit hole!

Thanks,

-Jim

See the part on the gauge that is Red? Don't go there.

Your rabbit hole doesn't exist.

Depending on the parts, I use the minimum Chuck pressure possible. If you bore soft jaws for soft work, generally the bore has more to do with holding the part than the actual pressure. On 2nd operations, I turn it down until the jaws don't move, then slowly turn it up until the jaws barely close.

R

I think i remember hearing that chuck pressure when boring jaws should be set the same as what it is going to be set at when the jaws are being used.