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Why do we have two standard filament sizes, 1.75 mm and 3 mm? Does it really make a difference when printing? Or is the 1.75 mm just for smaller printers?

In what situations should I be using 1.75 mm?

When should I be using 3 mm?

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There's no appreciable difference. Just use the filament that fits your particular printer.

If you don't yet have a printer, then I'd get one that uses 1.75 mm filament:

  • 1.75 mm is increasingly becoming the "standard", thus being easier to get. Some filaments are not available as 3 mm.

  • 1.75 mm filament allows for finer control, because feeding in 1 mm of filament corresponds to less plastic extruded.

  • 1.75 mm filament requires less force to extrude. Compressing 1.75 mm down to 0.3 mm takes less force than doing the same to 3 mm filament.

However, the advantages are fairly minor. I don't see any reason to replace a functioning 3 mm extruder with a 1.75 mm one (yet).

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    $\begingroup$ You mention some very good points! Do you think this mean printers with 1.75 mm extruders struggle less with - for instance - stringing? $\endgroup$ – Tormod Haugene Jan 15 '16 at 8:49
  • $\begingroup$ Do note that 3 mm filament is becoming rare, 2.85 mm is more common (but not so common as 1.75 mm filament) and for instance used by Ultimaker printers and to date easily available. $\endgroup$ – 0scar Dec 3 at 17:15
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There are a few factors to consider those two:

3 mm

  • More rigid - easier to print with flexible plastics. I couldn't make my 1.75 mm printer print with NinjaFlex using standard bowden extruder.
  • Can extrude faster
  • Quality is less affected by changes in diameter - it is a concern mostly when using cheap plastics

1.75 mm

  • More popular, easier to buy
  • Needs smaller extruder than 3 mm
  • Easier to use with bowden tube
  • More precise when printing
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I generally agree with the points in masteusz's and Tom van der Zanden's answers, but I would add a bit more detail. Generally, the differences are minimal, however:

  • Generally speaking, a 1.75 mm filament will make it easier to use a smaller nozzle diameter (<0.4 mm), allowing for more precise prints in some cases.
  • 1.75 mm filament will give you better flexibility with flow rates as it has a higher surface to volume ratio, allowing for faster melting in the nozzle, and allowing you to push your printer to higher volume extrusion rates.
  • The converse of the above points is also usually true. "3 mm" filament (which is usually actually 2.85 mm) will allow for better control and higher extrusion rates on wider nozzle diameters.
  • 1.75 mm filament is indeed more popular than 2.85 mm, however the smaller diameter means that manufacturing tolerances really need to be tighter along the length of the filament—a ±0.1 mm difference in width along the length of your filament is only ±3.5 % for 2.85 mm and more like ±6.7 % for 1.75 mm, so you're going to have a bigger difference in actual flow rates compared to your expected flow rate set in your slicer, resulting in lower-than-expected print quality. That means you're probably going to want to spring for more expensive, higher quality 1.75 mm filament in order to get good prints.
  • Your printer's hardware setup matters, too: Bowden-based printers, like the Ultimaker 2, generally have more luck with the thicker filament because thinner stuff will usually compress more in the Bowden tube and create a stronger spring effect, causing extra pressure in the nozzle. This will often cause blobbing, stringing, and over-extrusion and hamper the positive effect of your retractions.

Ultimately, you can tune your printer and slicer settings to create or negate most any of the differences in print quality caused by filament diameter, but you may have an easier time with certain prints and printers with one diameter over the other.

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I think (as do a lot of others) that the differences are rather minor. So just my 2 things I know from experience. We've been using 3 mm for some years and now we are moving towards 1.75.

1.75 mm filament is very easy to entangle, especially, if it is not on spool. You can even easily create knots on the filament and it is very hard to untangle. As long as you keep it on spool and always buy on spool, you should be fine.

3 mm filament on the other hand, creates very high tension when the spool is about to end. Sometimes the last couple of meters are unusable because of this and you have to throw the rest of the spool away.

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As I read the history, 3 mm filament was an accident of the supply chain when 3D filament printers were first being developed by hobbyists. There was a product called a "plastic welder" which consisted of a melting device and a source of filler material. This filler was 3 mm plastic.

As the techniques and equipment developed, the market for filament grew to a size where it could support companies producing filament specifically for 3D printing. The benefits of 1.75 mm filament over 3 mm were, IMO, huge -- especially the easier melting and lower force needed by the extruder.

Except for special purposes like pushing soft plastics through Bowden tubes, it seems from the marketplace that 1.75 mm filament as completely overtaken 3 mm filament.

A possible second-order disadvantage of 1.75 mm filament can be water absorption. The surface-to-volume ratio is higher -- there is more surface per unit of the filament through which water vapor can be absorbed. It is important to keep filament dry, and sometimes necessary with both 3 mm and 1.75 mm to dry the filament in an oven before use.

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  • $\begingroup$ +1 for the historical context. From mass produced printers appearing (2010-2012?) to 1.75mm filament becoming the norm for new printers (2017?) shows how long this iteration took. I base these dates on Prusa, but don't really know the history. $\endgroup$ – Sean Houlihane Aug 4 '18 at 10:45
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I agree with all the answers above but only would like to add if you want to build a very large printer using 0.8 mm or 1.2 mm nozzle, i would advice to go 3 mm. 1.75 mm filament then just can't be fed in fast enough.

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    $\begingroup$ Actually the opposite is true, since the 1.75 mm is easier to heat up since it is thinner. But that is only a problem at the high speeds you need for 1.2 mm nozzles. $\endgroup$ – plaisthos Apr 29 '17 at 0:06
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One thing I haven't seen anyone mention yet is the issue of the size vis-a-vis time of the final print. 3 mm filament allows the printer to spit out a lot of plastic at once, letting you build must taller prints much faster. Larger filament can also provide a much wider base for the next layer to rest on; smaller filament needs to print multiple times side-by-side to get the same width.

Of course the fineness of the layers will suffer, but you can go about twice as high in one pass compared to when you use the smaller filament. On the flip side, the smaller filament will more easily print extremely fine layers than the bigger filament. So it's a trade off.

Consider the printers building items feet or tens of feet in height. They use "filaments" that are measured in centimeters or decimeter a instead of millimeters.

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    $\begingroup$ Actually, this is a pretty common misconception. I've done a fair few tests, and the filament diameter is basically irrellevant. The main factors in determining how much material your printer can spit out in a period of time (volume extrusion rate, commonly measured in mm^3/sec) are the nozzle diameter of the extruder and rate that your heating element can transmit heat to melt the filament. In fact, if you can hold everything else constant, 3mm filament typically cannot print as quickly as 1.75mm filament because it takes longer to heat the filament through to the core. $\endgroup$ – PostEpoch Apr 13 '16 at 1:51
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    $\begingroup$ Now, to add to my above comment, in practice, your filament feed rate is usually limited (due to firmware, mechanics of nozzle pressure, or something else) in such a way that you'll rarely hit the point where you can't heat the material fast enough, so nozzle diameter is usually your limiting factor, since it tends to be quite small. $\endgroup$ – PostEpoch Apr 13 '16 at 1:56
  • $\begingroup$ @PostEpoch - IMHO, you should turn these two comments into an answer - referring back to this answer if need be, or adding a comment here to refer forward to your newly posted answer. $\endgroup$ – Greenonline Aug 17 '18 at 6:47

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