So, I'm planning on building a set of wheels calculating spoke length using Spocalc, the Excel program by Damon Rinard (http://www.sheldonbrown.com/rinard/spocalc.htm). I'm going to calculate ERD manually, but Spocalc's directions for ERD has raised some questions.
In calculating ERD, Spocalc states: "Effective Rim Diameter (ERD) is the diameter on which you want the ends of the spokes to lie. Most people prefer it near the end of the spoke nipple." Really? The end of the spoke nipple as they show in their diagram, as opposed to the bottom of the driver slot? What if it needs to be tensioned a little more, wouldn't that push the spoke past the end of the nipple?
So my questions:
1. Which is correct, bottom of slot or end of spoke nipple?
2. If end of nipple, I can understand why people recommend rounding down in spoke size, but what if your calculation is right on? Along that thinking, would it be wise to round up if calculating from bottom of slot?
3. Any obvious problems if I use bottom of slot using Spocalc?
4. What if I measure actual inside rim diameter? Is there a recommended amount to add to rim diameter to compensate for length of spoke that pushes through the rim to achieve necessary depth in the spoke nipple? Or is that based on characteristics of the specific spoke nipple, thickness of rim material, etc?
On one hand, I want to stay consistent w/ Spocalc's methodolgies to achieve the "correct" spoke size, on the other hand, I'm not quite convinced I agree w/ what it considers "correct" (which led to question #3).
-Thanks for your help