Gas station without pumps

2023 January 26

3D-printed clay-extruder die

Filed under: Uncategorized — gasstationwithoutpumps @ 10:18
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In UCSC’s soon to be fab lab (and an existing one), I talked about two of the fab labs on campus and mentioned that I was planning to try using the DSI studio in the basement of the “Science and Engineering Library” (which no longer has any science or engineering books or journals, so should be called the “Study Space on Science Hill” instead). On Monday, I got certified to use the Ultimaker 3 printers and attempted printing the clay-extruder die I had designed:

The Scott Creek extruder is designed to work with ⅛” aluminum dies, with no allowance for different thickness of dies. So plastic ones have to be made with an ⅛” flange, with the body of the die as a plug that goes into the extruder tube.

I printed the design in PLA with a 0.4mm nozzle and 0.2mm layers, with 4 walls, 20% gyroid infill, and 20% infill overlap.  I chose gyroid infill, because the stresses on the die would be both compressive and bending. I was worried that the 3mm flange might not be strong enough, especially as I expected some stress raising around the inner edge of the ring that holds the die in place.

The die printed fine, with no visible blobbing and only tiny amounts of stringing, easily brushed away.

On Tuesday, I took the die to my ceramics class and tried extruding some clay with it (I had a scrape on one of my fingers and did not want to get my hands wet practicing throwing pots). The die worked just fine and showed no damage from being used—the photo above was taken after the die was used and cleaned. So it seems that the 3mm flange is thick enough not to cause problems (at least for a few uses—I’ve no idea how long the die would last in production use, and I don’t really care). Next week I’ll trim the soap dishes, stamp them on the bottom, and leave them to dry on the greenware shelf.  Trimming should not take too long, so I should have time to try throwing again.

If I design other clay-extruder dies, I think I’ll make the bevel on entrance to the die bigger, so that there is more “wedging” of the clay as it is pushed through the die.  I had intended a wider bevel, but I had a bug in my OpenSCAD code, where I had used a constant “3” instead of the parameter “extend” in one function, and I had not noticed that the bevel was narrower than intended in the final STL file.  Of course, there wasn’t really room on the die for more bevel (unless I made the soap dish even smaller), so perhaps the bug was not such a bad thing.  I’ll have to think about how I could modify the OpenSCAD program to make the bevel large in the middle of the die, but reduce it near the edges, so that the die entrance does not get too close to the sides.

2023 January 19

UCSC’s soon to be fab lab (and an existing one)

Filed under: Uncategorized — gasstationwithoutpumps @ 22:21
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Yesterday, I took a tour of the space in the basement of Baskin Engineering that is being converted to an “Experiential Learning Facility” (a name only a bureaucrat could love—but at least they are looking for a new name!). The space used to be two machine shops: a professional one that only the lone machinist was ever allowed into, and a student machine shop that was never used, because you had to get someone with a recharge number to pay several hundred dollars for the once-a-year training then $12 an hour to step into the room.

Most of the old machine tools were sold as surplus, because they were too difficult to use for a student space. Some of the more basic metal working tools were kept (a bending brake, a large shear, an arbor press, a Rotex punch).  There is also a small CNC mill and a lathe.  There are some basic woodworking tools and a laser cutter, and some 3D printers will be moved in once they get the next room over (before March, I think).  I believe they will also get some sewing machines, though what sort is far from clear.

The space looks like it could become a fabulous maker space for students, but I suspect that it will not, because of stupid policies by the administration.  They outlined 4 uses for the space: a first-year design course, 1-year group projects (like senior capstones), thematic areas (like the S-lab on sustainability that has moved into much of the space and provided equipment for that portion of the space), and engineering clubs.  The engineering clubs will get permanently (or at least annually) reserved spaces for the club to meet, work on their projects, and store their projects and tools.  The lion’s share of the space is reserved for 4 clubs, which will have to apply for the space, but it is expected that FormulaSlug (car building), SlugBotics (robot building), and Rocket Club (rocket building) will get 3 of the 4 spaces.

Note: what is missing?  There is no provision for someone to come in and use any of the tools unless they are in one of the classes or clubs! You take the freshman design course (which has not been created yet) and learn to use some tools—great!  Now you never get to use those tools again until your senior design course—too bad!  Unless you are interested in one of the 4 things that the 4 clubs are doing, in which case you are set up in style!  Why the administration omitted such a critical part of the facility is a mystery to me.

