Mini CNC limit switch error

Tags: #<Tag:0x00007fa4992ac520>
#1

Hi @cnctechs,

Struggling to get off the ground with the cnc today. The spindle was in the near left hand corner of the bed when I arrived. I went to press the soft power on button but I repeatedly got the message ‘joint 0 on limit switch error’.

This is where I may have made it worse and if so I apologise, I looked at the trouble shooting page and saw it was a common error, and then tried to override limits so I could jog the arm back. The machine jogged a slightly but then came up with the same error.

I wonder if someone might be able to help?
Thank you

#2

Turn the machine off, and then you should be able to push it off the limits…

@clem will be there soon and can show you…

#3

Thanks for the quick reply. Had a look with @Clem but we couldn’t work it out. I heard you’re on your way but unfortunately I have to run tonight!

I’ll be back in tomorrow. I’d love to know what the problem was if you have time to get to the bottom of it.

Thanks for your help

#4

This may make it clearer - but please wait for @CNCtechs to confirm or correct this.

This can happen when either the spindle or table move on the axis and get carried by momentum past the ‘soft limit switch’ (in software) on to the hard limit position - the physical switch at the extreme end of the range of movement on that axis. Once pressing against that hard limit switch , the machine won’t move. It has hit the end of the rails and the brakes are now on - the servos are locked to stop it moving further. (The soft limit switch will simple stop it - but if going fast, momentum can mean it doesn’t stop before hitting that hard limit switch).

To correct / reset this, the machine must be turned off. That is essential. Doing so disengages the servos. If you try to move and adjust without doing so, you will be trying to force locked servos and the servos will get damaged. Make sure you don’t do that!

Once turned off and servos are disengaged, the spindle or table can be physically dragged by hand along the axis to move it off the hard limit switch so it is no longer pressing against it. Once that is done, the CNC can be turned back on and can be operated as usual again. Depending on which joint (I.e. axis), that might mean pulling the spindle along the gantry towards the middle of the machine or moving the table towards the centre of the machine. It can take a wee bit of force - that’s ok if not over aggressive and provided the machine is turned off (use the eStop to do that). It only needs to shift an inch or so - enough to get it off the hard limit switch.

This ‘fix’ only applies to the Desktop CNC. Do not attempt this with the Big CNC.

Best to try to avoid this happening. Be aware of the limits and use the jog speed adjustment so that you don’t move to that at full speed.

#5

Thank for the clear explanation Dan. I’ll try the fix again tomorrow if @CNCtechs confirm when everything is turned off. We did try manually moving the bed with @Clem and still no access to the soft power button once restarted.

Also realised I said left instead of right for where the spindle was when I arrived!

Will keep you updated. Didn’t want to touch anything physically without supervision earlier.

#6

Yeah, it was that error.
Wiggled the drill, but probably wasn’t enough.
When we tried again it worked straight away.

Clem

#7

I’m not 100% certain as not with the machine and I mainly use the big CNC - I believe joint 0 is assigned to the x axis. That then would mean moving the spindle along the gantry rather than moving the table - which is y axis and, AFAIK, joint 1.

@cnctechs can advise, but that might explain the difficulty you had with this.