Home > CAD Parts

This page documents parts I have designed for 3D printing.

Materials and Tech

CAD software

I started out with FreeCAD. I was impressed by the range of capabilities that comes with the software and the quality with which they are delivered—at least initially. Everything worked well for small parts and the initial phases of the larger arm project. However, as the design grew, the tree-structure representation of design elements became unwieldy. It was difficult to predict how the tree would rearrange following an operation. Ultimately, a bug surfaced in the FreeCAD software, and I was unable to undo and recover my design. I started looking elsewhere and found Autodesk Fusion 360, which can be obtained free of charge for personal use. I was, and still am, quite new to CAD; however, Fusion 360 is obviously a top-notch product. Everything just works. The operations are stunningly intuitive and well-crafted. It is difficult to imagine a reason for looking elsewhere except, of course, for the facts that the free version cannot be used commercially and the commercial version is quite expensive.

Mesh Slicer

UltiMaker Cura is a simple tool with a single purpose: slice the mesh outputs of a mesh model into horizontal layers of 3D printer instructions. I used Cura successfully for quite a while, but eventually ran into issues with filament stringing. After trying many (many) alternative configurations, I found that the PrusaSlicer default settings are very effective, and I’ve been using this tool ever since.

3D Printer

With endless options on the market it can be difficult to choose; however, at under $200 (in 2022) with generally quite positive reviews, it was difficult to get past the Creality Ender 3. It was simple to assemble and has been cranking out high-quality pieces since the start.

Web Interface

I use OctoPrint with my Raspberry Pi as an efficient and easy way to manage print jobs. See here for tips on configuring OctoPrint on the Pi.

Automatic Bed Leveling

I added the CR Touch Automatic Leveling Kit to my Ender 3. The sensor comes with a mounting bracket for the Ender 3; however, it isn’t truly designed for this model, and I had previously replaced the hot end with something different. As a result, the sensor was mounted too far above the bed, which caused the hot end to drop down into the bed. After much experimenting and searching, I found that the sensor needed to be offset down toward the bed in order for everything to work. I did this by adding spacers as shown below:

cr-touch-spacers

After installing the hardware, flash the printer with the correct firmware here. Download the firmware bundle prefixed with the printer name (e.g., “Ender-3 CR Touch Firmware” for an Ender 3 printer, or “Ender-3 V2 CR Touch Firmware” for an Ender 3 V2 printer). Within the bundle, select the board version. Note that 4.2.2 is an early board that requires a special adapter to plug the bed leveling probe into, whereas the 4.2.7 board has a direct connection for the probe. Clear an SD card and place the firmware binary onto the card as the only file. Name the file “firmware.bin”, insert the SD card, and turn the printer off/on. The display should indicate that the firmware has been updated. Sometimes this is finicky, and the board doesn’t take the firmware. Renaming the file “firmware-123.bin” or “Ender 3 firmware.bin” might work. The steps for calibrating the leveling probe’s z-offset are as follows:

  1. Auto-home the printer.
  2. Move the z-axis to identify the appropriate z-offset using a sheet of A4 paper for thickness. Note the z-offset that causes the nozzle to just slightly grab the paper. Call this adjustment.
  3. Auto-home the printer again.
  4. Access the leveling probe’s z-offset and note its value. Call this current. Then set the leveling probe’s z-offset to current + adjustment.
  5. Save the configuration settings.
  6. Level the bed. The hot end should be in the correct position above the bed, with the z-value showing 0.0 on the printer display and a very small gap between the nozzle and bed.
  7. Add G28 G29 to your slicer’s g-code preamble. The G28 (home) command is probably already present, in which case you just tack on G29 (level bed).
  8. Octoprint has a bed leveling visualizer plugin, which displays the bed mesh as shown below: bed-mesh
  9. Add G28 G29 to your slicer’s g-code preamble. The G28 (home) command is probably already present, in which case you just tack on G29 (level bed).

