The large hole diameter on the South Bend 9" tailstock is 5/32" as measured by a punch of that size. The small hole was somewhere between 1/8" and 9/16". From "Machinery's Handbook" the standard taper pin sizes run from 1/16" to 1.52". The large diameter is the basis for pin size. The taper on all pins is 0.250" per foot (or 1.194°). The table below provides an overview of the standard taper pin sizes.
The calculator returns the diameter of the small end of the pin given the pin diameter (or pin number) and the length of the desired pin. The diameter at the small end is computed by multiplying the nominal length of the pin by the factor 0.02083 and subtracting the result from the basic pin diameter.
| Pin Number | Pin Size (in) | End Crown Radius (Min-Max) (in) | Range of Lengths (in) | Standard Reamer (in) |
|---|---|---|---|---|
| 7/0 | 0.0625 | 0.052 - 0.072 | 1/4 - 1 | … |
| 6/0 | 0.0780 | 0.068 - 0.088 | 1/4 - 1/2 | … |
| 5/0 | 0.0940 | 0.084 - 0.104 | 1 1/4 - 1 1/2 | 1/4 - 1 |
| 4/0 | 0.1090 | 0.099 - 0.119 | 1 1/4 - 2 | 1/4 - 1 |
| 3/0 | 0.1250 | 0.115 - 0.135 | 1/4 - 1 | 1/4 - 1 |
| 2/0 | 0.0625 | 0.052 - 0.072 | 1 1/2 - 2 | 1/2 - 1 1/4 |
| 0 | 0.1560 | 0.146 - 0.166 | 1 1/2 - 3 | 1/2 - 1 1/4 |
| 1 | 0.1720 | 0.162 - 0.182 | 1 1/2 - 3 | 3/4 - 1 1/4 |
| 2 | 0.1930 | 0.183 - 0.203 | 1 3/4 - 3 | 3/4 - 1 1/2 |
| 3 | 0.2190 | 0.209 - 0.229 | 2 - 4 | 3/4 - 1 3/4 |
| 4 | 0.2500 | 0.240 - 0.260 | 2 1/4 - 4 | 3/4 - 2 |
| 5 | 0.2890 | 0.279 - 0.299 | 2 3/4 - 6 | 1 - 2 1/2 |
| 6 | 0.3410 | 0.331 - 0.351 | 3 1/4 - 6 | 1 1/4 - 3 |
| 7 | 0.4090 | 0.399 - 0.419 | 4 - 8 | 1 1/4 - 3 1/4 |
| 8 | 0.4920 | 0.482 - 0.502 | 4 3/4 - 8 | 1 1/4 - 4 1/2 |
| 9 | 0.5910 | 0.581 - 0.601 | 5 1/2 - 8 | 1 1/4 - 5 1/4 |
| 10 | 0.7060 | 0.696 - 0.716 | 6 1/4 - 8 | 1 1/2 - 6 |
| 11 | 0.8600 | 0.850 - 0.870 | 2 - 8 | … |
| 12 | 1.0320 | 1.022 - 1.042 | 2 - 9 | … |
| 13 | 1.2410 | 1.231 - 1.251 | 3 - 11 | … |
| 14 | 1.5210 | 1.511 - 1.531 | 3 - 13 | … |
A second concern for taper pins is drilling and reaming the hole. For short pins the drill size is the small diameter of the pin. Drilling is followed by reaming with the appropriate tapered reamer. If you have spiral fluted tapered reamers, you do not need more than the single hole drilled with this small drill even for longer pins. However, if you are using straight fluted tapered reamers, then for longer pins it is necessary to step drill the hole first. Determining which drills to use and how deep to drill can be looked up in a chart on page 1755 in "Machinery's Handbook" 29th ed. Alternatively the calculator below can be used. Simply enter the required parameters and hit the calculate button. The output will be a table with the drills and depths needed prior to using your tapered reamer. This calculator, like "Machinery's Handbook", only returns fractional size drills.
The following calculator only works for pin numbers 7/0 - 10. These are the only sizes covered in the graph in "Machinery's Handbook".