Calculate the set over of the tailstock given a 15″ long workpiece and a .0625″ TPI. Is this a safe setup?
The correct answer and explanation is :
To calculate the set over of the tailstock for taper turning using the tailstock offset method, we use the following formula:
$$
\text{Tailstock Set Over} = \frac{L \cdot D}{2 \cdot 12}
$$
Where:
- $L$ = length of the taper (in inches)
- $D$ = difference in diameter between the large and small ends of the taper (in inches)
- 12 = converts the measurement from inches to a foot scale (when required for some lathes)
- However, if the taper per inch (TPI) is given, we use:
$$
\text{Set Over} = \frac{L \cdot TPI}{2}
$$
Given:
- Length of workpiece $L = 15″$
- Taper per inch (TPI) = 0.0625″
Step-by-Step Calculation
$$
\text{Set Over} = \frac{15 \cdot 0.0625}{2} = \frac{0.9375}{2} = 0.46875″
$$
So, the tailstock must be set over by 0.46875 inches (or 15/32″) from its centerline.
Is this a safe setup?
Probably not. Tailstock offset method is generally suitable for small, short tapers (typically < 12″ length and < 0.25″ offset). In this case, an offset of 0.46875″ is relatively large and could:
- Stress the lathe bed – Since you’re forcing the tailstock out of alignment.
- Deflect the workpiece – Due to side forces during turning, which may cause inaccuracies.
- Compromise the tailstock alignment – After returning it to center, some lathes don’t self-align perfectly.
- Cause wear or damage – On ways and centers, especially during heavy cuts.
Conclusion:
- Tailstock set over required: 0.46875 inches
- Safety: Not recommended – Consider using taper attachment or CNC lathe for precision and safety.