Filament

The filament you use is incredibly important. The wrong filament will result in failure. Unfortunately, there are tradeoffs between different filaments and there is no one best filament that you can choose. Here are some things to consider.

Tensile strength. This is the basic unit of strength. Most testing is absolute tensile strength, the amount of stress required to fully break the sample. This is a good metric to use when comparing the strength of stiff materials, however, you need to consider other metrics as well.

Youngs modules, or the elastic modules is a metric of stiffness. It’s a great way of comparing different filaments, stiffness is very important.

Impact resistance is important, but can be hard to compare between filament manufactures as testing methods vary.

Heat deflection temperature is another very important metric. This is basically a unit of temperature resistance. Different testing methods will give different results, so keep an eye on the amount pressure / force that was used in the test.

Print temperature is also important, not from a durability standpoint, but from a printability standpoint. If you can’t print it, it won’t help you. So keep in mind the limits of your printer when you are looking for filaments.

How much strength is enough? Here are some starting points:

  • Tensile strength of 7000 PSA (48 MPa) or greater.
  • Young’s modulus of 350,000 PSI (2400 MPa) or greater.
  • Try and compare impact testing data to other filaments from the same manufacture or testing house. You want consistency.
  • Higher the heat deflection temperature the better, other then the potential printing difficulty of higher temp filaments.

Just because a filament has all the right metrics and the data sheet checks out, does not mean it’s a good option. Keep an eye on what filaments others are using successfully, or unsuccessfully.

There is another metric that can be hard to nail down. Layer adhesion. Layer adhesion is dependent on many factors, but one of them is is the filament. Some filaments have better adhesion then others.

Here are some specific filaments and there pros and cons. If you are new to printing, start with PLA+. I recommend the Polymaker PLA Pro.

PLA. This is the most common filament, and comes with a wide variety of properties. Standard PLA tends to be stiff, strong, and brittle. PLA+, Pro PLA, Performance PLA, and other “improved” PLA’s is what we normally use. They are weaker and more ductile then regular PLA, but have very good impact resistance, giving them great mechanical properties. PLA+ is a great option for your first prints. Don’t let it get hot, and it will serve you well. If PLA+ had good heat resistance, it would be the go to filament.

Pros:

  • Acceptable strength and stiffness.
  • Excellent impact resistance.
  • Great layer adhesion.
  • Easy to print.
  • Low cost.

Cons:

  • Poor heat resistance.
  • Lacks good wear resistance.

ABS (or ASA). Often it is said that these filaments are stronger or “tougher” then PLA+. This is untrue. Very untrue. ABS has poor tensile strength and decent impact resistance. Layer adhesion tends to be poor without a heated chamber. ABS does have good temperature resistance, and that can make it a good option for some parts. I tend to use Nylons or Polycarbonates instead. However, ABS has potential because of its low cost. ABS is also harder to print with and is prone to warping. I do not recommend it, but think it is worth experimenting with.

Pros:

  • Good heat resistance.
  • Low cost.

Cons:

  • Poor strength.
  • Poor layer adhesion.
  • Lacks good wear resistance.
  • Hard to print.

PETG. A popular filament often said to be “tougher” then PLA+. As with ABS, this is untrue. PETG has mediocre strength and very poor impact resistance. It’s a deceptive material, and can appear to be tough and ductile, but under sharp impact it can shatter. PETG does have better heat resistance then PLA+, but it’s not that great. PETG is very stable and does have very good chemical resistance, however its not good for parts subject to mechanical stress or impact. I do not recommend PETG at all. Don’t waist your time.

Pros:

  • Good layer adhesion.
  • Great chemical resistance.
  • Easy to print.
  • Low cost.

Cons:

  • Mediocre strength.
  • Poor impact resistance.
  • Lacks good wear resistance.
  • Mediocre heat resistance.

PC. Polycarbonate is a strange material. I’m not quite sure about it myself. It’s strong and stiff. Can have good impact resistance. Can also have poor impact resistance. Great temperature resistance. But I’ve had issues with it cracking under stress. PC tends to warp, and is difficult to print larger parts. I use it for smaller parts that need strength because of it’s relatively low cost and high stiffness. I don’t use it for lowers or frames because of the potential for cracking. Fiber filled PC filament is available, and can be much easier to print with, however, layer adhesion and impact resistance may suffer. It has potential, but requires more research.

Pros:

  • High strength.
  • Great temperature resistance.
  • Good layer adhesion.
  • Relatively low cost.

Cons:

  • Hard to print.
  • Can be brittle.
  • Can fail under stress.

PA. Nylon is a very wide category. It is the most common filament to add a fiber fill to, and in my experience it benefits from fiber fill more then other filaments. Different types of Nylons absorb water more then others. When Nylon absorbs water it becomes tougher, more impact resistant, but loses strength and stiffness. This can be a huge problem. Unfilled Nylons tend to have mediocre impact resistance and good strength. However, after water absorption much strength and stiffness is lost.

Carbon filled Nylons are much stronger and stiffer, and if the fiber content is high they can retain there properties even after absorbing water, but high fiber content will degrade impact resistance, and possibly layer adhesion. The carbon fibers also make the filament much easier to print with.

Glass filled Nylons are not generally as strong or stiff as carbon filled Nylons, but do have higher impact resistance, how much depends on the type, and my not be significant. I prefer carbon fiber for most applications, but it depends on the brand and type of Nylon.

Some types of Nylon, such as PA11 and PA12, absorb much less water, and that makes them good candidates. They can retain there mechanical properties with lower carbon fiber contents, which allows them to have better layer adhesion and impact resistance.

Creep is a huge problem with many Nylons, and requires annealing to prevent. Higher fiber content Nylons tend to do better.

Do not under estimate the effect of water! Many Nylon filaments may appear good, but after water absorption the part will become unsuitable for use. Same goes with creep, do not ignore it. Anneal your Nylons unless you know for certain it is not an issue.

I have never had an issue with Nylon parts cracking under load or shattering, which is one reason I like it so much.

I hate to list pros and cons here, as it is such a wide category. But I will do so for the sake of consistency.

Pros:

  • High strength if fiber filled.
  • Excellent wear resistance.
  • Generally easy to print if fiber filled.
  • Can have great heat resistance.

Cons:

  • Can lose properties with water absorption.
  • Creep can be an issue.

There are other less common filaments, but I have not found one yet that is worth mentioning. I list the common ones here, and the ones I think are good. Be sure to take all of this info with a grain of salt, I am learning just like you, and make lots of mistakes. Do your research, read data sheets, conduct testing. Do not take anything for granted. Be carful of hype, especially from me.

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