Rosettes


Rosettes are cams, and they are used to produce the rocking or pumping actions needed on rose engine lathes. The rosette is truly what makes the magic happen.

Typically, rosettes with the patterns on the edge (like those shown below on the left) are used to produce rocking action, and rosettes with the patterns on the face (side) are used for pumping action.


Set of 12 Rosettes
Image courtesy Mandala Rose Works

Pat Miller made a very innovative device which uses the rosette designed to move the object in a rocking motion, and converts that motion into a pumping action. A YouTube video showing that device in operation is shown above in the pumping section of this dictionary.


One of the really cool things about rosettes is that the piece can be made very differently using the various options with the given rosette on the rose engine lathe. For example:

  • Positioning the cutting frame so that it cuts on the near side of the piece makes the typically expected design. The video to the right shows near side cutting on the side of the piece in the first 5.5 minutes.

  • Positioning the cutting frame so that it cuts on the far side of the piece makes an inverse of the rosette. The video to the right shows far side cutting on the end of the piece. That starts around 5:33 into the video. At the end, you can see the clover leaf design produced.

  • The shape of the rubber can change the shape of the piece made. Eddie Bell gave a presentation about this the 2018 Ornamental Turners International Symposium, and you can watch that video on the rubbers page in this dictionary.

  • Moving the cutter towards the center, or away from it, certainly changes what happens with the resultant shape. A rosette is designed for a certain size diameter, and cutting at a different one will make the shape change.

    This is very evident with the plain-sided rosettes, which get rounded when the cut radius is larger than designed, and collapse in the middle when smaller. If that is not what the artist wishes to do, an amplitude adjuster can be used to compensate for this.

  • Fading can also be employed to produce shape changes. (That page in this dictionary has a video outlining how it works.)

  • Using two rosettes and separate rubbers for each can produce some shapes that are really amazing. The picture to the right shows a piece that was made using a P-4 and an A-24 rosettes together. (You can click on the picture to see a bigger version of it.)

Holtzapffel Rosettes
F-4

A-10

P-5

Holtzapffel was probably the first to put a structure in place for how rosettes are named, and the Holtzapffel company made a machine for making them (today, most manufacturers use CNC-driven milling machines).

There is a good web site, Traduction de l'Aide du logiciel CornLathe3, which has this convention outlined well, so I won't repeat it here. The page is partly in French, and partly in English, but you should be able to get the general idea. (By the way, a number of the earliest books on ornamental turning are in French, and there is a great school which teaches OT in southern France. So learning French could be a useful skill for OT, and for impressing your spouse!)

The overarching idea in the rosette numbering scheme is that the number represents a multiple of a base shape. Sometimes, the multiple doesn't really work well to produce a pleasing outcome. Using the F-1 as an example,

  • F-1 is used to produce a heart shape - ♡
  • F-2 would probably not work well as it would be hard to lay the shapes out around the perimeter in a way that would make a pleasing shape, and the amplitude change might be too large.
  • F-4 is where it begins to work again, and you end up with a shape like in the picture to the right.

Final note: Not all rosette manufacturers follow the Holtzapffel scheme in labelling what they make, but they follow a similar scheme. And, there have been rosette shapes made since that time that follow their own naming convention.

My recommendation is to start with one of each of these rosettes,

  1. A series : sine wave, maybe a P-24
  2. P series : plain polygon rosettes, maybe a P-4
and then move on to more complicated ones as you grow your skills and your understanding of where you want to go with the hobby.


Rosette with Phasing Holes
Image courtesy OrnamentalRoseEngine.com

It is now common to see rosettes which have phasing holes pre-drilled in them, removing the need for a crossing wheel. The advantage noted for using the phrasing holes in the rosette is that it takes a lot of the math out of the process as you don't have to calculate how much to move the crossing wheel to achieve the phasing you want.

Additionally, you are provided phasing outcomes which would be difficult to do otherwise (i.e., phasing a 7-lobed rosetted by half a lobe is difficult when 25.7° of rotation is needed.

Lastly, each rosette can be phased relative to another rosette, not just the object.

This opens up a whole new set of artistic options for the ornamental turner, AND will give more abilities to stay out of your spouse's way when you retire !

This is the approach that Jon Magill has purposefully taken with the design of the MDF Rose Engine.

Note: an indexing wheel could also be used to phase the rosettes, and that is how I made my first rose engine lathe. But an indexing wheel this small usually only has 5° increments, and that is cumbersome for rosettes with lobes that are not increments of 5%. And even when the increments are divisible by 5, the actual use of this approach is tedious and mistakes are easy to make ("Did I advance it 4 holes or 5?"). This is why machinists typically use an indexing wheel with stops so that each advance is equal.


Ornamental turners can make their own rosettes; however that requires :

  1. Strong knowledge of how to make rosettes which achieve the desired result. Some recommendations for learning more are :
    1. Charles Marie de la Condamine's papers presented to the Royal Academy of Sciences (in French, by the way)
      1. Paul L. Ferraglio's translations of M. de la Condamine's papers (1975)
    2. Books by Louis-Eloi Bergeron (1796 -- also in French)
      1. Norman Tweedle's translation of Bergeron's book (1950)
      2. Martin Matthews' translation of Bergeron's book (1984)
      3. Jeremy Soulsby's translation of Bergeron's book (2010 - available from the Society of Ornamental Turners)
    3. Society of Ornamental Turners' Bulletins #46 and #52

  2. Software to design the rosette

  3. CNC-driven milling machine to cut the rosette

This video is about the history, design, and production of rosettes. It was given by Jon Magill at the 2018 Ornamental Turners International Symposium. As you will probably note, this is not for the faint of heart. He lost me when he discussed Rectangular Lissajous Curves.

It is cheaper (and a whole lot faster) to buy pre-made rosettes than to learn how to design a rosette, and acquire a CNC milling machine. But, if you are seeking a reason to buy (and learn to use) a CNC milling machine, this is as good a reason as any. And, you can make rosettes that are very special-purpose in nature (Jon Magill designed a rosette which produces shamrocks ☘️ -- very cool!).

Theoretically, they could be 3D printed; though I have never seen nor heard of any made that way, and the people with whom I've spoken who tried it said it doesn't work well. Maybe as that technology continues to mature and become more affordable, it will be the wave of the future.

I purchased acrylic rosettes from Mandala Rose Works (for the rose engine lathe I made from a Delta Midi lathe). Jon Magill uses HDPE for his. Various other plastics, including Corian, are also used. Of course, the ornamental turner could always go old school and buy brass rosettes.


Al Collins is one of the current day masters on the rose engine lathe, and this is a video of his machine, showing rose engine turning with a ridiculously complicated, 3D rosette!

I am pretty sure there are less than 10 people in the world who can make something like this, and only a handful more who know how to use it.


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Disclaimer : eMail comments to me at OTBookOfKnowledge @ Gmail.com. The process of woodturning involves the use of tools, machinery and materials which could cause injury or be a health hazard unless proper precautions are taken, including the wearing of appropriate protective equipment.