I am printing with PLA at 190C with first layer at 200C. (Marlin firmware, Repetier Host).

I noticed that my self made nozzle/hot-end extrudes plastic normally, but then it slows down extrusion of filament fairly regularly during printing - causing layering effect on the print. In the image of the print attached, the right side infill of the print is missing one layer, but the left side infill is normal. Also notice the layering effect at the top of the print caused due to regularly missing plastic.

How do I fix this problem? What am I missing? Any hints will be much appreciated.

Nozzle size 0.35mm, layer height 0.25mm.
Speed 30 mm/sec

I also used a Ni-steel (or Zinc) coupler with PTFE tape on brass threads. I am using a fan to blow on this coupler and PTFE tube. This fixed my previous intermittent extrusion issue where plastic was oozing out of PTFE and messing up the hot-end.

NOTE: Though I accurately calibrated the E-steps per mm, I increased its value to ooze out more PLA to hopefully fill some gaps, but that did not help much.

Edited 1 time(s). Last edit at 09/27/2012 01:11AM by peddiparth.

what speed are you printing at?

All speed settings = 30 mm/sec
Travel speed = 100 mm/sec

Additional config from Marlin

#define DEFAULT_AXIS_STEPS_PER_UNIT {73.6894, 73.6894, 2275, 760*1.1}//{78.7402,78.7402,200*8/3,760*1.1} // default steps per unit for ultimaker
#define DEFAULT_MAX_FEEDRATE {500, 500, 4, 45} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {500,500,500,9000} // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

#define DEFAULT_ACCELERATION 500 // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION 500 // X, Y, Z and E max acceleration in mm/s^2 for r retracts

//
#define DEFAULT_XYJERK 10.0 // (mm/sec)
#define DEFAULT_ZJERK 0.4 // (mm/sec)
#define DEFAULT_EJERK 5.0 // (mm/sec)

Edited 1 time(s). Last edit at 09/27/2012 01:17AM by peddiparth.

With gaps like that you are either skipping steps on the extruder, or the filament is slipping.
You can try adjusting the pot on the extruder driver a small ammount.
How consistent is the diameter of the PLA, some of the cheap PLA I have here does that to a lesser extent, because the diameter is inconsistent, which causes it to jam in the Hobbes bolt or slip.

I am assuming you are using 3mm feedstock.

pla when it grinds it will eventually quit pulling thru. this seems like filament is not being laid down thick enough. turn up your extruder motor steps. if you have a knurled bolt turn it up to 880, if you have a hobbled bold turn it up to 911 from the 760 it is at currently. then fine tune from there.

change this:
#define DEFAULT_AXIS_STEPS_PER_UNIT {73.6894, 73.6894, 2275, 760*1.1}//{78.7402,78.7402,200*8/3,760*1.1} //

to this

#define DEFAULT_AXIS_STEPS_PER_UNIT {73.6894, 73.6894, 2275, 880}//{78.7402,78.7402,200*8/3,760*1.1} //

or this

#define DEFAULT_AXIS_STEPS_PER_UNIT {73.6894, 73.6894, 2275, 911}//{78.7402,78.7402,200*8/3,760*1.1} //

Edited 1 time(s). Last edit at 09/27/2012 03:09AM by jamesdanielv.

Thanks jamesdanielv and polygonhell for the following hints.

1. PLA jamming or skipping at the Hobbed bolt due to diameter inconsistency:
I purchased the PLA from onlinefilament.com for $38. I always keep it in ziplock bag (with desiccant) and cut portions of it for printing.
I clean the hobbed bolt of plastic for every new load. The bolts on Greggs extruder are turned tight, so I suspect no skipping of plastic at the hobbed bolt, but could it be jamming? I will triple-check for jamming/skipping at Hobbed bolt as the problem repeats frequently at different temperature ranges (187C, 190C, 192C, 195C). It fails miserably at 185C though.

2. Extruder skipping steps:
The pot is turned high for extruder, and it makes this wierd noise when it skips. I verified it is not skipping steps.

3, Increase axis steps per unit
I changed my previous setting from 723.xxx to 760*1.1 = 836. I will increase it further to check if that resolves the problem.

Other thoughts:
Could it be that the .35mm hole length in the nozzle is too long causing pressure related issues? Extrusion of filament in air (30mm) does not show this problem. I will try to replicate the issue by extruding 500 mm of plastic.

Edited 1 time(s). Last edit at 09/27/2012 09:20AM by peddiparth.

The issue turns out to be related to Hobbed Bolt. Some of the grooves (metal sticking out of the hobbed bolt) were smaller compared to the others causing slipping of filament. This explains why the problem repeats regularly.

The easiest way to determine this problem is to look at the extruded filament (image attached).
Some of the grooves in the filament are lighter than the rest. The groove count does not add up to the number in the hobbed bolt either.
This confirms the problem of hobbed bolt slipping on the filament.

A quick fix is to add extra pressure on the filament so all groves on the hobbed bolt get traction.

Thanks for your responses. I can now try to double/triple my printing speed

Edited 1 time(s). Last edit at 09/28/2012 08:44AM by peddiparth.

Did you hob the bolt yourself? If you paid someone for that I would ask for an exchange for a new, properly cut bolt, or a refund.

If you cut it yourself, you can correct the short teeth by re-cutting the hob with the original tap.

Applying more pressure is a stop-gap solution. You're still going to get inconsistent extrusion because the effective diameter of the contact circle between the hob and the filament is not constant.

It was given to me by a friend. I plan to replace it with a Hobbed bolt of my own shortly.
Waiting for the weekend to get more time

Edited 1 time(s). Last edit at 09/28/2012 02:18PM by peddiparth.