[Sterno]

Hi, I'm working on a Fadal VMC4020 with an 88HS control, AC axis motors.

The problem the machine is having is that it will only rotate the tool carousel in clockwise direction. When it is instructed to turn CCW, it turns a very small amount, stops and shows ATC TURRET FAIlURE. This is the case 90% of the time, occcasionally it will turn and index properly. If I "assist" the turret by pushing on it in the CCW direction it works every time.

Turning the turret motor/drivebelt by hand (when powered down), I sense no difference in either direction so I somewhat doubt it is a mechanical issue

I have swapped the spindle and turret grayhill relays as well as the cube relays to no effect. The turret motor and its encoder are less than 2 years old, brushes look fine.
The machine will also intermittently refuse to resume a program other than from the beginning.

Any thoughts on where the issue could lie? Is there a current sensing circuit for the turret motor that could be adjusted?

[rodney247]

Sounds to me like its the engagement of the Geneva drive. Fadal uses the motors coast after it sees the halleffect to stop in the correct position but if its coasting to far and then you can the direction it may jam when it trys to grab the slot. So there may just be too much slop in the engagement.

[Sterno]

Sounds to me like its the engagement of the Geneva drive.

I forgot to mention, this unit is equipped with a servo turret drive, not a Geneva drive.

Still, thank you for the reply.

[rodney247]

The Amp is located in the back control cabinet upper Right. Dont think there is an current limit adjustment. it may be the servo motor itself.

[Sterno]

Update:

Pulled the turret amp and had a close look at it. It was pretty dirty with oil residue, so decided to clean circuit boards with Isoprpyl alcohol. As stated, there is no current limit adjustment on the amplifier card, but there is both a current sensing transformer (circled in 1st picture) and a LED labelled "Current".




Very close inspection of the Current sense transformer and the PCB revealed a cracked solder joint on the center sense lead (arrow in 2nd picture). This failure was extremely small and required magnification to see. I resoldered this connection and inspected entire board for solder failure, no other failed solder joints were found. The H-Bridge transistors were also checked, all appear to be OK.





The amplifier cards have been reinstalled and i have done approximately 30 manual tool changes in the CCW direction with zero failures. Before this repair, the turret would jam up on a CCW rotation about 90% of the time.
Our CNC operator is going to write a quick program to do continual tool changes and we will torture test the unit for a couple of hours and I will report our findings.

[Tedger]

Excellent catch! Thanks for posting your outcome. Many times people never post the end result not realizing that specific information can help someone in the future.

[Sterno]

Update #2

Unfortunately the "fix" didn't appear to do the trick.
We ran the machine for hours with no problems, however when we loaded up with tools for machining a hydraulic valve block (large/heavy tools) the problem came right back.

Next on the list is disassembling the turret and inspecting the worm gear assembly for wear, then I don't know what to do next, maybe replace the turret motor (again) and hope for the best.

Anyone have any better ideas?

[Tedger]

I have zero experience with the servo turret but have you referred to the manual? I have attached some pages that may help.
Just a thought but is your heavy tooling pulling the umbrella down far enough to set off the limit switch?

[rodney247]

this may help

https://itscnc.com/images/Automatic_Tool_Changers.pdf read pages 117-119

http://itscnc.com/images/Troubleshooting.pdf

[rodney247]

I agree with Tedger . The amount of wieght can be a problem, Also i have seen that when the turret spindle is not aligned well (from a crash) rotating the turret can bind and cause it to trigger that limit switch. good luck

[Sterno]

I have zero experience with the servo turret but have you referred to the manual? I have attached some pages that may help.
Just a thought but is your heavy tooling pulling the umbrella down far enough to set off the limit switch?

Tedger, yes I have gone through al the steps in the service manual (thanks for posting PDF versions) to no avail. I also thought of the limit switch being triggered due to weight and so removed the shims as an experiment to set the switch roller lower in the groove, no change in behaviour.

I disassembled the turret, cleaned and relubricated the worm gear assembly and the needle bearings. I did note uneven wear on the transmission ring gear, but nothing that would worry me if i saw it anywhere else. After reassembly and adjustment, the turret seems to move smoother and more quietly, howener as soon as we loaded tools, the problem came right back.

Next step is to take the motor and send it to a rebuilder for testing.

