FP2NC z axis shudder and fault when using rapids

[rimcanyon]

I have been having a problem using G0 to move my table up (Z-) on my FP2NC for a few years now. If I dial back the speed to 50% no problem, but at full speed the machine shudders and faults if I do a Z- move of 75mm. I cleaned the tachs and recently adjusted the Bosch cards drift and tach settings after upgrading to D4. The behavior was the same when the machine was running on D2. What else to check?

 

[AlfaGTA]

I would check the max voltage that you get on the servo control input when doing rapids. (Input X31:1 and X31:2)
My guess is that the Z servo is running too fast, likely being fed more than 10v at rapid.

As a quick check, try swapping the Z axis cards ( both amplifier and regulator) from the other machine.
Note: the axis cards on the X and Y axis are the same, the Z card is different (resistor)
Also, DO NOT mix the the two different styles of regulator board with the two different styles of amplifier boards, DAMAGE WiIL RESULT!!!!!!!
Late style regulator boards(piggy back resistor board) can only be run with the late amplifier board

Cheers Ross

 

[rimcanyon]

The large green cabinet and all the console boards have been swapped in from Rich's machine, and I am seeing the same behavior before and after the swap.

 

[AlfaGTA]

Including the Bosch cards?
What is the control voltage to the servo cards when doing a rapid?
Cheers Ross

 

[AlfaGTA]

When you say “it faults” exactly are the indications?
Error code, E stop?
Does it make any noise, maybe a sort of machine gun sound?
Does it happen going both directions(up/down) ?
Cheers Ross

 

[rimcanyon]

Yes, Bosch cards are from Rich's machine, they were swapped as part of the large green cabinet. Yes E-stop and yes machine gun sound.. The control takes a minute or so to reinitialize after. Error displayed is 14. Voltage at X21 pins 1 and 2 is around 6V DC. Only happens when the knee is moved up using G0. I can use mode 5 to move the knee up even with very high speed. The problem started a couple of years ago, and it was 90% resolved by cleaning the Z axis tacho. I will try cleaning it again.

 

[rklopp]

How's your Z gib clearance? Any signs of nascent galling disease?

 

[AlfaGTA]

Sounds like you are provoking the Z axis overload clutch.
Clutch might need adjustment or you have developed higher than normal friction. Ways or lube could be an issue.
Could try cycling the axis over full travel while cycling the lube pump.
Should feel lube oil on the inside faces of the box.
Could try the rapids again with the “over oil”
What are you using for way oil?
Check the “rock”of the X slide at three heights of the Z slide (upper 1/3, mid,and lower1/3. Use test indicator to read movement of X (knee) as you go full right and full left on the X.

Cheers Ross

 

[Martin P]

Very interesting thread.

I just experienced this with my new 2836 FP2NC moving Z up in rapid. I never had this with any machine before.
I figured it to be a weak clutch and/or trade school abuse.

Then I next had the same thing happen on the other 2836 FP2NC (one owner prototyping lab, lots of use, but no abuse).
This time it was with the Vactra 4 just filled in and the tempearture being at about 5 degree Celsius.
Vactra was very gooey looking filling it in like viscosity of some honeys.
So this is no fluke!!!
After many lube cycles no noticable oil exciting on z way. To be investigated!

Then I found this technical bulletin from Deckel:

"KUNDENDIENST-INFORMATION: 17/89 10.10.89
BETREFF: Neue Z- Kupplung an FP2/ 3 NC 2836/2837
Je nach Maschinenstandard und Tischbelastung ist es vorgekommen, daß die Z-Kollisionsschutzkupplung beim
Eilgangfahren ausgelöst hat.
Aus diesen Grund wurde das Moment der Kupplung von 10 auf 12 Nm erhöht.
alte Kupplung 2803- 1225 = 10 Nm
neue Kupplung 2238- 4499 = 12 Nm
Im Bedarfs oder Reparaturfall soll in jeden Fall die neue Kupplung eingebaut werden."

This says that the clutches have been tightend from 10 to 12 NM.
Interestingly the old number is an 2803 FP3NC number, which I have many spare servos of.

These are MAYR clutches (I think) and I think they are adjustable.

This is of no direct help for your 2801 FP2NC, but I find it interesting.

I can see oil residue on ways coupled with stiff way oil and load accelerating up to be an error possibility.

Anyone ever take one of these clutches apart? I have never even removed one.

