Quite often, we hear from the customers that the multi axis machines like engraving, routing, CNC machines, and other similar type machines lose steps in the middle of a job. The evidences may be;
- Sudden and unpredictable move in either the X or Y axis in the middle of a job
- Big and unusual scratching sound
- Unnecessary moves in either X or the Y axis while the tool is going up or coming down in the Z axis
- Z axis unable to hold its positions in the up and down positions. Sometimes it is referred to as Z axis creep.
Following are some of the things to check out to get to the bottom of the problem or problems:
(1) If it happens repeatedly in the same area of the machine, check the part of the lead screw in X or Y axis, where the problem is occurring again and again, for damage, collection of dirt, and/or any obvious problems including wear and tear.
(2) It is always a good idea to check and tighten, if necessary, the couplers between step motors and the lead screws about every six months to a year based on the usage of the machine.
(3) It is always a good idea to check and adjust the anti-backlash nut in each of the axis periodically.
(4) Lubricate the machine on a regular basis. Some lead screws are coated. If they are, do not lubricate them. Simply, clean them.
(5) Check the acceleration in Motor Parameters tab of LinkMotion applet and try reducing the number for Toolhead Maximum Acceleration.
(6) Check and make sure that the tool used for the job is proper and sharp.
(7) Check the speed in Materials Properties and try reducing Job feed rate as well as move speed. Remember, job feed rate is the speed of the tool while it is engaged in the material. Move speed is when the tool is moving from one shape to the next and the tool is retracted. If either of the speeds is too high for the design of the machine, it could result in losing steps.
(8) Check and if necessary, increase the spindle speed to match with the feed rate and the density of the material under operation. If the spindle speed is not high enough, it may not cut the material properly while running at a relatively high feed rate and is likely to cause problems.
(9) If the problem seen is more prevalent when spindle motor is ON then it is possible that spindle motor is generating electrical noise (white noise of all frequencies) and could possibly be disturbing the step patterns for the axis movement. Certain spindle motors are notorious for causing these problems. Following are inexpensive solutions:
- Enclose the spindle motor in a metal casing to cut down on the white noise radiation.
- We recommend highly that the cables for step motors, spindle motor, and home switches be replaced with twisted and shielded pairs type cables to cut down on such noise problem. This is also an effective solution if the home switches show sensitivity to the noise.
- It is important to make sure that the shield of the cables shall be terminated at one end and not on both the ends.
The above mentioned simple steps may help to determine the source of problem. It may also save you unnecessary downtime and/or expensive repair.
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Dhiren Shah, Director of Operations