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Author Topic: Problem with Z axis  (Read 1409 times)
imr700x
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« on: May 30, 2019, 11:59:04 am »

Recently I have been doing some 3D stuff and when I cut a dome shape where the Z is constantly moving up and down I get problems. The motor gets hot (40C) in about 10 minutes and the Z doesn't come right down each time but does rise the correct amount so that there is a curved ramp sort of shape rising up at the end of the cut. I rough the surface with a 6mm then do a finishing pass with a 3mm round nose and a 0.1 step over and it happens on the finishing pass. The domes are 160mm diameter with a 6mm rise in the middle and the dome is a regular arc.

The Z always fails to come down correctly and the cut rises gradually and regularly. On normal curves where the Z only moves at the end of the cut it works fine for hours.

So far I have dismantled the axis and check all the part and looked for anything caught in there,changed motors (425 inch oz Nema 23 with a 1605 ball screw), driver and put it on its own power supply,replaced the breakout board, changed the micro stepping from none up to eight, raised and lowered the current on the driver to the motor, raised and lowered the acceleration, going across the grain and with the grain, reinstalled Mach 3 and just today tried it with another PC (XP). The machine has shielded wiring and ferrite rings already everywhere that could be fitted.

Now I am totally out of ideas and any suggestions will be appreciated.

Dennis
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Bubba
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« Reply #1 on: May 30, 2019, 13:31:47 pm »

Sound like you losing steps, slow the velocity down(about 10%) in Motor Tuning & Settings, in Mach3. Wink
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onekk
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« Reply #2 on: May 30, 2019, 17:01:46 pm »

Maybe is a driver current settings, I don't know what driver you are using, but in my recent Z axis failure I have repaced the entire Z-Axis assembly, with an OpenBuilds C-Beam type, but this type has a trapezoidal screw with a pitch that is not holding the weight of the Z-Axis, so the if the Z-motor is not energize it slowly come down by itself.

I don't know if the ball screw are "not reversible" and maybe the driver is not energized in some situation (some controllers have to be set to matain them energized after some time).

If the motor is warming, maybe the current is too high and the internal protection of the driver is engaded and result in losing step and loss of "holding torque" that cause the Z-axis to go down.

The stepper motor circuit has to be tuned if you change the motor and also the wiring, as generally it is done with a circuit that sense the curretn flowing in a resistor and derive from the voltage loss the current. Generally speaking, there is a trimmer or maybe some "eletronic settings" in the driver to set the correct current that depends on the motor specifications.

What driver are you using?

Regards
Carlo D.
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Carlo D. (onekk)

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lloydsp
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« Reply #3 on: May 30, 2019, 17:33:57 pm »

I agree with Carlo.  I don't see any reason why too-high a step rate would overheat the motor.  It's more likely to be a driver current setting.

I still think you should adjust the step speed, in order to avoid those missed steps.  I just don't think that relates to the overheating issue.

Carlo, have you considered adding an air cylinder to counter-balance the spindle weight?  My router has such, and (so long as the air supply is on), it will not rise or fall, even when power is totally removed from the Z motor.

Lloyd
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dave benson
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« Reply #4 on: May 31, 2019, 02:42:16 am »

Hi Dennis

Quote
The Z always fails to come down correctly and the cut rises gradually and regularly.
On normal curves where the Z only moves at the end of the cut it works fine for hours.

The problem may lay in the 3D Mop in your file and not your machine, David gave a good explanation in this thread
http://www.cambam.co.uk/forum/index.php?topic=7980.msg64006;topicseen#msg64006
Where he gave some good advice about 3D settings to Geoff about a similar issue.
If you post the CB file perhaps someone could spot your problem and save you some Headaches.

Dave
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imr700x
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« Reply #5 on: June 01, 2019, 03:08:05 am »

Thank you to all for your thoughts.

The more that I played with setting the worse it got until the z stopped working altogether but I have found the problem. When I reloaded Mach3 I couldn't find the flash drive with the version that I installed originally so I downloaded the latest version and when I installed it it found my licence and I thought nothing more about it until I noticed yesterday when playing with the accel and speed setting Z saved so I downloaded and installed an older version R2.63 and now it is working as it was before.

