If you’ve been designing parts for 3D printing, you probably have some tricks and standards for your designs. [Rahix] decided to write out a well-thought-out set of design rules for FDM prints, and we can all benefit.
One of the things we liked about the list is that it’s written in a way that explains everything. Every so often, there’s a box with a summarized rule for that topic. At the end, there’s a list of all the rules. The rules are also in categories, including part strength, tolerance, optimization, integration, machine elements, appearance, and vase mode.
For example, section two deals with tolerance and finish. So, rule R2.8 says, “Do not use circular holes for interference fits. Use hexagon or square holes instead.”
We also appreciate that [Rahix] touched on some of the counter-intuitive aspects of designing for FDM printing. For example, you might think adding voids in your part will reduce the filament and time required to print it, but in many cases it can have the opposite effect.
Some of these — maybe even most of these — won’t surprise you, but you still might take away a tidbit or two. But having it all down in a checklist and then the ability to scroll up and find the rationale for the rule is great.
Do you have any rules you’d add? Or change? Let us know. Meanwhile, we were eyeing our favorites about adding machine elements to prints.
Did not expect to learn much new, but I ended up liking its style and attention
to details.
“Covers the basics well, and I ended up liking its style and attention to detail.”
Ftfy, Even a bloated corpse even might have sounded less critical with it’s exhausted praise.
the excerpted diagram for threaded parts is a frustrating example of a bad mentality to have when 3d printing.
the difference in tensile strength between vertical and horizontal printing is almost nothing compared to the dramatic unsuitability of most 3d printed plastics for static tension, full stop. if it’s holding tension, both are insufficient and it doesn’t matter whether one is 20% stronger by not carrying stress through layer adhesion. if you’re so close to “is plastic strong enough for this” that the difference in printing orientation matters then you should be using a metal bolt duh.
but if you’re going to 3d print threads, the factor that will encourage the horizontal orientation is your printer’s overhang behavior. threads-as-overhangs is asking for a different kind of problem than a truncated cylinder-as-overhang.
it seems to me like they’re obscuring the real substantive unavoidable difference between printing orientations by meditating on some strength difference that is almost irrelevant
Feel free to craft your own treatise on a repeatably better way of doing things.
I’m sure the Hackaday would highlight it…..
He doesn’t need to write his own treatise. The article itself described better ways to do it. Greg A merely pointed out how bad it is to rely on plastic threads alone. Sorry you didn’t grasp that.
Well-meaning comments pointing out an issue often receive a belligerent response like that. Just because I may not be able to do better doesn’t mean I can’t recognize a potential problem.
Maybe some people can see through the veneer of “well-meaning” and recognise the underlying intent to grandstand based on nothing substantive. A so called wisdom-signalling if you will…
A comment containing the phrase “bad mentality” is not a well-meaning comment.
Why? Here we do have a bad mentality because it’s focusing on optimizing the process without considering the wider implications.
Consider a person who is trying to invent a perpetual motion machine, but friction keeps getting in their way, so they start to focus on ways to eliminate friction. Will this help them invent a perpetual motion machine, or was the attempt futile to begin with? That is what “bad mentality” means – misguided and faulty ideas and thought processes that lead to future frustration and further problems because they’re missing the point.
Pointing this out can be very well meaning indeed.
@Busticati Hardly. Yes, some people grandstand, but here (the site) that’s definitely not a significant enough problem to act like this. In this thread? That’s nothing at all.
Somebody said something in a way that was poorly worded and contextually unnecessary given their only point we are talking about general approaches in tooling, the issue is discussed in the article, and everything does has a place somewhere, even printed screws.
Thank you for proving you’ve actually never read a single engineering manual in your life.
look, i’m going to be straight up here. i have no idea what you mean by ‘engineering manual’, and honestly i’d appreciate it if you’d fill me in with your idea.
i’ve read a ton of ‘data sheets’, where they will tell you that the tensile strength of plastic across layer adhesion is 0 and the tensile strength within a layer is 20% or 300% more than that and it’s up to the engineer to determine if 1.20 times 0 or 4.00 times 0 is bigger than their tensile load.
i’ve also read a bunch of ‘application notes’ or ‘best practices’, where they ought to tell you straight up “don’t use plastic for tensile loads.” and in such a document, they would tell you not to print threads vertically even if there’s no tensile load, because the overhang will deform them.
is there a third kind of document you have in your mind, which maybe i haven’t read?
Meh.. use the appropriate material for the appropriate loads. Plastic is fine for static tension, just not as high a static tension as metal. That is still better when you have better layer adhesion than when you don’t. This has been tested and shown many times.
Pure plastics without fillers or other reinforcing materials will give in to static tension – it’s just a matter of time. If your product is supposed to last for a year, then you can design with some tension, but if it’s supposed to maintain the tension “forever” then you simply cannot design the part in plastic.
It only takes a tiny bit of thought to discount this. We are talking light duty (often very, very lightly) with next to no operational stresses compared to what would be expected of a metal screw.
