Prints with height don't adhere to base

Hi,

My first few layers come out perfect for the most part. My issue basically starts with prints with height. Whenever there is a semi-high height/width ratio for the print I start getting issues where the print is removed from its base and is stuck to the extruder and the mess ensues.

I'm not sure where to start with this because my prints are generally stuck to the print bed when completed (at least for the succesful ones). I have rather large fans on which batter the glass on the heat bed with air which might be an issue but I'm not sure honestly if this changes anything or if the cooling effect on the glass is the issue?

Any help or direction is highly appreciated. Thanks

I looked back at some of your previous posts, but I did not see mention of the type of printer you built.

In any case, I see you are printing with PLA. PLA is nice because there is lees problems with warping on large prints, but it does require a bit of a balancing act when trying to figure out how much cooling is needed. Depending on the hot end you are using, PLA may not be a good choice. If the hot end heats up slowly, has a lot of exposed metal, or requires a good amount of pressure to push filament, change the print head.

The ideal hot end for PLA will have a very short melt pot, very good thermal insulation in the transition between hot and cold ends, and will generally not cause your extruder stepper to run so hot that you cannot touch it. The J-head (from hotends.com, the original) works well. Others too, but I only use J-head 0.5 MK Vb

As for tall prints getting knocked down, it could be that you need to keep the Z-axis steppers enabled all the time, or that you need to calculate the Z steps/mm and layer height to match better, if using imperial lead screws. See reprapcalculator.

My printer is a mendelmax 1.5. I am also using a j-head

as far as the z steps/mm and layer height I'll fiddle with those later on when I get a few hours where I can work on the machine. As far as keeping my z axis steppers enabled... you lost me there. Could you clarify what you meant?

Another thing which might be an issue and ill check up on it tomorrow is the extruder is becoming too hot now that you mentioned the cold/hot issue. I did recently change my PLA and I remembered it being a bit too hot but I shrugged the issue to the side when it printed my small pieces fine.

ill fiddle around with the temperature to see if that was the root cause or not. I'll post an update friday, ill have a few hours with my machine.

When a stepper motor is off you don't need a lot of external force to manually rotate it. This is called its "detent torque". A stepper motor can be "on" without actually rotating. The power is used to hold its position, and it you need much more external force to overcome it. This is called its "holding torque". However, in your case the z-steppers might be a red herring. Can you slide your x-carriage up and down by hand, without manually turning the z-rods? Maybe if you have amazing lead-screws designed for high speed operation then you might need to keep the z-steppers energised, but if you're just using cheapo threaded rods then their friction should be more than enough resistance to stop the x-carriage sinking under its own weight.

Are you printing directly on the glass bed? You could try putting down a layer of blue painter's tape, which PLA adheres well to. It might be all you need to stop the parts from lifting up and snagging on the extruder.

Now it makes sense. Thanks for the definition of enabling motors.

yeah as you guessed correctly I dont have frictionless thread. lower the temp by 5 C did make a difference but it was not the full solution. im simply going higher now before it is pulled off its base. I will pass by a shop today to get me some painters tape and see how that goes and yes I am printing directly on glass.

will update later on