This is a reel of 1.75mm diameter 3d printing filament.
Obviously.
But what if it's not? Brace yourselves, this is going to get quite technical.
Let's go down a rabbit hole. An exactly 1.75mm diameter rabbit hole. For very small rabbits.
This video is sponsored by PCBWay. More on that, later on.
Filament. Plastic pooped out of a hole into a long thin cable of shiny circular potential,
ready to be loaded into your funny machine that can turn it into anything you want. We buy tonnes
of the stuff, probably quite literally in some cases, and we buy it for its colour, or its
finish, or its material properties, but we don't, ever, ever think of buying it for its size.
Because it's 1.75mm. Right? They measure it at the factory,
right? To within some parameters we never really think of because they look small.
But let's stop plasticking lyrical and consider the potential issues if
it _wasn't_ 1.75mm. If your filament was too thin or too wide, so what? What would happen?
Not a lot - to a point. Here's two XYZ Cubes. One is overextruded by changing
the flow to 5% more than it should be, the other is underextruded by the same amount.
So this would be the equivalent of 5% more and 5% less surface area on the incoming filament,
area is pi r squared as we know so it doesn't mean 5% less diameter. But that
is how an incorrect diameter would manifest on a properly calibrated printer. But lets
entertain the idea that you're printing 15 solid layers and there's nowhere for the
extra filament to go, how confident are we exactly that our filament is 1.75mm?
I called this the narwhal. I mean, I could call it anything but it seems like a funny
name. This abomination is what happens when I am on a deadline and need to make a device to
demonstrate filament variation over length. It looks marginally less dumb in real life.
Steve won't mind this. I'll give it back. Probably.
It's pretty simple, two wheels guide the filament through and the top moves up and down as the
thickness varies. Not, as it happens, enough to make the arrow move particularly well, not
unless your filament was basically string, which is why it also has this flat bit on the front,
I can mount one of these fancy engineering devices here and ...
The interesting thing is, I can mark areas that move a lot with a pen then measure them with an
actual micrometer, and confirm that this thing actually does work. I was able to identify some
particularly thick areas on the filament. In the axis it's measuring. We'll....talk about that.
The diameter, in fact, varies a lot. I'll show you on this spreadsheet the kind of numbers I'm
seeing. These are measured with the micrometer at semi random spots on the filament. If you're
in the market for a micrometer by the way, there's two types. Some have these vernier scales on them,
which means they can measure an extra order of magnitude compared to the ones
without. Or you could go with a digital one, but that's boring. This oxford brand
seems to be british, and they are quite reasonable, I got it from cromwell tools.
With these kind of variances you would think, would you not,
that the extrusion would be all over the place. So why doesn't this mean what it looks like it means?
Well...it's pretty simple actually, filament isn't round. The assumption that you can measure its
diameter from one axis is substantially flawed. Is filament oval? I don't want to spoil the fun
just yet, but it is a ...reasonable assumption. If the filament was oval then the actual area is
what matters not the diameter on any particular side. So, you have to measure the longest and
shortest diameter, work out the area, and if that's the right amount, it doesn't matter that
it's slightly oval. Doesn't matter one bit. As long as it fits into the machine, anyway.
So, here's some samples where I've done that, to the best of my ability. Measure one axis,
turn about 90 degrees, measure again. Area is pi times both those numbers.
Let's take a minute to consider how filament is actually made. As in, in the factory.
And I would like to thank Sunlu for some of the information that's helped me with this section,
I sent them a list of fairly technical questions and they were kind enough to answer them.
The process of making filament starts with , and this is weird,
I don't know why but all machines seem to be built backwards from what I've seen, with
the raw plastic on the very right side. This is the bit you probably already know
because duh, your 3d printer does it, heat up the input plastic, and push it out of a hole.
Thing is you probably figured out if you watch my videos because I say this all the time,
there's not a lot of a relationship between the size of this hole and the width of the filament
that comes out of it. The next bit of the process is referred to as drawing, the filament is pulled
through water tanks that are really long and thin, they essentially cool the filament gradually, at
the other end of these tanks is some mechanism to pull the filament and just before that typically
is the measurement system. The speed you pull the filament, of all things, determines the width.
I don't know how sunlu measures the filament, but they did tell me they measure what I believe is
two axes and from what I've seen of other machines that works out to be the measurement across the x
axis, the y axis, and then essentially an average of the two which is exactly the parameter that you
can use to determine the cross sectional area. But this image from Prusa is clearly not
a trade secret. I think this uses optical lasers to measure.
