I really liked this design but decided to reduce the petal thickness to save printing time, filament and weight. Whilst I was at it I thought I'd have a go at converting it from a single flower to a double, with the idea of having two sets of different coloured petals. So far I have only done it for the small 12 petal version. I also designed a fitting to mount the windmills onto 11mm garden stakes. These are readily available (in the UK at least) from garden centres, Ebay, Amazon etc. I got mine from Toolstation. https://www.toolstation.com/garden-stake/p95466 You could also use bamboo canes. Don't be put off by the number of files, most of them are optional. The hub is unchanged from Letofred's design.

For a single flower just use Single petal.stl and Flower windmill hub.stl. For a double flower you have a couple of options:

1. If your printer can print two or more colours or you are happy to use pause/resume and change colour manually mid-print, use Double petal.stl or
2. Use Double petal outer.stl and Double petal inner.stl to print the outer and inner petals separately, then glue them together with CA glue. Use the alignment jig to easily get the two positioned correctly for gluing. I glued the alignment jig to a piece of scrap wood.

For the axle I use 4mm fibreglass rod simply because I have plenty available from my other hobby, kite building. You could also use carbon fibre, brass, stainless steel etc. You need a length of around 50mm. You will need to print 2 end caps, one Axle tube 4.1mm and one Axle tube holder. These parts are best printed with 100% infill for strength. Not all 4mm rod is exactly 4mm so it's a good idea to do a test print of the axle tube first to check tolerances. The axle tube should be a tight push fit into the axle tube holder, but again, if tolerances are off you may need break out the files/ sandpaper.

Glue an end cap to one end of the axle with CA, insert the axle through the hub and axle tube, then secure with the other end cap. You will need to trim the axle so that there is just a slight gap between the end cap and axle tube. Check that the hub spins freely.

Another (simpler) option is to use a 25mm M4 bolt as the axle. For this you need to print Axle tube M4 and the bolt should self-tap into it.

Short video clip: https://youtube.com/shorts/HJgJeTH-YXw