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Haas VF-2 z axis crashing down on e stop

SchultzProducts

Plastic
Joined
Jun 25, 2020
Let me start off with that i am not a machinist. i am the project manager for the company. i have a lot of mechanical experience but some terminology i may not understand. we have an older VF-2 thats been giving us a laundry list of problems. about a month ago when the z axis was sent to home and e stop was depressed the z axis dropped suddenly crashing into the table. Some times hitting the e stop the z axis would only drop a few inches some times all the way to out wood block on the table. we changed the z axis servo amp and z axis dive motor and it didnt give us any further issues. about a week ago while milling 24 303 SS pieces on a rotating fixture with a 47/64s jobber drill the drill siezed in a part and when the z axis atempted to lift it released the tool holder and drill leaving them stuck in the part. we disassebled the spindle to check the belleville washers and they were in perfect conditon. we did notice some scoring marks near the ball bearing latch mechanism for the tool holder. we polished them down cleaned and regreased the spindle. zero issues since. then last friday june 26th 2020 that same 47/64 size drill was not cutting well and our machinist stopped the operation and slid the table towards the door to make inspection easier. the cut from the drill was not smooth and making a lot of noise and he moved on to another machine to address the issue at a later time. end of the that day he went to shut the machine down and apon hitting e stop the z axis came crashing down again onto the table thankfully not hitting the work or the fixture.

My question for everyone is what could be causing the z axis to suddenly drop upon hitting the e stop? we have hundreds of parts to run on this machine and and its been a work in progress and a pain to accomplish. we are only 25 parts in.

thanks in advance for any help!
 
No idea if this is the cause, but some Haas machines use a pressurized Z counterbalance, essentially a gas-nitrogen over oil cylinder like a lift for a hatchback on a car.

If the cylinder is low or absent of pressure, the weight of the Z head and spindle/motor may overcome the braking or frictional resistance of the Z drive, causing the head to fall.

What year is your machine? On my 1997 VF-2, the cylinder and pressure gauge are on the left side of the machine column, in between the main electronics enclosure and the back sheetmetal of the machine enclosure. The gauge/cylinder are within a rectangular sheetmetal box with warning labels about proper pressure that must be maintained.
 
I just sold one with the nitrogen counterbalance, for about 15 years I had to add a squirt of nitrogen to avoid just this condition.

I have 4 machines now that have never had the emergency stop pressed in the 5-20 years I have had them, not pressing it may help you some until you get the nitrogen put in. When I am done using a machine I press the "off" button.
 
The VF-2 was made on march-2001, there is no counter balance "shock" per say and no physical counter balance. there was also a z-axis overload on friday that would not reset untill this morning. i believe we replaced the z axis drive motor because the brake was worn out. i wonder if an intermitted signal to the brake could be causing it to wear out prematurly?vf2 for forum 1 of 2.jpgVF2 for forum 1 of 1.jpg
 
Sounds like a faulty brake...although I understood it was the servo's holding the head up.

In either case...I'd get it sorted out quick as its Dangerous with a Capitol D having th eheadstock coming down that way....not to mention not great for the machine.
 
It used to be an option you had to pay extra for to get the "early power failure detection module". Without it installed the head can drop some before the brake can engage at estop or power failure. If I recall they are about $700
 
It used to be an option you had to pay extra for to get the "early power failure detection module". Without it installed the head can drop some before the brake can engage at estop or power failure. If I recall they are about $700

i believe we do not have that module then. before the motor change out we had the head drop an inch or two but it caught during testing. just now testing it it dropped 2 out of 10 tests. the two drops were without homing raising the z axis about a 1/4" above a wood block, e stop, and crash, the 4 tests after homing it did not drop. we shut machine off and tried to replicate the the drop again without homing and it did not drop. total of around 10 tests and we can not seem to replicate the issue.
 
A call to your HFO with your SN: should be able to tell you if it was ever purchased for that machine. 1/4 seems excessive for that to be the sole issue but it may be part of it.
 








 
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