So now I’m trying to figure out which filament to go with. “Just use PLA!” is our common refrain, but both according to tech sheets and the V1 community’s variousinvestigations, there can be fairly significant differences in stiffness between PLAs from the same manufacturer. Case in point, my current favorite, go-to PLA is PolyTerra Matte from Polymaker:
Unfortunately, it’s about half as stiff as their PolyLite PLA, which is itself half as stiff as their PA6-CF:
I don’t mind picking up a hardened 0.6mm nozzle just to print some fancy material, though the $100 increase in cost over normal PLA isn’t ideal, it’s not a dealbreaker either. Reviews of it indicate it’s not that bad to print with and I already have a heated filament drybox and an enclosed printer.
Is this a complete waste of time/money, or does it actually make sense? Would it make sense to just do it for a Z-gantry? Some other part?
Edit: To clarify, I’m trying to make my MPCNC as rigid as I can for its size. I’m going with upgraded tubes and will use a shorter Z travel distance this time. I’m aware of the extra frame supports, but I’m not sure they’ll be necessary with 1" SS.
Is it worth trying to increase the stiffness of the plastic parts next or is there some large set of other choices I can make at this stage? Is there one single part I could focus on making as stiff as possible that has a particularly large impact, like the Z gantry?
For all the many forum debates about various potential ways to stiffen MPCNCs, there is very little real-word data. No one has built a series of identical machines with just one variable and run them through their paces. And it is not just the filament selection. You also have the infill percent and infill type as a variable. And, for infill type and percent, more may not be better. Greater infill means greater mass that must be accelerated by the steppers. But no one really knows.
My guess is that investing in stiffer PLA will have marginal additional benefits. The NEMA17 motors just don’t have enough torque to make additional stiffness beneficial. If you are planning on significant aluminum or brass milling you might consider stepping up to carbon fiber PLA as insurance…especially since many CF PLA filaments are only a bit more expensive than just PLA filaments.
Not totally related but throwing out my 2 cents… I printed all my parts on a markforged with onyx filament which is touted as “black aluminum” by the manufacturer. It is a nylon filament with chopped carbon fiber . $20k printer, filament is $180 a kg. My anecdotal experience is that this filament may have higher ultimate tensile strength but its much more flexible than my $200 printer using PLA
@LazyLevy, I’ve seen a bunch of mentions of Onyx, but the data sheet for it says its modulus of elasticity is about 3GPa, which is similar to PLA. You’re saying that your experience was that it’s bendier than PLA?
I wonder if I’m using the wrong material property for comparison - I checked with a mech eng, but it’s possible I miscommunicated something.
FWIW Ryan uses Hatchbox PLA for all the printed parts he sells. My machines are printed in Overture PLA. And i have done a fair amount of aluminum milling on both of my LR3s with no issues. And they are in a garage that gets to 95º in the heat of the summer with no issues at all (other than me overtightening things but thats not the filaments fault lol)
In general carbon fiber will stiffen PLA, but manufacturers may change the formulation to get it to print better. You might take a look at CarbonX PLA filament. The datasheet shows a Young’s modulus of 4950 MPa.
I think the best course is to just print with PLA. Avoid matte, “tough”, “terra”, and “eco” types. Just regular old PLA with nothing special added. The only thing that might do slightly better is Polycarbonate but 1) it’s expensive 2) it’s not easy to print with 3) it doesn’t bridge well and 4) may have some issues with tolerances.
I did use Prusa’s PC Blend for a few parts, but I don’t know that it was necessary. You just can’t beat standard PLA for the value, print accuracy, and stiffness.
Oh and nylons should be at the very bottom of the list of filaments, even CF ones.
OK you are doing research. That’s good. To be sure PLA is the best choice since the parts were designed for the material and that is what is supported. Remember these parts are large and uneven temps within the part becomes a consideration.
Anecdotally, I can say stay away from PLA, ABS, ASA as CF negatively affects layer bonding. Your parts will crack eventually. I’ve only had luck with CF variants of PETG, PA and PC and in this application the CF is necessary to produce the overhangs these parts require.
PC-CF is really hard to print if you don’t have a really toasty chamber - at least 60°C throughout. I’ve never printed large PA6-CF parts - only small parts - but I’d imagine it’s a similar situation. For the money PETG-CF is a wonderful material. I’ve used it for LR2 parts and it worked phenomenally. More rigid than PLA, higher heat tolerance and superb layer bonding.
All this to say PLA is spec and that is what you should use. If you want to experiment go for it. It’s a lot fun to learn and use new materials. But be prepared to print everything again in PLA and rebuild your machine if it fails.
I think he means deformation under load over time. One way to test is to make a hook, hang some weight off of it and measure deformation over time. You are measuring how the plastic keeps the deformation after the load is released. Most plastics will creep over time. Some are worse than others.
@brenavich980 PETG-CF is interesting with some products like 3DXTech CarbonX CF PETG but not very impressive with other CF variants like Atomic CF PETG (which I love but not for stiffness). Good CF filaments are often stronger in the direction of the CF strands but pretty much the same as the base plastic in the other direction. So layer orientation to the load is a big factor on whether the CF helps or does much of nothing. In addition, the CF does impact layer adhesion which can make the part fragile between the layer lines.
CF PC like Prusa’s blend is the ultimate in some ways but it needs a printer that can print it and it does have some issues bridging just because of the print temp. Manageable but not a set and forget thing for complex parts with lots of bridges. It also does have some shrinkage, though again manageable.
Nope, I meant parts that worked fine for a while then just… broke in half a month or three later. It’s why you never use PLA for shelf brackets and stuff.
My current build is a 525 that I printed with random PLA I had lying around and it could definitely use more stiffness, but I don’t know how much of that is the 525 being the first design, not using enough perimeters or infill, etc.
I’m not really questioning whether it’s going to be stiffer, more whether stiffness of the plastic parts is anywhere near the top of the list in terms of stuff I should pay attention to when building up a Primo and trying to maximize rigidity. I could’ve done a better job stating that clearly.
Looking at Polymaker’s materials at least, what you’re saying matches up with their tests for PLA but not for Nylon - PA6-CF has the highest Z-orientation tensile strength of everything they’ve got:
