»Coin« style corners on cast acrylic. How can i improve?

[typomaniac]

Hey,

i am struggling with the right settings for cutting cast acrlic. My laser is a buildlog 2.x with LO x7 controller. It works fine when it comes to straight cuts in 3 mm cast acrylic. However as soon as i try to cut more curved objects the corners are always »jagged/coin style« (or how do you call that). How can i improve that? More speed or less speed? More power or less power? Changes in the resolution setting? Microstepping? I have no idea where to start My current setting is 25.375 micrometers/pulse on the y axis and 25 on the x-axis. (I changed belts to gt2 on x and still use mxl on y) Both axis use 1,8 degree / step motors with 1/8step/ pulse on the driver.

thank you!
tm

[Tech_Marco]

What speed did you use? How powerful of your laser tube?
Did you turn on air-assist? For acrylic cutting, you may not want to have to strong air but just high enough to blow the smoke from the lens

Marco

[typomaniac]

Hey Marco,

my tube has 40 w and i engraved and i cut with 50 % power settings (which translates to 20 ma on my meter and the maximum my tube can handle). Cut speed is
set to 5. Air assist is on but since i do not have a real nozzle yet the air pressure on the object is pretty low.

thank you!

tm

[Tech_Marco]

Try double speed and run it in two passes see if getting improvement

Marco

[typomaniac]

i already tried this but it did not make a noticeable difference ...

[typomaniac]

I just recognized, that this corner quality also appears on straight cuts. I had a few good cuts before but now this is the result. The straight cuts are smoother but you can see the coin style on every corner. I did not change anything on the settings of the laser but it seems that the dsp sometimes forgets settings.

[waltfl]

hi
first a power of 20mA is waty to high for a 40W tube max should be 16mA or you loose your tube very fast.
second check your drawing if it has lots of nodes try to eliminate as many as you can because this are one major reason for this jagged cuts.
gretings
walt

I just recognized, that this corner quality also appears on straight cuts. I had a few good cuts before but now this is the result. The straight cuts are smoother but you can see the coin style on every corner. I did not change anything on the settings of the laser but it seems that the dsp sometimes forgets settings.

[typomaniac]

ok i did not know that this was to high. I decreased the power to 16 mA. The drawing is fine. I made a test circle within lasercad which has only 4 nodes and nothing in between ... i have no idea : (. I also decreased microstepping as suggested on the buildlog forum but without better results so far

tm

[Tech_Marco]

Check the belt tension. Make it a little firm but not very firm. You may press it down with finger and the belt should be able to down 20mm. If it is too soft, you may get distortion or non-linear result. If the belt tension is too tight, it will slow down the machine, and the belt will wore out quick.

Micro-stepping should be set in between 1/16 (3200) to 1/25 (5000). Usually, I set it to either 3200 or 4000.

You may want to swap the motor driver and give it a try. Also, you may want to try low speed cutting like 1mm/s or 2mm/s see if there is any change.

Download two testing files that I used for machine testing from the "Manual Download" area and check the alignment and the pattern result


Marco

[typomaniac]

Thank you Marco,

ok i checked belt tension. It moves around 20 mm (maybe a little more in the middle on and a little less on the sides. Microstepping is now reduced to 1/16 as suggested. Motor driver swapping is something i would like to do as a last step because of the money. I will try ultra low speed cutting tomorrow. I already made the test pattern and will attach it to this post. The picture is a little bit grainy. If the quality is not good enough please let me know and i will take a better one in daylight. The outer line already shows wobbles. I made a second version where i highlighted what i can see in the grainy picture. One thing i noticed: When the laser head moves on the x-axis i can see that there is vibration on the belt - i do not know if that helps with finding the problem.

thanks

tm

[Tech_Marco]

Send me the setting on the DSP. I need to see the "User parameters" and "Manufacturer parameters"

Marco

[typomaniac]

of course! Please find them attached ...

[Tech_Marco]

Change the "Speed_Factor" from '3' to '1'
Space_Jerk: Change it from 50,000 to 30,000
Cut_Jerk: Change it from 20,000 to 10,000

Give it a try and let me know what you found

Marco

[typomaniac]

Hey Marco,

ok we are getting closer. I tried your settings and they helped with corners which were way more edgy before. The coin effect did not improve that much but the
overall cut. Additionally i did the following: The drivers were set to 0.63a as in the wiring diagram. The nema 17s are rated for up to 2.5a. I increased current to 1.5 a
and the edge (together with your settings) is better. It is still jagged but you can notice a difference. Is this a coincidence? Can i make more changes in the settings?

thank you
tm

[Tech_Marco]

Set the driver current to 2.8~3A and give it a try
Your system was under current a lot

Also, what is the hardware version on the DSP?
I will post an update today for better curve handling.

Marco