1300 Pro Z axis brake applied on rapid home or toolchange

[johnparker]

I started a thread in VR Milling, thinking I had a software problem, but further diagnosis shows a problem with my 1300 Pro Z axis brake.
The symptoms are for commands
G91 G28 X0 Y0 Z50
or
M0 T06

the machine starts to go up in Z, but makes a really bad noise and Z stops moving without going home.
Video here https://crcccc.org.uk/downloads/Denford2.mp4

Having read this thread viewtopic.php?f=4&t=2534&p=9214#p9214 about the brake, I removed the Z brake and tried again - all fine.

I suspect that the brake solenoid is starved of power when the three drive motors all start together in rapid. Machine in unheated garage, so grease is cold. I wonder if I can reduce the speed or rapid home for G28 or M0, or sequence the motors so they start Z - X - Y phased instead of all together to reduce surge power.

[TDIPower]

I keep one of these tubular heaters inside the case of my Microrouter pro only set to come on at 7c to keep condensation off things though, I had considered setting it to higher for when I want to do work.

https://www.screwfix.com/p/dimplex-ecot ... lsrc=aw.ds

Pete

[Steve]

The machine stalled while making the rapid z movement. this could be for various reasons. Have you greased the machine rails as stated in the manual? Disconnecting the brake could be just a coincidence as I doubt that this is the issue. The brake needs to be connected otherwise the axes will fall when the power is disconnected and the machine may not home correctly.

It may be possible to increase the power to the Z motor by changing the switches on the Z axis drive. The homing feed rate is slower than the rapid so is less likely to stall.

If you go into Setup machine parameters enter the password of denny

you can then reduce the Z maximum feedrate but I would also reduce the max rapid rate to match this.

If you set it to 3000 or 4000 I think this will be fine.

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[johnparker]

Thanks for that info Steve, just what I need I think.
I have just done a full greasing on all the ballscrews, including the really tricky to get at ones!

I did disconnect the Z brake, noting the axis will fall under it's own weight. I then tested the same rapid homing without any issues. I reattached the brake, and the first toolchange rapid home screamed and the Z axis stayed where it was, as in the video. The screaming noise was just like the handbrake left on, so I'm pretty certain the Z brake solenoid was letting go when all the steppers were max loaded.

I think I will employ a combination of gentle heating and lowering the speeds. I may also test the current being drawn by the brake solenoid.

[Steve]

John,

I would also check the version of software you are using and make sure you have the latest. I don't think there will be an issue with the power. The brake is on the 24V DC rail and the steppers use a 63V supply so they would not effect that.
In fact with stepper motors the load is higher when stationary. Its possible the brake fiber washer is rubbing slightly causing the stall. Once a motor stalls it cannot correct its self but so will just sit there screaming.

If you take a photo of the stepper drives in the back of the machine there is a current option on the Z axis that can be changed.
The settings are by default:
MSD880
1 OFF
2 ON
3 OFF
4 OFF
5 OFF
6 OFF
7 ON
8 OFF

5000 Pulses/Rev 4.6A RMS

I would just lower the rapid on all 3 axes to 4000mm / Min and all will be well.

[johnparker]

I am up to date with V5_68

My drives are set:
1 ON
2 ON
3 OFF
4 OFF
5 OFF
6 ON
7 OFF
8 ON
Which the datasheet tells me is 5.7 Peak, 4.1 RMS, so one setting softer than your default listing

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stepperdrivers.jpg (105.34 KiB) Viewed 15704 times

[Steve]

Set as our default should help.

[johnparker]

Thanks, will set per your default and lower the speed next week and see what happens

[johnparker]

I did the adjustments per Steve's posts and added the heater on lowest setting and now can home and toolchange without issue. I'm happy the G28 goes to top of Z before homing X and Y. Thanks both