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Print is not centered correctly on Bed


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Posted · Print is not centered correctly on Bed

Hi
I have encountered a problem with the bed in Cura not matching the actual bed on my Tevo Tarantula Pro?
When I load a model (.stl) into Cura it appears fine within the bed, there are no error messages and review indicates that it looks fine.
When I then pull the gcode onto an SD card and start printing, it hits next to the bed, ie the print head runs towards the end stop.
the print is pushed on the bed approx. 1 cm to the right and approx. 1 cm backwards. The home position looks fine, hitting the left front corner of the bed. I have not encountered this problem before, as it is the first time I utilize the size of the bed all the way to the edges, about 2 mm in from all sides.
Hope there is someone who can give a hint where I in Cura need to adjust for it to hit correctly?
The black square in picture 2 is the bed and the blue transparent is where the print is in relation to the bed.

Cura01.png

Cura02.png

TTP - Cura test1.png

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    Posted · Print is not centered correctly on Bed

    This is a complicated subject.  I believe the Tevo uses Marlin firmware which probably has an offset from the homing switches in order to print over the build plate (and not off the edge).  Maybe?  All printers are different.  So 0,0 might be inward a bit.

     

    Anyway in the PREPARE mode of Cura go into the machine settings for your particular printer and in there you can set the width and height of your print bed.  Whatever numbers you put in there - cura divides those 2 numbers by 2 to get the center.

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    Posted · Print is not centered correctly on Bed

    Problem solved! I have changed the extruder settings in Cura, (Machine Settings Extruder). Now the print hits exactly 120 mm in from all sides.
    After some measurement, adding and subtracting, I ended up with Nozzle offset, X = 15, and Y = 6, in Machine Settings in Cura, and my test print (sight grain), now hits exactly in the middle.

    Cura machine settings - Tevo tarantula Pro- Final.png

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    Posted · Print is not centered correctly on Bed
    On 3/3/2022 at 9:59 PM, gr5 said:

    This is a complicated subject.  I believe the Tevo uses Marlin firmware which probably has an offset from the homing switches in order to print over the build plate (and not off the edge).  Maybe?  All printers are different.  So 0,0 might be inward a bit.

     

    Anyway in the PREPARE mode of Cura go into the machine settings for your particular printer and in there you can set the width and height of your print bed.  Whatever numbers you put in there - cura divides those 2 numbers by 2 to get the center.

    If this is correct, Cura is not very good at calculating, bed size was correctly stated, but the print still did not hit the middle of the bed. 🙂

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    Posted · Print is not centered correctly on Bed
    46 minutes ago, Brassovits said:

    If this is correct, Cura is not very good at calculating,

    No, your firmware is not good at homing.

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    Posted (edited) · Print is not centered correctly on Bed

    The printer will take the coordinates of a gcode file and place that "origin point of the print" at the Home Offset position of the printer.  If you have not defined a Home Offset location in the printer then the default is the Auto-Home location.  That location is often in space just off the build plate.  It is the main reason prints are not centered.  If your build surface is 240 x 240 then the mid-point of the print will be X120 and Y120 from the Home Offset origin.

     

    When you define a Home Offset location then Marlin will assign that Home Offset location as 0,0,0.  The Auto-Home location will be related to that 0,0,0.  When you Auto-Home and look at the LCD it will show its location to be the same as your Home Offsets.  The X and Y values will often be negative because the Auto-Home location is often in the negative quadrant of the ordinate system that is centered upon the Home Offset position.  For reference, my home offset is:

    M206 X-1.00 Y-5.00 Z0.00

     

    And that is why gr5 says it's complicated.  I don't understand the comment about the Extruder Settings though.  They aren't involved in this even for a multiple extruder machine.

    Edited by GregValiant
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    Posted (edited) · Print is not centered correctly on Bed

    I am also encountering the same 'centering' issue as Brassovits.  I've set Cura to my Ender 3 Pro.  I see that the Settings | Printer | Manage Printers | Machine Settings | Printer Settings are: X=220.0, Y=220.0, and Z=250.0 and the Extruder Settings on that same page are: Xmin= -26, Ymin = -32, Xmax = 32, Ymax = 34, Gantry Height = 25.

     

    This is the first time I've tried to print something that extends nearly to the limits of the printable area (209 mm X 209 mm).

     

    Yet, as you can see in the images, Cura places the print FAR to the front and left side of the print mat.  This centering ultimately, I think, interferes with adherance to the mat where the heating element of the bed is 5 mm inset from the edge, causing the surface, there, to be too cool.

     

    I'm printing with SunLu PLA+ Silk Black and don't have any experience with this product.  I'm only guessing that the adherance problem is not actually a problem with the filament itself.  The extruder temp is 220 C, Bed 60 C as recommended in the resources that I can find.  So, there's that! (Whew, did someone say complicated?)

     

    I know as stated above that "centering" is complicated.  Is it possible for a genius to look at the numbers above and the photos and tell a novice like myself exactly what I might try to correct this and get the print centered?

