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Slice settings for Nylon

SusanOKC
(@susanokc)
Famed Member

Hi, Luke! I'm wondering if you have advice on Prusa settings for printing with Nylon.  I'm using the eSun PA-CF and a Prusa i3 MK3S+ with glass plate.  I've dried the filament for 48 hours.  My first test was okay but not fabulous.  Attached are my test settings with the pieces I'm trying to print.  Any suggestions?

Thanks!

 

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Topic starter Posted : 08/09/2021 2:58 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Susan! Nice to hear from you again! 🙂

I have no first-hand experience with this material, but I managed to dig up this site which goes into a lot of detail on what worked for one user with this particular filament - https://www.schweinert.com/my-recipe-for-3d-printing-with-esun-pa-cf/

Basically it's carbon-fiber filled nylon. Since carbon fiber is abrasive, you'll need a hardened nozzle (stainless steel or hardened steel). If you try to use a regular brass nozzle the filament will rapidly eat away the orifice, increasing its diameter until it punches straight through..

Being nylon, you'll want to make sure it's as dry as possible, so you're already on the right track. In fact, for best results you can build or buy an enclosure for the spools which keeps them dry even while printing (which become important on prints that run for longer than a few hours). Esun themselves also offer such a solution (in case you don't already have a food dehydrator and a filament drybox) - https://www.aliexpress.com/item/32930660621.html . Keeping nylon dry is the single biggest factor in preventing the prints from turning out weak and stringy.

Onto the profile. Is there a reason you felt you needed 2.5mm of retraction distance? Eg. were you getting bad results with smaller distance?

Some settings I suggest changing:

  • Layer height - increase to 0.2mm. Since it's filled with solid carbon fibers, you don't want to squeeze it into too tight a space (it could increase the risk of clogging). In fact some sources recommend a minimum nozzle size of 0.5 or 0.6mm to reduce clogging risk, although many users report printing fine with an 0.4mm nozzle so no need for you to change diameter just yet, just make sure the material is hardened not brass
  • Infill - I don't recommend 100% infill. If you need more strength, add perimeters not infill (it's far more effective at increasing strength). 50% gyroid is a good high-strength infill pattern to complement walls made up of a great number of perimeters. For regular prints where you want to print light and fast, 15% adaptive cubic infill is my recommended selection (because it skips lines in the centers of thick parts, thus saving time where infill is not needed)
  • Print Settings -> Advanced -> Extrusion width - if you set all the width numbers to "0" it will automatically calculate them based on the nozzle diameter (that you enter under Printer Settings -> Extruder 1 -> Size -> Nozzle Diameter). This won't really affect your print quality, but it makes it much more convenient to change nozzle sizes because you only have to change one number and all the extrusion widths update by themselves 🙂
  • Lift Z - increase to 0.6mm. Since this material is abrasive, you want to avoid the possibility of the nozzle dragging across its surface (as it will wear away the tip of the nozzle). This extra z-hop distance gives you an additional margin of safety to prevent nozzle-to-print contact during fast travel moves where the wear would be greatest.

That's about it for now. Your speeds and temperatures look well-tuned (as checked against manufacturer's recommendations and anecdotal reports from the users on the Prusa forums here), so not much that immediately needs tuning there. Focus on really drying the filament well and you might notice a further improvement in print quality. If you could post some pics of test prints I can try and give more advice 🙂

Looking forward to hearing from you! 🙂

 

Regards,
Luke

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Posted : 08/09/2021 9:59 pm
SusanOKC
(@susanokc)
Famed Member
IMG 3393
IMG 3392
IMG 3391

 

Hi, I've continued to tweak a bit and have attached an updated file. These are the slice settings I used for the attached Benchy (except my designs need to be printed at .1 layer height and 100% infill, or at least they do when printed with PLA. The Benchy was with .2 LH and 15% infill.) Thanks again! 

 

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Topic starter Posted : 08/09/2021 11:24 pm
SusanOKC
(@susanokc)
Famed Member

Hi, and thanks so much! I didn't see your post until I sent the update so please disregard.  I'll try again with your suggestions. I did indeed start with the Schweinert article and then incorporated suggestions from a few others (including the change to the retraction, which may not be necessary.  I was getting some stringing that got better after that change.)  We do have a hardened steel nozzle, although I admit I hadn't installed it yet - I'll do that now. I found the filament got a lot better after a full 48 hours in the dehydrator. 

