Hi Togeir, thanks for the reply!
It looks like the S3D print might be a much thicker layer height, which could explain the color difference.
Maybe we should start a thread to compare resonant test prints at comparable speeds and max accelerations. It would be interesting to benchmark different modifications.
Recommended Posts
andywalter 7
I've taken the other approach to solving the ripple at corners problem, by removing all the drive-belts and replacing with a helical-shaft direct-drive system. I'm now printing at 60mm/sec, and I've reduced the accelerations in Cura to 750 mm/sec**2 . Pics in the thread here, on page 9:
See what you think; I still have the 6mm shafts & bowden cable. I don't think they're the worst offender on UMO, I think the belts are.
I don't seem to have any Z layering problems - even when I still had belt drives. I put that down to changing the table support, I replaced 2 of the wooden arms with aluminium ones, so the HBP is now firmly located to the Z bearings via the aluminium bits.
Edited by andywaltertypo
Link to post
Share on other sites
lars86 42
Wow, that is quite a modification you made there!
I'm surprised with the lengths you went to on the motion control, that you are still using the stock print head. Looking through your pictures, it seems like you have inconsistent extrusion and could benefit from some improvements there. Are you running the original extruder drive?
I'm still not so convinced that most ringing is caused by the belts. For sure, running the short belts contributes a good bit. But with a direct drive setup and GT2 belts (a big improvement over MXL), I don't think belt stretch is a significant factor. For example, with the printer stopped, I can push the head in an X or Y direction, and see noticeable deflection of the head form the 6mm rods bending, but essentially no movement of the XY blocks:
Also, the bronze 8mm bushings aren't a bad thing in my eyes either (so long as they fit well and are kept clean). Yes, they suffer from more static friction to overcome during starts/reversals. Once moving though, they move quite nicely (as long as they are not put into bind by an improperly squared machine). Since they are driven directly from the belts, their friction will not increase ringing. It increases the load on the steppers, and at the very worst, could affect micro stepping precision. But I think the amount of force they contribute is negligible on a well tuned machine. They are super easy to deform though. So, if your XY bocks clamp too aggressively, they will bind like crazy.
The print head bearings on the other hand can really mess with head precision and ringing, since any friction in them acts with inertial forces, making them worse. Since linear ball bearings will always have some radial lash, I think that minimizing the distance from the bearings, down to the nozzle tip is an important aspect. Radial bearing freeplay causes angular misalignment of the print head. So, the longer the head is, the greater the imprecision of the nozzle's XY position. My print head is nearly 1" shorter than the stock head! This is about the practical minimum height, as I am nearly out of Z travel:
Link to post
Share on other sites
andywalter 7
All I can say is, I think I've pretty much eliminated the ringing I used to see. Maybe reducing my acceleration has helped that a lot, but I also have far better precision than before, with each layer sitting very neatly exactly above the earlier ones.
Coincidentally, I've just repaired a Makerbot 2X, which I believe has the GT belts you mention - as far as I can read what's on the belts, they're Gates GT 2MR 283 which I can't see in their catalogue. The tooth shape looks much nicer than the MXL; MXL looks very trapezoidal, while GTs look more like the circular-ish ones designed to fit a curved-tooth pulley rather than the trapezoidal MXLs. When I worked with the trapezoidal belts years ago, they had a small amount of backlash as the belt teeth were a slightly loose fit in the pulleys; but the later HTD belts with a curved rounded profile were designed to sit tightly into the pulley at the tip of the rubber teeth, and as the belt transmitted greater power, the teeth progressively sheared a tiny bit more, bring more of the tooth into contact with the pulley. At max power you then had the entire tooth face with equal pressure at all points. The trapezoidals didn't do that, the teeth matched the pulley shape exactly, so with increasign power, the pressure increased most at the base of the tooth close to the fibreglass belt, and the tip of the tooth was under almost no stress. So these belts tended to rip the teeth from the belt, starting at the base of the tooth. The HTD belts had zero backlash in theory, and thanks to the better stress-distribution they had better power capability for the same dimensioned belt. The GT belts look to have this better profile, as far as I can see.
Having repaired the MakerBot, I ran the same resonance-test box-thing. The print speed was slower than I use, 40mm/sec, and there's definitely some ringing-like features showing. But the precision was good - the box has a wall 1.0mm thick, which gets printed as 2 walls of 0.4mm each with 0.2mm gap between; on my UMO the gap exists everywhere (except at corners); in the Makerbot the gap was there mostly, but a few places the 2 walls had bridged. But definitely better than I ever got using the original MXL belts.
I like the look of your printhead, is it aluminium? Must admit, I hadn't given any thought to the nozzle wobbling around. I've got plenty of 8mm bearing shaft around, so I'm rather tempted now to try your 8mm idea with a custom printhead designed to minimise vertical distance. I'm not yet 100% happy with the circularity of my printed cylinders, there's some radial error which looks a bit like backlash, as I'm getting that slight flattening effect on the 0, 90, 180, 270 degree directions which is where the X & Y axes reverse direction. Maybe some of that is springing of the thin 6mm shafts as you suggest.
Is thare a cooling fan on your head, and do you direct any cooling air around the nozzle itself? I've got a rather badly made & bodged-up circular diffuser thing which could be improved.
