Z Axis Intermittent Drop After Homing

j-kelley

J.Kelley
Hope you folks can help.

I just finished the mechanical portions of my machine build and have reached the tail end of my tuning of the each axis. I wired up the homing switches on Wednesday and everything has been working great where homing is concerned. Tonight I setup my tool pre-setter and selected "auto tool zero" in the setup (F1) screen. When I home the machine now, the Z axis triggers the home switch then starts to rapidly drop about three to four inches, stops, then does it again, all the way to the mill's table. A $60 end mill bit the dust in the process before I could stop it. The only thing I changed from last night to now was selecting "auto tool zero" in the setup menu. Now, even with "auto tool zero" deselected, the Z axis does this intermittent drop to towards the table like it has a mind of its own. I literally just had a successful homing to zero the machine out for the purpose of locating the tool presetter. Prior to the conversion from DC servos to the DMM Technologies, this auto zero worked flawless.

Any ideas?
 

breezy

Arie
Staff member
When I was having that problem I had the physical homing location in the right rear corner but my machine XYZ zero location in the left front corner so in the homing screen I set homing values as X1103 & Y1075 but in the axis setup I had X1100 & Y1070 as the axis length, so my homing position was outside the soft limits. Since then I have modified the machine with new homing sensors and homing location in the left front corner, the home values are X0 & Y0. The tool setter location is inside the homing location so the machine homes and then move to about X20 & Y 100 to the tool setter plate and measures the tool. WCS is approximately a further 200mm inside that point so the tool setter is outside the work envelope.
Quote from J.Kelley on November 30, 2019, 5:52 am

When I home the machine now, the Z axis triggers the home switch then starts to rapidly drop about three to four inches, stops, then does it again, all the way to the mill's table. The only thing I changed from last night to now was selecting "auto tool zero" in the setup menu.

In the ATZ screen what is the XY position, safe Z distance and Z feed rate set at? Is the machine homing correctly before moving into the ATZ phase of the homing cycle?
A $60 end mill bit the dust in the process before I could stop it.

Ouch!!! But that is cheaper than bending a Drewtronics probe. When I change to the Drewtronics I have to connect the probe tip to machine common with a fly lead so that the tool length can be measured.

Regards,

Arie.
 

j-kelley

J.Kelley
Mr. Brown,

Thank you for your reply and the help. While you were typing your reply, I was in the shop seeing how frustrated I could get myself. I deselected the Z axis in the homing order and X and Y homed fine by themselves. I then deselected the X and Y while selecting only the Z and it worked fine as well. With all selected (Z first then X and Y simultaneous) it worked, then it didn't. Growling at this point, me not the machine, I tested it a few more times and occasionally would get a homing alarm on the Z followed by flawless action. If I hadn't started to lose my hair at 40 years of age, it would have started tonight. The machine works great if I jog it, haven't tested any code yet. The DMM servos have encoders preset to around 4096. I turned it down to 1000 to get the max speed out of the machine but that possibly could be an issue, not sure. I don't think that would do it, but I'll re-tune the Z axis tomorrow and turn the encoder count back up to its default to see if that stabilizes things. I'll let you and the community know for everyone's benefit. The head unit on the Z weighs over 200 pounds, so that one servo is a bit more stressed than the other two.



Thanks again for the help!

Regards,

Jason
 

j-kelley

J.Kelley
Arie,

I'll look at those settings tomorrow and respond with better answers than I can generate tonight. It's after 2am here in Texas and I'm a little spent. Thank you for kicking in and trying to help. More to follow in the morning, but for now I can say that due to intermittently working, my settings there likely aren't the issue. Stranger things have happened though.

Many, many thanks,

Jason
 

breezy

Arie
Staff member
Jason,

Been thinking about your problem, you say you adjusted the servo settings to get speed, this could be the cause of the Z axis dropping.

When I was setting up the Bicton Men's Shed CNC router I had the Zaxis speed and acceleration settings to high, which cause the stepper to stall, so I went to very conservative settings and when the machine was moving smoothly I started increasing speed and acceleration by about 10% increase at a time until I was happy. The machine could probably go faster but I'm not going to push it.

Regards,

Arie.
 

wrexler

Wrexler
For giggles... turn off the WiFi

I had my machine homing perfectly. I setup some other options (wifi included) and the thing seemed to go to pot.

it may help, it may not.. easy enough to try.

Good luck
 
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