Of course a screw should be picked for a job it can do, but these are perfectly fine for most small objects. You are also skipping over aspects of design just as important or moreso.
Sure, these things will fail, eventually. But “eventually” might be more than long enough. A poorly made outdoor children’s toy might last… decades with minor repairs? A phone cradle on the wall with plastic screws could easily outlast the phone you asked using in it.
Note that your metal screw in the wrong application could easily cause an earlier failure as it’s lack of deformation causes it damage to surrounding material.
the difference between plastic and metal in this function is something like 1000 to 1. the difference in printing orientation is much less than 2 to 1.
it’s bad to meditate on the small end of amdahl’s law.
Agreeing, if the difference in strength is only 20%, meaning there is virtually no safety margin.
But: directly above the figure a factor 3 in strength is mentioned!
Surely, there is a certain threshold tensile load before creepage starts?
Factor 3 tensile strength from layer orientation should give you a fighting chance to avoid creepage in one orientation, even if layer adhesion is the limiting factor in the other orientation.
No. It just happens more slowly. At low enough loads it might take a century, but creep it will.
Nope. Plastic creep is a real thing at any level of tension. It’s just a matter of time.
you’re imagining a world where you print it vertically, it fails, and then you print it horizontally and it succeeds because 20% or 300% more strength is sufficient.
but, as others have pointed out, 1.200 = 4.000 = 0. tensile loading plastic is not going to work in any orientation.
BUT the true fact is, if you print it vertically, your threads will be garfed from overhang deformation. the whole tensile strength meditation is a distraction even if you truly do have a featherweight loading
ugh formatting. 1.20 times 0 = 4.00 times 0 = 0. 20% or 300% improvement on 0 is still 0
This point was better made, even with the number formatting. Definitely, most things these are used in will be featherweight, or close enough that the failure will not likely be an issue.
Maybe mounting a chandelier is a terrible idea, but we can in fact point and laugh when that happens, because a flag should have been tripped there somewhere.
I know! We just need all slicers to also include industrial fine element analysis, of course it has to run in realtime on the 10 year old laptop for the printer which was fished out of the garbage./s
Sounds to me like you didn’t even bother to read the whole article in order to find some triviality to
meditatebloviate on and share your profound engineering wisdom…Plastic creep is measurable down to 5% of the UTS in common plastics. What that tells you is, your plastic parts will creep and ultimately will not hold tension, so engineering a plastic screw that should hold appreciable sustained force is really an exercise in futility.
It is a real issue in engineering with plastics, and one that should not be ignored, yet is commonly ignored by engineers because the exact information is not readily available. This leads to a ton of bad designs that eventually fail.
LOL. Just because he identified a real problem doesn’t mean only stopped reading when he found it. What is with you anyway? Dude is clearly smarter than you are, so maybe that’s the real issue here.
look someone posts their engineering advice then i’m going to post my engineering advice. that’s the platonic ideal of the purpose of the comments section. if you don’t like my advice, i’ll give you a full refund
I present Exhibit A: The Nylon Screw. You can buy them. In the shops. They’re made of, wait, are you sitting down? They’re made of… plastic.
Well said.
I use printed threads ALL the time, even printed NPT threads that fully sealed an outdoor enclosure. However I never rely on printed threads to serve a function (static tension) that the thermoplastic cannot inherently provide.
Attempting to optimize a feature for a function it cannot provide is misleading and ultimately a waste of time.
I have done quite a bit of design for fff parts, and while I already know many of the tips presented here, I particularly appreciate the mechanical engineering basis for why the tips are useful. I don’t have a mechanical engineering background, and so I don’t typically understand the forces impacting design very well. The example of vase mode for the tray was also quite interesting. I’m really curious about the source of some of the photos. The part on zip tie channels looks like it contains pneumatics and optical fibers…
I’m happy to have spent quite a while reading Rahix’s well written guide!
I have done quite a bit of design for fff parts, and while I already know many of the tips presented here, I particularly appreciate the mechanical engineering basis for why the tips are useful. I don’t have a mechanical engineering background, and so I don’t typically understand the forces impacting design very well. The example of vase mode for the tray was also quite interesting. I’m really curious about the source of some of the photos. The part on zip tie channels looks like it contains pneumatics and optical fibers…
I’m happy to have spent quite a while reading Rahix’s well written guide!
One of the best writeups on the topic I have ever seen – great job!
I’ve been FFM printing for a decade (mostly functional but not super high mechanical load parts) and have a degree in mechanical engineering and I still learned a few things from this – well worth the time to read.
Agreed, one thing that has really gotten to me working with educational systems and materials is how you gain a progressively more complete crystallized perspective of the nature and components of the things being taught, including the edges reaching into far more advanced topics. They aren’t always gems of insight, but sometimes simply hearing a description crafted differently enough from the ones you have heard a thousand times is enough to give that insight to you directly.
Awesome guide. I feel inspired just looking through it.
While not learning anything new, it was a good read – 10 years ago I would have paid for that!