There are these mooncake molds you can get for $10-$15 online. They have swappable design plates. I finally got around to making a custom mooncake mold faceplate. I’m not super happy about the design (it just is a moon cat), but as a proof-of-concept happy I finally finished it.

Have not tested it yet by actually baking mooncake — this is important to make sure that the depth and draft angle are correct such that the design is sharp on the baked good and also releases cleanly.

In the meantime, this is what the front and back look like.

CAD

The workflow is to roughly SVG -> inkscape save as dxf -> import into onshape -> extrude cut.

1. Make or get an SVG online (or use PNG and trace bitmap in inkscape)
2. Open it up in inkscape, then use Ctrl-L to simplify the path (so that when we include a draft later to make the mold release more cleanly, we have fewer faces to select).
3. Alternatively, if you want text to a path, write the text in inkscape, then select “object to path”. Then you can simplify that.
4. Save as AutoCAD DXF.
5. In Onshape, import the DXF: At the bottom, use the “+” to import an STL. This pops up the file as a 2D-CAD tab inside onshape.
6. Go back to the original part. Create a new sketch, then at the top there is a file icon that says “DXF” and select the dxf we just imported from the dropdown.
7. Use the transform tool to scale the outline
8. Extrude-cut
9. Add some appropriate looking amount of draft (slope to the sides so the cake comes out more easily). This requires likely selecting all the faces by hand. If there’s errors, try decreasing the draft angle.
10. Add holes for heat-set inserts that we use as the connectors to the mold press.

Some pictures of selected steps as follows.

Dimensions

• Heat set inserts: 5.123 cm apart
• Outer diameter: 7.137cm; inner diameter (at bottom of arcs): 6.731cm; Circles: 16x of them, so 22.5deg apart.
• Height of plate: 1.27 cm (much thicker than original plate — this is to accomodate the heat set inserts)
• Depth of cut: 0.377cm down (matching original. Deeper = harder to release)

Dane helped me print this in ~30 mins or so using some nice printer set up (fancy fast flow nozzles etc).

After Printing:

The main other trick is to use heat-set inserts and bolts to take the place of the mold retaining features. Matching the original design would require printing the mold upside down (Design facing down) as otherwise it’d be a big block floating over two small pegs. But this means the cake surface would likely be quite messy since the design is a big overhang at that point. The solution is to use bolts instead.

(Make holes a mm or two less than the diameter of the heat set insert.)

Dane showed me this method of using a heat gun to heat up the whole insert — with a bolt acting as a handle for pliers to hold the insert — and this way when you push it in no plastic ends up inside. Less likely to mess up soldering iron tip with plastic gunk, but also harder to control how straight it goes in because you’re handling the insert from the side instead of pushing down (and takes a bit more patience waiting for the heat to transfer). It looks like this:

 

Side Note on the imported DXF (things I tried and do not recommend): All the points will actually not be connected (it’s a bunch of individual lines). You can connect them if desired, by drag-selecting each pair and clicking “coincident” — but doing so didn’t actually let me run a fillet or draft along the entire (cat) outline at once. In the end I gave up and just selected all the faces by hand.

yea, made some bolts — these are notes for myself (as is the rest of this blog). the tl;dr is https://makerworld.com/en/models/791309-flat-thumb-screw

backstory

Needed some 5/16” x 40mm (lol) bolts for furniture assembly recently. Lost the parts, found the parts, lost the bolts. Such is life. Debated buying off Amazon, suffered through the amazon interface for picking hardware (no, I actually want a 51/6, don’t give me results for 3/8), got chatgpt to give me incorrect info (no, they’re not dome head because i said “it’s more of a dome”, they’re button heads), pondered if it was worth $10 to save an hour of my time (it was, but man, $1 a bolt?) then decided heck it they’re not structural anyway. They’re just for keeping the feet mostly attached to the mostly stationary bookends of the sofa. (ehehe I got an experimental sofa where one end is a bookshelf and the other end is a sorta-laptop-able surface with two stools).

ok actually useful tidbit

Found these flat-wise printed bolts so that the layer direction is in the “correct” direction and it doesn’t shear so easily.

https://makerworld.com/en/models/791309-flat-thumb-screw?

 

There’s really only two key parameters: thread outer diameter, which is 5/16 in to mm so 7.9375mm, and thread step, which (looking online – UNC coarse, the default vs. fine, is 18 threads per inch for 5/16”) is 1/18 in to mm is 1.4122.

side note

Note: the ones on the screenshot/the makerworld javascript app are off by one. I looked at the original source code to figure this out. Src on that says

//Thread step or Pitch (2mm works well for most applications ref. ISO262: M3=0.5,M4=0.7,M5=0.8,M6=1,M8=1.25,M10=1.5) — CC BY NC SA mike_linus thingiverse 2013 “Nut Job”.

which matches charts online.)

CAD source code online

Interesting to see the code wandering around for hardware. I always been reluctant to code what is inherently a 3d process.

This pops ups a window where you can even see the source code, and there’s version history too. Which is great since I accidentally lost the thread parameters but could just go back in time to it.

Is this not the dream of open source hardware? Look at this:

# It also uses the library polyScrewThread_r1.scad license: CC Public Domain, originally created by aubenc, modified by Mike_mattala.

other notable models

I think the idea of using woodscrews to reinforce inside bolts works well for this nonstructural purpose also. I dig it. https://makerworld.com/en/models/980896-collection-metric-bolts-reinforced-by-wood-screws?from=search#profileId-968781

 

the world of makerworld

Interestingly, the “boost” tokens (which are for free when you print models using a bambulab printer / makerworld model, but are like a decent amount of money — $1 each) I always used as a “hey thanks this was useful and saved me time”. But apparently they are for “ambitious” projects like CADing an entire wind model. But still, super neat way to convince people to make lots of models. It’s very smart — the general idea of some novel hardware, e.g. stepper motor control but most of the innovation and competitive advantage is in the software — the mobile app and the desktop site, sharing features, etc.

I wonder now that fiber lasers are a thing and once the cost for that comes down from $3k to $1k if we’ll start seeing a new era of sharing circuits as well. There are certainly companies making in-browser circuit CAD and design review a thing. Went to a career fair and there was a company there making github (eg pull requests) a thing for circuits (allspice).

Goals check

well, not doing great on my goals.

• turn thesis into paper: not even started
• hamster iot / mcup / pov yoyo: not even started
• learning algorithms: barely started, stalled out

been making lecture notes, but those are taking wayyyy too long. playing around with the llms for that. i guess it gets me out of writers block, i mostly have to rewrite everything.

need to update portfolio, and i want to learn well, everything. there’s really digging into tools like kicad and onshape and spice (instead of learning haphazardly). there’s refreshing on computer vision fundamentals, re-learning control theory, taking an llm from scratch class, and on top of that algorithms and i’m making progress on RL by sheer dint of having to make the lecture notes but i’m not actually getting any hands-on experience in implementing.

ah! somehow i’ve made funmployment stressful. and when it’s not stressful i am stressed that i should be stressed. and i’m still perpetually behind. heh.