     

    Thanks,

    Dave

    CenteringIssue.png

    Edited by Dave90807
    Correcting grammar.
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    Posted (edited) · Print is not centered correctly on Bed

    To say this another way...

    The virtual build plate in Cura has to match the real build plate of the printer.  Leveling takes care of the "Z" and it is the "Home Offset" that takes care of the X and Y.  When the printer receives a gcode it will put the X0 Y0 of the print at your Home Offset 0,0 position.  If you have never changed the Home Offset then it is the same as the Auto Home position.  That is why the print is off.

    You will need a ruler.  (2.5mm is about 1/10".)

    Your build surface is 235 x 235 but you can't use the whole thing.  Creality asks for a very conservative 7.5mm non-printable border (235 - 7.5 - 7.5 = 220) around the build surface.  You can make the border smaller than that and increase the printable area.  Measure your build plate edge to edge in the X and in the Y.  We'll call those Xmeas and Ymeas.

    • Auto Home the printer.
    • Use the LCD and raise the Z axis 5mm or so.
    • Move the nozzle in the X to a point 2.5mm in from the left edge of the build surface.
    • Move the nozzle in the Y to a point 2.5mm in from the front edge of the build surface.
    • Drop the Z back down to "0".
    • On the LCD find "Set Home Offset" (on my older 3 Pro it's under "Prepare") and click on it.
    • Raise the Z 5mm
    • Send the nozzle to Xmeas - 5 and Ymeas - 5.
    • The nozzle should be 2.5mm from the back edge of the build surface and 2.5mm in from the right edge of the build surface.
    • In Cura - goto Manage Printers and then Machine Settings.  Make the X(width) = Xmeas - 5 and the Y(depth) = Ymeas - 5.

    If you find that the nozzle is too far back or too far to the right when you move to the back right corner, then you will need to make an adjustment.  If you find that you have to set your Home Offsets with the nozzle 5mm in from the left and 5mm in from the front then you would set Cura up as Xmeas - 10 and Ymeas - 10.

    When you are happy with how you have set it up find "Save Settings" on the LCD and click on it.  That will make your new Home Offset the new default.

    The midpoint of the Cura build surface should end up matching the midpoint of the actual bed.  That will center all your prints.

    Edited by GregValiant
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    Posted · Print is not centered correctly on Bed

    Thankyou Greg.  I will study your procedure and update my progress as I work through this 'personal steep learning curve.' Your notes are very detailed, explaining why each step is performed and I am very grateful to you for the time it took to meticulously present the process.

     

    I have never knowingly or intentionally changed the Home Offset.  So, I assume the Home Offset is still the same as the Auto Home position.   The printer alway returns to a position just in front of the print bed when I click the knob with 'Home Position' selected.  I'm still  leary about fiddling around with settings when I don't completely understand them.  But, I'm not getting any younger.  It's time to learn.

     

    Furthermore, It seems everything goes haywire at once.  Now, I suspect that the cause of the filament not sticking to the bed (as shown in the photos) could be caused by a very slightly clogged bodum tube.  As I feed the material past the pinched-open advancement gear, I feel a tiny bit more drag than usual.   Does the photo above tell you that I'm onto something, with this shot-in-the-dark?

     

    But to eliminate that the failure to stick to the printbed is not a problem with this brand new roll of Sunlu filament, I've tried printing a bit of the same model, with the same settings, with a previously dependable roll of SunLu PLA that has worked flawlessly in the past.  The result is better than than the newest roll, but not without suspicious looking areas marginally adhered to the mat.  (see the image of the newest test print)

    CenterAndFilamentCheck.JPG

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    Posted · Print is not centered correctly on Bed

    It's a well rehearsed post.  I think I've put that up half a dozen times here and there.

    There are two things that you should consider here...

    • Use a carpenters square or similar tool and make sure that each axis is at 90° to the other two.  If the frame is straight and square your prints will be straight and square.
    • If you calibrate the extruder motor (the "E-steps") then the machine will push the correct amount of plastic into each extrusion.  Do not use a "single wall calibration cube" when you calibrate the extruder.  Just make sure that when it's told to push 100mm of filament that it actually pushes 100mm of filament.

    All the "kit" printers need both of those done.  Remember that "Just because parts of it were assembled at a factory doesn't mean they were assembled correctly."  Check everything, trolley wheel alignment, the hot end is tight, no loose screws, etc.

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    Posted (edited) · Print is not centered correctly on Bed

    Greg,

    Now, I'm sweating bullets.  Carpenter's square, extruder calibration, calibration cube!  I bought the "kit" printer, it worked for a number of years. So far everything has been 'fixable' and straight forward when it didn't.  I'm going to take a deep breath and let all this sink-in.

    Thanks for everything so far,

    Dave

     

    Follow-up (3 days after above post):

    Special thanks to those who created the YouTube videos explaining all and to you Greg for the description of the process.  As shown the solution is straight forward.  There was no need to panic.  The annotations next to the images shown should be enough to explain the end of this successful post.  Good luck to all who read this.

    Dave

    ExtruderCentering.jpeg

    Edited by Dave90807
    Adding images and documenting solution.
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