Helical Spring Mandrel Design Calculator
Hand made springs/coils are typically wound around a mandrel, that is inserted into a chuck on a milling machine, or lathe. When the spring is released from the jig it will spring back and will have a greater diameter than the diameter of the mandrel. It is therefore useful to know what mandrel diameter is needed, to render a given spring diameter.
This calculator takes as input the diameter of the wire, the desired spring diameter, and the wire material types, and outputs the diameter of the mandrel.
Units can be inches or mm, just be consitent.
| Coil Diameter | |
|---|---|
| Wire Diameter | |
| Material | |
| Mandrel Diameter: | |
This calculator is based on the following article:
"Helical Springs" by Kozo Hiraoka, in Home Shop Machinist, May/June and July/August issues, 1987
Equations:
Dm= kD - dwhere:
Dm is the diameter of the mandrel,
k is the diameter coefficient,
D is the final diameter of the spring, measured from the center of the wire (not the outer or the inner spring diameter).
d is the diameter of the wire.
Wire Diameter Coefficients
Music Wire and Stainless Steel:
k = -0.01245x + 0.98425
Phosphor Bronze Wire:
k = -0.011x + 0.987
where:
k is the diameter coefficient,
x is the spring index: D/d.
