weird rough patch on ball

[greenieboy 0]

i'm trying to make a bouncy ball out of tpu but on the lower half above wehre the support comes off theres a rough patch that goes all the way around, it happens every time and i don't know why can anyone help me with this. i've already tried using a different stl but the same thing happens

[GregValiant 1,256]

@Slashee_the_Cow has been printing a lot of TPU.  Maybe she has some thoughts on this.

 

If it was me, I'd print two halves and glue them together.  That would get rid of the entire "horrible support surface" problem.

Super-glue works well with PLA/PETG but I don't know about TPU.  Some sort of bonding agent should work though.

[gr5 2,176]

The type of 3d printer that melts plastic through a nozzle doesn't do overhangs very well as you just learned.  You can use support structures but they leave a rough surface behind.  That's why you rarely see 3d printed balls.  You could consider 3d printing a mold that comes apart in 2 halves and use 2 part silicone mix.  That comes with it's own learning curve (bubble issues, how to make proper fill tubes, mold release, shore hardness) but you can get great results.

 

Or if you have a dual material printer like an Ultimaker S3/S5/S7 you can use a dissolvable support material or a "breakaway" support material in the second nozzle that will leave a much nicer surface finish when you remove the support.

[Slashee_the_Cow 269]

12 hours ago, GregValiant said:

@Slashee_the_Cow has been printing a lot of TPU.  Maybe she has some thoughts on this.

 

If it was me, I'd print two halves and glue them together.  That would get rid of the entire "horrible support surface" problem.

Super-glue works well with PLA/PETG but I don't know about TPU.  Some sort of bonding agent should work though.

Can't say I've seen this one myself, though I haven't tried balls, mostly square-ish stuff with rounded edges (and some flat out cubes). I might have to have a crack at it myself and see what happens. Seems like my kind of fun "why not?" thing.

 

@GregValiant I've never particularly tried gluing any of my TPU stuff, but once or twice while testing voxel-ish cows I've used superglue to stick bits back on, but I haven't tried to break them again after I did that. Not sure I'd count on great results, just given how squishy TPU is I'm not sure you're going to get a great bond. No idea if it would survive (and not affect the bounciness of) a bouncy ball but I guess there's only one way to find out.

[GregValiant 1,256]

Here ya go.  Half a ball with a guide hole in it.  Put a little piece of filament into the guide hole in one half and glue the two halves together.  DO NOT hit it with a golf club a baseball bat or a cricket bat as a first test.

Ball.stl

 

My TPU profile makes 2 halves of the 50mm ball an 8 hour print.  Just sayin'.

[greenieboy 0]

2 hours ago, GregValiant said:

Here ya go.  Half a ball with a guide hole in it.  Put a little piece of filament into the guide hole in one half and glue the two halves together.  DO NOT hit it with a golf club a baseball bat or a cricket bat as a first test.

Ball.stl 192.27 kB · 0 downloads

 

My TPU profile makes 2 halves of the 50mm ball an 8 hour print.  Just sayin'.

i'm looking at the layer view and yours is filled in at the bottom, wont that make the middle of it hard and the rest is soft when i glue it?

[Slashee_the_Cow 269]

1 hour ago, greenieboy said:

i'm looking at the layer view and yours is filled in at the bottom, wont that make the middle of it hard and the rest is soft when i glue it?

You could prevent that by going to Top/Bottom > Bottom Thickness > Initial Bottom Layers and setting it to 0, but then you'll have the problem that the centre connector is being held in place just by the infill (which I'm guessing isn't going to be too dense because bouncing = deformation = squishing, to a point).

 

And even then... actually seems like a decent way to do a 3D Pac-Man. Given that it's only connected in the middle the edge should flap around a bit. As long as you don't bounce it parallel to the single piece of filament holding it together, I know a few layers printed can actually be pretty damn strong but I've never tried to tear apart loose filament.

[Slashee_the_Cow 269]

Test results time! And sorry @GregValiant but since I'm trying to make bouncy balls, not accidents waiting to happen, I'm just using spheres that will get support. But for comparison purposes, I'm leaving the supports attached for the first photos so we can see what is support scarring and what is regular scarring. I've printed these at different sizes, not only to see what makes the best ball (recording the settings used for each ball) , but also to see if that makes a difference. As well as some changes to infill and such looking for the best bounciness.

 

(Oh, and remind me to turn up my flash EV compensation next time I do some shots, these are white TPU)

Family photo!

 

30mm, infill pattern: Cross 3D:

Doesn't look too bad, other than the pocks where the random Z seam is. Bounciness 4/10.

 

35mm, infill pattern: Cubic:

Some scarring in a couple of places, but not randomly all around like @greenieboy's. Bounciness: 7/10. Which I'm actually surprised about for Cubic.