I urged the few students who were there (interns working on helping create and advertise the space) to get students to start a new Maker Club and apply for one of the club bays.  That way anyone could join the Maker Club and (after getting suitable safety training) use the space and tools! The Maker Club could also provide “super users”, who could help maintain the facility, providing training and safety supervision. It would also be good to open the tool use up to faculty, staff, and emeriti (again, with appropriate training), so that a community can be built that has some continuity from year to year. With the current administration, though, I’m not holding my breath waiting for a sensible outcome.

If the administration gets their heads out of their behinds and figures out how they are going to make the space actually useful to individual students (rather than just instructional space and a clubhouse), then I’d be glad to help out with things like short workshops, 1-unit courses, and even some scheduled supervision of the space.  But I fear that the administration is going to silo it up so that very few students and no faculty or staff have access—repeating the mistake that PBSci made with the old machine shop (though not quite as badly, since a few hundred students will have access, instead of 1 or 2).

This bad management is not an essential part of creating a makerspace at UCSC.  The Digital Scholarship Innovation Studio (DSI) on the lower level of the Science and Engineering Library has a much more open policy—anyone with a address can take their training (online), do a simple in-person assessment, and use the equipment. Actually, I’m not 100% certain about alumni—they can take the training and sign up for the assessment, but they may need a current ID to actually use the equipment. The answer in the FAQ for “Who is allowed to use DSI equipment?” is “Any UCSC affiliate (students, faculty, and staff) who has completed Library training.”  That is a little ambiguous about affiliates who have retired or graduated.

DSI has 4 Ultimaker 3 (2-nozzle) printers and plan to get 2 Mini Prusa printers with a Mosaic Palette accessory (for 8 colors) set up during Winter quarter. They also have 4 small GlowForge laser cutters (11″×19.5″), but lack the ventilation to cut acrylic—so just cardboard, MDF, and thin plywood (or engraving on some harder materials). Currently you need to use materials provided by DSI, but they don’t have a recharge mechanism: they provide a small amount free to students. They provide PLA filament (the 3mm Ultimaker filament, not the more common 1.75mm filament) and sheets of birch plywood. I imagine that they’ll have to set up a way to charge for materials if they get really popular.

I took the online training for the 3D printer this evening—it is fairly simple, though there are a few bugs in the Canvas course that I pointed out in the feedback form at the end.  I suspect that they’ll get those bugs cleared up soon. I’ve signed up the in-person assessment Monday morning, and I’ll see if they let me use the 3D printer.  If they do, I’ll take the online training for the GlowForge laser cutter and get checked out on that also.  I’ll also find out if there is any role for me to play in their space—I’d be glad to help students learn to use Cura or OpenSCAD—perhaps even FreeCAD, once I’ve learned how to use that myself.

I have something to print that is too big for my little Monoprice Delta Mini: a die for a clay extruder, to fit a 4″ round Scott Creek extruder. Unfortunately, the extruder die design I had to match my broken soap dish will not fit—the biggest dimension is more than the 4″ diameter.  I decided to try scaling the design down, making a soap dish only 80% of the size of the existing one.

The Scott Creek extruder is designed to work with ⅛” aluminum dies, with no allowance for different thickness of dies. So plastic ones have to be made with an ⅛” flange, with the body of the die as a plug that goes into the extruder tube. I think I like the NorthStar extruder design better, but I’m not about to spend $400–500 to get one.

If they let me, I’ll try printing this on Monday (it uses 50g of PLA, for a cost of about $3.33, or about 13 minutes of minimum-wage staff time).

2023 January 2

Ceramics class?

Filed under: Uncategorized — gasstationwithoutpumps @ 17:17
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I’m hoping to be able to get into the beginning ceramics course taught through adult education at Santa Cruz High.  It is one of those courses where the registration opens at a specific time, and if you aren’t on the computer obsessively refreshing, then you might not get in. (I’m not telling when the window opens—I don’t want more people competing for the slot!)

Although I have long had a fondness for pottery as objects, I’ve never learned to shape clay myself. I don’t expect to get good at it, but it should be fun to learn first-hand how much skill is involved.

I do have one specific project I’m interested in doing—replacing a broken (and badly mended) soap dish.

I had two of these soap dishes, but at various times they have been knocked off the counter in the bathroom and broken. This one was mended with superglue, but I’d really like to replace it.

I can’t remember who we bought the soap dishes from originally (I showed one to a few potters that I thought might have made it, but they did not recognize it as anything they or anyone they knew made), so now I’m thinking of making one myself. I think it should be a doable project for the beginning ceramics course.

One of the potters I showed it to suggested that the soap dish had been made with a clay extruder, which seems extremely likely to me. I sent email to the instructor of the ceramics course, asking about whether there was a clay extruder available in the studio. There is, but she did not know what model, and she suggested that I wait to see whether I get into the course before looking into it further.

