[jaztau]

I hope someone can help with this, I had a jerking Y axis and after searching the forums most people advised me to change the brushes and blow the carbon out the servo motor, that didnt help this time so I opted to take a servo motor from a identical spare machine and fit it. But now it rams against the end when it is suppose to move over the reference points, then a friend said that the encoder dosnt know where the table is now and that i should loosen the servo pulley and turn the pulley a few degrees till it stops doing it, well that worked but now it keeps on giving the message "Wrong reference point"!!!

[graemeian]

Many machines with incremental encoders find home using a version of the following protocol. There can two limit together switches on one end. The machines goes to the first limit switch. Then the servo rotates until it reaches the the z-trigger. Usually, that is about a 1/2 turn more. Now the machine knows where it is per that axis. What could be happening is the following: It reaches the limit switch just after a z-trigger passes. It now has to rotate...say 350 degrees... to find that z-trigger. Before that occurs, it has hit the wall. One way to test it is to put a block in front of the switch making it stop early.
Another note... Some machines may be adjusted to yield maximum bed travel and may require fine adjustment. Some have a second switch as a safety limit. Also, if the encoder is not working properly, it may speed to the end until it crashes. Servo motors work on a feed-back system. If there is no feed-back, the motor may hit the wall. It sends power and waits for movement. It does not know if the motor needs a little extra power or the servo is broken. Some other systems may use the shake method. They remember where they were when under power last . It can then back-up to the next z-trigger and now it is calibrated. I do not know this particular machine but some will let you jog the axes before finding home. From your error message, I think it wants the z-trigger at a range after the limit switch. Good luck.

[gus]

Mine does this sometimes

i think it is either the trip dog switch is too close to the zero spot on the encoder or the trip dog switch is dying