 

40mm, double thickness walls and skin, infill pattern: Gyroid:

Couple of fairly major scars near bottom, pock marks from random Z seam very prominent. Bounciness 1/10 (the extra walls and skin may not have been a good idea).

 

Conclusions: able to replicate results. Not sure why they happen though. Requires further testing. Welcome to any input.

Edited January 24 by Slashee_the_Cow
fixed size for one of them

[Slashee_the_Cow 269]

It's everyone's favourite time of day, it's

MORE TESTING TIME!

 

This time it's twins!

The sharp eyed amongst you may have noticed something: I was wondering if resolution had anything to do with it. Not all sphere STLs are made equal.

 

45mm, low resolution (faces: 780), infill: Gyroid (I figured I'd give it a second chance with fewer walls in the way:

Yeah, it's as bad as it looked from the preview. There's scarring for the whole circumference of the bottom section. The Z seam pock marks are especially visible when they land on an edge or join. Also I shouldn't have given Gyroid that chance. Bounciness 3/10.

 

50mm, high resolution (4,194,300 faces... the STL file is 200MB), infill: Cubic (slightly higher density than before), Z seam in back right, 0.2mm outer wall wipe distance:

The lower area seems to be about 50% fine and 50% massive scarring. The Z seam is in the last photo (bit hard to see) but it's a raised line. I'll try coasting next time. Probably a better idea for TPU anyway, come to think of it. Also the extra infill did not do the fun factor any favours. Bounciness 3/10.

 

Conclusions: I still have none. Other than that resolution of the input file seems to not be a huge factor.

Oh, and for these two I had concentric support on with no support interface. Bottom ends up being a mix of smooth rings and messed up rings.

Bonus points to whoever can tell what the stuff on my desk that looks like black thread in the last photo is.

 

[Carbon 28]

Good efforts STC 👍.....Just wondered what it would look like if it was printed "solid"? (inside out...?)

 

Am keen to see if a near perfect ball is achievable.......

[Slashee_the_Cow 269]

37 minutes ago, Carbon said:

Am keen to see if a near perfect ball is achievable.......

If I had a dual extruder printer (donations gladly accepted) I could print the supports in something soluble and that would solve that part of the problem. If I could solve this other part of the problem (seriously I'm wracking my brain trying to figure this one out), just slap on the tiniest nozzle you can get and set it to the minimum layer height and line width.

 

You could make a ball which is a solid shell without too much difficulty by printing in parts and making sure the inside side gets the Z seam and carefully gluing the parts together (I don't know if you'd have to do something to make the seams where the parts join less visible though).

 

And with that folks...

IT'S TESTING TIME!

I noticed (after I'd printed it) that when I set up the print for the 40mm ball I'd accidentally dropped it through the floor a few mm (d'oh!) so it printed a flat bottom. I figured printing a replacement would be a good test to try something else. Things I haven't tried changing yet:

• Different filament (I'm not made of TPU)
• Speed (I've just been running at the recommended speed of the filament)
• Layer height / line width (Just left it on the default for a 0.4mm nozzle, so 0.2mm height and 0.4mm lines)
• A zillion other settings in Cura

But of those I know the most common fix is just to slow the hell down. So let's try that (and if you want to compare this to the other 40mm ball, it's the last set of pictures in the first testing post).

The filament I'm using recommends 25-45mm/s. I'd been running it at 45 so I brought it down to 20.

And you'll have to forgive me for the brightness (or lack thereof) of some of these photos, white object + ring flash = great combination for blowing out detail.

First impressions are good.

I wasn't sure if that was a little dent until I got this close to it. I think it is. Unfortunately, here's the bad news:

THE Z SEAM

Oooh, that's nasty. And I honestly can't tell by feel if that seam is underextruded or overextruded. I think it's under, especially because I had coasting on. If anyone has, unlike me, spatial reasoning ability, and thinks they can tell based on that photo, here's a full res version.

 

But um, yeah, that scar is still nasty.

 

The support actually came away pretty easily, at least for TPU (I've had it stretch so far before breaking that the snap back actually hurt):

The scarring pretty much stops where the support went up to. A clue? Who knows. But the bottom didn't come out too badly.

 

Conclusions:

Speed might be an important factor. But you can only go so slowly before you need to start messing around with flow rates and temperatures, and I'm not sure it's the whole answer. Also, you really need to get your Z seam perfect which is going to be trial and error basically messing with coasting/wiping/retraction/travel speeds/half a zillion other settings. Oh, and bounciness 3/10.