I'm going to make your suggested changes and try printing our actual parts again, then will let you know how it goes.  I suppose I should go back a step and ask a basic question - these are parts that go inside our sock knitting machine. Metal needles run across them constantly, which wore down the PLA pieces after only 1000 rows of knitting. That won't work at all so we started researching alternatives. We couldn't find any affordable machines that print in metal. Of the other choices, nylon seemed like it would be the best thing to try given the high friction and small size of the parts.  Unless you have a better idea?

Thanks again! 

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Topic starter Posted : 08/09/2021 11:32 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Susan,

That benchy actually looks close to perfect! When you change to a steel nozzle from brass don't be surprised if you have to raise the temperature by 10°C to get the same print behaviour. Steel is less conductive than brass and behaves as though the nozzle is colder so you'll have to compensate by bumping up the temperature. It actually performs worse than brass in almost every way, but is a necessity for reasonable nozzle life with abrasive materials 😐.

---

To help you with your material selection, I will start with a primer about the different kinds of strength used to quantify materials (I am a mechanical engineer by profession so I studied these in depth during my degree). The most commonly available three parameters are stiffness, toughness and hardness.

For starters stiffness is a measure of how much force is required to deflect the material. So cast iron has high stiffness because it takes monumental force to bend it. Aluminium has less stiffness. Plastic has much less stiffness because it bends visibly even under its own weight, let alone when a force is applied. Rubber has very little stiffness because it bends with minimal force. Stiffness is measured simply by compressing or bending a sample of the material and measuring deflection vs force.

Toughness is a measure of a material's ability to absorb force (impact). So glass has very little toughness because is shatters even if dropped from a small height. Rubber is extremely tough because it will absorb huge impacts and still stay intact.  The way you measure toughness is with a contraption with a swinging hammer. A heavy hammer is suspended from its handle like a pendulum and a small bar of the material under test is placed directly underneath in its path. The hammer is raised and released so it crashes through the material, and the maximum distance it rises on the other end after the crash is measured and correlated to a hardness measurement. Glass will hardly stop the hammer. Rubber will almost make the hammer bounce straight back.

Hardness is a measurement of the strength of the material's surface. Diamond is extremely hard because nothing will scratch it except diamond. Chalk is not hard because you can scratch it with a fingernail. Hardness is measured by pressing a diamond or carbide ball into the surface of the material with a predetermined force. The size of the indent left by the diamond or ball is then correlated to the hardness of the material (the harder the material the smaller the size of the indent).

---

Given the above, since you have a wear problem, the key material property to look for is hardness. Steel is very hard. Plastic is not. In any sliding contact between steel and plastic, although both materials will wear away with every stroke, the plastic will wear away hundreds of times faster than the steel. The harder you make the plastic, the less material gets worn away with every stroke.

Aside from harder materials, another way to reduce wear rate is by lubrication. PTFE (Teflon) is the most slippery plastic in existence, which is why it's used in printer Bowden tubes and non-stick frying pans. Nylon is tough and self-lubricating, which is why it's used for gears.

You'll find that the nylon will probably last longer than the PLA due to its self-lubricating property. However you may also start to observe accelerated wear on the needles now, because the carbon fiber is very hard and hence abrasive. If this becomes a problem you may be better served by a nylon blend that doesn't incorporate carbon fiber filler.

Other ways to reduce wear rate would be to use an external lubricant and to minimise the force on the surfaces. For the latter, perhaps the sewing machine has some adjustment to tweak the path of the needles so they don't press into the plastic so hard? For the former, I suggest using a grease based on Boron Nitride. The one I use is called "Ceramic Grease" by Tamiya (you can buy small tubes online). I highly recommend it. A tiny almost imperceptible smear on the rubbing surfaces will drastically reduce friction and wear. In theory, grease or oil should form a film which will actually stop the materials from touching each other at all, though in practice that is probably only partially true.

Start with those, and if nylon doesn't cut it, we can look for an even harder plastic than that. Companies like Polymaker list material properties on their site, though prices can get quite high once you start dealing with exotic super-high-performance plastics like PEI and Delrin, so you'll have to measure the lifetime in terms of cycles and the cost of printing a replacement part and find the optimum based on how much extra life you get by upgrading to a plastic with 2x or 3x or more of the cost.

At some point it might be more cost effective to machine the part out of tool steel or use regular steel with a hardened surface.

Hope this helps a bit 🙂

Regards,
Luke

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Posted : 09/09/2021 2:40 pm
SusanOKC
(@susanokc)
Famed Member

That’s fantastic, thank you! My print quality did go down with the new nozzle - I’ll try bumping up the temperature. 

We use PTFE now and that helps but doesn’t eliminate the problem. Can the ceramic grease be used safely with PLA? 

