Author Topic: Very slow and "vibrating" movements in turns.  (Read 247 times)

Offline kobu83

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Very slow and "vibrating" movements in turns.
« on: August 30, 2022, 22:53:02 pm »
Hello, i have a new cnc machine, and used cambam with mach3 before on an other machine.

New its gonna very slow when i do v-engrave letters. For example, when i v-engrave the U.. first its gonna down, then the straight moves are normal speed, the "u-turn" is vibrating/jerking and very slow.

i know that are many very little steps/lines there, but i cant get it right.

i used different post proccesors, no effect.

Can it be that the cnc mainboard, is to slow/ to low memory or something?

its an usb board, AKZ250 mach3 board.

See the gcode file for the result.

Hope someone can help

Offline dh42

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Re: Very slow and "vibrating" movements in turns.
« Reply #1 on: August 31, 2022, 11:31:10 am »
Hello

Quote
i know that are many very little steps/lines there, but i cant get it right.

Yes this is a normal result, the bottom of the U is not only a curve on XY plane but also in XZ and YZ plane too, so no way to use true arcs (G2/G3), all is done with small segments (~ 0.1mm / segment)

The Gcode contain a G64 so Constant velocity is used and the movement should be smooth ...

What I see is that you're using a hight speed (2500 mm/min) ; With small segments + hight speed you also needs an heavy acceleration so the constant velocity is able to work properly. If the acceleration value is too small, you'll get jerking movement. (and if too hight you'll lose steps)

1) what is your acceleration values ?

2) check the Settings panel on Mach3 to see if both "CV distance" and "CV feedrate" are disabled (LED must be turned off)

++
David

Offline kobu83

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Re: Very slow and "vibrating" movements in turns.
« Reply #2 on: August 31, 2022, 11:49:30 am »
Motor tuning X and Y are:

Velocity 6000
Acceleration 400

Z is   1500 and 300

The CV distance and feedrate are turned off.

Hope u can give me advice :)

Offline lloydsp

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Re: Very slow and "vibrating" movements in turns.
« Reply #3 on: August 31, 2022, 12:21:25 pm »
Make sure your machine's own configuration is not set for 'dead stop' after a vector has been cut.

Lloyd
"Pyro for Fun and Profit for More Than Fifty Years"

Offline kobu83

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Re: Very slow and "vibrating" movements in turns.
« Reply #4 on: August 31, 2022, 12:24:33 pm »
Make sure your machine's own configuration is not set for 'dead stop' after a vector has been cut.

Lloyd

Where can i change/see that?

Offline lloydsp

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Re: Very slow and "vibrating" movements in turns.
« Reply #5 on: August 31, 2022, 12:26:01 pm »
It's not normally a CB setting.  Rather, it would be something in your machine's config file(s).

Lloyd
"Pyro for Fun and Profit for More Than Fifty Years"

Offline dh42

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Re: Very slow and "vibrating" movements in turns.
« Reply #6 on: August 31, 2022, 12:30:48 pm »
The G64 is present in the GCode so constant velocity is enabled in Mach3 ..

can you have a try with slower feedrate (like 1000 mm/min)

also be sure that the Feedrate Overidde is not used (FRO = 100%), when an override is used this can give jerking movements even with constant velocity enabled.

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David

Offline kobu83

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Re: Very slow and "vibrating" movements in turns.
« Reply #7 on: August 31, 2022, 12:55:35 pm »
It's not normally a CB setting.  Rather, it would be something in your machine's config file(s).

Lloyd

Maybe a dumb question, but where can i find machine config files? I only have mach3 for change settings next to cb

Offline kobu83

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Re: Very slow and "vibrating" movements in turns.
« Reply #8 on: August 31, 2022, 13:00:01 pm »
The G64 is present in the GCode so constant velocity is enabled in Mach3 ..

can you have a try with slower feedrate (like 1000 mm/min)

also be sure that the Feedrate Overidde is not used (FRO = 100%), when an override is used this can give jerking movements even with constant velocity enabled.

++
David

FRO is 100%, i tried feedrate 1000 and its almost okay, with feedrate 800 no jerking movements.

But.. when i speed up acceleration, then i see no differences at feedrate 1000, so 800 is my max?


Is it possible that my cnc mainboard can't get to the gcode files that fast, that that causes the jerking? I'm thinking of getting a newer usb/mach3 card for my cnc machine to make sure this causes not my speed limits in this files with very much gcode lines in a very small workpiece

Offline dh42

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Re: Very slow and "vibrating" movements in turns.
« Reply #9 on: August 31, 2022, 13:21:09 pm »
Ok, so the acceleration at 400 is not sufficient for the constant velocity to work well at 2500 mm/min

Quote
But.. when i speed up acceleration, then i see no differences at feedrate 1000, so 800 is my max?

I don't know, unfortunately I have no machine available to try your file to see what happen with 2500/400 ...

Quote
Is it possible that my cnc mainboard can't get to the gcode files that fast, that that causes the jerking? I'm thinking of getting a newer usb/mach3 card for my cnc machine to make sure this causes not my speed limits in this files with very much gcode lines in a very small workpiece

Have a look in the board plugin, maybe there is other settings that are not mach3 native and that control the constant velocity/exact stop ..

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David
« Last Edit: August 31, 2022, 13:26:57 pm by dh42 »

Offline kobu83

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Re: Very slow and "vibrating" movements in turns.
« Reply #10 on: August 31, 2022, 13:35:54 pm »
Guys!  I have found it, was reading on an other cnc forum via google on jerky movements cnc.

The mach3 general settings have a option  "gcode look-ahead"

This is in my opinion a sort of buffer, that the machine looks forward in the gcode lines for what is coming.


This was set to 20 lines, i set it to 200 lines, and all was smooth! Now i set it at 500 lines for be sure that is causing no problems for me anymore.

I can run the same jerky files at feedrate 5000!! And all is working smooth!

See picture, hope to help some else with this solution who is searching here in the future for this.


Thanks to all for trying to help

See picture for what i changed.

Offline dh42

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Re: Very slow and "vibrating" movements in turns.
« Reply #11 on: August 31, 2022, 13:36:53 pm »
One thing you can try in the V-Engrave mop is to use a larger value for "Path Step Size" so you'll get longer segment, maybe it can improve things ...

also you can try to increase the "lookAhead" value in the Mach3 general settings, so more GCode lines will be processed for the path planner (for constant velocity)

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David

Offline dh42

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Re: Very slow and "vibrating" movements in turns.
« Reply #12 on: August 31, 2022, 13:38:33 pm »
ah! you were faster than me ;)

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David

Offline kobu83

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Re: Very slow and "vibrating" movements in turns.
« Reply #13 on: August 31, 2022, 13:45:58 pm »
ah! you were faster than me ;)

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David


Hehe okay... just a minute earlyer! Give u some credits too! Thanks! ;D ;D

Offline dh42

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Re: Very slow and "vibrating" movements in turns.
« Reply #14 on: August 31, 2022, 13:53:34 pm »
some additional infos about Constant Velocity ;)

https://www.machsupport.com/wp-content/uploads/2013/02/Mach3_CVSettings_v2.pdf

++
David