H-Bot 3D Printer
Updated: Dec 23, 2018
For the last few years, I have been working on a custom built and designed H-Bot 3D printer. I built an iteration of it in summer 2017, which had a few successful prints. But I was generally unhappy with the result and had a lot of new ideas form throughout the process of building it. This second iteration is going much better, and is generally better designed for manufacturing and assembly - even though it's only being built at a scale of 1, I appreciate good industrial design and try to integrate it when possible
Print as fast as possible with commercially available hardware
Create a modular printing system
Create a sturdy frame and bed
There are essentially 3 aspects to printing fast using an FDM 3D printer. In order from the least limiting to the most limiting, these are computation, motion, and extrusion.
For more simple motor designs (i.e. dedicated motors for movement in X, Y, and Z), 8-bit controllers like those based off of the Arduino Mega, can handle any G-code command without slowing down below reasonable specified feedrates. Anything above these feedrates would likely exceed top-speed and top-acceleration capabilities of any printer. But the Delta or Core-XY kinematics require significantly more computation on the controller-side in order to translate X, Y, and Z into steps.
The H-Bot kinematics are computationally identical to those of the Core-XY, though the mechancial differences will be discussed later. Using this type of motion, high enough feedrates (especially on complicated motions like arcs) can become unrepresentative of what the printer is actually doing - using an 8-bit processor can cause a 'speedwall' for the printer.
In the last few years, however, 32-bit boards like the Smoothieboard and those based on the Arduino Duet have become available - these are more than capable of handling any complicated high-speed kinematics while simultaneously adding functionality to printers. I will be using the Azteeg X5-mini running Smoothieware as my controller - a WiFi enabled 32-bit board with 4 motor inputs and several auxillary inputs.
The most intuitive part of fast printing is fast motion. Since Z-axis movements occur much less frequently than X/Y movements, the speed of the Z-axis isn't quite as important here. Stepper motor speed is not extremely limiting in this case, though the torque can be important for improving acceleration. The most important factor is moving mass.
Using a bowden setup takes one motor off of the gantry. A bowden extruder can cause some issues with more difficult filaments - like flexibles - but using the dual-drive Bondtech extruder will mitigate some of the typical performance issues.
Additionally, the H-bot configuration takes away another moving motor from the motion system when compared to a Cartesian XY motion system as seen in most consumer printers.
In order to truly maximize performance here, I am using carbon fiber X-axis rails and Igus polymer bushings - a 1/6th and 1/8th weight to a typical steel rod and metal linear bearing setup, respectively. This will allow for extremely high accelerations and top speeds - and the effect of the extra torque added from the H-Bot belt configuration will be greatly reduced,.
The speed that both the extruder and the hotend can go through filament is most limiting of speed. For the extruder, using a gear reduced Bondtech extruder is about as good of a compromise between gripping strength/torque and speed as it gets - an extruder without a gear reduction would be able to turn faster, but not grip the filament as well. Using 3mm filament will extend the capabilities of the extruder because pushing filament at the same speed will result in a 2x speed increase over using 1.75mm filament. For the hotend, it's all about the heater block and the nozzle. A big heater block will be able to melt filament much more quickly, and therefore I will be using the E3D Volcano to get the most out of my printer. The only drawback is that you essentially have to print fast using this hotend - if you don't, you will burn filament. This is why the nozzles used on the Volcano are typically bigger (0.6mm, 0.8mm, 1.0mm etc.); because if you use a 0.2mm nozzle, for example, you will have to print extremely fast to keep the filament from being too hot for too long. Ideally, this printer will be able to cope with this well by being fast in every respect.