I decided to start designing a clay-extruder die to roughly match the cross-section of the soap dish. I used SVG (manually edited as text, but viewed with Inkscape) to create the outline. I then printed a thin piece of plastic with half the outline cut out, to see how close I had come. It took me 3 iterations to get an SVG file that satisfied me as being close enough.

Here is a PNG rendition (from Inkscape) of the 3D shape. The image is upside down (because Inkscape has positive Y down the page).

I looked around for ways to create custom extruder dies, and found that there are various materials used for the dies: ⅛” aluminum,  ½” HDPE, marine-grade plywood, and 3D-printed PLA. I have no way to do precision cutting of aluminum, HDPE, or plywood (though I could probably get a membership at Idea Fab Labs and learn to use their CNC mill), so I decided to try designing for 3D printing, even though my 3D printer is not big enough for the approximately 112mm square dies used by the North Star extruders. I can find other 3D printers around town or on campus and use them, if needed.

I used OpenSCAD to create the model. It was very easy to do a simple linear extrusion of the SVG file, but the clay extruder dies I’ve found online all have heavily beveled edges on the top side of the die, to compress the clay as it enters the die. That was a bit harder to manage in OpenSCAD.  I ended up using the plugin for Inkscape to convert the SVG file into an OpenSCAD file that could generate points along the curve, then I used the BOSL2 library for OpenSCAD to generate an offset outline for the entrance shape on the top surface of the die and to “skin” between the exit shape and the entrance shape. I had to fix one bug in, as it had a check for strings that only worked in Python 2, not Python 3.

Here is an image of the STL file showing the beveled edge on the top of the die.

I don’t think that I’ll end up printing this STL file, as it would take 40 hours to print on an Ultimaker 3 (at 0.1mm resolution and 100% fill). I could make a cruder version in about 5 hours (at 0.2 mm resolution and 30% fill), but I don’t know whether it would be strong enough to withstand the pressure of the clay. Even if I never 3D print this die, it was fun figuring out how to create it in OpenSCAD.

I looked for other ways to convert my design to an actual die and found a few:

  1. I could use a commercial 3D printing service, but ones like Shapeways would charge around $140.
  2. I could get North Star (who make extruders) to use their CNC mill to make one for about $40 out of HDPE. I’d have to get them the SVG file somehow, as their ordering procedure for custom dies involves making a hand sketch on a paper form! Update 2023 Jan 3: North Star no long offers this service. “Unfortunately, we have discontinued our custom die service until further notice. North Star is focusing primarily on production of our main product line. Equipment, manpower, and materials are dedicated solely to this effort. We will review our ability to offer custom die services sometime in 2023.”
  3. I could order a 3D-printed custom die from a shop on Etsy ( for about $12—the procedure for submitting the SVG file there is pretty clear.  I need to find out how solid the dies are and how well they hold up—I’ll need to decide between their cheap dies and the more expensive ones from North Star (which are almost certainly stronger and smoother). Update: I contacted the seller, and the dies are printed with 20% fill and 0.2 mm height, which Cura estimates would take about 4:25 to print. The seller claims that they work as well as the North Star dies, but hasn’t used them long enough to know how durable they are. Prices are likely to go up as they get more experience with selling them.
  4. There is another Etsy shop selling custom dies for 4″ clay extruders, but they are a bit more expensive, and their images don’t show the beveling—I would certainly be better off with a North-Star-made die.
  5. I could join Idea Fab Labs and learn to use their CNC mill, which would cost me at least $150 (for a one-month “pro” membership).
  6. I could join Idea Fab Labs and 3D print there (I suspect that they’d allow a long print, especially if it was on one of their Ender 5 printers, rather than the more popular Prusas). But that would still cost me $110 for a one-month membership, and the 3D-printed version would probably not be as good as one milled by North Star.

Right now, I’m leaning towards getting a 3D printed die from the Etsy shop, since the price is low and I can live with wasting the money if the print fails. The North Star die is a safe backup.

But first, I have to get into the class and then find out what model extruder the classroom has.

Update 2023 Jan 6: I registered for the class successfully.

2022 December 27

Improved red bean paste buns

Filed under: Uncategorized — gasstationwithoutpumps @ 22:14
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I’ve posted about red-bean-paste buns a few times before: the recipe I used for making the koshi-an (sweet red-bean paste), a recipe for the bao dough,  an updated recipe for the dough, and some photos of one of my attempts). I’ve not been happy with the dough—it was always too dry and didn’t seal well, so I tried modifying it today, as I had some koshi-an in my refrigerator that I had to use up (from a rather unsuccessful batch of buns a couple of weeks ago).  This recipe takes about 6½ hours from start to finish (if you already have koshi-an, which may take longer to cook, depending how dry your azuki beans are).

