Whats with the "ribbing" on my prints
March 29, 2012 08:17AM
I have been noticing this "ribbing" on my prints lately. I have recently switched to the newest versions of prontoface and slic3r. Not sure if that has something to do with it. Other than that I haven't changed much, and this just can into existence in the past week or so.

Slic3r or SF(depending on the part) --> Marlin --> RAMPS 1.4 --> JHEAD. ABS

I have played with different layer heights but to no avail. Any idea where this is coming from? I assume it isn't missed steps since the "rib" is symmetrical around the part. i.e. it isn't indented on one side and sticking out on the other; it's indented all the way around.

It seems to happen for a few layers, then go away, then come back a few layers later.

Need help!
Attachments:
open | download - photo.JPG (67.5 KB)
Re: Whats with the "ribbing" on my prints
March 29, 2012 08:26AM
Hold it against your z rod and check if it matches the threads. If it does your z axis is over-constrained, meaning the z rods pulls the entire x gantry out of alignment.

This is the reason why using smaller diameter floating lead screws seems like a good idea. I'm going to try out m5 on my current new build.


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-Nudel
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Re: Whats with the "ribbing" on my prints
March 29, 2012 08:46AM
The ribbing on this part seems to be uniform, on other parts its not as pretty. It appears more random. While I'm not ruling the Z out, I haven't made any changes to my X or Z axis and this wasn't happening before.
Re: Whats with the "ribbing" on my prints
March 29, 2012 09:20AM
Maybe time to drop a few oil on your leading threaded rod and in your bearings ?


Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.
Re: Whats with the "ribbing" on my prints
March 29, 2012 10:40AM
That definitely looks like a problem with your Z threaded rods, which is why I'm not a big fan of using them for motion. I'd suggest picking up some inexpensive leadscrews. Banding like that can also be caused by loose belts, but the regularity I see there really points to Z threaded rod problems.
Re: Whats with the "ribbing" on my prints
March 29, 2012 11:02AM
Can someone explain how the Z rods might have cause this? And why it happens all of a sudden?
Re: Whats with the "ribbing" on my prints
March 29, 2012 11:34AM
There are may reasons why it might have started happening suddenly. For example, if your Z threaded rod nuts have, for whatever reason, started to wobble in your X-ends' nut traps, then each rotation of the Z rods will not raise the X gantry by a consistent amount. And if your threaded rods have a periodic issue with the threads, it's possible that they were rotating in tune with one another before, masking the issue.
Re: Whats with the "ribbing" on my prints
March 29, 2012 11:35AM
Is the banding in sync with your layers,e.g. every second layer, or is it equal to your lead screw pitch, i.e. 1.25mm for M8?

It looks too gross for a lead screw problem to me. It could be Z missing steps, so making the filament fatter on those layers. What sort of machine is this, i.e. single Z motor or two?


[www.hydraraptor.blogspot.com]
Re: Whats with the "ribbing" on my prints
March 29, 2012 11:37AM
Do the objects come out the right height or are they short?


[www.hydraraptor.blogspot.com]
Re: Whats with the "ribbing" on my prints
March 29, 2012 11:41AM
This is a tech zone huxley. Basically a mini Sells mendel. It has one Z stepper. I was thinking the same thing. That the layers were compressed and causing the banding. I'll check out my Z axis. I just got some machined pulleys in, so maybe I'll install one on there and check it out. Thanks for the help everyone!
Re: Whats with the "ribbing" on my prints
March 29, 2012 11:41AM
No Bowden cable on the Huxley, replaced it with a direct wades.
Re: Whats with the "ribbing" on my prints
March 30, 2012 09:47AM
It doesn't seem to be directly related to a specific axis. I'm leaning more towards either a temperature issue or filament thickness.

The machine is set up in my basement which is pretty cold. I'm thinking the differences may be to the heater in the print bed shutting off after it meets it's temp and then turning back on, or may the hot end, or a combo of both. Not too sure how to prove it.

My other idea is that my filament is not uniform in thickness. I am using an accessible wades without springs. Could the "thick" and "thin" layers be due to more filament being pushed out? I've noticed that with smaller parts that take less time, the ribbing is not as noticeable. Has anyone see anything like this before?
Re: Whats with the "ribbing" on my prints
March 30, 2012 12:28PM
If the ribs go out on both sides and in on both sides together it must either be the layer height changing or the flow rate changing.

If it was the flow rate changing it could be due to filament diameter variation but it would have to change by about 0.2mm over quite short distances, so I think you would be able to see that on the filament. Have you tried measuring it in a few places?

What happens if you build two of the same object at the same time? If it was filament you would get ribs of twice the frequency. If it was layer height they would be the same frequency.

