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Velocity Acceleration Settings Heavy Gantry

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woodgraver
Posts: 1
Joined: Wed Nov 29, 2017 9:56 am

Velocity Acceleration Settings Heavy Gantry

Postby woodgraver » Sat Apr 21, 2018 11:07 am

First time posting. I have a Bullington Industries plasma table with a heavy gantry. Bottom line up front, everything I cut is "compressed" along the y axis (associated with gantry movement). The x axis comes out spot on. I have done the motor tuning and get repeatable results with accurate movement in both y and x, but when I go to cut something out...only the x movement is correct. I feel like everything is working the way it is suppose to...it just seems that it must be the acceleration setting that should be changed to compensate for the extra weight. I'm assuming velocity is just a matter of the cut settings used in sheetcam. Originally my CommandCNC Configurator was set up at 35 units/sec...I just adjusted that to 50 units/sec in both x and y...and really didn't notice any difference. Any insight would be appreciated. Thanks Jim

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Rodw
Posts: 133
Joined: Sun Aug 21, 2016 1:49 am

Re: Velocity Acceleration Settings Heavy Gantry

Postby Rodw » Mon Apr 23, 2018 5:33 am

I'd start by checking the axis is not binding at all. If its a stepper system, you could be loosing steps particularly if it has been working correctly before.
Reducing acceleration might help but that is a LinuxCNC INI file setting and not something you can control from Gcode (or sheetcam).
I think that CandCNC have a utility that changes these settings but...

.INI Settings in Linuxcnc for scale, velocity and acceleration are based on the device units (mm or inch)

Code: Select all

LINEAR_UNITS = mm


Each axis has settings for maximum velocity and maximum acceleration (in device units per second)
Max acceleration below is 2000 mm/second

Code: Select all

STEPGEN_MAXVEL = 700
STEPGEN_MAXACCEL = 2000


And axis scale is controlled for each axis (number of steps per device unit) by

Code: Select all

STEP_SCALE = 261.130715645

In this case 261.1 steps per mm

Of course it goes without saying to keep a backup of your system files before you play....

tcaudle
Posts: 1051
Joined: Tue Feb 28, 2012 6:47 pm

Re: Velocity Acceleration Settings Heavy Gantry

Postby tcaudle » Fri Apr 27, 2018 7:18 pm

woodgraver wrote:First time posting. I have a Bullington Industries plasma table with a heavy gantry. Bottom line up front, everything I cut is "compressed" along the y axis (associated with gantry movement). The x axis comes out spot on. I have done the motor tuning and get repeatable results with accurate movement in both y and x, but when I go to cut something out...only the x movement is correct. I feel like everything is working the way it is suppose to...it just seems that it must be the acceleration setting that should be changed to compensate for the extra weight. I'm assuming velocity is just a matter of the cut settings used in sheetcam. Originally my CommandCNC Configurator was set up at 35 units/sec...I just adjusted that to 50 units/sec in both x and y...and really didn't notice any difference. Any insight would be appreciated. Thanks Jim



1. The only parameter it could be that is off is the Steps per Unit on each Motor in the CommandCNC configurator
Screenshot-200.png




2. Make sure you are actually tuning the CONFIG that you are running. Worked with a guy for two days to finally find out he was changing one COnfig but running another

Screenshot-147.png


3. Acceleration is not going to be the issue unless its so high that its causing the motors to stall. Its set for each axis on the Configurator

Screenshot-121.png


So the gantry axis being Y has two motors assigned. It would be unusual for BOTH motors to be losing the exact same number of steps in both directions.

We have an online steps calculator where you use a simple tape measure and input the results and it tells yout the correct steps per unit to use. The velocity and acceleration have nothing to do with the POSITION and scaling of an axis.

Hint: After you have a working running Config make a TEMPLATE of it using the NEW tab in the configurator. A TEMPLATE is a Config taht can only be used to create a new CONFIG. You can't accidental mess it up. You can have as many different configs as you want.

Steps per unit calculator is and video is here https://www.candcnc.com/knowledgebase/tuning-stepper-motors-for-cnc/

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tcaudle
Posts: 1051
Joined: Tue Feb 28, 2012 6:47 pm

Re: Velocity Acceleration Settings Heavy Gantry

Postby tcaudle » Fri Apr 27, 2018 7:19 pm

Also: The screen shots are samples and your numbers and settings will be different


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