Select the Modeling section of Maya, choose from upper left, status line.
Use this chart to size your finger for the ring.
Add the chart to an image plane to match the size
Select Create->Free Image Plane
Use the Attribute Editor
Select Image Name, add the ring chart
Bring down the Color Gain a bit darker
Use the Channel Box
Hit the arrow up button to see the transformation options.
Choose the image plane, Rotate X -90 degrees
(Each grid unit = 1 CM)
Choose the image plane, Scale X,Y,Z 1.599
Input Type, Relative Transformations
Draw a couple straight curves to use as guides.
Switch the selection button to Relative transformation in the Input Type box, on the status line, way over on the top right side of the screen. (Sometimes this is hidden if your screen is small, click on the show/hide buttons to expand hidden sections.) When you enter a value in the box for a transformation, such as scale, rotate, or move, the object or component will transform will move relative to its position.
Create->Curve Tools->CV Curve Tool->
Select Curve degree: 1 Linear
Click the first point in the top view at the edge of your ring
Input the second point in the Input Type box X: check your ring size, mine is a size 9 so I will input 1.9 cm (19mm).
Use the curve as a guide.
In addition, make a .1 cm guide, Shapeways does not let you print metal objects thinner than .1 cm. The height of the ring will need to be 2 cm.
Select Create->NURBS Primitives->Circle->
Normal axis: Y
Radius input half your ring size (my ring size 9 - 19 mm, or 1.9 cm / 2 = .95 cm)
Number of sections 80
If you need to know the circumference use
Pi * diameter (for my size 9: 3.14159 * 1.9 cm = 5.969021
Use any tools to model a ring.
Inspect your model for holes or flipped faces.
Use Mesh->Fill Hole to fill holes
Use Edit Mesh->Merge to clean up your mesh, careful the tolerance does not delete the wrong points.
Check the outer diameter of you ring so you can compare it to the Shapeways scale.
Select your ring.
Use Create->Measure Tools->Distance Tool
Use v point snap and shift to constrain to measure from the outer edge of the ring
Exporting your model
Select your model.
Choose File->Export Selection...
File type: DAE_FBX export
(Do not use OBJ or STL_DCE these formats do not always retain the scale information.)
Uploading to Shapeways
Go to www.shapeways.com and select upload
Make an account, make sure you apply for the 15% student discount.
Select this menu and upload your DAE file, choose your material.
Shapeways offers a preview where you should inspect your model again.
Check the scale and look for missing/flipped faces.
You are ready to print!