WS SC-15 "W" axis servo-motor noise

I have a SC-15 4-axis machine. The "w" axis servo motor makes an unusual noise even when the slide is not moving. This noise sounds as if the motor could be under some type of load even when there is no slide movement. This noise could be compared to a rattling/humming type of noise. This noise appears as soon as the machine ready light powers up. The other three axis motors are quiet. I turned the (3) breaker switches off on the "w" axis and turned the machine on. There was no noise naturally. I am positive the "w" axis motor is making the noise. I changed out the motor with another one off of a parts machine. The same noise was still there. The "w" axis responds to both manual and automatic slide movements in both directions. The outside case of the motor will get noticeably hot even if there is no slide movement. This happens even though there is a cooling fan forcing air thru the motor.
I would appreciate any help on this problem.

When the motor is sitting there is a null current flowing to hold position. The SCR's all fire lightly, 3 in each direction when sitting. Too much null current will make a buzz, and heat. On the front of the servo module (not the pre-amp) there is a vertical row of six little pots. You have to have an scope to set them correctly but if you turn them all CCW to the stop and the noise stops you will know that is the problem. Mark the pots first so you can put them back if it makes no difference. The correct setting is 10 mv peak on each phase with T-15 grounded.
Before you do that try turning off the W servo breakers one at a time to see if that quiets the noise. If it does you may only have one or two pots set incorrectly - or there is something wrong with the servo module.
Another thought, take a brush cover off the motor so you can see the armature. If it is dithering instead of sitting still the gain may be too high. A dirty tach will raise the gain until the axis becomes unstable. You can clean the tach with a typing eraser while jogging but be careful around the armature terminals on the rectifier in the end cap. If the W is unstable and dithering you will also get a bad finish on faces.
Feel free to e-mail me if you don't think this is interesting to others.

John,I for one find this post interesting and I`m sure others can use the info too.While I knew the answer to this particular problem there will be others that I don`t know so I personally would prefer you to post your answers rather than emailing them direct to the guy with the problem.
While I`m aware that Don made this forum available primarily as a way for ex W&S people to stay in touch it has turned into a useful resource for W&S machine owners.I get almost weekly emails from people all over the world asking questions about WSC model lathes because I have them listed on my website.As well as helping them as best I can I also tell them about this site and I hope that one day this will be the best source of W&S info on the net.Due to recent changes in the ownership of W&S again more knowledge will inevitably be lost and I think this site will even more useful.
Mark
www.ems-fife.co.uk

Just trying not to take up space with non-interesting stuff.

Folder D-320209 Sheet 7 of 11
"14.0 Set Servo Motor Null current"
"14.3 Connect an oscilloscope to the heater block located on the right-hand side of the SCR amplifier behind the printed circuit card. Connect the oscilloscope probe to the lower terminal and the probe ground to the upper terminal of the heater block."

What is the heater block being referred to?

Jim Peck
Application Engineer
Ampion Corp
248-765-4273
[email protected]

Feel free to e-mail me if you don't think this is interesting to others.

Click to expand...

John,I for one find this post interesting and I`m sure others can use the info too..... so I personally would prefer you to post your answers rather than emailing them direct to the guy with the problem.

Click to expand...

I obviously can not speak for all, bu I would like to see this kind of Post here also.
IMHO there are not many of us W/S Alumni left who care to participate in this forum, or maybe they do not know about it. W/S closed it's doors for good in 1993 - hard to believe it has been so many years ago. (edited to correct year)

Maybe the guys who still make chips with these fine old beasts of burden can use this forum to help preserve the W/S legacy.

Regards,
John