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Thread: help: arc/circle cutting offset start and end points on a Shenhui machine

  1. #1
    Join Date
    Mar 2012
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    Menomonee Falls, WI
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    help: arc/circle cutting offset start and end points on a Shenhui machine

    To all Shenhui owners:

    I have an issue when cutting circles or arcs in that the start and end points are slightly skewed leaving a line on the edge of the piece it cuts. The end of the cut seems to always be very slightly to the inside of the arc. I've done quite a bit of testing and trials and can't seem to find a solution but here is what I have tried and the results that follow.

    laser head has to move across the table to the start point from another cut:
    cutting a circle clockwise from the 9 o'clock position: start point just to the left of the end point
    cutting a circle counter-clockwise from the 9 o'clock position: start point just to the left of the end point
    cutting a circle clockwise from the 12 o'clock position: start point just above the end point
    cutting a circle counter-clockwise from the 12 o'clock position: start point just above the end point

    laser head is at the upper left of the start point already:
    circle is cut in the 4 above ways and turns out perfect each time.

    slowed down idle laser move speed: still starts and ends slightly off.

    adjust "X" belt tension: no effect, still slightly off

    adjusted "X" backlash in user settings: shifted the bottom and top of circle to create and offset circle with horizontal lines on the left and right side. if I got it accurate enough to to line up the starting side of the circle it left a horizontal line on the right..

    size of circle doesn't seem to matter, the start and end point are always the same tiny distance apart.

    This only happens when cutting circles and arcs, cutting squares, even starting in the middle of the side of the square instead of the corner ends up it perfect start and end points.

    Please Help!!!
    Shenhui dual head 80W 1200x900

  2. #2
    Join Date
    Oct 2004
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    Use the Lead in , lead out in the software , its in the menu under Edit then Edit cut in properties
    Basically it allows a start and end point inside (or outside) the circle , if you want the plate with the circle cut out of it , start your lead in and lead out INSIDE the circle and then the plate and perfect circle cut out remains , if you want the circle and not the surrounding materal , start your lead in and lead out OUTSIDE the circle - using it will give you perfect circles without the "ridge"

    You can control angles and type of line/curve and its length for lead in and out and control whether it comes from outside or inside the circle (to or at centre)
    Rodney Gold, Toker Bros trophies, Cape Town , South Africa :
    Roland 2300 rotary . 3 x ISEL's ..1m x 500mm CnC .
    Tekcel 1200x2400 router , 900 x 600 60w Shenui laser , 1200 x 800 80w Reci tube Shenhui Laser
    6 x longtai lasers 400x600 60w , 1 x longtai 20w fiber
    2x Gravo manual engravers , Roland 540 large format printer/cutter. CLTT setup
    1600mm hot and cold laminator , 3x Dopag resin dispensers , sandblasting setup, acid etcher

  3. #3
    Join Date
    Mar 2011
    Location
    Olalla, WA
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    I had the exact same problem. Tried the lead in, lead out but it did not fix it. What helped the most was fine tuning the backlash settings.
    Shenhui 1440x850, 130 Watt Reci Z6
    Gerber Sabre 408

  4. #4
    Join Date
    Mar 2012
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    Menomonee Falls, WI
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    I agree with Rich, I did try the lead in/out settings, I forgot to post that as well. it did not help correct the issue as you could still see the offset, plus one of the project I'm currently working, doesn't allow for scrap on either side of the circle cut.

    Rich, what setting did you modify for the backlash to get it to help?
    Shenhui dual head 80W 1200x900

  5. #5
    Join Date
    Mar 2011
    Location
    Olalla, WA
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    1,532
    It's under the "User" tab on the right side of the screen.

    My settings now are;

    X 0.06
    Y 0.15

    You will need to readjust the scan line offset if you change the backlash.

    I have also replaced the X axis belt with a much better one which has made a noticeable difference. Someday I will get around to replacing the Y axis belts too.
    Shenhui 1440x850, 130 Watt Reci Z6
    Gerber Sabre 408

  6. #6
    Join Date
    Mar 2012
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    Menomonee Falls, WI
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    ok, great, where do I find the scan line offset values?
    Shenhui dual head 80W 1200x900

  7. #7
    Join Date
    Mar 2011
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    It's under Config(S) - System, they call it Scanning(Reverse interval). You'll need to tune that so that the bi directional scan lines line up. When you do unidirectional scanning it has no effect.
    Shenhui 1440x850, 130 Watt Reci Z6
    Gerber Sabre 408

  8. #8
    Join Date
    Mar 2012
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    Menomonee Falls, WI
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    got it, been in there before, just didn't know that t was also called scan line offset! thanks again.
    Shenhui dual head 80W 1200x900

  9. #9
    Join Date
    Mar 2011
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    Well, I don't know what it is officially called - just what I could think of at the moment.
    Shenhui 1440x850, 130 Watt Reci Z6
    Gerber Sabre 408

  10. #10
    hI

    How do you do testing for backlslash corrections?
    Shenhui laser 60W, corel Draw X5.

