[ED209]

Fanuc Spindle Encoder Problem. Not sure if this is the right forum for this, if not let me know where, please & thanks.

Have a 1990 Leadwell LTC-20CP 2-axis slant bed lathe with Fanuc OT-C control. Blew the syncronus drive belt on it. Removed the spindle motor, installed the new drive belt & motor. Test ran everything, checked tension alignment etc all seemed good.

Started running a part, rough turning the OD, feed rate was fine on 1st depth of cut and about half way through second depth pass seemed like feed stopped, but didn't just slowed down to near zero feed rate. The big thing is the spindle was turning around 300 rpm, but on the display screen it only shows 1 to 2 rpm ?. Then encoder timing belt is rotating ? Any ideas ?

Thanks in advance

[underthetire]

When the drive belt broke did it hit the encoder? My guess is it did and broke it.

[ED209]

well the belt didn't exactly break had to cut it off, all the drive teeth are basically gone.

[Perfect Circle]

In manual operation do the rpms match what you input?
Did you get it out of time with the spindle?
Try some manual jogging of the spindle and MDI and see if they differ.
I know if the sync wheel is moved while the machine power is off that can affect the control...had that prob..(group)

[jj lockwood]

u need to check damage to encoder.. inside most is a glass scale that counts pulses... always handle encodes with care..

[ED209]

ok will check that out tonight when home. This machine sits at a friends property, not at my workplace.

[ED209]

ok checked the machine last night. The spindle speed will increase & decrease in manual or MDI mode G97, input S200 & spindle seems to be going 200 rpm, input 500 rpm & same thing. But spindle speed readout on CRT screen shows 1 to 2 rpm. Pulled the encoder out & carefully removed glass scale, all clean inside.

[underthetire]

If it's running ok, and just the screen RPM shows off, you might want to look for a external prox sensor on the spindle. We have 2 machines that use it for spindle speed display only. I had one do the same thing, after adjustment it was fine.

[Al_The_Man]

It sounds to me like you are missing the encoder pulses, the 1-2 rpm could be accounted for noise in place of the pulse.
The spindle does not require the encoder unless you are doing threading or engage SFM, otherwise it is just for display.
Check the wiring and connections, unscrew the MS connector on the back of the encoder and check for broken wire or contamination.
While you have it off, just ensure you have +5v supply on the power pins.
There is a way to check the encoder on the bench but it is difficult without a test MS connector and test cable.
Al.

[underthetire]

It sounds to me like you are missing the encoder pulses, the 1-2 rpm could be accounted for noise in place of the pulse.
The spindle does not require the encoder unless you are doing threading or engage SFM, otherwise it is just for display.
Check the wiring and connections, unscrew the MS connector on the back of the encoder and check for broken wire or contamination.
While you have it off, just ensure you have +5v supply on the power pins.
There is a way to check the encoder on the bench but it is difficult without a test MS connector and test cable.
Al.

Al, I have to disagree. All standard lathe programming is in inches per rev, so even standard turning will use the encoder. Seen plenty of belts break, and the lathe will no longer feed.

[ED209]

Also we can put it in dry run & vary the feed that way but not in manual jog or automatic, it just crawls along. Is there any wiring that runs from the encoder to the spindle ?. Just wondering if we broke or loosened a wire at the spindle motor end when we pulled the motor out to put the new belt on, as we did not disconnect the wiring to the spindle motor.

[Al_The_Man]

IIRC, the encoder goes directly back to the control, not the spindle controller.
M27 connector.
Al.

[ED209]

ok we had the encoder checked & the electronics tech said it was good, was getting signals from A, B, A" B" something like that. Guess we need to start tracing wires back to cabinet ?

[Dan Fritz]

Make sure that the MS connector on the encoder is fully engaged. Sometimes the threaded ring starts to give some resistance when the pins begin to engage, and it feels tight, but it's not. Give it an extra bit of twist to see if it engages farther.

Sounds like it worked for a few minutes after your reassembly, but then stopped. If it's not an "iffy" electrical connection, then something probably broke inside the encoder.

[ED209]

Ya machine was running fine before we changed the spindle drive belt & ran briefly after putting new belt on. The electronics tech guy tested the encoder & says he's getting all the correct signals/feed back from the encoder, so encoder is fine.

[Al_The_Man]

Did he check it back to the 20pin Honda connector?
This may be yours?
Al.

[ED209]

No he didn't Al. We pulled the encoder off the machine & brought it into the city.

[gbowne1]

Al, where is M27? I looked for that one the other day.

[Al_The_Man]

The Connection manual just shows it on the memory card?
Al.

[ED209]

Found a cable plug wire that had broke off one of the pins that goes into the encoder, soldered it & we are up & running

Thanks for input people, much appreciated