Today we're going to be talking about the BMG extruders and why I like them so much,
and I figured what better way to explain how a BMG works than with a clear injection molded BMG.
Let's go over the basics of how everything is handled on this.
Right here is where your stepper motor would enter and you would have a gear that is
mounted to the shaft of the stepper motor, and that would spin this wheel right here.
Now, that wheel is then connected to
a hobbed gear, where your filaments is going to get grabbed by. You can see we've got a insert,
a brass insert to hold this screw and this spring. Now, depending on how tight you have
this screw or how far this screw is screwed in determines how tight the dual gear system
holds the filaments. We're going to unscrew this really quick so I can show you. Now,
this door comes completely unhinged for a few reasons. If you ever get a clog, you may need
to open up this hinged portion to undo a clog. If the gears are super, super tight, you may end up
squeezing the filament to the point where it gets stuck on the gear and spins around the gear.
I've had that happen a few times but it takes just a few times of that happening to figure out just
how much tension you really need, which really isn't all that much but in addition to that,
this is also how you remove the gears if you want to replace them with new ones as
they do eventually wear out, and that's going to happen to any BMG honestly if you use it enough.
Closing this back up, this whole system runs a little different than something like the creality
dual gear extruder because this is a three to one gear reduction, meaning that these gears
require that the stepper motor spin three times as much for the same amount of revolution
compared to your typical type of extruder. The reason why that's important is because,
by doing that, yes, your stepper motor for the extruder does have to spin more but you get
considerably more torque. The chance of filament slipping in the extruder is considerably reduced.
Let's go ahead and screw this back together. I'm going to show you how to load filament
through this, and we don't really need this all that tight. You'll notice that you got to leave
some room for this door to swing open a little bit, because we're going to put some filaments
in here and in fact, we're going to zoom in so you guys can really see what's going on here,
the real meat and potatoes of the situation. As we get filaments in, see now it's
touching the gears. If we spin the gears a little bit, it pulls the filaments in
and now, it's pushing it through. You need a little bit of flex on the door, or you need
a little bit of looseness on this spring so that the door can swing open just a little bit, so that
these gears can move away from each other, I'm going to move it back so that way there's enough
room for the filament to squeeze on through there. Now, these gears are connected to each other,
as such, you'll see there's gears on the filaments grabbing portion and then
it's also connected to this gear reduction right here. It just shoves filament through so well.
Now, this is a typical V6 style connection that you can put directly on here for a direct drive,
but this is a tapered M10 connection for something like your standard pneumatic couplers
that you'll find. Now, just to also demonstrate something, because not all BMGs are the same,
the concept of how it moves filaments is pretty similar, but how it gets the filaments in and out,
is slightly different. I've got an all metal BMG which works a little different than this one.
This Bowden tube should actually fit up to a certain point
right in there. If that was held in with a pneumatic coupler of sorts, then
it would stay in place a little better but just keep on moving that,
and huzzah, filament goes through. This one I like in particular, even better than my
all-metal ones for a few reasons. One, if there's an issue with, let's say that filament getting
wrapped around the gears, you're going to be able to see it because it's clear plastic, but two,
this one loads filament through the Bowden tubes so much more cleanly than my metal one. There's
various reasons for that, the metal one has a different style connection,
where the Bowden tube sits further out and that makes the lining up the Bowden tube entrance a
little difficult when filming is getting shoved through, but also because this is made of plastic,
it's not going to conduct heat. I've had situations where my metal BMG conducted
enough heat to be at the glass transition temperature of PLA when I'm printing inside of
an enclosure and that would make the filament just a little bit too malleable. This is a lot of force
that is put on the film and so when filament's malleable going through this thing,
it has a tendency to cause that wraparound issue. Now, these BMGs, pretty much universally speaking,
just grip filament so well. That's what I like about them is, if there's a problem, usually
you can diagnose it to probably something after the BMG typically, because the chance
of filaments slipping on a BMG is so small that if your filament is slipping on the BMG,
this thing's got enough grip and torque to just push filament for days.
You can pretty much assume that the issue is down the line away from the BMG after hearing that,
which is nice. These things are very reliable,
but not all of them are as good as each other so I like this one and this was only $10.
You can't really get too much better than that and don't let the fact that it's made of plastic deter
you, this injection-molded plastic is actually a good thing because if you look at dual gear
extruders like for instance my all-metal BMG or just the dual gear extruders from Creality,
those upgraded ones, you're going to find that this gear right here, being metal
has a tendency to eat away at the material underneath it, and that is not good if you're
metal on metal, because that metal on metal action is going to create friction and eventually you may
even sieze this gear in position on the bottom of the door hinge or the bottom of wherever this
rests like that upgraded Creality dual gear thing. The fact that this is plastic is actually a
good idea because plastic, in a way, is self-lubricating. I'm not going to say
that it definitely is self-lubricating because I don't know the properties of this particular
plastic. I'm not sure what particular plastic this is made out of, but that's definitely something
I've noticed and that's something I've seen other people know about that Creality dual gear setup,
so it's something to take into consideration. However, if your BMG is doing its job properly,
you should never actually have that gear sitting in a position where it is going to rub up again,
or rub down on the door because once the filament is in there, the position of that filament should
make it so that the gear is sloped in such a way that it's never going to touch the bottom there.
You won't actually have anywhere on this particular BMG. This is not something that
is guaranteed to every BMG because even the metal ones have some variations between the
years that I've bought them. You just want to make sure, and you really can't make sure
unless it's like clear plastic like this, that the gears down there are not grinding
away on the bottom of this door flap. This one actually has remarkably well placements
for how it sends the filament through everything, I really like this one.
I may even swap over to this just because ease of diagnostics, if something goes wrong,
you can tell because you can see what's going on in the inside and this one just plain is better
than the metal ones that I have from Vice Tech. You can get these on AliExpress for
$10 all day long from 100 different sellers. Hopefully, this gives you some more insight as
to how BMG works and why I like them so much because they're very good at what they do.