  11. #11
    Join Date
    Oct 2004
    Location
    Cape Town, South Africa
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    For scanning backlash corrections , you need to do corrections at 3 or 4 speeds , once the machine has those , it extrapolates correction for all other speeds
    so do one for slow , one for medium slow , one for medium and one for high speed.
    The way to do it is to buy a 10x loupe from a stamp shop or a printers loupe (magnifying glass)
    Engrave using bidirectional (back and forth) scanning a 5mm thick vertical line. Use something like a .5mm "interval" (dpi) so the gaps between the lines are largish.
    You will see that at each speed , the lines do not line up at their ends , you need to apply a backlash compensation so they DO line up (this will be a very small amount that is the difference between the start point of a left to right line and the end of the right to left line), re engrave the thick line and inspect it again , fine tuning the backlash till all the lines line up, do this for all the speeds you have chosen.
    IE you want
    _
    _
    _
    _
    and NOT
    _
    .._
    _
    .._

    The section you enter your corrections in is under Config/System setting.
    Rodney Gold, Toker Bros trophies, Cape Town , South Africa :
    Roland 2300 rotary . 3 x ISEL's ..1m x 500mm CnC .
    Tekcel 1200x2400 router , 900 x 600 60w Shenui laser , 1200 x 800 80w Reci tube Shenhui Laser
    6 x longtai lasers 400x600 60w , 1 x longtai 20w fiber
    2x Gravo manual engravers , Roland 540 large format printer/cutter. CLTT setup
    1600mm hot and cold laminator , 3x Dopag resin dispensers , sandblasting setup, acid etcher

  12. #12
    I tried what Rodney has suggested and i was shocked by resoult. Something isnt wright with my machine. I try to adjust acceleration and bounch of other settings, check the belts and still getting same missery.
    What can cause that?DSCF7157.jpg
    Shenhui laser 60W, corel Draw X5.

  13. #13
    Join Date
    Oct 2004
    Location
    Cape Town, South Africa
    Posts
    3,922
    Something looks "loose" , its odd that the x axis sort of dips in the Y direction at the ends.... almost like some sort of harmonic vibration where it starts to accelerate....
    Check your mirror and lenses to see that they aren't the cause of it , check the laser tube is not vibrating either...
    Rodney Gold, Toker Bros trophies, Cape Town , South Africa :
    Roland 2300 rotary . 3 x ISEL's ..1m x 500mm CnC .
    Tekcel 1200x2400 router , 900 x 600 60w Shenui laser , 1200 x 800 80w Reci tube Shenhui Laser
    6 x longtai lasers 400x600 60w , 1 x longtai 20w fiber
    2x Gravo manual engravers , Roland 540 large format printer/cutter. CLTT setup
    1600mm hot and cold laminator , 3x Dopag resin dispensers , sandblasting setup, acid etcher

  14. #14
    I found that in original settings file that i had uploaded in program settings for jump of speed was way to high and not equal for Y and X. I try to set jump off speed for boath axis on 10 and get much better resoult. I will play now with details to fix it 100%.
    Also have noticed that laser freq. is now set to 5000 but as i can remember it should be 20000. This file settings was sent to me by shenhui. I will change freq. to 20000.
    DSCF7159.jpg
    Shenhui laser 60W, corel Draw X5.

  15. #15
    Join Date
    Oct 2004
    Location
    Cape Town, South Africa
    Posts
    3,922
    That last picture you posted looks very good compared to the first one...
    Rodney Gold, Toker Bros trophies, Cape Town , South Africa :
    Roland 2300 rotary . 3 x ISEL's ..1m x 500mm CnC .
    Tekcel 1200x2400 router , 900 x 600 60w Shenui laser , 1200 x 800 80w Reci tube Shenhui Laser
    6 x longtai lasers 400x600 60w , 1 x longtai 20w fiber
    2x Gravo manual engravers , Roland 540 large format printer/cutter. CLTT setup
    1600mm hot and cold laminator , 3x Dopag resin dispensers , sandblasting setup, acid etcher

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