3D Printed Darning Mushroom

One of my kids likes to do “visible mending” and after borrowing several household objects as darning eggs, asked that we print a “darning mushroom.” I didn’t think to search Yeggi, and part of the fun was to design it together, so we sat down on the couch together with FreeCAD open and lots of pictures of different darning mushrooms for inspiration.

We quickly came to the conclusion that we wanted to print it in two pieces. Taking the mushroom as the model, as a “cap” and a “stalk.”

On the first design, I used FreeCAD to model a threaded hole in the cap, and a piece of threaded rod embedded in the stalk, to screw them together. But the default tolerance was too tight, and it broke when I tried to screw it in.

I increased the hole tolerance and tried again. This time, it did screw together properly, but I heard a crack as I screwed it together, so I glued it together permanently.

I realized that it would probably work a lot better if I used a taper to fit. A 2° taper angle seems to work well for 3D printed parts, so I changed the model and printed a third time. It’s a solid fit, but can be pulled apart. Success!

Now I finally remembered to do a Yeggi search. I found several designs. None of them matched the preferred stalk profile. Some of them were threaded, and others were tapered. But there was one thing I’d missed: Many had a hollow stalk, intended to store needles, floss, elastic bands, and such.

So I redesigned the stalk to include storage space inside it.

I sanded the top down with 60 grit, 220 grit, and 500 grit on top of foam to help conform with the eliptical cross section, and then vapor smoothed the top in acetone vapor for about 40 minutes.

I’m not sure whether I then made two so that one is to give away or so that there’s always a contrasting color available, but in any case, I did.


DarningMushroom.FCStd (24.3 KB)


That vapor smoothing really did the trick. I haven’t tried that process but your nice results have piqued my interest.

Now that my printers are enclosed with carbon filters, I print more ABS than anything else.

My way isn’t very scientific. I use a splash of acetone on paper towels, and wait about 40 minutes. I understand the right way is to use a clear polypropylene or glass container so you can sit there and watch it, but I don’t have that kind of patience.

One light surprise for me was that if you have sanded layer lines off, you’ll see them more after smoothing. This was really visible in black in my Replacement KROMEX flour lid even after two attempts at smoothing. I assume this is due to anisotrophic residual stress.

There’s an old Makers Muse video where Markus flash-smooths parts using a metal tin with acetone in it and a heater. to generate a heavy vapour (outdoors!). Quite interesting in a “don’t try this at home” way (common with his videos). By rapidly and evenly melting the whole surface he gets some nice results, possibly at the cost of yet more brain cells :wink:


The heating process could be done inside once you know what you’re looking for as far as the vapor in the jar. The method I saw has you warming the acetone and watching the vapor level rise in the jar. When it reaches a height which allows you to encase/cover your model, your turn off the heat, lower the model into the jar(suspended from the lid), count to something like 20-30 seconds and then remove and let it hang/dry for a few hours.

I would think the vapor would be mostly contained. But no doubt some might add heat too fast and break jars and then you’re in trouble.

I’m definitely too anxious to heat acetone inside so that’ll have to wait until the weather turns warm. My workshop’s ventilation is good but not clean-room good. :smiley_cat:

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I’m guessing this isn’t the carbon fibre filament test print then.

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Heh! Actually, I tried that for the first print (in which the screw tolerances were too tight) because the PET-CF was already loaded in the printer, and I wondered whether the texture would be helpful. I got feedback: No, the texture wasn’t helpful. So back to ABS for this project.