Very odd printing problems

Hi all

I have a pretty modified Monoprice maker select. Its running on a ramps board with the repetier firmware. I have been printing happily through many many spools of filament (mainly ABS).

I recently had some issues where my extruder would underextrude randomly through the print, mainly larger prints. After much faffing around, I replaced the whole hot end with a china special. Works well enough, after calibrating it etc, I can print a pretty good benchy:



I was messing with the flow rate, so ignore the under extruded section at the bottom

The issue comes when I try and print a large round object (jack stand adapter). I have successfully printed this on the old hot end (before the issues). I attempted to re-print the exact same g code on this new hot end and I get odd issues. I get bobbly outer edges and bubbles showing, the print head ends up rumbling over these imperfections and it gets worse and worse until I cancel the print.







You can see where it starts off OK and then ends up mangling it self.

I have also figured out that its only affecting solid inlif models (which I had no issue printing before).

I printed a 100mm rectangle with 36 solid layers and then 10% infill from then on, you can see the issue:



Not quite sure where to go from here. This printer has printed this model perfectly before. Benchy printed on my normal settings straight off, without any changes. I am using simplify3d with a set of profiles I have honed down for various end results.

Any thoughts are much appreciated.

Edited 1 time(s). Last edit at 12/12/2016 03:45AM by alexanderfitu.

Looks like your hotend is losing heat or you are trying to print faster than what the hotend can pomp out.

Sorry, didnt see the response.

Tried slow it right down. Makes no difference. The filament is being fed consistently, no issues with that.

I have also, installed a glass bed, no difference.
New bearings on all rods, no difference
new stepper driver on the Z motors, no difference.

I can print a calibration circle (entire bed width) without issue.

I can also print a 30mmx40mm high solid cylinder, without the same thing happening.

Its almost like the Z axis is missing steps randomly as it always starts at 1.5mm +

Cant think of what it is, tearing my hair out!

Any chance of heat creep in the hotend? Does your hotend fan work during the duration of the print?

Also, did you try a different filament just to make sure it's not a bad spool?

The hotend fan works well, I thought that it might be overcooling of the print, so I rotated the heatsink to the ends blew forwards and backwards instead of up and down. No difference.

Yes, I have the same issues with 3 different types of filament (see the black and gold) I also have a green colour change that has the same issue.

Surely if it where heatcreap, it would look like underextrusion? To me, it looks like the Z axis isnt moving far enough and the print head is dragging on the print...... A calibration cube prints with the right dimensions though...

Z axis not moving far enough doesn't explain why the center section turns out ok, or why your 40mm high solid cylinder doesn't fail. You could check for that though, at least partially, by (1) measuring the height of your objects with calipers to make sure they aren't too short or (2) taping a pencil to your extruder horizontally and drawing a line on a vertical object with a piece of paper glued to it, then measuring the length of the line and comparing to the distance you told it to move. That would give indication whether you might indeed be missing steps, unless it corrects itself which seems unlikely.

Did you try changing layer thickness? Perhaps with thicker layers you can ascertain whether it's the head dragging.

Another thing I'd try is building a calibration tower (something like a 20x20mm thin wall square) next to your print.

When you say 'solid' infill, is that 100% infill,
Have you tried reducing to say, 95%.

Quote
obewan
When you say 'solid' infill, is that 100% infill,
Have you tried reducing to say, 95%.

Yes, sounds like over-extrusion to me, and on the 100% fill layers the only place for the excess to go is out the sides.

Alexander, have you done the fine extruder calibration as described on the following page: [reprap.org]

Quote
anvoice
Z axis not moving far enough doesn't explain why the center section turns out ok, or why your 40mm high solid cylinder doesn't fail. You could check for that though, at least partially, by (1) measuring the height of your objects with calipers to make sure they aren't too short or (2) taping a pencil to your extruder horizontally and drawing a line on a vertical object with a piece of paper glued to it, then measuring the length of the line and comparing to the distance you told it to move. That would give indication whether you might indeed be missing steps, unless it corrects itself which seems unlikely.

Did you try changing layer thickness? Perhaps with thicker layers you can ascertain whether it's the head dragging.

Another thing I'd try is building a calibration tower (something like a 20x20mm thin wall square) next to your print.

True.

As I have 2 Z motors, I had a thought that one was going out ever so slightly.

A 40mm calibration cube prints nearly spot on (+- 0.2mm).

I havent tried a calibration tower on the same print, good idea.

Quote
obewan
When you say 'solid' infill, is that 100% infill,
Have you tried reducing to say, 95%.

Yes 100%. The odd thing is, I have been able to print this model with 100%infill previously.

Are you saying reduce the flow rate to 95% or just the infill percentage?

Quote
JamesK

Quote
obewan
When you say 'solid' infill, is that 100% infill,
Have you tried reducing to say, 95%.

Yes, sounds like over-extrusion to me, and on the 100% fill layers the only place for the excess to go is out the sides.

Alexander, have you done the fine extruder calibration as described on the following page: [reprap.org]

Interesting. I have done this when I replaced the extruder and hot end (recently)

Oh, that's my idea out then Would it be possible to print 4 or 5 solid layers and post some close-up photos showing the top surface? A 20mm square would be plenty big enough to see how the layers are going down.

Yes, try reducing the infill % to allow for any epansion .

Some thoughts:-
Presumably your new hot end has a different nozzle.
Might be worth a close look at the flat area. Do you have a fixed width for your print width and is it more than 20% larger than the nozzle.
You could be trying to print widths wider than the flat area of the nozzle which will cause it to print a V groove that the next layer bounces over. I am thinking this is probably more pronounced on infill as we tend to specify non concentric patterns.
It wont actually bounce but every high spot restricts flow which builds pressure then the groove provides a bigger gap and the pressure is relieved with a large blob due to local over extrusion.
Reducing the infill will allow the filament to flow side ways and reduce the build up.
Also if the nozzle is not square to the bed or has a burr I assume we could get the same effect but without the extrusion width being relevant.
1.5mm height could be a result of the temperature of the previous layer. The colder the previous layer the more solid it will be so the ruts would be permanent as opposed to a hot a layer that can have the ruts smeared down.

Quote
MCcarman
Some thoughts:-

You make a good observation there, and I think might be near to the issue.

Here is the old nozzle:





New nozzle:




As you can see, the older nozzle is wider and flatter.

Reducing the overall extrusion rate to 92% did not make a difference to the issue. I flipped the Z rods, which also made no difference.

I will try reducing the infill rate only to 90/95% and report back.

This some how seems familiar.
Looks like the new nozzle is "taller". Can't tell if the across flats is smaller but it looks it.
If the tip is further from the heater and/or the across flats is smaller then it will run cooler at the outlet. Try bumping the temperature up a bit?
Is your infill speed higher than your perimeter speed? If so this may contribute to why the infill is having an affect.
Is it a 0.4 nozzle and your line width on auto or less than 0.48.