@Bubba when you say 10% do you mean that as a percentage of the current setting or set to 10 as I notice that the GRBL default is 10, I have had it at 100 for the last 4 years but do get jittery movements when engraving on 3D surfaces. I only chose that setting because I saw it on the Mach3 screen on a youtube video.

@Carlo  My Z does come down very slowly when I turn the power off to the steppers and sometimes breaks the tips of engraving bits but I usually catch it in time.  The drivers (HY-DIV268N-5A) are rated at 5 Chinese amps so are probably good for 4 amps but I have had them set at 3.3 amps normally.

@Lloyd I have it running now and am lowering the current settings each half hour until it stops working.

@Dave  I did see that thread before I posted while looking for ideas. The search function in this forum is a major learning source for me. I think that I might have found the problem but here is the file.

Thanks again to the brains trust.

Dennis

* text on surface.cb (1047.47 KB - downloaded 37 times.)
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EddyCurrent
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« Reply #6 on: June 01, 2019, 09:59:04 am »

The preferred version of Mach3 is 3.043.062 (even if you are not using the warp9 Smooth Stepper)

https://warp9td.com/index.php/sw/software-mach

All Mach3 versions are here;
https://www.mmnt.net/db/0/0/machsupport.com/Mach3
« Last Edit: June 01, 2019, 10:04:03 am by EddyCurrent » Logged

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Bubba
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« Reply #7 on: June 01, 2019, 13:24:28 pm »

@Bubba when you say 10% do you mean that as a percentage of the current setting or set to 10 as I notice that the GRBL default is 10, I have had it at 100 for the last 4 years but do get jittery movements when engraving on 3D surfaces. I only chose that setting because I saw it on the Mach3 screen on a youtube video.
*****************************

I meant, after you set the axis velocity to max speed where you see the machine movement is smooth and without stalling , etc, set it back about 10% (percent)as safety margin. That how I set my machines and never lose steps. Knock on wood.. Hope this helps. Wink    
« Last Edit: June 02, 2019, 11:56:57 am by Bubba » Logged

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onekk
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« Reply #8 on: June 02, 2019, 10:55:00 am »

@lloydspy thanks for the advice, but for now adding an air cilynder seem too overkill for my hobby cnc router, I have seen a more cheap system using a pulley and a counter weight that seem more "affordable", but for now keeping energized the coils it seem a good solution, as the driver are not overheating so much and when not i use I put in sleep mode my GRBL controller.

Regards

Carlo D.
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Carlo D. (onekk)

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lloydsp
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« Reply #9 on: June 02, 2019, 13:22:25 pm »

Carlo wrote:
"...I have seen a more cheap system using a pulley and a counter weight that seem more "affordable",..."

-----------

It's very easy to move in Z faster than the acceleration of gravity.  Weights are a poor system.

But if you don't need a counterbalance, then any system is a poor substitute for "none at all".

Lloyd
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onekk
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« Reply #10 on: June 02, 2019, 15:51:21 pm »

@lloydspy

Yes, but in my case is an hobby cnc with this type of Z axis added:

https://openbuildspartstore.com/c-beam-linear-actuator-bundle/

with some cheap and compact Nema 23 motors, (1.8 A max)

So I'm aware of the limitation of such configuration and can live with them.

Regards

Carlo D.
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Carlo D. (onekk)

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imr700x
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« Reply #11 on: June 23, 2019, 00:05:55 am »

Update. The problem started to happen intermittently again so I tried a FLIR app on my phone to see if there was something getting hot and sure enough, the connector at the Z motor was getting hot but not at the pins but inside the plastic housing. I nested ten of the tops, disabled the X and Y axes and ran the file and watched the plug on the phone and it started to glow after about 10 minutes on one of the wires so cut off the plug and soldered the wires ran it over night simulating cutting 200 tops and checked the Z zero this morning and it is at zero.

I had checked the resistance of the entire wiring system earlier but not when it was hot and running so a $1 plug was the culprit.

Thanks again for all the advice.
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lloydsp
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« Reply #12 on: June 23, 2019, 00:36:22 am »

Hooray!  Sometimes, it takes a bit of trouble-shooting -- for sure!

Good job!

Lloyd
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