My extruder is a replacement for the nasty original, uses 2 geared pinch-rollers. I think it's pretty accurate & repeatable. Yes there's a dodgy corner in my test-box print, not sure what caused that. I'm not sure I'm getting the layers to bond properly; last night's MakerBot was extruding very molten plastic at 230C, and getting the layers very well fused together. I tend to suffer delamination, so I acetone-vapour my prints later to melt the surface into a strong skin, but my print walls tend to be matt-black when just off the HBP, whereas the MakerBot print came off looking very glossy, which I think means I'm not yet melting my plastic as I should. But I print at 240C, and I'm using Voltivo ExcelFil ABS, while the MakerBot is probably on MakerBot's own stuff. Could that be the difference? I might try setting my nozzle to run at 250C for most of my print, cooling it as I get to the last few layers as I don't want to bake any plastic left inside the nozzle after the print has ended. Even the MakerBot nozzles had some charcoal-like burnt-plastic when cleaned them out, so >240C is to be avoided if poss, I think.
Link to post
Share on other sites
lars86 42
Reducing max acceleration has a huge impact on ringing. Remember, Force = Mass * Acceleration. Deflection (ringing) is proportional to force. You won't see a true comparison of your modification unless you match the print settings from your older tests.
Makerbots do use GT2 belts but they are direct drive printers. With all that extra weight on the print head, it's no wonder you see ringing.
My print head is a printed assembly. I'm working on a new revision of it to hold an E3D V6. I have been running a sort of Franken-hot-end with a stock heater block & nozzle, but a custom stainless heat break and heatsink. I actually designed an entire hot end from scratch and made all the parts on my CNC machines. But was shocked that my press fit connections between the heat break and heater block leaked molten filament! I never came back around to remake it.
If I were you, I would print some big circles at very slow speed (20mm/s). This should remove any inertial flex. If you still get the flat spots, then you likely just have too much backlash in your spiral followers.
Yes. That photo doesn't show the fan configuration. I currently run two 30mm radial fans with light ducting to direct flow. I print almost exclusively high-end PLA and feel like cooling is very key to high quality prints.
In addition to not wanting to breathe styrene gas, generally I find printing ABS a nightmare with very little upside. Modified PLAs tend to have better stiffness, less shrinkage, similar strength, great bed and inter-layer adhesion, etc. I just don't see the allure of ABS. Having prints that look good, but peel apart along layers does not interest me. Also, not being able to run adequate cooling means overhangs will be garbage.
If I were you, I would grab some Polymax or Protopasta PLA and do some test prints to get your printer dialed in. You can run much cooler nozzle temps 200 or less, full speed fans, prints stay stuck to even a cold bed (with blue tape). This will make sure you aren't trying to calibrate a printer off warped ABS. $0.02
Link to post
Share on other sites
Torgeir 259
Hi Lars86,
Yes, I've been going the other way-, trying to decrease the weight and eventually the "moment of inertia" for the whole gantry (sure not easy, but fun, -because it is all about those small little details)..![:) :)](//content.invisioncic.com/ultimake/emoticons/5a33abdf6d109_1f60acopy.png)
Thought about hollow, or gun drilled shafts and even thin walled straight stainless tubes. The latter one is interesting, as a 8 mm shaft with wall thickness of 0.25 mm (same length) will weight only 11.3 Gram!
Seems unreal? Well, had two 8 mm shafts scrapped due to too much play.
There's some smart things to do, -then we can use such shaft's in your UM's... So, what can we do???
Short 8 mm shaft weight; 131.4 Gram and length 337 mm. (I have a precision weight that's calibrated!)
Long 8 mm shaft weight; 135.9 Gram and length 347 mm.
I'll fully agree with you that it is the self resonant frequency of the extruder head is what cause "most" of the ringing in the print and NOT the short belt. Well, -as I do not have an UMO (the grand father of UM2) but an "UM2 ext", I'll believe this issue is valid for all UM's -more or less if the speed is set to high.. Hint; there is a wider belt to try!
As I've never seen this test object Andy refer too, I just downloaded the square one (for resonance test) to see what this print would look's like.
To be fair, I downloaded the new Cura ver. 3.1.0. Used all default values, and let it go in order to see what it could be. Also, I just recently got a mail from S3D about there was a new ver. 4 out to download for me. So, downloaded this one as well. Did a monitor view of the model and saw that the writhed text was very bad "melted and over extruded". So, deselected the retraction and print looked good.
So I printed the object sliced by the two different slicers, Cura ver. 3.1.0 and Simplyfi3D ver. 4.0.1
The left one is S3D and right is Cura.
Funny, but the one made with S3D is darker than the right done with Cura.
Both is smooth, but S3D has better smoothness.. However, Cura's measuring is way better; 50.0 mm X 50.0 mm and 16.0 mm height (with 0.1 res perfect!) and finally wall thickness 1.0 mm same accuracy (amazing)..
It's a little unfair over S3D as I did not do any correction for the line width etc. with S3d, but been using Cura as a standard for my print of course..
Some more details from the Cura printed object.
The texture inside the box.
See the small bubbles in the middle, oscillation.. Cura 4.0.1
Corner with bubbles. Cura 4.0.1
Same here, but otherwise very good.. Cura 4.0.1![:) :)](//content.invisioncic.com/ultimake/emoticons/5a33abdf6d109_1f60acopy.png)
Ps. All pictures is high res. so just zoom!
Keep up the good works (with an Ultimaker).
Thanks.
Torgeir.
Link to post
Share on other sites