Wiggly Box

Hello to everyone, It's my first post and my first experience with 3D printers.
Yesterday, with my fellow friend, I made my first print of the calibration cube 20 mm.
The machine is not a reprap, but more similar to an old CNC converted in a 3D printer :-)
Anyway, the first test was quite fine, but the most notable thing is that all the piece has a kind of "wiggly borders". I see in this section of the forum that the wiggly line depends on incorrect height from bed, but it seems that the problem is for first layer; in my case all of the piece is like that :-) (see Photo)

What I can check in order to have straight line borders?

- The slicing was made with Slic3r, the nozzle is 0.35 mm and layer height 0.35 mm
- The machine si quite slow due to mechanics and is about 10 mm/s on all axis.
- The extruder was calibrated with pronterface measuring the material entering the extruder to be correct and is fine
- Material is ABS and temperature of 220 °C
- I don't have an heated bed, but extrusion is on polycarbonate covered with PVC tape (insulating tape for electricians) and it is not the best thing I know, but the layer sticks quite well anyway (see the photo of the nack of the piece)

Thank you in advace for your hepling, Bye
Stefano

Your layer height MUST always be less than the nozzle size, say 0.2. for your 0.35 nozzle.
Also, was the wall thickness of the calibration cube equal to what it is supposed to be? i.e. if its a 0.5mm wall thickness, did it actually measure 0.5mm? Your extruder calibration is not finished if it's not.

Thank you very much for these information, now I know which can be the way to take to manage this problem.

Today I will try reducing the layer height and checking with the caliper the thickness of the wall.
Do you suggest me to print a sample of a "only wall" cube? without filling in order to easily check different settings?
Another question, if I set in Slic3r 3 line per wall do you mean to measure the total thickness or the tickness of a single line extruded?

Thank you :-)

Sorry for late reply..
First, check the gap when the Z axis is homed - it should be about 1 paper thickness gap. Then, change the "layer height" in 'Print settings' in Slic3r to maybe 0.2mm.
Yes, you want to print the 0.5mm hollow calibration cube to measure the wall thickness. When the print is done, take your calipers and measure the top 5-mm or so of the cleanest looking side wall to get your measurement - don't try and measure a single thread!

Thank you for the info, sorry too for my late reply. I have non time to make more experiment these weeks.
We try as you suggest and the first issue was resolved I think. I make an height calibration with paper sheet and the printing quality with 0.2 is higher.
There was another problem, it is not like the first "wiggly" line, but the wall of my cube are strangely printed. Look at the picture: seems that the filament became fat and thin at regular interval.. What can be the problem? Vibration? Extruder step not small enough (I'm using half step, I don't a driver to do 1/16 step)? Temperature too low?
Any suggestion can be helpful to do more practice

Thank you

its remarkable how consistent the wiggly is

my question is what extuder are you using ??

my guess is its too regular to be heat related . Id take a good look at your extuder ...maybe an oval hobbed bolt or bent but this wiggle is too fine to be directly related to the hobbed bolt but it has to be something in the extuder to be so regular in occurance

Edited 1 time(s). Last edit at 03/22/2013 04:20AM by bigfilsing.

Yeah, also might be worth watching the axes as it prints to see if there is side to side movement that would create such a thing. Slicing error?

the fact it is so regular is still bugging me. almost like your X & Y stepper motors are doing 2 step 1 step 2 step 1 step or something.

Maybe they cant follow the commands being sent ..what control board are you using ? if your sending steps/ micro steps that cant be followed then maybe this is the issue

Thank you again,
unfortunately I have no much time to experiment, so my replies are quite late.

The stepper controller is the following one, but only 3 Axis. I know that there was a lot of problem of reliability with this kind of chinese clone, but I solve most of the them with the reverse engineering made on this reprap page, so I think that, a part from the low speed due to mechanic that uses leadscrews, the XY axis I think are good.

[reprap.org]

From the last experiments, and observing closely the extrusion from the nozzle during print I'm pretty sure that is extruder-related.
This is my extruder:

[store.qu-bd.com]

Already modified with the following things:
A new bearing and spring to allow grip of the extruding gear with the filament
[www.thingiverse.com]

and a new gear, becasue the original one does not guarantee correct grip to the filament.
[www.ebay.com]

After these modification the extruder never jam or other and extrude (in air) perfecty

I notice that, considering that I have a 200 step/round motor that drives directly the gear that has a 10,55 diameter and with only 1/2step driver I have only 12,88 steps per unit of filament.
I see the shaft of the motor moving very slowly during extrusion, it is possible that each of that wiggly line is a simple step of the extruder that apply pressure and there is to much time before the next step was made? A sort of "pressure/No pressure/pressure/No pressure" like a sort of aliasing.
If I observe the extruded plastic during printing it is noticeable that seems like a chef that extrude cream on a cake with a sac-à-poche :-) :-)
Do you think that a 1/16 stepper driver can improve this thing?

Thank you.

it certainly looks like your stepper driver is a fault
did you get the standard stepper motor with the extuder or supply your own ? ( i saw there was an option to buy without stepper)
if your sure your stepper motor is working fine then chances are its the controller

It looks like that controller can be set to 1/8 or 1/16 steps by using the dip switches.

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Thingiverse ID Alan1279