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CNC Lathe Tailstock light not lighting up and looses pressure


Mar 25, 2023
Hello Guys,
I'm wondering if somebody can give me a hint where I can look for my problem with the Tailstock on my
NISSIN NSK40/150 CNC Lathe.
When I clamp a WP with the hydraulic Tailstock it first clamps the WP but looses pressure after some time.
The Pressure gauge shows me 220PSI but after a couple of minutes the pressure goes down up to 0.
In this case the light for showing tailsock clamped is not lighting up.
Last time I had it that suddenly the light in the control lights up and the pressure doesn't drop.
Next day different tailstock postion and different WP the light doesn't light up and the pressure drops.
So I guess it's an electrical problem with a pressure switch.
But did somebody had a similar issue with his tailsock and found a solution?
Where can I start to search on the machine for the problem?
What indicates to the machine that the tailstock is clamped?
The machine is an old CNC Lathe (NISSIN NSK40/150 from 1984 with a FANUC 6T B control).
I think it's some pressure switch which is not working in all positions or is this some kind of scale?
Totally confused where to start searching Because sometimes it works and sometimes not.
Any idea?
Thanks in advance and
Could be the directional valves are sticking or worn.
Low hydraulic level.
The pump itself may be weak from age.
Leaky hoses that bleed out.
Hi Douglas,
the pump has full pressure and the hoses are looking good too.
Hydraulic Level is ok.
I guess you are right with the directional valves. Do you have an idea where I can look for them?
I guess they are somewhere directly at the tailstock.
Any chance the tailstock body is sliding away from the chuck? My QT was doing something similar, I had to adjust the clamp shoe on the tailstock base.
I don't think so.
Did you measure it or did you see it? Was it visible to see that the TS moved?
Anyway I'm just on the way to take the valves apart and look if hey are sticky or worn.
A little update to my problem.
With a Service technician we've found out that in front of the tailstock is a cover. Inside is a kind of cam and a sensor.
When you put a Workpiece in and clamp it with the tailstock the light doesn't go on and it's loosing pressure. But when you
loosen a setscrew in the cam and move it so that the cam is pushing the sensor-pin down and you hit another time the pedal to close the tailstock the light stays on and no pressure loss.
That was the solution for the problem.
Unfortunately in the books from the machine it's not explained there.
So problem solved, thanks for your input.