interest in pellet Bowden extruder for deltas?

[MK-X]

There hasn't been too much recent research in direct pellet Bowden drive and this may be a missed opportunity. Specifically for delta printers, I feel like we aren't maximizing the vertical space that deltas have which consumer Cartesian machines do not have.

Cartesian machines typically use direct drive extruders while 99% of deltas use a Bowden system. Research in direct filament extruders fr on pellets have proven to be far too large, heavy and unwieldy to use with retraction issues.

To install a filament extruder to a Bowden system in a machine such as an ultimaker takes much modification above the system and is seemingly impossible to mount on the frame itself staying within frame dimensions.

However, I believe we can utilize the space above the effector and stay within reasonable dimensional constraints for larger delta machines.

The most common filament extruder today is the Lyman filament extruder which the designs can be found on thingiverse. It's large, heavy, and a horizontal extruder.

There was research done with makibox ramen pellet extruder last seen Q4 of 2012 loading pellets in a linear fashion, but nothing has come to fruition.

The current hot end design is well established and wide spread and thus keeping that in place for the Bowden Is essential for ease of adoption at this time.

With that being said, the focus of current filament extruders is speed to be spooled up. This mean very long auger screws are used to transport as many pellets to the heated orifice as possible. This requires very high torque from a windshield wiper usually.

I hope to replace this long auger screw with a much shorter one pushing less pellets through as we do not need filament delivered that quickly ( only a theory, research and experimentation required) or just a standard screw. This would imply less necessary torque, so that we can possibly use a geared stepper to drive the rotation. This is an important point using this motor.

Using a stepper motor allows us to directly integrate control to already established controller boards as a second extruder. However with this current design theory, retraction is not possible as pellets are continually fed down to the hotend. This means our current standard extruder will probably be necessary to control retraction and extrusion to the printing hot end. With the filament extruder motor being seen as a second extruder. I theorize that we may be able to synchronize both extruders. One to stop filament production and the other for retraction.

Hopper -> screw driven by stepper motor -> Heating element -> 1.75mm diameter die -> Extrusion (cooled?) -> filament detector via mechanical endstop switch -> Main extruder -> bowden tube -> hotend

More research and experimentation is necessary in:

-If stepper motor is a viable replacement to the windshield motor
-Temp of plastic extrusion and how soft/ solid the plastic immediately after pellet to filament extrusion point
-Whether or not cooling is necessary prior to main extruder to retain rigid shape, if so, how much cooling? Direct fan cooling, tube directed blower fan across the the extruded filament
-Temp of hot end required to print the fresh filament as the filament will be soft/warm/hot?


This could very well lead to developments in directing masterbatch pellets to allow for full color printing. As I continue my research and development, this may very well fail or not, but I would really like just to facilitate discussion about this topic.

[LambdaFF]

Hi MK-X. From what I see the filament extrusion process is far from being a 100% failure free process. So putting 2 in line for a printing process will probably increase failure occurences. Do you have ideas on how to adjust on the fly to material properties and other parameters to reduce these occurences ?

[MK-X]

For the most part, variance in filament diameter is due to high temps to garner faster extrusion speed. If we aren't extruding that fast, it shouldn't be too much of a problem. However, to mitigate variance in filament diameter, one could conceivably include a sensor to monitor filament diameter and adjust the software as such on the fly. Because the extrusion motor is still tied to the controller board and the heating element would also be tied to the board, software could alter speed and temp on the fly to adjust.

This design however, is in attempt to keep the established hotend design in place. If I needed to completely revamp it:

I would use a hopper of pellets into a heated region/funnel, making sure it got to temp, down a heated tube to an effector mount screw drive to extrude. This would skip filament completely. Any waste filament can be placed off to the side during extrusion, only to be placed back into the heated funnel as now there is no need for tight tolerances for the plastic.

[3dkarma]

Given that printing is not a continuous extrusion process, you'll need to consider how halts and retraction impact the pellet extruder.

Old computer magnetic tape drives (I'm giving away how old I am) used a moving arm to dynamically adjust tension under similar circumstances - keeping one reel moving at a constant speed as another wound or halted as needed.

[MK-X]

Do you have any suggestion on how to implement this tension reliever?

[3dkarma]

Thinking about it, a buffer of a length of extrusion would be better than a tensioner. A reasonable length of slack extrusion between the printer and pellet extruder would suffice. You'd need to do something to keep it from fouling, though.