Dobble Makerbot MK6 extruder design

[johan 0]

While trying to get the Mintemp trigger fixed on my Ultimaker, I am doing tests on my new Prusa style Mendel.

It has a Bowden extruder and a build envelop of 300 x 300 x 260mm (at the moment)

I am using a Makerbot Mk6 hotend, and the MK6 Stepstruder. When testprinting with a feedrate of 150mm/s, it seem to get the same problem as you get with the Ultimaker: to little filament extruded. The MK6 has a Delrin plunger, to push the filament against the drive gear. I have to tighten it very much, to avoid slipping, and when I am tightening to much, it misses steps.

I was planing to use a Wades extruder with a ballbearing instead of the Delrin plunger, but then I came up with another idea I am going to test: the dobble Makerbot MK6.

This means having to steppermotors with drive gears on each side of the filament. I have just started moddeling, but here are some pictures to show the idea:

http://dl.dropbox.com/u/55953222/My%20P ... Mendel.JPG

http://dl.dropbox.com/u/55953222/Dobble ... %20MK6.JPG

http://dl.dropbox.com/u/55953222/Dobble ... K6%202.JPG

Any thoughts?

Johan

[johan 0]

I just want to say that this was ment to be a posible solution to the filament drive problems at high speed printing, not seeking for advice for my Prusa-verson... .

I think pushing filament between to drivegears, will mean much better grip on the filament. I hope this will result in less grinding and deformation and much more predictible amount of extruded filament.

Johan

[owen 19]

Seems like a good idea you probably still need to use a gear between each motor and it's gripping part. It will be important that the gripping parts are made with the right amount and size of teeth to grip without stripping filament or squashing it out of shape.

Wiring should be easy, you should be able to wire the the same coil on each motor in series.

Good luck.

[johan 0]

I have a Makerbot TOM, wish I have upgraded with the MK6 + exstruder. It has a big hi-torque Nema 17 steppermotor, wich drives the drivegear directly. On my Prusa verson it skips steps because I have to push the Delrin plunger so hard against the filament to avoid slipping. With the filament between to drivegears, and to hi-torque steppers, I hope to push the filament without to much truble.

Another thing I have observed when printing at a feedrate of 150mm/s with my Prusaverson, is that the themperature is going down 8-10 degrees when printing layers with 100% fill.

I have a 40W cartridge heater in the hotend, wich I think is the same as the standard Ultimaker? The nozzle is made of stainless steel, so maybe it can't transmit the heat fast enough?

Johan

[mastory 44]

Here's an Idea. I realize the extra motor gives twice the torque, but why not just use one motor, add a couple of pinions to the drive train so the 'idler' hobbed wheel can become drive, slaved off the main drive wheel. This could be done just by adding a pinion on the same axle as both hobbed parts that mesh when the clamp is closed.

[johan 0]

I have thought of something similar, but at the moment I think that it will be a more simple solution with to steppers, almost like the to steppers on the z-axis on the Prusa versus Sells. I want the posibillity to adjust the pressure on the filament. I think it would be more complicated to achive this with one stepper, and pinions to drive the second drivegear. Now I can just print out some parts ( and wait for the the new stepper) and assemble and test! :-)

[johan 0]

Hi,

I have made some progress with the new exstruderdesign, and have started to print the parts parts on my Makerbot. I will test the extruder on my Reprap first, and if it works fine, I will adapt it to my Ultimaker. ( I still have my Mintemp trigger problem on the UM... :cry: som shortsircuit with the TC)

Here are some screenshots new extruder:

Stretchlet Ultimaker original 100x.g.zip

Stretchlet Ultimaker2 100x.gcode.zip

[jngf 0]

My first thought was about the accurancy tolerance of a stepper motor like Nema 14.

What problem will be caused by the imparity of the two motors?

[jelleatprotospace 0]

why not use a gear to drive the opposite gripper?

I've drawn a herringbone gear here, but with hindsight it might be better to use just a helical gear. The undriven gear will tend to be pushed along the axis, gripping the filament even tighter.

It should not be too expensive to have this made in stainless steel at shapeways, I think. I've left drawing the larger drive gear, that should be on top of one of the gears, as an exercise for the reader...

[johan 0]

This looks like a good solution. Will adjusting the preasure from the second gear influence the performance of the gear? This will mean that the center distance will change?

I have printed the parts an made some tests. It workt well with a Feedrate of 250mm/s but started to fail at 300mm/s. To me it seems to be a problem that comes with the fast reversal at this speed. When it returns to the position from before the reversal, it has to push the filament at fast speed against the buildt up preassure in the Bowden tube. On my printer (Reprap Prusa derivat. My Ultimaker is still not up and running... :-( ) I got a Makerbot MK6+ hotend, wich uses a stainless steel nozzle and a inner tube made of PTFE. The filament is not in contact with the heater core: the inner tube is going all the way down into the nozzle. I wonder if the inner tube insulate to much, so that the filament isn't melting fast enough and actually block the nozzle at high speeds. When I monitor the hotend themperature during fast infill, I can se it drop 5-7 degrees. The Mk6+ got a 40W cartridge heater wich is the same as the default Ultimaker cartridge heater. I have got 2 J-head nozzles laying around so I think I will try one of those, before I make further changes to the driving mechanism.

Johan