There is nothing worse than a nice and uniform 3D printed surface being ruined by the nozzle dragging itself across the top of the print. Not only does the nozzle dragging across the print cause an undesirable finish it also can damage the nozzle as well as the print and potential could cause the 3D print to fail mid print.
The most common things that cause nozzle drag while 3D printing are the gantry rollers being loose, the gantry frame not being square or level, the Z coupler being loose, the Z hop set too low, over extrusion of the nozzle, print warping mid cycle, and the print bed being warped.
I have broken all of these common issues down into greater detail and have also outlined ways to fix your machine and solve your dragging issues.
Gantry Rollers Loose.
Not all 3D printers are belt driven but the ones that are typically operate on extruded aluminum with roller wheels to reduce friction. If the rollers on the gantry are loose then it will cause the printer head to lean forward and potentially will cause the nozzle to push off when extruding and drop back down when it is not extruding. This push and drop causes the nozzle to sit below the printed material and when rapiding across the printed parts surface will drag the nozzle across the print.
To tighten the roller wheels on the head all you need to do is tighten the nuts on the back of the wheel until the head feels rigid but is still able to move freely along the rail with relatively low resistance.
3D Printer Frame Not Square.
It is not likely that your 3D printer will shift and this will become an issue after you have had successful prints, but if you set up your 3D printer and you are immediately having issues with your nozzle dragging against the part your 3D printer frame may not be square. You can check the squareness of your 3D printer frame by validating it with a 90 degree square or you can use the edge of a new sheet of paper to verify the squareness.
You can adjust the squareness of your 3D printer frame by loosening all the bolts that are holding it in place and moving the frame until it is square against your point of reference and then tightening all the bolts.
Gantry Not Level.
If the gantry is not level you will essentially be climbing in the X axis as you are printing.
As long as the gantry angle is relatively square it is possible for you to tram the bed of the 3D printer at the same angle parallel with the gantry and not have any issues while 3D printing. As you can see in the photo below this 3D printer’s gantry is not perfectly square with the frame and I have printed many successful prints on this machine without an issue.
If your gantry does need to be releveled you can loosen the screws on the back of the rail where the rollers are and make an adjustment to get the 3D printer back to square.
Z Axis Coupler Loose.
If the Z axis coupler is loose, the Z axis can lose location which can then make the nozzle too close in the minus Z axis. If your Z axis coupler is loose all you have to do is tighten the bolts on the coupler and re-home the machine. If you are already mid print and notice your nozzle is scraping and the z axis coupler is loose you will need to abort the print and start your print over.
Z Hop Set Too Low.
The Z hop setting controls the amount that the Z axis will raise when the filament is retracted. If your nozzle is scraping the top of the part as it is rapiding between its extrusions you may be able to fix this by enabling the Z Hop setting. A well tuned 3D printer that is built correctly should be able to function without the Z hop setting on. If your printer is unable to run without the Z Hop setting you may need to make an adjustment to your gantry or your 3D printer frame.
If your flow rate is too high you may be over extruding your material which can result in blobs, stringiness, and layer height issues. Always double check that you have the correct material and nozzle diameter selected in your slicer settings. If you are having flow rate issues there are a lot of great calculators to calculate flow rate.
It is possible for your print to lose adhesion mid print and warp causing the material to be too close to the nozzle which can make the nozzle drag. It is very common for materials like ABS to lose adhesion to the build surface especially if they are not in the correct working environment.
If you need some tips on how to achieve better adhesion to keep prints from moving check out this article for more information.
A warped bed can cause the nozzle to drag in some areas and be too far in others. Typically if you are able to get through the first few layers and the only issue is that the bed is warped you will be able to finish your print successfully. If you are unable to establish the first layer you may need to replace the build plate with a glass plate or another 3D printer build plate that is flatter.
Why Is My 3D Printer Nozzle Dragging Against The Bed?
As a general rule if a 3D printer nozzle is dragging against the 3D printer’s bed this means the 3D printer’s Z offset is set too low or the bed needs to be leveled. If your nozzle is dragging against the bed you should stop the printer immediately to avoid damage to the machine.
If you need help leveling your bed check out this article for a step by step guide to leveling a 3D printer bed.
Sometimes a nozzle scraping against a print is only a minor issue and can be ignored all together but if you are having major issues with your nozzle scraping check your 3D printer for all the issues that I have outlined above.