You haven't answered any of my questions so it is hard to make a remote diagnosis.

What is the pitch of the ribs?
It is synchronised to the layer height, or the Z leadscrew pitch, or neither?
Are the objects the correct height?

An eccentric Z motor pulley would do it.

It is hard to see how temperature fluctuations would do it as it doesn't affect flow rate unless it gets too viscous and slips. This looks too regular for anything slipping.


[www.hydraraptor.blogspot.com]
Re: Whats with the "ribbing" on my prints
March 30, 2012 12:39PM
I've measured the thickness of the filament and its pretty uniform. Also, I switched colors and I'm still seeing the ribs.

I have changed out my Z axis pulley to a machined one so I don't imagine that would be it, but I could check again.

I will try printing two at the same time and see.

The pitch of the ribs changes based on the height of the object printed. If its a smaller part, then they seem to be closer together, if its taller, then it seems to be farther apart. I haven't measured specifically but I will.
Re: Whats with the "ribbing" on my prints
March 30, 2012 05:36PM
This is clearly Z-Axis wobble. Post a picture of your vertical threaded rod, including the bit where stepper meets rod, and I can tell you where the problem is.
Re: Whats with the "ribbing" on my prints
March 31, 2012 07:28AM
Pointedstick Wrote:
-------------------------------------------------------
> That definitely looks like a problem with your Z
> threaded rods, which is why I'm not a big fan of
> using them for motion. I'd suggest picking up some
> inexpensive leadscrews. Banding like that can also
> be caused by loose belts, but the regularity I see
> there really points to Z threaded rod problems.

I got the same problem banding problem with cheap threaded rod.

I bought a cheapish leadscrew, but I am still looking for truly inexpensive leadscrews. I also haven't worked out how to replace M8 threaded rod, since the leadscrew won't take an M8 nut. The nuts and accessories for leadscrews are expensive too.

I am looking for someone with a lathe to machine M8 threads onto the ends, then maybe I can fit it to my printer using standard parts.

An alternative is more expensive threaded rod (machined not rolled?) but I'm not finding that easily either.
Re: Whats with the "ribbing" on my prints
March 31, 2012 11:24AM
jcabrer Wrote:
-------------------------------------------------------
> This is clearly Z-Axis wobble. Post a picture of
> your vertical threaded rod, including the bit
> where stepper meets rod, and I can tell you where
> the problem is.

I'm not so sure. I had some Z axis wobble that clearly measured the same pitch as my Z rod. The pattern in the parts noticeably followed a helical pattern around the part. Now that I've added my Z screw isolators (Thingiverse), the wobble is gone and I see a pattern that looks like what Entropy is showing, but not as severe. The bulges on the part are uniform all the way around a part (not wrapped helically around the part), and very definitely not the same pitch as the screws. They measure close to 1.0, and the screws are 1.25. (I also checked 10.0 mm v 12.5.) The spacing stays the same for layers with both large and small total areas, so I don't think it's a filament diameter issue for me. I do see that the banding doesn't appear in the layers within about 8-10 mm of the heated bed (I'm presently using 1.75mm white ABS from MakerGear).

Since installing the isolators, I haven't printed any parts that don't have sections so thin they end up being filled 100% despite Fill being set to 35%. I was thinking that perhaps the bulges are a symptom of a slight overfill condition resulting in a periodic overflow. I need to try a part now that has room inside for properly sparse fill to see if that looks any metter.

There are no guarantees that what I'm seeing and what Entropy is seeing are two instances of the same problem. I just don't think it's clearly a Z wobble problem. I'll try to remember to report back here what I find.

Edited 1 time(s). Last edit at 03/31/2012 11:27AM by Dale Dunn.
Re: Whats with the "ribbing" on my prints
March 31, 2012 03:10PM
Looks like Z binding or wobble to me. I get banding like that on my sells mendel when the leadscrews need lubing. Once I add some lube it is gone. Probably skipping steps on the Z stepper due to binding which causes the bulges because the layer does not go up enough which makes the layer overfill.

Check your Z axis for binding/calibration...then lube it with something (I have been using lithium spray lately).


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Re: Whats with the "ribbing" on my prints
March 31, 2012 03:50PM
bobc Wrote:
> I bought a cheapish leadscrew, but I am still
> looking for truly inexpensive leadscrews. I also
> haven't worked out how to replace M8 threaded rod,
> since the leadscrew won't take an M8 nut. The nuts
> and accessories for leadscrews are expensive too.

