When I built my first 3D printer which was based on the Prusa I3, I went with MK7 extruder clone from Aliexpress and it worked great. Great to my standards (at the time) that is. It is no longer available so when I designed the Core3D printer, I went with the MK8 extruder found on the same site. The dimensions are pretty much the same as those for the MK7.
MK8 design and issues with it.
I designed the extruder to be “suspended” underneath the extruder assembly. I went for mounting it under because the MK8 has the stepper motor mounted behind the actual extruder. The design in Fusion 360 below shows the MK7 extruder as I never updated it to MK8. The specs remain the same though.
Here is the actual implementation of the full extruder assembly.
A few things have bothered me with this design and implementation.
-Top to bottom the entire setup is 120 mm (4.72″) which is too much, the space below the X-axis used would make for close to 70 mm more build space (along the Z-axis).
-The use of aluminum and the shear size of the assembly, make it weigh close to 825 grams. Too much weight (in my opinion) to be accelerating/jerking around.
-The MK8 is a knock-off. A $1,200 printer (parts only) deserves better. I keep hearing how much better the E3d extruders are, compared to the knock-offs.
-Lots of issues loading new filament. The space between the top and the heater nozzle have too much room allowing for the filament to miss the hole.
Redesign with E3D titan extruder and hotend
Following are a few of things I wanted to achieve with the redesign:
- Lower the height of the extruder assembly.
- Lower the weight of the the assembly.
- Possibly lower the width allowing for more motion along the X-axis
- Achieve higher quality of prints.
Lowering the height
The E3D titan extruder (direct) has much more room between the stepper motor and actual hot end (Compared tot the MK8). The image below shows both extruder designs. Notice how the new Titan Extruder is much higher in height but what matters is the distance between Stepper and hot-end.
For the MK8, the distance between the bottom of the extruder and bottom of nozzle is about 25 mm.
For the Titan Extuder, this is closer to 46 mm. The difference means that I can mount the stepper motor/extruder above the X-axis rail and let the hot-end bridge the distance to below the rail.
The following image shows the true gains in Z-axis space when I place the two extuders in relationship to the X-axis rail they are riding on.
By “wrapping” the extruder around the rail, I gain about 45 mm more Z-axis to print at.
Interestingly, my bed wasn’t designed to go that high originally. It turns out the cable drag chain wasn’t put in place with that much height in mind. I had to remove some shackles to accommodate the extra gained space.
Lowering weight of Extruder Assembly
Here is the break down of what my old extruder assembly weighs:
Top Plate: 41 gr
Bottom plate: 41 gr
extruder bracket: 80 gr
plastic: 80 gr
belt clips: 11 gr
bolts/nut: 18 gr
Stepper: 280 gr
extruder: 96 gr
Hot end: 74 gr
Slider: 32 gr
cooling fan: 13 gr
fan duct: 11 gr
Inductive Sensor: 46 gr
Total: 823 gram
The numbers for the new extruder are as follows:
Top Plate: Gone
Bottom plate: Gone
extruder bracket: Gone
plastic: 27 gr
belt clips: 8 gr
bolts/nut: 8 gr
Stepper: 127 gr
extruder: 60 gr
Hot end: 44 gr
Slider: 32 gr
cooling fan: 16 gr
fan duct: 11 gr
Inductive Sensor: 46 gr
Total: 386 gram
By far the heaviest component is the stepper motor and since the Titan extruder has a 3:1 gear reduction, I can get away with a pancake stepper motor. This reduces the weight be an additional 140 grams.
New weight would come down to 386 grams
Bigger impact on rest of CoreXY
The nature of the Titan’s extruder allows me to “wrap” the entire extruder assembly around the X-axis rail. This “Wrapping will gain me close to 50 mm of additional Z-axis range.
All belts in the former Core3D design run over the X-axis as follows:
in the new design the stepper motor mounted behind the extruder glides fairly closely to the rail so no more room for the belts.
The new extruder assembly required a new belt configuration. In the new implementation all belts will run underneath X-axis and inside the extrusion frame.
The most notable difference are:
Both X/Y stepper motors now have been turned upside down (had to figure out the firmware on that one).
The X-axis end-stop has been moved on top of the rail (in a adjustable slider)
The idlers opposite of the steppers have been placed on a single axis below/inside of extrusion frame.
A minor concern with this design is the idlers being held in place by an ABS printed corner bracket. The actual layers holding the idlers aren’t very thick. Since the belts are kept pretty tight, I wonder if this will break (it hasn’t yet).
When all is said and done
The new design has been up and running for a week now and I’m happy with the results. The new extruder operates as expected. The first 3D Benchy came out great.
This is what the new setup looks like:
Here it is at work:
