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Machine Week

This week’s assignment was to design and build a machine that includes mechanism+actuation+automation+application. First, we were to build the mechanical parts and operate it manually. After that, we needed to actuate and automate your machine

Machine Purpose

The purpose of our machine was to ‘buff’ a PCB board after it is milled. I’ve noticed that sometimes the only mistake students have on their custom boards is a simple short caused by a ‘dirty’ board that has some burrs left from the machining process. Hand deburring is a tedious process that takes practice, so we thought we’d try to automate the process with a machine.

Goals

After watching the machine presentations on Monday and Neil’s lecture on machines, we decided to incorporate a few of the ideas/technology presented in our buffing machine to make is as cost-effective as possible. Namely:

  1. CoreXY-(Based on the UrumbotXY-Fall2022 design)
  2. Kevlar String Drive
  3. 2020 Aluminum Extrusion Frame
  4. Readily available Ender 3 stepper motors
  5. 3D printed parts from the Urumbu and Beehive-Axes projects
  6. Spindle based on a quadcopter motor
  7. USB-C hub power driven(stretch goal)
  8. Custom motors drivers with the Seeed Xiao as the microcontroller based on Urumbot designs(stretch goal)
  9. Add powered Z-axis control to the bed (stretch goal)

The Design

We needed to scale the CoreXY machine down to a size that we could use for a PCB milled board. Initially, we thought about a larger format machine with approximate dimensions of around 18” x 22”, but quickly realized that was too large after mocking it up with some available Kinex pieces from the lab. We eventually settle on 12” (w)x 9”(l) x 6”(h) inside dimensions of our frame. The stepper motors will sit outside the frame.

While we used the UrumbotXY-Fall2022 as our base design, we modified it a bit for our purposes as a buffing machine. I was in charge of CAD the mounting the quad copter motor we used as a spindle and the kevlar string drive system.

  1. I’m still fairly new to solid modeling and Fsuion360, so I used this week to work on improving my CAD skills by setting up out machine in Fusion 360. It was an experience.
  2. I learned how to download model folders from GitLab and import as components in machines in Fusion.
  3. I learned how to manipulate and align components to assemble them in a machine model. However, resizing the model taught me that I had a long way to go as my components were all left out in space when I rezised the frame. Oops.
  4. I learned how to open and modify components to customize them for our application.

Here is a link to the model I was able to generate. It was helpful in that I was able to better understand how the pieces worked together and what modifications I would need to the carriage, so the spindle mount could be attached.

Here is a copy of the under carriage spindle mount that I created for this project.

I took the original carriage string holder model and modified it to add space for a bolt attachment to the spindle mount. I also added 1.5 mm (39.5mm to 41.0 mm) to the bolt spacing on the main carriage axis.

Here is a Fusion a viewer of the final design.

It took five iterations to get a working design and I could have kept going to optimize it, but time constraints dictated otherwise.

The same hold true for the complete machine design in Fusion. As an engineer, I generally prefer to fail on paper first and then test out real world options. In FabAcademy, I’m learning that sometimes the best teacher is a rough physical prototype to get hands on feedback that can be missing in a CAD model.

The Drive System

Our goal was to minimize cost by using 2020 aluminum extrusion with a Kevlar string drive system. I accidentally left the Kevlar string at the lab over the weekend and used some basic kite string I had lying around my garage for the rough manual build of the machine. The v-wheel bearing and pulleys turned out to be a bit tricky to mount correctly. It required a basic attachment and then a fair amount of fine-tuning to get the bearing wheels to move freely on the extrusions without binding or being too loose. There is a slot on the bearing plate that needed to be tweaked to get the right fit.

The largest issue that I had to overcome was aligning the motor capstan and pulley, so the string would be able to easily move with the motor yet stay in the correct grooves while spinning. After some trial and error I figured out that the ext of one pullet or motor needed to be equal distance between the prior and next groove in the assembly. After that it was just a matter of figuring out the best attachment method to the carriage string holder which turned out to be attaching the wire to a bolt screwed in the carriage string holder.

None of the work was extremely hard, but it did require patience and attention to detail.

Here is a link to our group work for the week.