Hi,
I am nearly going around the bend.
Have a self build CNC and all of a sudden I have a problem with the Z axis gaining steps for NO apparent reason.I have tried anything I can think of to fix the problem to NO avail,
Can anyone help please!
Terry
Hi,
I am nearly going around the bend.
Have a self build CNC and all of a sudden I have a problem with the Z axis gaining steps for NO apparent reason.I have tried anything I can think of to fix the problem to NO avail,
Can anyone help please!
Terry
Terry,
Post a video so we can try and evaluate your machine.
Jeff...
Patience and perseverance have a magical effect before which difficulties disappear and obstacles vanish.
What do you mean by 'gaining steps'?
Z axis ends up being lower or higher at the end of a job?
It HAS been running ok in the past?
Steve
Hi Jeff,
Thanks for your quick reply. I have to go away for a couple of days, but will post a video as soon as I get back. Thanks again.
Regards
Terry
Hi Steve,
The Z axis ends up lower. Mach 3 programme tells me it should be at a depth of 3mm but the read out is showing the actual depth of the bit is say 15mm.
It never done this in the 10 years since I built it.
I have not used it in about three months.
Regards
Terry
When it is supposed to be cutting at a depth of 3mm, it is actually cutting 15mm deep.
Sounds like Sterob is right, it normally means losing steps on it's way up. Measure it. Set the Z zero carefully and then issue a G0 Z100 command and check if it is raised 100mm or more. If it is more then you get extra steps, if less then you have lost steps, if at 100mm then you have no problems with the upward movement (at least once). Now issue a G0 Z0 command and see where the Z ends up. Be careful, you need to have space between the Z zero and the table just in case you get extra steps on the way down. Anyway, measure again and see where the Z is. Is it below zero then you get extra steps, is it over zero then you lost steps on the way down.
But... not necessary steps gain/loss, may be mechanical issue or some configuration change. Maybe your Z speed or acceleration (or both) is too high. A video to demonstrate the problem would really help.
When it is supposed to be cutting at a depth of 3mm, it is actually cutting 15mm deep.
Blimey. That is not missing a FEW steps, that is wholesale failure.
Acceleration and max velocity being too high is one thing which comes to mind.
Slipping of couplings is another thing. Grub screws wear loose.
Electrical noise somewhere is always a serious possibility, but we would need to know about the motors and drivers and the whole layout.
A serious question: are the X and Y axes running dead right? Does G0 X100 (from 0) give exactly 100.00 mm?
Cheers
Roger
Thanks Roger,
I thought of grub screws, but, the problem is that the bit cuts deeper into the wood so would require more grip, which sort of rules out loose grub screws.
All other axis are OK. I have direct drive stepper motors, no pulleys..I like your suggestion of noise. My "Drivertest.exe" file wont work in Mach3 so I can test noise in the driver file. I have emailed Scott at Mach3 to see if he can help.
Yes, I have reset Z Axis to 100mm Mach3 agrees that is the distance that it has moved, and I have measured the distance to be 100mm as well.
Other than noise, I am at a loss..
This problem has occurred only after about a six month of the CNC laying idle. I think it's a female!!!!!! (fighting words)
Regards
Terry
Hi Mate,
I have checked the distance moved, it is correct. I will play with the dip switches on the motor drivers and slow down the Acce and velocity in Mach3 to see if that helps.
Regards
Terry
Thanks for the videos.
the bit cuts deeper into the wood so would require more grip, which sort of rules out loose grub screws.
Not really.
At high spin speed, it does not take much to sink a cutter into timber. Timber is SOFT. But if the Z motor has to work hard to lift the weight of the spindle, it could be slipping on the upwards without slipping on the downwards.
This problem has occurred only after about a six month of the CNC laying idle.
That is curious. That does not sound like SW, and it does not sound like a change in electrical screening - unless things were changed when you powered the machine back up recently.
Some fairly boring detailed testing is going to be necessary. Find two blocks of plastic or aluminium, one thin and one thick/long. Align Z axis to thin block height, then run up to where the bigger block just fits. Now cycle up and down, one stroke at a time, checking to see what happens at both top and bottom. Use the two blocks as reference points.
I find a short bit of 1/8" PVC welding rod with a clean end to be very good for this sort of thing. If there are any hiccups, the PVC rod just bends or breaks. No harm done.
Cheers
Roger
Thanks Roger I'll try that and report back.
Regards
Terry
Also try with and without the spindle running. Interference (noise) from the spindle drive is notorious.
Cheers
Roger
Agree with roger.
When fault finding,dont make any assumptions. Check everything and work methodically through.
I even suggest removing the z stepper and spinning ball by hand ( power off ) to see if you can feel any binding at all.
Steve
Sent from my SM-G920I using Tapatalk
Mate, all the trials that I have run has been without the spindle running. It is a 3KW spindle which produces a lot of noise. All cables running to and from the VFD are heavily insulated and mains earthed.
My guess as said earlier is the Z is loosing steps when moving up against the force of gravity. Say for example, you move up 10mm and the machine looses some steps and only moves up 5mm.. Before long, you are a lot lower than you should be. Maybe something has seized while sitting there or you need some lube. Reduce your acceleration and velocities. I have experienced this. I set speeds and velocities for my plasma cutter after testing with a dial indicator under the Z without loosing steps. But in the real world, there was a lot more jerky movement (short moves at high speed). And yes, my plasma torch was trying to cut 7mm below the surface so I got to test my magnetic break away mount!
Rod Webster
www.vehiclemods.net.au
Thanks guys, I really appreciate your suggestions. I will try them all. If I can't get it to behave I think I'll rewire the Z Axis stepper motor from BOB to motor.
Thanks again everyone.
Regards
Terry
How did you go? Did you find any problems?