Ghosting laser while rastering



  • I am having another go at running my K40 laser using a duet 2 rather than an MKS Sbase running grbl.
    I am having issues with raster images having ghosting and not coming out with clean edges. This results in all images being blurry.
    PXL_20201103_140631583.jpg
    The PWM control is connected to the negative terminal of the bed MOSFET.
    I use M452 c"bed heat" F5000 in my config and I have tried in both S0 and S1 modes.
    Does anyone have any thoughts?

    I should add that it works fine with grbl


  • administrators

    Which firmware version are you using, and what PWM frequency have you set for the bed heater?



  • 3.1.1 and I have set a frequency of 5000


  • administrators

    That sounds good, but please post your config.g file.



  • ; Configuration file for Duet WiFi (firmware version 3)
    ; executed by the firmware on start-up
    ;
    ; generated by RepRapFirmware Configuration Tool v3.1.4 on Tue Jul 21 2020 12:06:50 GMT+0100 (British Summer Time)
    
    ; General preferences
    G90                                            ; send absolute coordinates...
    M83                                            ; ...but relative extruder moves
    M550 P"K40 Laser"                             ; set printer name
    
    ; Network
    M552 S1                                        ; enable network
    M586 P0 S1                                     ; enable HTTP
    M586 P1 S0                                     ; disable FTP
    M586 P2 S0                                     ; disable Telnet
    
    ; Drives
    M569 P0 S1                                     ; physical drive 0 goes forwards
    M569 P1 S1                                     ; physical drive 1 goes forwards
    M569 P2 S1                                     ; physical drive 2 goes forwards
    M569 P3 S1                                     ; physical drive 3 goes forwards
    M584 X0 Y1 Z2 E3                               ; set drive mapping
    M350 X16 Y16 Z16 E16 I1                        ; configure microstepping with interpolation
    M92 X160.00 Y160.00 Z400.00 E420.00              ; set steps per mm
    M566 X500.00 Y500.00 Z12.00 E120.00            ; set maximum instantaneous speed changes (mm/min)
    M203 X6000.00 Y6000.00 Z180.00 E1200.00        ; set maximum speeds (mm/min)
    M201 X500.00 Y500.00 Z20.00 E250.00            ; set accelerations (mm/s^2)
    M906 X400 Y800 Z800 E800 I30                   ; set motor currents (mA) and motor idle factor in per cent
    M84 S30                                        ; Set idle timeout
    
    ; Axis Limits
    M208 X-5 Y0 Z0 S1                               ; set axis minima
    M208 X300 Y205 Z200 S0                         ; set axis maxima
    
    ; Endstops
    M574 X1 S1 P"xstop"                            ; configure active-high endstop for low end on X via pin xstop
    M574 Y2 S1 P"ystop"                            ; configure active-high endstop for low end on Y via pin ystop
    
    ; Laser Mode
    M452 C"bedheat" F5000 S1
    


  • I can upload a gcode file if required



  • @dc42
    I have tried gcode from two different programs (lightburn and laserweb4) and they both do the same thing. I had thought that it was linked to the gcode being used but it doesn't seem to be.
    I also tried upping the frequency to 10000, 15000 and 20000 but the blurring is still present.
    I am happy to upgrade to the latest beta and retest



  • I've switched back to the grbl board as my wife wanted some laser cutting doing.
    Here is a comparison of grbl to duet.
    The grbl is the disc, the duet version is just the writing on the wood.
    Both generated using lightbulb
    PXL_20201104_183607566.jpg



  • I'm going to guess it has something to do with the speed that the Duet turns your laser tube on and off compared to the GRBL controller. You can fine tune this adjustment in Lightburn with the "Scanning offset adjustment". It's a pretty straightforward process and I imagine you'll be surprised at the results.

    Scanning Offset Adj. - How-To



  • @Arcnsparks great. Didn't know that guide existed. I'll swap the controllers back and take a look tomorrow.


  • Moderator

    Moved to the new laser category



  • @jay_s_uk said in Ghosting laser while rastering:

    I am having another go at running my K40 laser using a duet 2 rather than an MKS Sbase running grbl.
    I am having issues with raster images having ghosting and not coming out with clean edges. This results in all images being blurry.
    PXL_20201103_140631583.jpg
    The PWM control is connected to the negative terminal of the bed MOSFET.
    I use M452 c"bed heat" F5000 in my config and I have tried in both S0 and S1 modes.
    Does anyone have any thoughts?

    I should add that it works fine with grbl

    Hi,

    I am looking to do something similar. Have you noticed any other differences or quirks moving from GRBL-lpc to duet other than the ghosting? I am interested in increasing my raster speed. This is for a faster laser than a k40



  • Hi @jay_s_uk , have any luck with your setup? Just curious if the scanning offset adjustment helped out any.



  • @Arcnsparks tbh I've gone back to grbl for the moment. Too many other projects and the Mrs wanted some stuff cutting



  • @jay_s_uk Definitely understand that!


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