Mathematical rosette iron

Two months of intermittent effort, and I finally succeeded! :tada:

A (named after the rose) rosette cookie iron in the shape of a (named after the rose) rose or rhodonea curve. If you know that I didn’t invent this, please let me know! :relaxed:

Project History

My wife is a mathematician. She also has some Scandinavian heritage, and she has a family heirloom that typically gets used around Christmas: Cast-iron rosette irons in two classic shapes:

However, the threads on one of the handles were a bit damaged, and when I cleaned them up, I got the bright idea that there are a lot of beautiful mathematical shapes. Maybe I could make something that honors both my wife’s Scandinavian heritage and her calling as a mathematician. Both of us enjoyed spirograph as kids, and the idea of using the simplest of those shapes, the rose or rhodonea curve, as the basis of a rosette iron got hold of me and I couldn’t seem to let go of it. Especially when I learned that new rosette “irons” today are made of aluminum, and I remembered that I had some ¾" cast aluminum plate that I picked up from the scrap yard a couple years ago.

I Updated a fun math shape generator that used OpenSCAD to model these shapes, but sadly OpenSCAD mostly produced non-manifold objects, even when I essentially re-wrote it to work completely differently. My attempt to use FreeCAD to toolpath it wasn’t a great success. I asked for help on Twitter, and Arjan van de Ven pointed me to a gcode generator he wrote. It didn’t complain that my shape wasn’t manifold, but it had a few bugs that affected my model; it really wasn’t meant for this kind of model anyway.

Meanwhile, through LWN I had learned that Kiri:Moto exists. However, it couldn’t handle the non-manifold objects, so I had to heal them in meshlab to toolpath them. Separately, last summer I played with CascadeStudio right after it was released, and liked it. So I started over and modeled it completely differently in CascadeStudio. The resulting object was a valid manifold! It was also much simpler, so it was much faster to process.

Modeling it was only the first challenge. Breaking bits trying to cut ¾" mystery metal aluminum plate in my OX meant for wood was the next.

Here’s the whole family together now

The bright one in the middle is my new aluminum rosette iron. It’s a 5/7 rhodonea (rose) curve. The surface is rougher than I intended due to technical difficulties that prevented a finish pass, but this actually might be a feature that makes it work better; a smoother finish might not hold the batter as well.

My 10-24 tap is a piece of junk, which made tapping no fun, but I got it done. Here’s the back side of each iron. Note that the back is thicker than the front; this is the draft angle of the mold and is meant to help make it possible to remove the rosette cookie from the iron after it is cooked.

Breaking all those edges took a while even with a deburring knife, and I had to find several different files to touch up a few places. No one would mistake this for professional work, but I’m very happy that I found a way to make this work, and I’m looking forward to trying it out.

If the smallest holes in this pattern end up too small, the 3/5 and 3/7 curves might be simpler and work better. If I end up deciding to make another one, hopefully I’ll have the flaky router problem that resulted in not being able to do a finish pass diagnosed and fixed. :relaxed:


The first attempt stuck terribly to the iron and I was afraid that the surface finish was too rough. The second attempt wasn’t much better. But then the surface seasoned, my technique improved, or… some of each!

These exist in many cultures around the world by a variety of names. We tried Mexican Buñuelos de Viento, so they were dusted with cinnamon sugar rather than confectioners’ sugar:


Fabulous. I’ve enjoyed following your journey here and on Twitter as you figured this all out. Thanks for sharing.


15 posts were merged into an existing topic: Updated a fun math shape generator

Did you make this one from stainless steel or Aluminium?

Are those really made from Aluminium?

Aluminium is someway in discussion related to Alzheimer and the salts are under concern regarding brest cancer, not sure what cross reactions with boiling oil this one might bring out to the food… I like the tool you made and also like the sweet waffles done this way , so please do not take it as an offense…
My last attempt in the

food direction

Yes. I have learned that practically all the existing “irons” today are made from cast aluminum. No offense taken! I do try to limit cooking with aluminum. I do expect that seasoning them as I did reduces exposure.

In any case, there is no chance that my 1 x 1.5 meter router with an openbuilds extrusion frame would be remotely stiff enough to cut stainless. The frame is too flexible and I’m sure that I would break bits long before I even work-hardened the stainless, but there’s no chance it could go right.

If I were going to do this again, I’d do it on the mill. The reason I ran it on the router is that I was using small mills, so running them at high speed let me finish the project in reasonable time. The mill maxes out at 3K RPM whereas the router maxes out at ten times the speed, 30K RPM. This would have been an all day project on the mill, I think. But if I did that, I could choose to make it from cast iron instead of aluminum. It’s harder than aluminum, but also doesn’t have a tendency to create built-up edge clogging the mill flutes. The mill is more rigid, so I wouldn’t have to use 1/10th the feed of the router. That would let me take larger DoC and larger chip load than the router, but I’d still expect it to take 3-4 times as long on the mill — after experimenting and probably breaking a few bits.

I was confused how your stamp was readable without being in reverse, before I realized that you posted it in mirror image! :relaxed: Very nice! Is that a shortbread?


I also cut my watch case on an extruded frame router, but recognized that fast speed and low tork are not good for xsteel. With a 3mm bit you end up at about 6000 rpm and need liquid coolant not to heat the surface over rehardening temperature.

Yes, the cookies are a very old recipie using aniseed as a flavorer, originally they are very hard and have to be stored with a kind of humifier in a box to get biteable. But then they are delicious, (as they take a reasonable amount of effort, I’m not sure if they would be called “shortbread”)

As this is a local specialty it would be difficult to get translated recipies, but if you would need, I would help translate…


I didn’t know that the work hardening was purely a function of temperature. Thank you.

My router has a wood spoilboard and is on an unfinished wood table, so I can’t use coolant. I only intended it for wood when I built it. Also the gantry extrusion is one meter long so there is a lot of flexibility. And it runs on plastic wheels…

Those cookies must be a close relative of the Swedish anise cookies I grew up with. (I’m not Swedish, but Minnesota where I grew up has lots of Swedish culture.) Those maybe were a little softer than what you describe, but maybe that was an American adaptation. We had a special rolling pin to make the shapes. (“Shortbread” is a kind of cookie with no leavening in it, but I think usually softer.)


The air hardening xsteel (dependent on the alloy) should not exceed a rather low temperature short above room temperature… comming down from higher levels the surface gets harder. Even much harder to cut is temper cast as you have a pretty hard surface skin due to the temper structure below its pretty decent but gettin trough the skin is not easy… I bought an ER32 collet for my devider head which was cast and afterwards had been ground to finish… hard to even get the screwholes into


From Sweden I primarly know the hot dogs, the oat cookies, and the furniture… I…A…
Actually I made two cupboards and a media store out of Bamboo, but for the drawers I adapted Ikea kitchen drawers as they have much better mechanics then most furniture you can buy …