Centroid Community CNC Support Forum

I just finished converting a PM833 to CNC. I homed the machine a dozen times... No problem. I ran some test gcode (see attached file "Circular pocket"), no problem. I ran the same gcode again today and as the program prompted for the 1st tool change, and the z-axis moved up to the proximity switch(see attached), it over-ran the limit switch slightly and cracked the limit switch mounting bracket. I have also attached the recent report with all the settings.

Any idea as to why it overran the limit switch just enough to crack the bracket?

Thanks... Richard

Well, according to your report, those are home switches and not limit switches, so they would not have stopped movement anyway. Home switches are only active during the homing cycle.

If you do not have limit switches, then you need to be using soft limits which you also do not have configured.

Tom, thanks for your quick response.

I am a bit confused. When I setup the homing details, I entered the software travel limits (see attached). What are my missing here?

Thanks... Richard

0 is not used as a limit, use 0.1 or set up the home switches as ..HomeLimitOk
At the time the overriding occurs you have had lots of resends, maybe a cause for the problem also.

Uwe

Presumably your machine would have to decelerate down from your rapid speed in anticipation of stopping before over running the Z0 position. If the accel / decel values for your Z axis are not appropriate, I guess this could be an outcome. But as Uwe says, you should set a soft limit before the home position, to give yourself some margin.

Thanks for all your responses! I am sorry but I am still missing something.

I understand that I need to add a soft limit to give the machine some margin, but I am unclear as to where to add these numbers. The manual mentions a figure between .1 and .38 as Uwe noted, but where do I enter these numbers into the software? Should I be entering ".1" instead of "0" in the highlighted boxes on the attached?

Lastly, the proximity sensors are currently wired to an input configured as "Home All". I am not seeing the ability to define the input as "HomeLimitOk" that Uwe noted. What is difference between "Home All" and "HomeLimtOk"

Thanks... Richard

(Axis)HomeLimitOk is only if you have one input per axis, but you can use HomeAll and LimitAll

0 is ignored as Limit, so you have to use an other value as limit, or limit sensors if you want to use 0 on one end of axis travel.

Try out to drive slowly to each axis end, if configured ok you will get an axis travel limit message.

Uwe

Ok. I added the limits show on the attached. I am now getting errors when I instruct the machine to go beyond the limits. Thanks for all your help!

I was under the assumption that travel limit values were ignored if BOTH values were zero. I could be wrong

You are getting errors because your negative homing axes (M91) travel limits must be zero or positive. Positive homing axes (M92) must be zero or negative

Gary is right: as long as at least one of the travel limits for an axis is non-zero, then soft limits are active. There is no problem with having a plus limit of 0.0 and a minus limit of, for example, -23.6.

Soft limits only apply after the axis has been homed.