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GT-20 Hydraulic troubleshooting


Hot Rolled
May 15, 2008
Winona, MN, USA
Hi Guys,

I had a 2005 or 2006 vintage Haas GT-20 lathe land in my lap. One of my vendors wanted it off their floor and I got it for a song. This is the first Haas I have ever touched. I have Mazaks and have had various Fanuc type machines from various builders. So I am familiar with CNCs, just nothing HAAS specific.

Machine appears to be in good condition other than what probably caused them to get rid of it. It is giving a few alarms.

It gives a hydraulic alarm. I can hit reset a few times and it will clear. I can hear the pump running and pressure is showing on the gauge above the power pack and near the chuck pressure adjustment knob. Oil level is full.

It is giving a turret alarm. If I issue a M6Twhatever to change tools I see the turret pop out and then it gets the alarm. It doesn't rotate. Unfortunately I didn't take a picture of the alarm, but it was something turret related.

I also noticed that the hydraulic chuck is very very slow to actuate. On the order of about 10 seconds to clamp or unclamp.

While not doing anything, I do hear some variation in sound coming from the hydraulic pump.

I am thinking that there is something clogged in the hydraulic system. And that is causing the chuck to be slow. And perhaps is causing the turret to either not fully extend or not extend fast enough.

Is this a good hypothesis? Any suggestions on where I should start looking? Perhaps this is a common problem?

I also noticed that if I do a M19 P45; M14; it will orientate the spindle to 45 degrees. But it doesn't seem to clamp. At least when I open the door I can turn the spindle by hand. I am not even sure if it has a spindle brake or if this is more evidence of a hydraulic problem.

Thanks in advance for your suggestions!



Jul 10, 2008
I would consider blockage. Pumps do not create pressure just flow. If your getting proper pressure out of hydro unit, see what pressure your reading further down line. Other question is the pump out putting proper volume.
Also don't rule out prox switches and such. but owing to the fact that it is doing its job albeit slowly(?) I suspect a hydro issues.