Z Hops?

The fact that I am a newbie will soon be obvious and I hope this is the right place for this. I bought an ender 3 and ended up with a couple of problems that drove me nuts. 1 of the problems was that I kept on printing the same thing that was about 4 inches high. After like 6 prints I saw that the nozzle would start hitting the top of the build as it moved around while it was building it till it finally knocked it over. Because of this and another reason I bought another machine. Well, this happened again, I contacted the tech support and they were kind of rude to me so I returned the machine. I then bought a flsun (which I love) and this same print job gets knocked down too by the nozzle and another print job about the same height also gets knocked down by the nozzle (but not this other pring I printed a lot which is about 3/4 of an inch high). I posted this problem on some Facebook groups and some people mentioned Z hops… I’m using Cura. 1) Does this make sense, 2) what is a Z hop and where can I change it?
Thanks you in advance for any help.

Have you calibrated the Z steps of the printer? If Cura thinks the Z axis is moving up by such and such an amount, and it’s actually moving up less than that, eventually the model won’t be moving up high enough to stay on top of the print.

Do you think it could be that since it happened on 3 different machines?

I think every hobby level 3D printer must be tuned in right off the bat, before any printing is done. In fact, it might be that every FFF/FDM printer has to be dialed in, because the settings vary with the type, make, & model of filament. And, there are a bunch of things to dial in:

  • ​​​​​​bed level
  • X, Y, & Z steps
  • extruder feed rate
  • flow rate
  • print speed

I just published a video that might help you with some of your questions.

[video=youtube_share;R5oeUtuTnjQ]Troubleshooting 3d Printing Problems - YouTube

I also agree that calibrating your printer may help but I do understand that most people will expect a new 3d printer to work properly. With a perfectly calibrated printer and when using just the right temperature, you will not have to use Z-Hop. However, if your printer is not perfectly calibrated Z-Hop may help.

Just to make sure it is not a mechanical failure make sure you can smoothly move the hot end up the full range of the z axis with the front panel controls.

The bottom line, it is probably not a mechanical failure. More likely it is a calibration or temperature issue and Z-Hop may help.

If you post a photo of the print and include a link to the stl file I will take a look.

I have come to the conclusion that it must be a cura setting. It happened with 3 different machines. A Ender-3, a Tronxy and a Flsun, Ender-3 after about 5 successful prints of the same stl file, unsuccessful every attempt after that. The other 2 machines were brand new. It has also happened with 3 stl files compiled in Cura. The stl files have come off of Thing Universe. I have had successful prints with short items, but the 3 that I have had problems are more than like 3 inches. I have a video of the problem, but the file is too large to attach. At one point you can see the nozzle start hitting the top of the print where it is laying filament. You’ll see bang, then it lays the filament, then move and then bang, lay filament. It will continue this till it pulls it from the adhesion to the bed and move the print or knock it off. Since it has done this on different machines and different stl files compiled in the same cura, I think it must be a setting. I will provide you a stl file if you still want it and as far as the picture, it will just show 3/4 of a print moved or maybe laying down with a lot of stringy filament around. I appreciate any input you could provide.

Check if the part cooling fan is spinning after the first layer. It seems Cura 4.8.0 has an issues, where it sets the fan number to index 1, but most printers only have one fan, so the index should be zero. Check your printer setup and open the “extruder 1” section. On the left side there should be “extruder cooling fan” or so in the nozzle settings. The last input field should have a “0”. If there is a “1” you found your problem.

You can also check your GCode itself. Search for the M106 command. It should be after “layer:1” text. It should look like this: “M106 S255” If it looks like “M106 S255 P1”, Cura has the wrong setting.

Cura cost me several hours of trouble shooting changing the value to a wrong value by itself for some reason.

The result will be sagging overhands and every Z-Hop will cause a blob the nozzle will collide later, when the blob is cold. My calibration cubes finished fine, because the layer was still soft and the print resulted in a melting cube around the corners.

Another good tip @Geit.