Rosette Compass

recently, I built what I'll call a rosette-compass.

This is a tool which basically translates a base pattern into a template. Another machine (a rose engine) can then translate this back into the original pattern, with slight "balloonings" or expansions. The rose engine uses these expanded cams rather than the original pattern to avoid increased load through its rotation. This lets the machine run more smoothly and make a cleaner cut.

Confusing? Well that may be understandable. This project was in part a thought/design experiment to see if I could reverse the function of a rose engine, and part making a tool to make tools :)

Well, let's get into the construction and I'll see if I can elucidate further as we go

Step 1: Materials

This project is fairly inexpensive, costing around ten dollars.

Materials:

1/4 x 16 inch rod

1/2 x 1/8 x 8" flat stock

3/16" threaded rod

10- 24 screws

3d printed component set

tools:

drill

1/4" and 1/16" bit

small file

hacksaw

Step 2: Basic Design

This was one of those projects that just fell in my lap once I started the design. It needs one guide attached to a fixed pivot, a tracer which is free to slide along that guide, and a pencil mount that is coupled to the motion of the tracer.

I started with a few quick sketches of what it would end up looking like... line drawings with the basic components. There are two fixed guides from the pivot, the tracer, and a flat bar to mate the pencil assembly.

I originally thought to use brass round for all of the vertical components and drill/file the important features but decided that it would be easier and cheaper to 3d print those members, So at least for my first test, it's on to CAD.

Step 3: Just a Wee Bit O' CAD

The primary features of the 3d printed pieces are the holes that the two guide rods and the flat bar slide through. I allowed for various arrangements of set screws with a small hole intersecting each of the larger shaft holes. These are printed parallel to the layers and need to be drilled clean.

The pencil fixture is sized to have an interference fit with a Zebra mechanical pencil.

A note on the 3d printing. I like to print mechanical parts with 1.5mm skin thickness to make them stronger and to accommodate any slight modifications they might need.

Step 4: Putting It All Together

To start, cut all of the metal components to eight inches long and sand along their length with 320 grit paper to help them slide through the plastic pieces easily. slightly round over the ends of the rods. The threaded rods will be the tracers and compass point. Cut the threaded rod in 3', 1.5", and 1-inch sections. Chuck the sections in a drill and file the ends to a point, then epoxy the sections into their pieces. Short into the pivot section, 1.5" into the tracer/pencil, and 3" into the reproducing tracer.

Clean the printed parts by breaking the edges with a file, and by drilling ou the support from the screw holes. The sliding holes will also need to be reamed out with a quarter inch drill bit.

Also, file the ends of your screws round as the sharp lip they come with will easily mar the aluminum guide rods.

assemble per the picture and tighten the screws to light pressure. It's a balance between holding the rods effectively and ruining the plastic part.

Step 5: Using the Compass

This rosette compass preserves the amplitude changes of the pattern while adding to its radius.

To use, set the tracer so that the distance between it and the guide is the same as the change in radius as the base pattern. Then set the pivot so that the max/min amplitudes match up. This will produce the smallest rosette possible. Push the pencil through the end and

At this point, set the pivot at the center of the form and carefully move the tracer along the edge of the pattern.

And there you go, You're now making your own rosettes! I envisioned this project as a way to create forms for my future rose engine, but I'd love to see what ya'll come up with.

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