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Week 11 - Mechanical Design, Machine Design

group page // repo source files // objectives

Contents

objectives >

hero shot >

files >

link to repo

.
├── ecad
│   ├── a4988.zip
│   ├── outline.png
│   ├── top.png
│   └── vias.png
├── mcad
└── sw
    └── serialstep
        └── serialstep.ino

4 directories, 5 files

sequence >

foam crawler >

materials >

printing >

The parts were printed by Dan @ 0.3mm layer heights using a 0.4mm nozzle. For bigger prints, I’ve swapped to 1.0mm nozzles to print at 0.8mm layer heights before. I applied the same practice here.

Some of the parts lose enough resolution when sliced with a 1.0mm nozzle that it remained prudent to use the 0.4mm nozzle for those prints. I divided all of the printable parts into 0.4mm and 1.0mm layer height prints.

It’s been awhile since I’ve used the 1.0mm nozzle for printing, so I had to relearn some of the slicing settings for accomodating a bigger orifice, but not necessarily higher thermal conductivity. The key is to keep the speed capped at 25mm/s - 50mm/s (on my Ender 3 w/ a stock brass 1.0mm, at least). I need to run some more experiments to draw better conclusions here.

side panels >

I obtained an assortment of hdpe sheet stock from Dan in prep for this project. The mcad calls out 1.27mm thick hdpe, but a variety of commonly sourced thicknesses will work as well. The machine was designed to accomodate various thicknesses by compensating through adding or removing washers.

As usual, routing feels much longer when you have to stand there vs letting a machine handle the work. Spent ~2-3 hours in the shop, went from warm outside to very cold. Will want to plan ahead and bring layers from the get-go next time.

I used 1/8” bits for most of the finer features on the inside of the side panel, and used 1/4” for the bigger hole and the perimeter of the panel.

I should spend some time reevaluating speeds and feeds (at the time of writing, efab, cncBig, and mold week were my points of contact with speeds and feeds, and for various reasons haven’t evaluated in depth because either: default numbers mods were good enough; material being machined was forgiving enough; fear of breaking endmill in case I did math wrong.)

I accumulated a lot of hdpe material around the endmill a couple of times (probably due to not optimizing for speeds and feeds)

At one point, I went to clear the material. I made sure to unplug the spindle so I couldnt’ accidentally turn it on, but I cleared with my bare hand. Endmill is sharp, but not such that it’ll cut you while holding it in your hand. However, since I had been machining for a bit, it was also hot, so that combo left a deeper cut in my thumb. I’m alright, it’s healed quite a bit, but taught me a lesson about assumptions in the shop.

aluminum >

I have a workable enough solution for both constraining work pieces and making sure pieces fall predictably after being cut (you really don’t want some sort of kick-back scenario with metal in particular).

For cuts tolerance, Dan advised keeping cuts under required dimensions rather than over so I can compensate w/ washers if needed. I kept kerf in mind as I was cutting, something I am familiar with from cutting a lot of 2x4 for various furniture projects.

Cutting the maker slide wasn’t too bad, except that it was flanged and made it a bit harder to clamp normally to the side of the miter saw.

Cutting the aluminum conduit was a bit more difficult because the table the miter saw is constrained to is only ~8ft long, and the stock I bought was 10ft long. The position of the miter saw also dictates how long of a piece I can cut.

Good thing it’s only constrained to the table using clamps!

I don’t know how I forgot about this, but it came in handy for cutting the conduit. A perk of having a reconfigurable workshop.

For some reason, the aluminum conduit threw sparks when I tried to cut with my saw blade. Is it a different alloy, w/ different hardness properties? I donned some of my casting gear I haven’t gotten a chance to use for intended purposes yet, and it protected me fairly well from the sparks.

resupply - misumi & openbuilds >

A complete BoM is important for replicability. The more steps there are in the process of getting something done, the more room there is for error to accumulate and go uncorrected.

Having said that, I probably should’ve looked at the entire scope of both Foam Crawler and Urumbu from the get-go. Waited Unfamiliar systems tend to intimidate me, and I should prioritize looking at things to dispel fear of the unknown immediately after hearing about something.

spirals - pen plotter & urumbu >

While waiting on some parts to proceed with the Foam Crawler, I shifted gears and worked on the urumbu side of things. The machine assignment is supposed to be a collaborative assignment where we all partly contribute to building a machine. However, according to Blair, it does not need to be a “vertical slice” (eg it is possible for each member to specialize on only one of the following: mcad, ecad, software, etc.).

Since we are building Dan’s final project from a previous cycle, the idea is to both aid Dan by ironing out bugs in the build process, and contribute some variation/improvement that allows us to fulfill the assignment. Possible paths:

My plan is to accomplish both the pen plotter and the decentralized machine arch (urumbu), but they are branches that merge at the end.

urumbu >

Assuming murphy’s law, planned on implementing most basic urumbu machine example (tension driven pen plotter).

Initially aimed to hello-world urumbu using a corexy motion system, but tension driven appears to be the lowest barrier to entry (3d printed parts and fishing line from walmart).

personal supply chain >

My car is in the shop undergoing repairs, which has thrown an unexpected hurdle into my weekend. My lab footprint consists of a few spaces, but losing my car effectively renders all of them inaccessible except for my apartment.

murphy’s law:

Entropy is giving me a run for my money.

Fabacademy and the past year or so have been an eye opening experience towards supply chain resiliency on multiple levels. I hope to continue fortifying my ability to do things as I continue through fabacademy, and beyond.

dump >

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