Step 1:

1 tsp yeast
½ cup lukewarm water  (this is an increase over previous batches)
½ cup sifted all-purpose flour

Mix together and proof for fifteen minutes.

Step 2:

2 cups sifted all-purpose flour
½ cup powdered sugar
½ cup warm water

Mix with the sponge from step 1 and let rise for 2 hours (until doubled).

Step 3:

1 cup sifted all-purpose flour
2 teaspoons baking powder
1 tablespoon sunflower oil (a more liquid fat than I’ve previously used)
¼ cup slightly warm water

In a large mixing bowl, mix the flour and baking powder, then knead with the dough from Step 2, gradually adding the oil and water. The dough was much more manageable than previous batches—the extra ¼ cup of water seems to make a big difference.

Roll the dough into a sausage shape about 1½ inches in diameter, cut into 12 equal pieces and roll each one into a ball. Place them well apart on a lightly floured cookie sheet and cover with a damp towel. Let rise until doubled (about 3 hours).

Cut 12 3-inch squares of waxed paper.  Roll each ball into a circle about 2½ inches in diameter, but no thinner than ¼” thick. (Using my cookie sticks!) Pinch the outer edges to be a little thinner.

Put about 1 tablespoon of filling in the center of the circle, then pull up the edges and pinch and twist them to seal. Put the bun flat-side-down on a waxed paper square. Let the buns rise for 45 minutes before steaming.

Keep the buns at least ½ inch apart in the steamer, and steam for 20 minutes (somewhat longer than before). Serve hot.

Steamed buns can be frozen and thawed, then re-steamed.

The steam buns stuck a bit to the waxed paper (which is fairly normal), and only a few of them popped open, so this was probably the most successful batch so far, though I did not bother taking pictures this time.


Filed under: Uncategorized — gasstationwithoutpumps @ 13:17
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Like many other people (particularly in academia), I’ve been playing a bit with the new large language model from OpenAI, ChatGPT:  This artificial-intelligence program is going to change the game substantially in college courses, as it writes better than many college students, though it tends to write a lot of bullshit and fabulates citations.

Most of my experimenting was triggered by posts or comments on the r/Professors subreddit, where professors have been expressing concern about how this new tool will be used for cheating and how it will affect their courses.

My experience is that ChatGPT writes grammatical prose that sounds good, but doesn’t really understand what it is saying.  When I gave it quiz questions from my electronics course, it provided answers that would sound good to a non-expert, but which are clearly wrong, in the same ways that failing students in the course would be wrong. For example, the prompt “What is the impedance of 20kΩ resistor in parallel with a 50pF capacitor at 1kHz?” results in

The impedance of a resistor is simply its resistance, so the impedance of a 20kΩ resistor at any frequency is 20kΩ. The impedance of a capacitor, on the other hand, is determined by its capacitance and the frequency of the current passing through it. The impedance of a capacitor is given by the following formula:

Z = 1 / (2 * pi * f * C)

where Z is the impedance, f is the frequency of the current, and C is the capacitance of the capacitor. In this case, the impedance of the 50pF capacitor at 1kHz would be:

Z = 1 / (2 * pi * 1000 * 50 * 10^-12) = 1.59e5Ω

To find the total impedance of the 20kΩ resistor and the 50pF capacitor in parallel, we need to use the formula for the parallel combination of impedances:

1 / Ztotal = 1 / Z1 + 1 / Z2

where Z1 is the impedance of the first component (in this case, the 20kΩ resistor), Z2 is the impedance of the second component (in this case, the 50pF capacitor), and Ztotal is the total impedance of the two components in parallel. Plugging in the values from above, we get:

1 / Ztotal = 1 / 20,000 + 1 / 1.59e5

Solving for Ztotal, we get:

Ztotal = 1.19e5Ω

So the total impedance of the 20kΩ resistor and the 50pF capacitor in parallel at 1kHz is approximately 119,000Ω.

This “answer” replicates two of the common mistakes of failing students: it neglects that the impedance of a capacitor is a purely imaginary number and it gets the arithmetic of fractions wrong. Until the large language models can be appropriately merged with the math AIs (like Photomath or Wolfram Alpha), engineering faculty do not have much to fear from ChatGPT.  I guess that it will take 5–10 years to do that sort of merging, as the two approaches to AI are not very compatible.

