Unless your printer is shaking pretty hard I wouldn't think that would be an issue.. If it *is* shaking a lot, you might need more rigidity in your frame.

 

Only shaking when infill is being printed otherwise not. Well, lets see what tomorrow brings Might get the magic number of what amount of added weight bring ripples.

 

My D-Bot is direct drive as well and I do also see this exact pattern in some of my prints at higher speeds. I just assumed it was some sort of mechanical resonance since I have a full sized Nema 17 on the extruder. I was going to order a pancake stepper to lower the weight and see if this corrects the issue. My initial thought was that it was resonance, as if I slow the speed down, these artifacts become less apparent until the finally disappear. My frame is about as rigid as I can possibly get it and if I try to move the bed I end up moving the whole printer. Just something that goes with the territory when using direct drive at higher speeds?

 

Does your frame shake at higher speeds?

 

So I'm not sure this is the problem, but since there are 2 people with D-Bots running direct drive with ripple issues that may or may not be related to frame rigidity..

I have developed a series of C-Bot frame mods that greatly improve rigidity: SpiffBot CoreXY 3D Printer by spiffcow

These aren't directly usable with the D-Bot because certain parts of the D-Bot use 2020 instead of 2040. I would be happy to make the necessary changes to create a D-Bot version, but I don't have any 2020 to test it with directly. If you're interested in trying this out and willing to provide feedback, I can go ahead and produce a D-Bot version tonight.

I regularly run a heavy direct drive carriage at 120mm/s with this. It holds up at higher speeds too, but my steppers crap out at around 150mm/s

 

I would have to say yes. I attribute most of it to the rather soft rubber feet that I put on the printer when I built it. Wasn't sure how much would translate into the prints since the bed is rigidly tied to the frame and does not move independently. I was getting ready to either replace the feet this weekend or tie it to the table it is on (a very heavy butcher block kitchen island that I re-purposed). I'll report back results once I eliminate that as a potential source.

 

Hmm.. That's an interesting line of inquiry.. I have foam underneath mine because my floor is not very flat, and it does sway a bit during printing, though everything appears to move together...

 

For comparison, this is the ripple pattern I see on mine.. Its a bit hard to make out, but if you look close you can see a vertical ripple pattern along the flat sides. It's almost imperceptible to the touch though

 

That doesn't look like ringing from accel/decel, but i could be mistaken. Can't help but think it might be an issue with your rails or motion drive.

Answering these should help diagnose:
Is there any play in how the X or Y carriage wheels sit on the rail?

With all the motors unpowered, but the belts attached, does your X and Y carriage move smoothly in each axis? The belts and motors will resist movement slightly, but this should be constant along the whole axis.

Also, if you have a phone with slow-motion capability, post a video of the carriage when printing, as that might help. My iPhone at 240fps has helped me watch issues with retraction, and motion operations that would otherwise be way too fast to see.

 

Ok, some tests are in and this narrows down the problem to ............ wait for it ....... stepper motor causing some high frequencies or something like that As per the "adding weight" test I did now - and please tell me if this test does not really prove much - the D-Bot does not suffer from adding weight or vibrations and is just as robust as the C-Bot - well kinda .

I did four tests now:
1) Just bowden driven with no added weight to the gantry.
2) Bowden driven with a added 224g stepper mounted on the gantry for weight (this stepper is not driving the fillament)
Here is a photo:
3) Bowden driven with a added 308g stepper mounted on the gantry for weight (also not driving the fillament)
Here is a photo:
4) Bowden driven with both stepper motors on top of each other adding a total of 532g
here is a photo:

The first three tests I can at 40mm/s print and I cannot tell any difference in the lines. There are no ripples. The last test with both extra steppers mounted I ran a test at 60mm/s and it came out AMAZING. Much better then the first three tests.
Left to right: Test 1 and Test 2 and Test 3 just halve of it


Left to right: Test 3 and Test 4


Just Test 4


I am not sure what the tests are telling, but it seems like when the actual direct driven stepper motor is turning and pushing filament (and not just hanging there) it causes these oscillation vibes on the print ? Any input or criticism is welcome

 

Oh and I just want to mention that some of those lines on the print are just because of the flashlight I am holding and the iphone camera. In real life the print look very smooth.