Do you have sense of the wear and tear of brass vs nylon? We did get a quote to have the pieces machined out of steel - instead of the small parts costing a couple of dollars per machine they would cost us over $200!!! So that won’t work. In addition to testing with nylon, we’re testing adding thin strips of brass around the pieces that get the most wear. 

Thanks again! 

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Topic starter Posted : 09/09/2021 7:09 pm
SusanOKC
(@susanokc)
Famed Member

Part 2, after many frustrating hours of internet research. I'm open to paying a relatively high price for a filament that I can print on my Prusa that will have the longest possible life with metal needles running across the printed parts. I only need 12 grams per machine, so it can be pretty expensive per roll and still be affordable for my purpose. (Although I do need to be reasonably assured that I could get it to print successfully.  For example, I'm not sure that would be true for PEI.) It also needs to be something we can print in a home workshop (so can't be very toxic.) Is nylon my best option? Nylon with carbon fiber? Something else?

Thanks! 

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Topic starter Posted : 10/09/2021 5:19 am
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Susan,

All very interesting questions (always fun to tackle novel situations like this). You can use the ceramic grease with any plastic. It's very inert. It can also handle moderately high temperatures since it's a ceramic. I've been using it for at least 15 years on metals and plastics. As you might know Tamiya manufactures plastic model kits and high-performance radio control cars (both electric and fuel-powered). The ceramic grease is intended to lubricate moving parts inside the cars, including steel, aluminium and nylon gears and bronze bushings.

---

Let's go over the science of wear. Here's a good primer - https://en.wikipedia.org/wiki/Wear_coefficient

The article is quite complicated but the key equation is the first one -

image

V is your wear rate (volume of material worn off per second). You want this to be as small as possible.

P is the force pressing the needles into the plastic - I mentioned earlier that if you can adjust the machine to minimize this force, you will experience reduced wear. Based on this equation, if you can half the force your plastic part will last around twice as long.

L is the distance - in your case the stroke of the needle. Not much you can do about this because presumably it's fixed in the machine.

H is the hardness - the material property I talked about before. The harder the material, the less the wear rate, all other things being equal.

K is where it gets interesting - it's the wear coefficient. If you add grease or lubricant to the mix, K actually reduces and wear rate decreases, despite not changing the materials themselves. Because K depends on lubricity, different materials will exhibit vastly different wear amounts. The article gives this table -

image

Remember that we want to minimise V, so we want K to be as small as possible. The table is written in scientific notation, so for example mild steel (last one on the list) has K of 7x10^-3, meaning 7 x 1/1000 = 0.007. A trick to work it out quickly is, the negative power of 10 tells you how many zeros are in the number including the zero before the negative point. So if we look at brass, 6x10^-4 means K= 0.0006 (see, four zeros in all).

What that table is hiding (because of the scientific notation) is that the values are vastly different by many orders of magnitude. The K for brass is almost ten times smaller than that of mild steel, so a brass component will wear out 10x slower (i.e. lasts 10x longer).

Now, brass isn't particularly wear resistant. It's used in nozzles because it's got high thermal conductivity, and more importantly it's very soft and extremely easy to machine (meaning the factory uses cheap cutting tools, high feed rates, and the cutting tools last almost forever).

To compare materials, say brass and PTFE (Teflon) for example, you'll need the hardness and the K values since these are the two parameters that depend on material.

Brinell Hardness of Teflon = about 35 MPa

Brinell Hardness of Brass = about 60 MPa

K of Teflon (PTFE) = 0.000025

K of Brass = 0.0006

So as you can see, brass is harder, but Teflon is more lubricating so it has a lower K. Which factor wins?

---

Make everything else in the equation "1" (to eliminate their effect since we're not changing them), and you end up with V = K/3H

V for Teflon = 0.000025/3*35 = 0.002625

V for Brass = 0.0006/3*60 = 0.012. Oh dear.

Wear rate of Brass / Wear rate of Teflon = 0.012/0.002625 = 4.57

So in theory, brass wears out 4.57 times faster than Teflon. Or to put it another way, if your part lasts one day with a machined brass insert, it would last 4.5 days with Teflon inserts.

P.S. If you're wondering whether this means PTFE is better than tool steel, a quick google shows the Brinell hardness of tool steel is over 900 MPa 😮. But machining parts out of that will be multiple times more expensive than what you've been quoted already so not really an option ;).

---

So, having said all that, which 3D-printing filament wears out the slowest? Well, turns out wear rate isn't something that's really widely published for 3D printing filaments. Polymaker for example has quite comprehensive specs but don't list hardnesses of their materials.

