dumb quesion....

[John F]

I am new to 3d printing and trying to wrap my head around some of this stuff.....

one of my (many) questions is

as more and more of the new printers are coming with "full enclosures" to minimize the drafts and better control atmosphere around the print, other hints say to use a fan to "Blow across" the entire work piece or  finally a small blower to blow directly on the filament as it is extruded.each can be logically argued (at least to a newbie) can anyone clarify what the best solution is? does it make a difference whether your are printing ABS or PLA?

[Rob Hall]

The enclosure is not to control drafts its to control temp to prevent warping from shrinkage

Fans are used you blow directly on the printed object to solidify the molten filament.

And typically these are plastic related requirements

Pla benefits from the fan more than from the enclosure as it doesn't shrink as much

Where abs shrinks more and doesn't benefit from the fan as much so keeping the entire object warmer and letting it shrink as a whole is better

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[Nick Wimpney]

yes. pla needs to be cooled quickly as it prints.   I've had mixed results with the fans.   my first printer,  i just used some small fans blowing from the side,  and it worked great.  On my new one,  that didn't work,  and I ended up needing a fan right on the head.  I'm not sure what the difference was.   probably just different plastic.

with abs, you ideally want to keep the whole print quite warm,  so enclosures are useful.

On Jul 18, 2016 8:48 AM, "John F" <flan...@gmail.com> wrote:

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[Edward Simpson]

In a nutshell, 

Plastic type:          PLA                                ABS
Enclosed shell:      Doesn't care                    Yes,Critical for larger prints

Nozzle Fan:           Yes for best results          No, warps if cooled that way

Heated Bed:          Optional                           Yes,Critical for large stuff

Hope that clarifies things a bit, most off the shelf printers are optimized for PLA, mainly because it's non-toxic and has lower melt temperatures.

I'd recommend giving 3D Hubs guides to materials, 2016 printers, and what is 3D printing a look for a good overview.

Hope that clarifies things :)

Edward Simpson

My blog

[Loial Otter]

The action of shrinking is based on most materials, plastic included, shrink when they pass from liquid to solid multiple times. Meanwhile, the print needs to weld to itself on each layer. This leaves you with the wonderful position of making sure the top layer is warm enough that the hot layer being laid on top goes back into a nearly liquid state so you get full strength while also making sure that everything underneath that doesn't ever warm up or cool down again.

With ABS, the shrinkage is especially bad so keeping it hot and up in or near it's glass point or the point where the plastic is still malleable keeps the print from repeatedly shrinking and working itself loose from the bed.

On PLA the shrinkage is low enough that it's not really a problem having it pass between solid and glass repeatedly but PLA also has an enormous temperature band where it's still soft. Pushing it under that temperature as quickly as you can helps considerably to keep the print from turning into a blob or losing it's edges and details. The top layer still needs to stay hot enough to adhere, though, because otherwise you get a print that's easy to delaminate.

PETG has very nice properties in that it's similar to ABS in it has a narrower temperature band and high strength. It also is very much like PLA in that it doesn't shrink very much. I generally print that at the same temperature as ABS but with the fan on like PLA. I have to vary the fan up near fast print layers to make sure it doesn't start building up heat and I've even done things like run a print at 230C and then drop it to 215C when i'm getting to the faster part of it.

I have yet to try printing HIPS or PVA so couldn't tell you what to expect on those. I'm also still looking for a supplier of PVA if anyone knows of one.

One more interesting point, if you heated your build area to about 120C you could run the fans full bore on ABS and would get fantastic result... unfortunately 120C will also soften your fans and be hard to control or maintain and, though this isn't as important in Canada where you can do such things if it's in-house, it also infringes on a patent owned by Stratasys.

It also really comes down to experimentation. I've printed PLA at 235C and I've printed ABS at 195C for different cases. If your plastic is running hot and it's popping as it comes out of the nozzle, you've let too much water get into the material and somehow drying it will help with that. If it's jamming up in the tip you either are too cold or you need to print slower.

Oh, that's also another point; I can print up to 400-500mm/s on my printers but only on lighter weight materials. PLA I've found I can only get to 400mm/s while the fans are low or else my hot end can't keep up with everything (it starts cooling down). ABS is easier on that with the lack of fans and being a lighter material than PLA. I have to monitor when i'm doing things fast and will sometimes have to adjust the fans or bump the temperature up to compensate for the nozzle cooling down from the load of plastic.

uhm... I hope that's useful and not as confusing as I worry it'll be.

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