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Remove Z axis servo -- coupler question

miyano_cnc

Plastic
Joined
Jul 29, 2022
Hi,

I need to remove a Fanuc Z axis servo from my mill so that it can fit into my garage and I have some questions:
- do I just need to loosen the set screw in the picture below and pull the entire coupler off the ballscrew with the servo? (I didn't see any set screws on the top red section)
- or do I need to take apart the coupler with the 4 sets of studs / nuts (99.99% sure this isn't the path as I can't get a closed wrench on the nuts)

IMG_20220821_132430.jpg
Thanks
 
Take the 4 through-bolts out.
Mark which upper hole goes with which lower hole (paint or marker) and it will be spot on when you put it back together, even if either spins before you re-assemble.


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Think Snow Eh!
Ox
 
You can do it either way. Personally, I like to leave the coupler assembled as a unit and pull the motor. Easier to reassemble than trying to tighten those bolts up. Sometimes there will be 2 set screws 90 degrees apart to remove. Then you can use a small pry bar to help slide the coupling off if needed.
 
Take the 4 through-bolts out.
Mark which upper hole goes with which lower hole (paint or marker) and it will be spot on when you put it back together, even if either spins before you re-assemble.
Okay, if I do this will the washers (black) above and below the circular ring (silver) that goes through all 4 bolts come apart? Or are the washers and the silver ring 1 piece?
make sure the head is blocked if the motor has a brake.
Yup, got that ready under the spindle for when I take out the servo. Thanks for the info.
You can do it either way. Personally, I like to leave the coupler assembled as a unit and pull the motor. Easier to reassemble than trying to tighten those bolts up. Sometimes there will be 2 set screws 90 degrees apart to remove. Then you can use a small pry bar to help slide the coupling off if needed.
Good to know, I used this method on my smaller hobby mills and would prefer to use on this machine to take the coupler out as one piece. The access to it is horrendous. I will bring a better light to make sure I see the coupler/set screws better next time.
 
The flanges are opposites.
On two of them there is a small bolt hole above for just the bolt, with a larger hole below for a bushing.
Then the other two holes are the other way.
If you doo it this way - you will not have to adjust your Z HOME position, and there is always a chance of your HOME point on your encoder being too close to your HOME limit switch point, that you could get a full rotation difference when you home the machine. Not likely, but can happen.

So - even if you take it apart, and you have your holes marked, you can spin the motor shaft 'till Tuesday and it won't matter, it will still be dead nuts like it was before you took it apart.


If you must take the cinch loose on the motor shaft, then try to mark that as best as possible, like paint (Dykemm?) and then a scribe mark, and that will likely be good enough for who it's for.


You just don't want to take it apart willy nilly and then haft'a dink with tool change height and whatnot later.


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Think Snow Eh!
Ox
 
If you doo it this way - you will not have to adjust your Z HOME position, and there is always a chance of your HOME point on your encoder being too close to your HOME limit switch point, that you could get a full rotation difference when you home the machine. Not likely, but can happen
Does this apply only to servos with absolute encoders? Or to servos with relative encoders as well?
 
Well, I am actually replying with what you refer to as a relative encoder I guess.
One where you are HOMING the machine each day, and it looks for a HOME pulse on the encoder.

Now if you don't have that, then I guess the next question is - can you remove the motor w/o unhooking the encoder cable - AND make dead sure that the motor shaft doesn't turn during the move? (Maybe just duct tape it so that it can't turn?)

But if you have "absolute" encoders, and you will not be able to make the move w/o unhooking the cable, then you can doo it any which'a way that you want as you will have to set your Z zero point after you git it back together anyway.

Good points to ask as I didn't consider the other option.


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Think Snow Eh!
Ox
 
Well, I am actually replying with what you refer to as a relative encoder I guess.
One where you are HOMING the machine each day, and it looks for a HOME pulse on the encoder.
Okay, I have this type of a servo/encoder. I forgot about the home pulse output.
 
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Make your life easier and don't unhook the electrical cables. Should have plenty of slack to swing the servo down. I would undo the 4 bolts as OX suggested, comes apart easier. But up to you. I've moved several machines under low doors and had to do this.

Also once you power on, replace any batteries !
 
Got power to my machine finally this past weekend and I just want to follow up here in case someone else has to do this in the future.

I ended up loosening that little set screw in the first picture, unplugging the server and removing the 4 bolts that held the servo to the frame. My z axis was supported by a cradle made from 4*4's but I made the mistake of not slightly indenting the notches for the tool holder orientation into the wood and when I removed the servo, the z axis dropped slightly. I will address this later.

Since the ballscrew moved, the alignment of the key to the servo coupler was off. I thought about buying a cheap coupler and a shaft with a key to manually rotate it into place but the key size is around 7mm on the ballscrew (from what I remember) and you can only get a 6mm keyed coupler for cheap or an 8mm for not so cheap. I ended up placing the servo on the rear of the frame, connecting the cables, powering on the machine and then using the hand wheel to rotate the coupler into the correct position. Then placed the servo in the correct orientation, bolted it back into place and verified that the z axis worked correctly.

I was expecting a Z axis homing issue since the ballscrew had moved but the Z axis homed just fine. As did the X axis. My problem was the Y axis would throw an overtravel error (I think 500 error). During the Y axis homing I verified that it homed fast to the first limit switch and then slowed down for the precise homing to the second limit switch and then would throw the alarm. I then went into the parameters, and changed the +y value from 4000 to 999999 on param 1320. Then I did the home on all 3 axis again and everything worked out. At this point I changed the value back to 4000 on the +y and redid the home. Since this point, I've had no issues homing the machine. I tried the P+CAN boot up trick but it didn't work for me, I'm assuming I was just doing it wrong and/or there is a variation for my controller that I wasn't aware of.

Thanks for everyone's help on this issue.
 








 
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