As the notes say, you'll need to choose the TRIAC based on your load. Load ratings will be in the datasheet. Once you have the TRIAC, then R13 can be adjusted.
Aaron, thanks for the note. I have a single phase 120V 15A saw that currently runs around 3400 rpm. I would like to reduce the rpm to around 1300. I thought the above mentioned circuit, configured for the load, might allow for this.