Indices : How-To : How to make a font family

FontLab Interpolation Tutorial by John Hudson.

Discussion:

Interpolation
Creating a Bold Version
Making Things Bold
Extending a font to Several Weights
Type Weights New Thread...
Font Weights and Font Weight Scaling
Problems with Ultra Light

Additional Articles:

http://www.lucasfonts.com/ (go to 'Information' and then 'Interpolation Theory')