Even though measuring two axes is the best method manufacturers have, there is a fundamental at
least theoretical problem with measuring two axes, and this is even if we entertain oval
filament theory for a moment. It's been a while since I got the play doh out and this is getting
a bit serious so I reckon I need to show you what I mean visually, through a quiz and some play doh.
Question one. What's the cross sectional area of this circle? Easy right?
Question two. What's the cross sectional area of this oval? We just said, a x b x pi. Not too bad.
Question three. What's the cross sectional area of this oval? Hah.
I think you get the idea here - you can't just measure in two arbitrary
perpendicular locations and assume you have what we call the major and minor
axes. You can't do it. So even if you're an oval filamenter, you can't do this.
I'm gonna show you some real world examples of the cross
section of some filaments. After the sponsor section. Which is for PCBWay.
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Thank you PCBWay for sponsoring this episode.
So, I've painstakingly cut loads of filament, and I assure you, it's not easy to cleanly cut tiny
bits without smushing it,If I put one of these under the microscope, it looks circular. But
if I put a circle over it, it's not really, is it. I mean, it's close but it's not circular.
Here's some tri colour filament, this looks really cool under the microscope,
I've looked at this before and it looked cool then too. But it doesn't look circular
or oval. It's just whatever it wants to be. What's the cross sectional area of a whatever
this shape is? By the time you've worked it out, it's about 2 meters back in the print,
so ...good luck with that. I'll probably show you some more images,
because microscope images of filament is always cool and I spent far too long on this.
I want to briefly talk about the manufacturer stated tolerances, This is prusament. when you
buy it you get a chart on the side, and you can actually look this up on the website,
but I think deriving meaning from it is another matter entirely. The absolute and
standard deviation are over the whole reel, but they are maximum values so the bulk of
the reel will be below this. Prusa's aim for deviation is less than 2% on diameter,
but I would prefer a deviation on cross section to be a headline figure since its more important
as I've explained. In fact I measured a ton of different samples from short sections
of the reels and plotted the deviations, I should say that these are taken from a relatively small
subsection of the reels because I didn't want to waste a ton of filament getting them, but I would
argue it's still a pretty good indicator, given the average prusa graph. I would say there's a
good indication that the vast majority of manufacturers operate to a tolerance of 2%
on cross sectional area, in fact Sunlu confirmed that do on PLA, with typically 0.03mm on others.
So what does this mean for FDM printing? I think, in some ways a lot, but in most ways, not much at
all. While it sucks to not really have an obvious way to accurately measure the incoming filament
in any meaningful way as an end user, and it's disconcerting to think that its not possible even
as a manufacturer to create perfectly circular or even perfectly measured oval filament, and that
we have these tolerances in manufacturing that aren't negligible and translate to
real flow rate differences, at the same time, in the tests I've shown that most
manufacturers with a very small number of outliers, appear to be producing filament
that's within the same stringent tolerance parameters that the leading brands promise.
And, there are a lot of processes working together to make the object you're printing,
and those are equally inaccurate. Retraction, oozing and stringing,
losing material on corners due to slowing down, filament slipping or kinks after the extruder,
mathematical rounding on extruder steps, backlash, I could list things all day,
these are all equally inaccurate processes that we kind of fudge and move on. It's actually
surprising that we can get the results we get, but also, it's not surprising that changing the
lighting on those results will often show the harsh reality of the process and its inherent
inaccuracies. We are, I suppose, seeing the result of the law of diminishing returns.
Prints with modern hardware look good enough, and the remaining challenges including low single
digit percent filament accuracy are either too costly or not important enough to fix. Of course,
if you are buying your filament from a reputable manufacturer, I mean...the bulk of manufacturers
are making filaments well within the 2% mark on cross sectional area in the small tests I did.
So - anyway. That's where we are. I started this episode with a plan to measure filaments
and show you which were correct and which weren't, and I ended up telling you it
doesn't matter. If you're still bothered though, and this might be a recommendation
for you depending on whether you are bothered, it might be worth picking up a cheap micrometer
gauge to have ready to check whether that troublesome filament is in fact a rare outlier.
It was an interesting journey through filament accuracy,
I hope you agree and learned something. Comment below as always, and I will see you next time.