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Please Help with Layer Smash...

Posted by Komb' 
Please Help with Layer Smash...
December 12, 2012 09:47PM
I just finished a build of a Wallace printer.

I've gotten X,Y and E calibrated.

Z usually can be left at the default 3200/1.25 or 2560, but my test prints are showing layer smash.

I'm reasonably sure it's not Z-wobble as I've seen that before and it looks like threading on the print.

These prints look great, except for the periodic line. See Pic. smiling smiley

The holes are bubbles in the plastic. sad smiley Using up old stuff I wouldn't use for production.)

It doesn't seem to be caused by the heated bed as the bed cycles multiple times between lines.

I tried measuring 100mm Z travel and doing the calculations. It just gave me a different frequency of lines.

Suggestions Appreciated.
open | download - DSCF0009.JPG (354.5 KB)
Re: Please Help with Layer Smash...
December 13, 2012 04:52AM
I've had the same issue, lovely prints slightly ruined by banding.

Two main causes come to mind.

1) z-wobble
2) Temperature Variation

To test which it is, turn off any minimum layer times (important to ensure the next step actually takes twice as long) and print at a suitable slow rate a hollow cylinder. (or other similar non-plastic wasting object!)
Then with the same settings print two cylinders side by side.

If it's z-wobble (or similar) then the patterns will match between 1 part and 2 parts.

If it's temperature then the banding frequency will be doubled on the second print.

Have you checked that the filament doesn't have a periodic change in diameter?

A quick check to rule out z wobble is to measure the banding spacing, if it's not similar to your z screw pitch its unlikely to be the cause. (1.25mm for M8, 1mm for M6)
Re: Please Help with Layer Smash...
December 13, 2012 04:54AM
Just looking at your print though, that has got to be something mechanical, the spacing of the lines is too perfect to be temperature methinks.
Re: Please Help with Layer Smash...
December 13, 2012 01:21PM
You are correct sir!

I printed the maze cylinder and watched the machine closely.

I noticed that the Z couplers where in the same place every time a band showed up.

They were printer over a year ago with bad plastic on a not well tuned Prusa.

Replaced them with a clamping coupler and the results are noticeable. smiling smiley

Thanks for the help.

Glankonian Protoforms
open | download - DSCF0010.JPG (381.5 KB)
Re: Please Help with Layer Smash...
December 14, 2012 09:20AM
Tried doing a precision print and noticed the problem is still there. Just reduced.

What are the probable causes?
open | download - DSCF0011.JPG (385.8 KB)
Re: Please Help with Layer Smash...
December 14, 2012 10:06AM
... probably different Z-heights per layer ...

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Re: Please Help with Layer Smash...
December 14, 2012 11:13AM
Are the new couplings solid plastic or do you have to put a bit of rubber on the end of your motor? A rubberised coupling is far superior to a solid one! Changing to M6 z-axis screws is another good change. I changed to M6 threaded rod and 4.8mm ID fuel hose as couplings and the results are very good!

Are any of your z screws slightly bent (roll them on a piece of glass or other flat surface to see), do they spin freely with no binding in the nut, does your z axis slide up and down freely, are there any loose screws anywhere on your machine especially in the x and z axes, is your hotend still firmly attached to the carriage.

Do your filament or cables pull significantly on your x carriage?

I'm not that familiar with a Wallace, but it looks like the z rails are only supported at one end so check they are still firmly in place.

Are your z motors definitely not skipping steps every few layers? How are they wired? Parallel or series?

Oil your z screws and turn up the pot a bit (careful) to make certain they aren't skipping steps
Re: Please Help with Layer Smash...
December 14, 2012 01:23PM
konwiddak Wrote:
> ..., is your hotend
> still firmly attached to the carriage.

I think you may have something There.

The extender I'm using to get the shorter J-heads below the X carriage seems to have some play between the screws and top inner surface.

So much so, that I can see the head lift on every retract.

I will print and install an alternate extender design and try again...

Edited 1 time(s). Last edit at 12/14/2012 01:41PM by Komb'.
Re: Please Help with Layer Smash...
December 14, 2012 02:58PM
Are you using so-called "Z-stabilizers" by chance? My kit came with them, but they actually made z wobble worse. The non coupled end of the z rod seems to work much better if it's unsupported in free space.
Re: Please Help with Layer Smash...
December 20, 2012 10:02PM

The new extender doesn't let the J-head move at all and the lines are Gone!

Thanks to all who helped me figure this one out.
Re: Please Help with Layer Smash...
December 21, 2012 06:25AM
Great Komb smiling smiley
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