I'm trying to find tutorials or instructions on how to measure the angles to cut on the 1/4" round moldings for bay windows.

I know that 45 one way and 45 on another, another way makes 90 degrees corners.

But on a bay window?

Anyone can point me at the right direction. This is hard to explain but I'm stuck.

 

Actually, you need to measure the angles involved and go from there. If the angle is 45 degrees, then cut the two pieces 22.5 degrees and so forth.

 

Standard Bay windows are either 30 degrees or 45. Fold a square piece of paper in half, corner to corner - this yields a 45 degree triangle and will tell you which you have. Your option is to either cut each piece of moulding at one half the angle ( 15 for a 30 degree window or 22 1/2 for a 45) and match them together, or to leave one piece full to the end and cope the other to it.

 

The 45 or 30 angle is the inside wall. Think of the deck of the window
_________
as a trapezoid /_________ \ - longest leg is the one even with wall. Call that A. Opposite/parallel that is the outermost window (on many bays this does not open) - call that C. The two sides are B and D respectively.
a bay is labeled (45 or 30) measuring the angle between A and B, or between A and D.
The angle you are trying to figure is probably the one between B and C or between D and C (they are the same. ) On a 45 degree bay this angle is 135, On a 30 degree bay this angle is 150. Again, either use that angle for the ends of your piece for side C and cope the others (B and D) , or halve the angles and butt them.
Hope that helps.