 

[AlfaGTA]

Have had the clutches apart, yes.
They are adjustable. Nut tensions a “belvelle” washer that applies pressure to a disc.
The disc sandwiches sting of loose balls that nest into pockets on an opposing disc. Power is transmitted from one disc to the other through the balls nesting in the pockets.
If the load gets high enough the balls “jump” from pocket to pocket overcoming the ramps of the pockets.
This makes the “machine gun” report.
The slipping generates an E stop because the servo is running (tach output) but the axis is not. (Scale not reading a change)

Breakaway torque can be set by tightening or loosening the big nut.
Further believe that if the clutch is allowed to slip too much the pockets will likely become rounded allowing the breakaway torque to become lower.

Also, the small Allen bolts that couple the clutch output are a failure point.
They should be replaced when servicing the clutch or servo with high quality replacements of equal strength.

Cheers Ross

 

[AlfaGTA]

A bit of additional info:
The tension adjustment is actually a ring nut(OD fhread) face drilled (6) and tapped, with screw in one of the holes to secure the adjustment.
Also likely an engraved number indicating on the breakaway setting.
Easy to match mark the body to the ring and measure the setup depth so returning to the original setting is easy after disassembly.

Cheers Ross

 

[Martin P]

This seems very close:

 

[AlfaGTA]

Yes somewhat similar.
The Deckel setup is an inline input/output.
The vid example is a parallel in/out.
Also appears that that unit has self contained “detection”.
Cheers Ross

 

[rimcanyon]

I removed the z axis motor end cap and it was quite dirty inside. Also, one of the brushes was completely detached from the wire, it was making contact with the wire just because the spring held it there.

Evidently the right angle gearbox for the hand wheel shaft is leaking grease, even though it does not get used. Also way oil finds its way in, you can see it in the cavities in the motor end bell.

As soon as I locate some replacement brushes I will put it back together and see if that fixes the problem.

 

[AlfaGTA]

Some points:
First off that shaft should have a lip seal at the exit,(40 X 55 X 7) so you should not see any grease there. There is also an O-ring that seals the inner seal running sleeve to the shaft. Replace both.
Also, handwheel use has nothing to do with how much that bearing runs, it runs
All the time the servo runs, at the speed of the servo. It is coupled to the servo.
Cheers Ross

 

[rimcanyon]

Makes sense, I was thinking about the hand wheel and shaft not rotating while the servo is running ...

Speaking of which, the shaft that the hand wheel attaches to is very hard to rotate in the end support. Takes a fair amount of force, both with the shaft slid in or out. Is there a clutch in there or something? It never gets used, so maybe it is due to lack of use and hardened grease.

 

[AlfaGTA]

Dave:
That shaft has a friction device at the hand wheel. Has belvelle washers that apply force= friction to the handwheel
Can be changed by changing the way the washers stack. Never done this so not positive it can be done.
Normally the washers are stacked with the dish alternating ,which adds to the applied tension.

At the least remove , clean and grease with light grease.
There is a plain bushing at the right angle gearbox and in the plastic end cover of the hand wheel support.
Light grease on the friction faces inside the support casting.

Also be aware that the entire hand wheel support casting is made with oversize mounting holes.
This allows you to “float” the position to ease any pinch on the bushings on the shaft.
Also there is a spring loaded plunger that controls the in or out of the hand wheel. Tension of that plunger is adjustable, and its contact groove should also be lightly lubed.

Even with everything running free, the Z hand wheel feels pretty heavy owing to the mass of the slides being moved

Pretty sure with the D4 and the MPG you will almost never use that hand wheel.
Cheers Ross

 

[rimcanyon]

Ross, thanks for the explanation. Clean and lube everything sounds like the order of the day. This is a 40 year old machine, its amazing that it has kept on working reliably for so many years.

 

[rimcanyon]

Finally got the 40x55x7 oil seal. It is a double lip seal unlike the original, but I don't think that will be a problem. There are actually two o-rings in the assembly: 30x2.5 and 65x2.5, but the larger one did not need replacement, it is in a location that is not exposed to any lubricant. Here are some photos of the inside of the right angle gear. The gear mesh is set by three small washers (shown in the photo of the housing), which is a bit peculiar... I would have expected a ground spacer at the least.

 

[rimcanyon]

I reassembled Z axis with new brushes, cleaned commutator and new bearings on the vertical side of the right angle gearbox. The bearings on the horizontal side are sealed and were still ok. The wait for bearings was the main delay. Unfortunately, it did nothing to help the Z axis shudder and machine stop problem when using rapids. If I set the feed override to 80% there is no problem, so I can live with it until the bellevue washer clutch is adjusted. First I need to find some threads where that repair is covered; I am not sure where the clutch is even located at this point. i.e. is it inside the servo motor housing or down in the lower gearbox?