It's time to do a number 2!
Wait no
Let's just...get on with it.
This is the 2nd episode in the series intended to teach you how to make your own fast slicer
profiles, specifically cura ones.
And this one is probably the most important.
Let's go.
- This video is sponsored by PCBway, more about that later on.
-
Last time we looked at, let me get my weird mind map out...we covered line height, minimum
layer time, uhmm...z hop and some other stuff but you know what we didn't talk about?
Lots of things.
But we didn't talk about speed.
Makes sense if you want to print faster, to increase speed, right?
Not so fast...literally not so fast.
You do not have infinite speed.
And how much speed you have depends on a few things.
First one I want to look at is easily demonstrated by this voron I built.
The kinematics..meaning the actual motion system of the printer can go really fast.
Perhaps you can see what's happening though.
The printer is going fast but the print is failing.
There's nothing wrong with the printer, so why is this happening?
Segue to....flow rate..
How does a discussion of speed become a discussion of flow rate.
Well let me show you what the inside of a hotend looks like and we'll see where this
goes...
A hotend is made of a heatsink we dont care about in this episode, and this heat break
bit, which has a narrow section, and then it widens out again but the wide part and
the actual nozzle are in what's called the heat block.
This heat block contains the heating element.
So this bottom part is hot, and all of it is intended to be at the same temperature
- at least in a simplistic view, but the rest up here is supposed to be effectively cold.
Now - this is the key part so pay attention.
It takes TIME to heat up 1.75mm diameter filament.
This time is somewhat constant, at least given the same external parameters like temperature
and pressure.
There is nothing you can really do about that - it's a function of the thermal conductivity
of the actual plastic.
So if you are constantly printing, you could see the maximum flow rate the hotend can sustain
as a function of the time the filament is being subjected to the hot chamber of the
nozzle.
And you would, to my understanding, be correct.
This is why the volcano hotends have longer heat chambers.
And let's not forget the supervolcano.
Not sure if we SHOULD forget it, though.
Of course recently there has been a second hack to increase flow, this is the bondtech
CHT solution.
If you can split the filament into multiple thinner strands before it's fully melted,
you've increased the surface area and decreased the thickness,
so this increases performance significantly.
Why do we care about flow rate all of a sudden though?
It's demonstrated quite well with the voron.
Back in the ender 3 days your kinematics were the likely limit, so a nozzle with 15mm^3/s
max flow rate was unlikely to really be the bottleneck in most normal prints.
But more and more these days we see printers that hit that very easily - in fact you can
on an ender if you push it hard enough, but usually you have to be doing something "non
default" to get there, and this is my point I'm getting to, for flow rate.
The point, finally, is that you need to, in your slicer, depending which one you use,
monitor or limit the flow rate, if you want to print fast and not mess up.
In cura you need to show the preview and pick "flow rate" from the drop down to see the
max flow rate, in prusaslicer, you can do the same but prusaslicer has a max flow parameter
here, which I wish cura had, but it doesn't.
This is your ultimate speed limit.
This is one you can't break.
If you're wondering what that limit should be set to, then luckily it's pretty easy.
We literally just talked about it.
A normal hotend with a normal heat chamber, so this is a creality hotend, or a v6, or
a sprite, anything with a heat block like this, your answer is around 10 to 15mm^3/s.
If you have a high flow nozzle, which might have a bigger heat chamber, it might have
a longer one, like the volcano, you can pretty much double it.
30 mm^3/s.
If you have a CHT nozzle then refer to their spec sheets.
But it's likely to give you at least 50% on top of whatever you had, I think.
Somehow I've not actually used a CHT nozzle yet.
I really should.
Hmm.
So still before we get back to speed.
We know now that our speed is limited by our flow rate, which is also a function of our
line height.
They are all related.
Max Flow, is a function of the speed you're extruding, AND, how much you're extruding
per fixed length.
I can show you.
Here's an extruded thingy of 0.2mm line height and 0.4mm line width, this would be "normal".
Here's one of 0.3mm line height and 0.5mm line width.
Which one has extruded more filament for the same print speed?
Pretty obvious.
So the same applies as above.
You can print faster, by increasing your line height, your line width, this means less walls
which is why it's faster, but if you hit the flow rate, it's game over.
Finally we arrive back at speed, after that minor detour.
You can hopefully see that print speed is absolutely not the only factory in printing
faster!
You could be printing at 400mm/s at a 0.1 layer height and take longer than printing
at 200mm/s at a 0.3 layer height.
What should your aim be then?
Well, the answer to that, I think, is balance.
Let's do it.
I'm going to slice this model here and we'll try to aim for a fast speed.
We're making our own profile here, by the way.
Start with the default ender profile, slice and check the flow rate, and typically it
will be very, very low.
This gives a lot of room for improvement.
The first thing I would do is raise the line height, and you should see an immediate improvement
in time and an immediate increase in the maximum flow rate.
Then I would look for a speed that doesn't break the flow rate.
If I'm happy with that speed, I'll print it, and you're pretty much optimising for the
maximum flow.
So, I guess you would be able to get a decent time saving on this print which appears to
be the word pcbway which is, by total coincidence, the name of pcbway the sponsor of this video,
which is PCBWAY..
If you want to not care at all about your print times or in fact anything really about
the slicer settings then you can always send your stl over to PCBway and get it printed
by means of one of their manufacturing processes, be it resin, SLS, SLM which can be used for
metal even, FDM like this video, I wonder how they slice models for FDM, or if that's
not enough for you then how about come CNC machined parts in all these materials, some
you probably recognise, POM is this stuff, FR4 is circuit board material, PTFE is...we
all know what that is right?
Anyway - you provide the relevant format files and pick the options and they will make it
for you.
Go check out PCBWay's website at the link below in the description.
And thank you pcbway for sponsoring this episode
So, speed, actually, there's a bit more to speed than just print speed itself.
And this is the 1st derivative and that other thing that isn't the 2nd derivative of speed,
yeah we're not going there again, I am talking about acceleration and jerk.
And how much use these are is very very dependent on your hardware.
On this ender, the default acceleration is I think 1000 mm/s^2 but the default jerk is
I believe 10 and there's no units on that and I don't feel like explaining why right
now.
Acceleration is how fast the axis in question is allowed to speed up, and jerk is, meh,
a constraint on how fast that is allowed to happen, the reason jerk exists as it does
on printers is because without it, acceleration has to be fairly slow or this happens.
Which isn't good.
If you have newer marlin or, if you have klipper then you have things more like this to contend
with.
Same basic idea, accelerations, rates, square corner velocity, if I tried to explain that
I'd probably get it wrong or have to spend 10 minutes doing so...that's an episode in
itself, but the point is that you can tune each one of these to make your printer finish
sooner.
I should mention that if you're going to extremes with these controls, you need to be looking
at input shaping, again outside of the scope here.
It's quite hard to really quantify the time saving in the slicer on the derivatives of
speed and associated controls because quite often this is where the print times start
to drift from the slice times, so here's two parts and their respective speeds, printed
on the flsun v400 with klipper.
So what have we learned?
It's been a bit rambly but that's because the concepts are all mutually inclusive, but
we can print faster using increased flow rate, and by increasing the parameters around the
kinematics.
The former is very simple to get right, the latter is probably going to need some experimentation.
I hope this was of some help, let me know.
I think there's at least one more chapter that can be done on this with what's left,
so with that, I will see you next time!