Hope nobody minds the threadjacking, but I sell pretty cheap leadscrew sets that include nuts that are the same size as M8 nuts, so they're a drop-in replacement for your existing X-ends. The only printed parts that need replacing are your motor coupler since the leadscrews are 6.35mm in diameter, so you'll need to either print new couplers or upgrade to metal couplers.
Re: Whats with the "ribbing" on my prints
April 01, 2012 11:55AM
Dale Dunn Wrote:
-------------------------------------------------------
> I'm not so sure. I had some Z axis wobble that
> clearly measured the same pitch as my Z rod. The
> pattern in the parts noticeably followed a helical
> pattern around the part. Now that I've added my Z
> screw isolators (Thingiverse), the wobble is gone
> and I see a pattern that looks like what Entropy
> is showing, but not as severe.

I am open to the idea that it is not just Z wobble (XY wobble caused by Z), but also a problem with the Z movement. Cheap threaded rods are made by rolling, so while the average pitch is nominal, there may be a variation in pitch thread to thread. That is one reason why I want to try more accurate machined rods or leadscrew.

I had also wondered if there is accumulated error in the Z steps, but I would guess a step error of +/- 1 step per layer is not going to cause much problem.

I further wondered if this is a property of the extrusion. As each layer pushes down on existing layers, I guess there is a tendency for the new softer layer to ooze sideways. The layers meander back and forth from the nominal position.
Re: Whats with the "ribbing" on my prints
April 02, 2012 09:27AM
Pointedstick Wrote:
-------------------------------------------------------

> Hope nobody minds the threadjacking, but I sell
> pretty cheap leadscrew sets that include nuts that
> are the same size as M8 nuts, so they're a drop-in
> replacement for your existing X-ends. The only
> printed parts that need replacing are your motor
> coupler since the leadscrews are 6.35mm in
> diameter, so you'll need to either print new
> couplers or upgrade to metal couplers.

Nice try, but as this is a techzone huxley he needs M6 for his leadscrew (and M6 sized nuts).


I also got a TZ huxley and it exhibit a similar "horizontal banding" problem - only to a really lesser extent.

Once in the past I had to do something to lessen it - it was after I dismantled and rebuilt my Z and X axis. The problem was a slight mis-alignement of the z rods.


Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.
Re: Whats with the "ribbing" on my prints
April 02, 2012 11:27PM
If I can jump on this thread with a possibly related issue with my Prusa-

I'm reasonably happy with the quality of my prints, except I have some minor banding. I don't think it is threaded rod wobble, I've installed these to further decouple the carriage and the results are indistinguishable.

It seems to be more pronounced on layers with more detail, e.g. a simple cube appears almost flawless but anything with a region of more complicated layers has more banding on them.

I've tensioned my belts as well as possible and made sure they aren't rubbing against idlers.
Should I blame crappy chinese lm8uus? Recalibrate my extruder's steps/mm?

I would be happy with the parts if I couldn't produce better with my modified Cupcake.
Attachments:
open | download - banding.jpg (146.2 KB)
Re: Whats with the "ribbing" on my prints
April 03, 2012 03:57AM
Do the layers bulge all the way round are are they simply displaced laterally? The former implies a Z / flow rate problem, whereas the latter is an X /Y problem.

One thing to check is that the hot end is solidly attached. If it can wobble very slightly where it is joined to the extruder it can give a big offset at the nozzle.


[www.hydraraptor.blogspot.com]
Re: Whats with the "ribbing" on my prints
April 03, 2012 05:07AM
@tsb4k This looks like mechanical wobble. Try turning the acceleration and speed down, tighten the frame and perhaps add some crossbraces.


--
-Nudel
Blog with RepRap Comic
Re: Whats with the "ribbing" on my prints
April 03, 2012 07:22AM
Although it looks like a mechanical fault, I wouldn't mind that on my prints, looks pretty cool...
Re: Whats with the "ribbing" on my prints
April 03, 2012 12:00PM
Couldn't it be a temperature variation? PID problem?
Re: Whats with the "ribbing" on my prints
April 03, 2012 12:18PM
As far as wobble is concerned, are there any wobble constraints designed yet for the z axis of the original mendel? i think this is the last part of the puzzle to get my machine to have amazing results
Re: Whats with the "ribbing" on my prints
April 03, 2012 12:49PM
Why would temperature affect the dimensions?


[www.hydraraptor.blogspot.com]
Re: Whats with the "ribbing" on my prints
April 03, 2012 01:41PM
@morrist There are a few wobble arresters on thingiverse, though I have not tried any of them myself. Here's one of them: [www.thingiverse.com]


--
-Nudel
Blog with RepRap Comic
Re: Whats with the "ribbing" on my prints
April 03, 2012 04:24PM
@nudel,

Thank you. when i searched earlier i came across others but not one like this that would work well with the mendel smiling smiley


Morrist
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