[Tedger]

Tedger, yes I have gone through al the steps in the service manual (thanks for posting PDF versions) to no avail. I also thought of the limit switch being triggered due to weight and so removed the shims as an experiment to set the switch roller lower in the groove, no change in behaviour.

I disassembled the turret, cleaned and relubricated the worm gear assembly and the needle bearings. I did note uneven wear on the transmission ring gear, but nothing that would worry me if i saw it anywhere else. After reassembly and adjustment, the turret seems to move smoother and more quietly, howener as soon as we loaded tools, the problem came right back.

Next step is to take the motor and send it to a rebuilder for testing.

When you took the shims (Belleville washers) apart. How were the thrust bearings? They can have a bigger effect then one would think.

[Sterno]

The thrust bearings did show some wear on the race washers, more on the upper bearing than the lower.

Before servicing I had to use both hands holdin on to the bottom of the shaft to turn it (with worm gear removed). Afterwards I was just able to turn it with one hand in either direction.
How much resistance to turning should there be?

[Tedger]

Well, If the motor is pulled off the geneva type tool changer and everything is lubed and in good shape. It will spin easily. Two fingers will provide more than enough force. This may be your problem. Can you call a local tech for an opinion?

[rodney247]

a video would be nice a picture is worth a 1000 words

[Sterno]

I'm assuming you mean that you're pushing on the outside edge of the tool carrier plate with 2 fingers?

I have to remove the tool carrier plate to remove and disengage the transmission so this is not a quick check. That said I'm pretty sure I could turn it easily with two fingers if pushing the tool carrier's outer edge (like said earlier, I can turn the turret spindle one-handed just by grabbing the bottom of it).

The thrust bearings are relatively cheap and so I will get a set ordered in while the motor's out for testing.

When I have the machine back together, I will post a bit of video of the problem.

[Tedger]

Yes. I meant turn easily by rotating at the tool clip position. Although adding tools makes very little additional resistance, just a bit more inertia to get it started.
You say in your first post that you were working on this repair. Just curious, are you a tech sent to fix this problem or do you work at this shop and the problem just cropped up? I only ask since maybe some additional history may help.
You also stated that the machine didn't always want to mid-program start. Could this be a side effect of the tool changer not happy?

Just trying to brainstorm.

[Sterno]

I work as an Electronic Engineering Technologist at a small manufacturing firm, designing and building small industrial electric controls and embedded systems (PLCs, power cabinets and microcontrollers) for agricultural, fruit packing, and silviculture equipment. I'm also the go-to guy around here for networking and computer related repairs. I am not a machinist, g-code is not on my list of skills, I can manage to do tool changes, but that's about it.

This ATC failure has been an intermittent thing for a long time. I've been poking at it for about a year and only in the last few months has it become a really consistent occurrence.

The turret motor was removed and replaced a couple of years ago by the boss (same issues), he mangled the encoder in the process and I sourced and installed a replacement last winter and all appeared to be OK for about 3 months at which point it started acting up again, maybe once every 20 tool changes or so.
It hasn't been a high priority to repair until now as we have two VMC 4020s. Sadly the other unit is a geneva drive machine with DC axis motors so there's little to no parts interchangeability.
We're located somewhat in the sticks so getting a tech in to poke at it is a bit pricey and we've been managing to squeeze by with 1 machine for a good while now. When we need the problem-child milling machine, we've just been adding a couple extra tool changes to the programs to keep the turret going only clockwise on tool changes.

The mid-program failure to start has not been an issue of late, this could have been due to our new operator, who started with us this summer and was not familiar with Fadals (mainly Haas experience). As I have read and understand it, Fadal machines have a few idiosyncrasies when it comes to programming so I'm not chasing this problem until it rears its head again.

Thanks for all your help thus far.

[mmurray70]

How is the ATC Servo homed? Would it be possible to reverse the servo and encoder so everything works as normal, except backwards? If you did this at least you would know if the problem is in the control/drive or in the servo/gearbox.

[Sterno]

How is the ATC Servo homed? Would it be possible to reverse the servo and encoder so everything works as normal, except backwards? If you did this at least you would know if the problem is in the control/drive or in the servo/gearbox.

Im planning to do just that when I get the motor back, should the problem persist.

The motor is homed via a hall effect sensor, driven off a secondary shaft on the gearbox. The encoder is only responsible for speed and direction of rotation.