Infill is killing me!

[MattF]

So some of you may have seen my last cry for help in relation to blobs and zits. I've done a LOT of printing trying to eliminate them the best I can and I'm REALLY close. I've played to no end with coasting and extra restart distance but it never really seemed to make it go away on round pieces. In recalibrating my printer as I changed spools (using the cube here on the forums), I got the idea to print one of my trouble pieces similar to how I'd print the open cube. So I printed and guess what...there's a seam but NO blob or bump.

So I'm getting somewhere

I next changed my infill settings to have my outline overlap to 0%. I figured go big or go home. It still didn't make much of a noticeable difference. Are there any other settings related to my infill that I can do to stop this seam from appearing??

Here are some pics one of the empty piece and one with 15% fast honeycomb (it does it on retilinear as well)

[Jules]

Wow! That's a pretty print! Nice job!

The setting you're looking for is on the Layer tab....Start Points - Use random Start Points for all Perimeters.

[MattF]

If I do that, I get zits.

I have not yet tried it though with no infill. I will and see how it looks.

[Bratag]

If I do that, I get zits.

I have not yet tried it though with no infill. I will and see how it looks.

Infil is generally not responsible for the seam or the zits. You may just have to accept that FDM has limitations. You are talking about melting plastic and it reacts unpredictably. What I am seeing there is about as good as I have ever managed to achieve. That's why post processing is still a thing.

[MattF]

If I do that, I get zits.

I have not yet tried it though with no infill. I will and see how it looks.

Infil is generally not responsible for the seam or the zits. You may just have to accept that FDM has limitations. You are talking about melting plastic and it reacts unpredictably. What I am seeing there is about as good as I have ever managed to achieve. That's why post processing is still a thing.

The first picture (the one with the bump) has infill and 3 top and bottom layers. The second picture has no infill and no top and bottom layers. There's a small seam but no "bump" on it.

I've played with most of my retraction settings to no end and if I tell Simplify3d to print starting at random spots I'm back to zits on curved surfaces. If there anything I could be doing wrong with my infill or top and bottom layers?

[ednisley]

There's a small seam but no "bump" on it.

With no infill and only a single perimeter thread, the extruder simply steps upward by the layer height without retracting (assuming you have set a few millimeters of minimum distance before retracting), then continues onward around the perimeter.

When the object has infill, the extruder must:

• Stop at the end of the perimeter thread
• Retract
• Step upward in Z
• Move to the start of the infill pattern
• Un-retract
• Begin laying down infill

When it's done with the infill pattern, the extruder will:

• Stop at the end of the infill thread
• Retract
• Move to the start of the perimeter thread
• Un-retract
• Begin laying down the perimeter thread

Zits occur where perimeter threads start and end on each layer. The more time the extruder spends not moving while retracting or un-retracting, the more molten filament oozes out of the nozzle to become a zit. Coasting at the end of the extrusion helps, but AFAIK that applies only to the last straight segment and can't do much for circular perimeters made of many small segments.

Because perimeter threads wrap around the infill, there's no space on the "inside" of the object for the excess plastic: the zits will be (roughly) twice their no-infill size, because they can only bulge outward.

In order to reduce the zits, you must optimize every single one of those transitions. In general, that's impossible, although devoting an inordinate amount of time can produce better results for one specific object.

For example, you can put a minute "dent" into the perimeter of that round object, tell the slicer to align the seams (so it puts them along one edge that dent), optimize the retraction parameters so the inevitable zit has exactly enough volume to fill the dent, and get better looking results. Those slicer & model settings won't transfer to the next object, but getting them right will definitely keep you off the streets at night.

A while ago, I pulled together some of the physics behind FDM extrusion:
https://softsolder.com/2012/02/01/rever ... eleration/

The comments on that post from genuine experts showed me I know bupkis.

[MattF]

Thanks Ed - that was a good read. I have a lot to learn. I've only been 3d printing for about a year and I'm tend to chase perfection in everything I do. It can get me into trouble!

Here's the latest with some more tweaks. Looks pretty good to me!

[3dPrintingMD]

Now you must share your settings!!!

[jsc]

I spent some time a while ago trying to reduce seams. Made some progress, never completely eliminated them. Decided not to care.

I remember reading that some slicer had some clever method to deal with seams, but if you google "seam hiding", you'll encounter tons of people trying to solve the same problem over and over again, so I don't think it's a solved problem.

My suggestions:

• Don't use randomized start points. Better to have a seam than zits all over.
• Manually place the seam somewhere unobtrusive, generally in a corner. S3D lets you specify a coordinate where it will try to start each layer closest to. If you need to be precise, you can use a thin cylinder model, which you can place around the build plate and read off the XY coordinates.
• If your model does not have sharp corners and you care about the surface finish, post-process. A thin resin coating like XTC3D, or a thick coating of high fill primer, or Bondo, + sanding, can get great results.

[ednisley]

Decided not to care

Verily, true peace & contentment resides in the state of mind between Zen and apathy … [evil grin]