I tried some more “creative” prompts also and tweaking the prompts to get better results. I tried one series of prompts (I won’t show the results for any but the last iteration):

  • Write a song to be sung by students with the theme and title “When will I ever need this?”
  • Try again but with rhyming verses.
  • There is no rhyme there.
  • Try again with real rhymes.
  • Try again with a blues-song format and general air of depression.
  • Try again without the upbeat bridge.
  • Remove the current outro and end with singer being lost and forlorn.
  • Try again incorporating “1812”, “square root of 1066”, and “the quadratic formula”.

resulting in 

Verse 1: Sittin’ in this classroom
Feelin’ like a waste of space
Teacher’s talkin’ at me
But I can’t hear a word he’s sayin’

Chorus: When will I ever need this?
Will it help me find my way?
Will it make me rich or famous?
When will I ever need this?

Verse 2: I ain’t sayin’ it ain’t important
But it just don’t make no sense
Memorizin’ 1812 and the square root of 1066
And the quadratic formula too

Chorus: When will I ever need this?
Will it help me find my way?
Will it make me rich or famous?
When will I ever need this?

Outro: Feelin’ lost and forlorn
In this never-endin’ maze
I just don’t know where to turn
When will I ever need this?

Chorus: When will I ever need this?
Will it help me find my way?
Will it make me rich or famous?
When will I ever need this?

The main use case for faculty seems to be creating email templates or assignment prompts,  Here is an example of an email template (with the prompt provided from a question asked by a professor on the subreddit). Prompt: “Write an email telling a student that I will not change your grade because that is the grade you earned, and that there are no more opportunities for extra credit as the term is over.”  I had to reprompt with “Try again without inviting the student to reply.”

Dear Student,

I want to let you know that I have carefully reviewed your work and have determined that the grade you received is an accurate reflection of your performance in the course. As such, I will not be changing your grade.

Furthermore, the term is now over, so there are no more opportunities for extra credit. I understand that you may be disappointed with your grade, but please know that it is my belief that you earned the grade you received through your work in the class.


[Your Name]

The main ways that people have thought of to avoid or detect ChatGPT cheating have included highly technical content that requires math skill; checking citations (ChatGPT likes to fabulate them); making prompts that use a visual image (it will be a while before the large language models are merged with computer vision); requiring web lookup of current events (newer than the model’s training—the models currently do no search); requiring live, in-class writing; and requiring multiple stages of writing process (proposal, outline, draft, edited draft).  I don’t think that the last approach would work, as ChatGPT seems capable of doing outlines and editing drafts.

Someone suggested that real student writing could be detected by the cliched “hooks” that students use, but that is easily faked also: “Write a 200-word essay about cheating using AI, starting with ‘Since the dawn of education, students …’ “

Since the dawn of education, students have always looked for ways to cheat in order to get ahead. With the rise of technology, cheating has become even easier with the use of artificial intelligence (AI). AI can be used to generate answers to tests or homework assignments, or even to write essays.

While using AI to cheat may seem like an easy way to get good grades, it is ultimately a dishonest and unethical way to succeed. Not only does it go against the principles of fair competition and hard work, it also undermines the value of education. By cheating, students are not truly learning and are not gaining the skills and knowledge necessary for future success.

Furthermore, using AI to cheat can also have serious consequences. Students caught cheating can face disciplinary action from their schools, and in some cases, it can even result in expulsion. In addition, using AI to cheat can also have long-term consequences on a student’s future, as it can damage their reputation and make it more difficult to get into college or find a job.

In conclusion, while using AI to cheat may seem like an easy way to get ahead, it is ultimately a dishonest and unethical action that can have serious consequences. It is important for students to understand the importance of hard work and honesty in education, and to resist the temptation to cheat.

I’m convinced that Chegg will be buying a large language model and retraining it on their large database of cheating materials, resulting in an AI that can replace the “experts” that they hire in India. The results from ChatGPT are already about as good as Chegg answers, and training a dedicated CheatGPT bot will undoubtedly increase Chegg’s profit margin (no labor costs for “experts”).

For my Spring quarter class, I will have the students use ChatGPT (assuming it is still free then) to create the summaries that they need to write for the class—they will have to provide ChatGPT with the info and have it turn it into readable prose of about the right length.  I think that this approach will result in more readable summaries than in the past, while still challenging students to come up with the key points that need to be communicated. I suspect that a lot of writing in future will be done by a combination of human and artificial intelligence, and I think that this 2-unit, non-required, P/NP course will be a good way for students to experiment with that approach to writing (with no academic-integrity issues interfering).

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