Extruder-Step Calibration

After installing the new bed leveling firmware above, I kept running into under-extrusion issues. It took a while to realize that the new firmware was configured with a lower extrusion rate than the stock Ender 3 firmware. The process for calibrating the extrusion rate (or e-steps) is as follows:

  1. Use the menu options to manually extrude 10cm (100mm) of filament. Here, 100mm is expected mm.
  2. Measure how many mm of filament is actually extruded, and call this actual mm. If actual mm equals expected mm exactly, then there is no need to calibrate the e-steps. If actual mm does not equal expected mm, then proceed.
  3. View the extruder’s current steps/mm value. This is the number of steps that the printer expects it takes to extrude 1mm of filament. Multiply steps/mm * expected mm to obtain steps taken, the number of steps the extruder actually took to extrude actual mm.
  4. Calculate steps taken / actual mm to obtain the calibrated steps/mm value. Enter this into the settings. For example:
    1. Under-extrusion: (81 steps/mm * 100mm expected) / (93mm actual) = 87.097 steps/mm calibrated
    2. Over-extrusion: (81 steps/mm * 100mm expected) / (117mm actual) = 69.231 steps/mm calibrated
  5. Python function to obtain the calibrated steps/mm: 
    def calibrate(
    expected_mm: float, 
    actual_mm: float, 
    steps_per_mm: float
) -> float: 
    return (steps_per_mm * expected_mm) / actual_mm

Changing the Bowden Tube and Nozzle

This is particularly relevant when the extruder stepper motor is skipping, the extruder gear is slipping on the filament, or the printer is under-extruding.

  1. Remove the nozzle: The flat end should be clean without any filament sitting on top, which might indicate that the bowden tube isn’t tightly seated against the nozzle entry within the hot end.
  2. Replace the bowden tube.
    1. Replace the tube couplings in the extruder and hot end to ensure they will properly grab the new tube.
    2. Tighten the nozzle.
    3. Loosen the nozzle 3/4 a turn.
    4. Insert the bowden tube firmly and fully into the hot end coupling.
    5. Heat the hot end.
    6. Tighten the nozzle, which seats the bowden tube firmly against the nozzle.
    7. Trim the tube to length for the extruder so that it can easily reach all print positions.
    8. Insert the bowden tube firmly and fully into the extruder coupling.
    9. Level the bed if needed.

Heat Creep

Perhaps related to the new hot end mentioned above, I started having serious trouble with filament becoming stuck in the heat sink. Forums are littered with discussions of heat creep, with solutions ranging across filament drying, slicer settings (extrusion speeds and distances), cooling fans, and extruder upgrades. In my case, upgrading the hot-end fan ($13) and converting the extruder to direct drive ($15) solved my problems.

Reinforcement Learning for the Cart-Pole Apparatus

This is not a new concept. If you search for “cart-pole balancing”, you’ll see that this problem has been solved in a variety of ways. However, the details are always interesting, and I was curious whether my RLAI would find a solution. This is a work in progress.

H-Gantry

How to control a two-axis linear gantry system? The simple solution is to use two stepper motors, one attached to each axis. The harder solution: Use two fixed-position stepper motors with a crazy, winding belt. There are advantages each way. The former is simpler to design and build; however, the motor mass is attached to each axis, which is not ideal when the axes are changing direction quickly. In the latter design, the motors have fixed positions, so the motor mass is not attached to a moving axis. The control is more complicated, but this makes it interesting, which is also an advantage!

Robotic Arm

This was the first real project that I pursued with 3D printing. The concept is basic, including five degrees of freedom driven by SG90 servo motors. The design poses several good challenges for anyone starting out with CAD or—like me—returning to CAD after a very long time (9th grade high school, if my memory serves):

All of this adds up to a good bit of time, failure, iteration, and fun. Full details can be found here.

Related projects:

Freenove Smart Car Rear- and Front-Mounts

The smart car comes out of the box with a front-mounted camera. I designed this bracket to move the camera to the back and provide room for front-mounted parts like the robotic arm described above.

The files for this design can be downloaded from Thingiverse here.

Related projects:

Elevator

This is an elevator designed for the stepper motors found here.

Full details can be found here.

Related projects:

DC Motors

The following is a four-coil brushed direct-current (DC) motor:

Full details can be found here.

Tips and Tricks

  1. The small deboss labels on various components contain the Fusion 360 version numbers of the design file. This is a handy way to keep track of the design file version used to print each component, particularly when diagnosing issues, updating the design, and printing new versions. I use the ParametricText add-in to automatically update the version numbers when saving the design file.