Looking at research papers, glass-filled polymers had about twice the wear resistance of carbon-fiber filled polymers, so you can probably double the performance of your current blend by switching to Polymaker PolyMide PA6-GF.

Polycarbonate (PC) is widely considered to be one of the strongest, toughest filaments, but in real terms the numbers show it's not necessarily significantly better than nylon, so you might not see much of a change. It is tougher than nylon (in terms of impact strength) but needs an enclosure - and toughness won't help in your application because your problem is wear not impact resistance.

The highest-performance polymer on the market is PEEK, but that requires an extruder temperature of 400°C, so not something you can do on your Prusa without hotend upgrades. Plus the cost is about €150 for a little 200 gram spool 😉

If you want to go all-out, I think your best bet is IGUS - the company famous for their polymer bushings -

image

They offer a line of 3D printing filaments intended specifically for bearing applications with extremely high wear resistance. Since it's all proprietary I can't be of much help with the material selection, but their site does offer consultation with one of their in-house experts - https://www.igus.com/info/3d-printing-materials . I would try sending them a message and explaining the application. The graph on that page shows a wear rate for their filaments that's 50-100x slower than printed ABS, so they might very well be comparable with many metals in terms of wear rate.

Pricing isn't available on their site (you have to contact them), but I did find this on amazon - https://www.amazon.com/Iglide-Printer-Filament-Diameter-Yellow/dp/B00M92IDT2 and it's €70 for 250g which is 10x the cost of PLA but not as bad as PEEK.

Hope this helps - if you could send pics of the assembly I might come up with some other ideas. Until then do let me know how it goes with the nylon 🙂

 

Regards,
Luke

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Posted : 10/09/2021 9:39 am
SusanOKC
(@susanokc)
Famed Member

Amazing as always, thank you! I will contact the company you suggested today and also put together some additional illustrations for you. And will let you know how the nylon with ceramic grease tests go this weekend.

For so, so many reasons related to how circular sock machines work, some of the usability features we’ve been designing this upgrade to improve, and the fact that all of this has to fit inside a 5” cylinder (which means everything has to be curved in just the right way to still be able to move like it needs to do), we have very few options to redesign to reduce the wear on these parts. Our current machine has less wear on the parts but that design means there are some knitting techniques that are very time consuming, fiddly, and frustrating. This design allows one to perform those techniques 5-10 times faster and really will be a game changer in terms of both speed and enjoyability of knitting. But it means the new parts are very small, highly moveable, and have a lot more pressure on them than the old design. I’ll put together a video to show you. A team of us (a combination of circular sock machine knitting experts and engineers) have been tweaking the design for six months and often a 0.5mm change in the shape makes a huge difference. All of that to say that I’d love any ideas you might have while also having little hope we can really change the actual design at this point to solve the challenge. My best Plan B is to send several copies of the parts that are likely to wear out and simply acknowledge they’re going to have to be replaced. That wouldn’t be hard for the end user to do. And yet PLA wears out much too quickly - we must start with something stronger than that as our baseline. Fingers crossed a combination of these other options will do the trick! 

More soon! 

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Topic starter Posted : 10/09/2021 1:12 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Susan,

Thanks, looking forward to your explanations :). Based on my research and what you wrote above, nylon alone should already be a huge leap forward from PLA. Nylon filled with carbon fiber as you're using will be even better, and nylon filled with glass fiber will be better still (by a factor of two compared to carbon-filled). Any of these will improve again with adequate lubrication to form a film between sliding parts.

Really and truly though, if you want the absolute maximum wear resistance, IGUS materials would be the way to go since their polymers are formulated specifically to excel in this one area (minimizing sliding wear) rather than being optimised to be good all-round materials like ordinary 3D printer filaments. They claim wear resistance is 50x better than ABS. According to this paper (link), nylon wears about 10x slower than ABS - so by extrapolation the IGUS materials lasting 50x longer than ABS means they should last 2-5x longer than nylon :).

Let me know if you succeed in your consultation with them, and looking forward to reviewing your videos and hopefully offering some useful advice 🙂

 

Regards,
Luke

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Posted : 12/09/2021 1:00 am
SusanOKC
(@susanokc)
Famed Member

Hi, I had a fantastic call with the IGUS consultant yesterday - he was so helpful and the test roll of filament he recommended should arrive this week! That’s great to see your comparison of the plastics we’ve tried. Our ceramic grease also arrived yesterday. Fingers crossed! I’ll keep you posted. Thanks again, Luke! 

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Topic starter Posted : 12/09/2021 4:43 am
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Susan,

How did it go with the new materials? 🤞

Regards,
Luke

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Posted : 23/09/2021 12:09 am
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