Why does it reverses the feeding direction?
Bondtech Mini Geared BMG Standard vs Mirrored
When facing a stepper motor shaft, we see it rotate clockwise, by default, when a load command is sent. It rotates clockwise when feeding, and counter-clockwise when retracting.
This can be changed either by swapping one pair of cables on the connector, or by changing the rotation direction in the firmware, although the latter is not available on all printer models.
Inside the BMG, the motor gear engages the main gear (black POM gear) and makes it rotate the opposite direction (counter-clockwise on load).
The primary drive gear is attached to the same main shaft as the main gear, and rotates in synchrony with it.
Depending on its relative position to the filament path, it creates opposite effects.
It is important to notice these effects change, if the filament flows from top to bottom or from bottom to top.
BMG Mirrored: when the filament enters through the top push-fit and exits through the bottom groove mount, it keeps the feed direction.
Watch the motor gear (brass). On the mirrored version, where the filament path, from entry to exit, flows on the left hand side of the primary drive gear, the default feeding direction is kept without change. This is because the drive gears push the filament down an up accordingly with the default load or retract movements.
BMG Mirrored: when the filament enters through the bottom groove mount and exits through the top push-fit, it reverses the feed direction.
BMG Standard: when the filament enters through the top push-fit and exits through the bottom groove mount, it reverses the feed direction.
Watch the motor gear (brass). When the filament path, from entry to exit, flows on the right hand side of the primary drive gear, the default feeding direction is reversed. On load, when the motor gear rotates clockwise, the drive gears push the filament up. On retract, the drive gears push the filament down.
BMG Standard: when the filament enters through the bottom groove mount and exits through the top push-fit, it keeps the feed direction.
What BMG Best Fits A 3D Printer?
How to choose the right BMG?
To properly select the right BMG for your application, users should ask themselves and decide about these 3 questions:
- Bowden or Direct Drive?
- Where and how will I mount it?
- Which version gives me more clearance and the best access to the hinge and thumbscrew?
To evaluate access users take into consideration being right or left-handed. Dexter people usually like to use the hinge on the right hand side, using the right hand to apply pressure on the hinge and thumbscrew and the left hand to insert or extract the filament.
What are hinge and thumbscrew for?
The secondary drive gear is attached to the hinge through a shaft and needle bearings. The thumbscrew crosses the hinge and screws in the BMG housing.
The hinge and thumbscrew assembly is a lever mechanism that allows to vary the pressure the drive gears put on the filament. A tighter thumbscrew is a better setting for harder filaments. A more relaxed thumbscrew is a better fit to softer materials,
During manual loads and unloads of filament, a user can press the hinge against the thumbscrew to disengage the drive gears and allow a faster insertion or removal of the filament.
Our Bondtech Mini Geared BMG is available for 1.75mm filament only
and with 2 versions for each of the 2 different mounting systems.
It always has a push-fit on the top.
The BMG is equipped with a groove mount:
BMG standard and BMG Mirrored
The BMG is one of our most versatile extruders. It is possible to use it on both direct drive and bowden setups.
- on direct drive setups users can mount a V6 style hotend using the groove mount on the bottom.
- For bowden setups the BMG can be used in two ways:
With filament adapter
- Filament entering through the bottom, using a filament guide installed on the mount groove, and exiting through the top push-fit.
With bowden adapter
- Filament entering through the top push-fit and exiting through a bowden adapter installed inside the mount groove (the most robust bowden solution).
The BMG-M is equipped with the Mosquito mount:
BMG-M Standard and BMG-M Mirrored.
The BMG-M is our Mosquito and Mosquito Magnum best partner. The BMG-M was designed to be used in direct drive setups only.
Filaments always enters through the top push-fit and exits through the bottom.
BMG-M Standard always reverts the feed direction.
BMG-M Mirrored always keeps the feed direction.
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