Also just want to note that when I had it on direct drive, I did test with 1/16th and 1/32 stepping but no real change.

 

That sounds like the most plausible theory at this point.. Now the question is how to mitigate it? maybe a soft cushion between the carriage and the stepper?

Heh, or just get a pancake stepper and call it good..

 

Yea, I did order today the Titan extruder and still need to search for a good pancake stepper for it. Will only be here in about three weeks though :-(

I will try this rubber 17 nema damper that I once scrounged out of an old dot matrix printer and see if it helps

 

Looking forward to seeing what you find!

I'm wondering if this explains why I saw a reduction in ripples when I was testing my sliding carriage.. It might have distributed the force from the stepper over a wider area or prevented side to side movement since it pressed up against the sides of the 2040 in addition to the top and bottom.. My Printbite should be in any day now.. As soon as it is I'll try printing that in nylon again and see if it helps.

 

Just tossin' it out there; How about changing the microstepping on your extruder driver? I honestly don't know if it would have any impact, but I know that mine sounds quite different at 1/16 or 1/32, when printing at different speeds.

 

Hi, yes I did try that already, but there was not much of a difference.

Ok, first test being back on direct drive but added the stepper vibration damper is through.

Huge difference ! Not as good as with Bowden but compared to how is was before - amazing. I am now starting a second print after taking away some plastic with a dremel where the stepper touches the back plate on the one side (closest to the sensor) .

 

Interesting, have some questions if you don't mind.

What stl files did you use for the hot end carriage?
What plastic is the carriage printed in?
What infill percentage / pattern?
Layer height?
Permimeters?
Nozzle size?

It seems very odd that the stepper would be shaking that violently to cause that pronounced of ripples. But then after thinking about it some more, I have some theories. E.g.; resonance in the plastic carriage itself, carriage is too light to dampening stepper, carriage is not strong enough for a variety of reasons, etc....

EDIT: Oh if you're curious, I'm als0 asking because I want to see if there are design changes I need to make to the generator.

 

Very nice!

 

Yeah, it looks like it may have been a stepper vibration thing then, here's the stepper I use with my Titan extruder:
https://www.amazon.com/gp/product/B00PNEQ79Q/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

It's also available on ebay and omcstepperonline, it works well for me so far.

 

No Problem - we are all here to share
I used the one from Carl that are in the C-Bot_Rework stls but changed the rear one to allow my sensor (almost the same as what Spiffcow did)
All is printed in PLA (RS Component brand)
Infill was at 70% with honeycomb
0.25 mm height
3 Top bottom and sides
0.4mm nozzle

 

I am super happy

After taking away a bit of plastic on the one side to free the motor - there is no difference anymore between my Bowden print and the direct drive print
Thank you all for assisting me!

 

Thanks, I will give it a go

 

So moral of the story is to ensure the stepper is not touching anything other than the required srews for mounting? E.g.: not resting in a tray, etc....

 

That is the one and if you can, add a vibration damper on you motor

 

Perfect, thanks for the info and great job on the root cause determination!

 

Now the question is what impact does that have at high print speeds? I wonder if the inertia of a stepper that's only supported on one side will cause print issues when suddenly changing directions..

 

Not sure how Carl has his, but I have some smalll reinforcement triangles in mine for that reason. Similar to what was done for the XY steppers.

 

Since I am having a very similar issue -

Used the C-Bot rework direct extruder front/back plates
Hatchbox PLA
75% infll, rectilinear
.2mm layer height
3 shells, 3 bottom, 4 top
.4mm nozzle

Wonder if it is contributed to by the material? In any case, I know what I am doing this evening. Making some dampers!

 

Does that mean you have a direct drive option in your generator now?

 

Hmm, my parts are printed in makergeeks black pet... 40% triangle infill, .2mm layers, 2mm top/bottom/sides, .5mm nozzle

I can use a 42mm nema 17 on my titan and see what happens. Any specific shapes the pattern is apparent on?