 

BTW, here's some more full frontal Z seam if anyone's into that sort of thing:

(Full res)

 

[greenieboy 0]

wow slashee thanks for all that

the tpu i've been using says it's "fast tpu" that goes at 75mm/s but i'll try printing it real slow and see if it makes a difference

[Slashee_the_Cow 269]

Okay I must have lost my Aperture Science employee badge somewhere because it seems I god damn love testing. This time it was just one test ball, but I threw the kitchen sink of changes at it (not the scientific approach technically, but if it works fine you've at least narrowed the cause down to the contents of the sink):

• Used my high resolution model, but downscaled it to 40mm
• 0.12mm layer height
• 0.26mm line width
• 0.1mm outer wipe distance
• Wall ordering set to outside to inside
• Disabled "print thin walls"
• Z seam back, corner preference none
• Enabled infill before walls
• Printing at a glacial speed (20mm/s)
• Support pattern zigzag
• Support interface wall line count 0
• Minimum support area 0mm²
• Minimum support roof area 0mm² (I noticed a lot of layers just had support with no interface
• Arc welder enabled, dynamic precision on
• Minimum polygon circumference 0mm
• Raised model 0.3mm (initial layer height) off bed so that it would be printed entirely on support.

Was it worth it? Well the results speak for themselves:

That's a pretty decent looking ball. Some minor defects but could do a lot worse. Now, let me just examine the rest of...

AWWWWWWWWWWWW FARTKNUCKLES

Umm... at least I seem to have pretty much nailed the Z seam. And that's the only defect, which is something. But if you think it's just an errant line, let me rotate the ball slightly and get a bit closer:

Yeah, that's a dent. And am I the only who thinks the bit that's coming down (forming the line you saw front on) looks like a fingernail?

And then there's the inevitable taking off the support:

It's some nice smooth lines, then a maelstrom of plastic destruction.

 

Conclusions: So which settings do I think might have had an effect, given this is the best one yet? Well I already know that slower is better. I don't think the the line width or layer height made a difference since the scar is about the same size despite those. The infill before walls? Probably nothing. Outside wall first? Maybe, it's supposed to keep things dimensionally accurate. Arc welder? I'm also going to put that into the "maybe" pile. It was a significantly smaller gcode file than other balls that size due to the arcs. All those support interface changes? Probably not. It's about as messy as all the others, just in a different pattern.

Bounciness: 3.5/10.

[Slashee_the_Cow 269]

Oh god I'm beyond help. Someone please call the looney bin, because...

IT'S TESTING TIME!

 

So going small didn't work. Does going big?

Let's go over this version's stats:

• Line width: 0.6mm
• Layer height: 0.32mm (yes I'm still printing on a 0.4mm nozzle)
• 2 walls
• 3 layers skin
• Z seam at back
• Arc welder enabled (dynamic precision on)
• Still printing at glacial speed (I'm going to have to increase that over time)
• 0.1mm outer wall wipe
• Wall order inside to outside
• Disabled print thin walls
• Tree supports (minimum height to model 0mm) - it actually created a cute little ring which barely had anything on the ball
• 100% initial layer line width (usually 150% but line width is usually 0.4mm)
• Cross 3D infill, 10% density
• Print takes 30 minutes instead of 3 hours

Results!

Doesn't look too bad. Obviously you can see the individual lines, and they're a bit uneven at the top. And the bottom. How's the Z seam, often my bane?

A little bit of puckering, but no major scars. Hang on, what's this bit?

Is it actually pulling previous layers up and over the current one? It may be worth investigating the minimum layer time?

 

And hang on, I thought I saw something near the top.

Holes in my goddamn ball? How the <insert epithet of choice> did they get there?

 

Pro tip for how to to tell for sure if it's a hole in your goddamn ball (I mean, the evidence here is compelling, but it isn't always). Get a laser pointer cat toy (laser pointers are illegal around here because idiots keep using them to blind pilots).

If it just hits the side, it's not a hole:

If it lights it up like a crystal ball, you got yourself a hole:

 

Okay, so how does the (fairly minimal, but apparently enough) support comes off?

 

Not too bad, but... FARM ANIMALS ON A FERRIS WHEEL, IS THAT ANOTHER HOLE?

*sighs* Yes. Yes it is.

 

Conclusions:

Don't try this home. Although minimum layer time might be worth looking at, we already know speed is. It does take TPU a bit of time to set, to which I can testify by how long and far I can pull on a little bit coming out of the bottom of the nozzle before it finally stops coming.

Bounciness: 6/10. Though I'm not sure I want to do too much of that lest it start falling apart.

Edited January 26 by Slashee_the_Cow

[greenieboy 0]

ok wow slashee thanks i think you can stop printing balls now

i tried putting a few of your ideas together like the slow speed and outer wipe and setting the z seam and i think i got it almost as good as yours

its rough where the support came off and theres a few small blobs near the top but its a lot better than before

i think i'll try getting some different tpu and see if works any better

[Slashee_the_Cow 269]

14 hours ago, greenieboy said:

ok wow slashee thanks i think you can stop printing balls now

I can't. That's the problem. My brain must find the perfect formula and will not rest.

 

Nice to see you getting a lot better results though, means all the white balls I have littering my desk aren't for nothing.