Nozzle Drags, Jumps And Messes Up The Print

Hi there!

I've been trying for a few months to fine tune a Sunhokey prusa i3 printer, but so far I cannot print anything with it properly.
It originally came with something that looks like a chinese version of e3d v6 and printing wasn't too bad with it, but still I could only print a small cube.
Then it got clogged and while trying to clean it, I destroyed it, so I decided to get an original e3d v6. Interestingly prints with it became far worse than they were before, even after 1 day of fine tuning all kinds of stuff.

My latest problem now that I cannot figure out is that the nozzle sometimes needs to go to another place quickly and while moving it drags through the print, jumps and messes it up.
I made a video of it, the jump can be seen at 1:04:

[www.youtube.com]

In this video only 2 of these can be seen, but I get those all the time while printing the bottom layer and that pretty much messes up the whole print.

I imagine it should first go up a bit (z axis), then move to where it wants to go, and then go back down and continue printing. But instead it assumes it has printed everything perfectly with micron accuracy, and therefore it can move straight through it with no issues...

Any idea how to fix this?

Thanks in advance!

Edited 1 time(s). Last edit at 10/25/2015 10:04AM by ltomov.

Have you ever calibrated your extruder? If so, what's your EStep number? It seems like you are putting out a lot of plastic. The head should move up 0.3 or what ever layer thickness you chose. It won't go up higher and then come back down to that setting. Are you sure you have the extrusion rate set to 100% after the first layer?

The comment "even after 1 day of fine tuning all kinds of stuff." makes me wonder what you have messed with.

Edited 1 time(s). Last edit at 10/25/2015 10:21AM by tjnamtiw.

Thanks for the reply.

Yes, I've calibrated the esteps using that formula of extruding 10cm and measuring how much exactly comes out. My final setting for it was 100 esteps.
However I also assumed it may be too much so on this video I lowered that to 85. When the final cube came out, it's clear that the esteps should be more, because there are small holes on the print. Yet it still does this jumping.

The flow rate is currently set to 80%, but I've tried that with 100% also - still the same.
It's mostly those settings that I've played with, and also lowering the print speed, changing temperatures... nothing too fancy

Edited 3 time(s). Last edit at 10/25/2015 10:40AM by ltomov.

If 100 is your number, then that's what you set it at. Did you compile and then save the new configuration.h file to the machine using Arduino?

Yes I uploaded that setting with Arduino, but for testing I also change it occasionally from the Marlin settings.
Currently it's set to 100 in configuration.h

I suspect one thing, but I'm not sure if it's really that - that filament seems to be getting hard very quickly. Like 1-2 seconds after it goes off the nozzle, it's already hard. Which is a good thing I guess, makes printing easy, but I suspect if it wasn't that hard, the nozzle would have been able to move through it easier, without that big jump.
This is the chinese filament that came with the printer. I got another one which I thought should have been better (both are PLA), it costs ~$30 for 750 grams, but it cools off much slower and before that it's like a gum - I cannot print anything with it. But it doesn't have this problem, because the nozzle can easily cut through it.

I'm not sure if the above makes sense though and is really the root cause, just sharing thoughts

And one more thing - the design of the printer is such that the hotend can very easily move back and forth on the Y axis. It's just that the way it's been screwed - it's very loose and I cannot change that unless I print a new holder for it.

Is this a good thing? I'm looking at another holder - [www.thingiverse.com] and it seems to be screwed much better and the hotend cannot move that freely.
Is this a better frame design, should I try something like that?

I'm new to all this too but if my hot end moved that easily, I'd be looking at a new mount. It did seem to just flop around in the video. That link you sent points to a fan for cooling the extrusion. The most critical thing would be the distance between the two X rods. I don't know if that's standard among all repraps or not. I suspect it may be a standard so that the 'community' can print upgrades for anyone's printer.

I honestly don't see any dragging from layer to layer on my machine. What resolution are you printing at? 0.3 mm? That's what I usually use but I don't see any dragging at 0.2 either.

When you say you set the EStep in Marlin, do you mean by using the LCD screen? That's good for one cycle of the machine unless you enable the EEPROM by uncommenting two lines in the config.adv file.

Edited 1 time(s). Last edit at 10/25/2015 12:00PM by tjnamtiw.

Resolution is the layer thickness right? I use 0.2 currently.

I'll try to fix that hotend a bit better and see if I can print a new holder for it.

Thanks!

Start with 0.3 mm layer height (resolution) as a test. My prints look very good at that setting for most things. Also make sure your zero Z position is set to 0.1 mm everywhere and your first layer is set to 150% extrusion in the slicer. That works for me.

By all means see if there is a way to make that hot end more sturdy. Also, make sure that both sides of the X carrier are exactly the same distance from the bed.

Thanks, I'll try these settings.

And I was able to make the hotend more sturdy using some elastic band and that thing alone seems to have solved the jumping nozzle problem That's pretty amazing, it's such a small thing and comes like that by default... The quality of the prints is now way better, looks like the way it should be.

Thanks a lot!

Welcome to the world of 3D printing. Its the little things that get you.

Here is a repeat on my thoughts about the Sunhokey that I have posted elswhere. I hope you find some of it helpful. The comment about the X carriage is most relevant to this thread.


The basic Prusa I3 design is very good but it needs a stable base to hold its calibration and stay reliable. I used an off-cut of kitchen worktop (£5 from B&Q) and bolted it down with the z-motor clamps from [www.thingiverse.com] and some screwed in blocks front and rear to make it immovable on the base. I have mounted the base on a wheeled cabinet that I can easily move around that makes working on the back and sides very simple. I would regard this as essential before trying any of my other suggestions.

Basics
The Sunhokey implementation of the design is OK but as you have noticed there are a number of areas that can be improved. The 2015 model does address some of your observations about rod retention etc. but takes a step backwards with the control board as the new one is incapable of driving a second extruder. It is easy and relatively cheap to address this by replacing it with a standards RAMPS 1.4. I used [www.ebay.co.uk] which makes following standard How to's on the net easier than trying to translate them to a custom board.

Bed levelling
The Z-stop is a very bad design and will never hold calibration, a search for Sunhokey on Thingiverse gives a number of alternative designs to address this. I chose to go beyond this with an inductive sensor so that I could do auto bed levelling (basic concept shown here using a mechanical switch [www.thingiverse.com]). I have found that using a sensor rather than the servo/switch design better but glass on the heat bed can be a problem as inductive is very low range. I am waiting on delivery of a capacitive sensor which has a longer range to see if this is better I will also be trying an opto solution and will let you know my results when it arrives from America.

Hot ends
The hot end that comes with the kit is the cheapest of the cheap and not worth installing, I have tried various replacements from eBay and Amazon ranging from £6 to £30 which are a bit better but nowhere near as good as a genuine E3D-V6 [e3d-online.com] not cheap at £47 but less than the cost of all the failed replacements that I have tried.
Having a good hot end makes a huge difference in the reliability and quality of your prints.

X-Carriage
Although I haven't had a problem with X-Carriage stability, I decided to upgrade to this [www.thingiverse.com] so that I could different hot end mounts. This is a definite improvement on the original as you can easily switch mounts without having to disassemble the X-Carriage.

Dual Extruder
Having tried dual J-heads I now run an E3D Chimera [e3d-online.com] mounted with [www.thingiverse.com] this makes using PVA support very easy. My E3D-V6 is now used on my Kossel Delta printer. A second extruder drive is needed for this, I use [www.ebay.co.uk]

Thank you, I'll certainly try these.