Lots of pressure on bowden tube for first layer(s)

[umagi 8]

Hi.

I finally started printing with my self-built UM2!

Many thanks to Coen for helping me out with my Ulticontroller board problem. I reverted to using a power supply setup closer to the original UM2 setup. I no longer have voltage peaks on my Ulticontroller board that used to damage the U3 voltage level translator chip thereon.

This being the first time ever for me to 3D print anything (I haven't tried printing on other printers before setting out to build my own...) the first prints did not go smoothly.

I'm using a 1.75mm PLA silver filament rated for 190C to 220C with a 0.4mm nozzle and Cura 15.04.4 as slicer.

My first print was a simple test object, a hollow square vertical column 25mm x 100mm.

I changed the nozzle setting in Cura to 0.375mm, after my first attempt did not have fused shell walls.

My latest print of that object seems to go the right direction (Temperature was set to 214C,

no overrides of the settings on the machine - all 100%, except for the filament diameter set to 1.75mm):

The settings for this print were as follows:

However, I am faced with one constantly recurring problem: my bowden tube keeps popping out at both sides.This seems to happen mainly when printing the first layer(s). I try to keep the tube in place, but actually quite a lot of force is required, even when printing at these low speeds of 20mm/s.

In order to somewhat remediate the problem at the print head side, I printed a simple clip that I mounted on the knurled screw on the printhead. The teeth on the screw head and a tight hole diameter help maintain the tube and its fitting ring in place. This solution is effective in most cases so far, but sometimes, even that is not enough to prevent the tube being lifted out of the head.

At the feeder side, the tube keeps popping out however. This seems to start at the pruning stage before the printing starts. I can push it back in, but I must maintain it (and sometimes also the other end at the printing head) with quite some force for the few first layers of my print, after which things seem to go better and I can release the tube.

Even though I am not using the shoehorse clip that seems to be standard in the official UM2 build, I doubt that using such a clip would help, given the amount of force I need to apply to keep the tube in.

How come things seems to go better after the first layer(s)?

As shown in my settings above, I set all speed fields in Cura to the low value of 20mm/s, and even then, I have this problem.

I tested my extruder operation using Pronterface to extrude 100mm with the bowden tube removed from the printhead, and almost exactly 100mm was extruded by the E motor.

I use the following extruder driver nut:

I noticed that PTFE isolator in the printhead has an input hole diameter that is too wide for my bowden tube, which is for a 1.75mm filament, and I therefore fitted a short section of a wider bowden tube on it at that end. However, the fit is still not perfect as the PTFE isolator hole is still somewhat wider than even that thicker tube section. I don't know however if that is an issue?

Any ideas?

Thanks!!!

Edited March 30, 2016 by Guest