...
Overview
The Rocket Team uses bolts as its standard method of fastening the motor. This page will provide information on bolt torque, bolt shear stress, and bolt thread engagement calculations.
...
Motor Case Bolt Torque Specifications
Grade 8 Steel Fasteners
In order for a fastener to perform its job, it must be appropriately pre-loaded. All fasteners shall have an installation torque called out on their assembly document. To determine the appropriate torque for a fastener, a specific value may be determined or a value my be used from the reference tables below.
Grade 8 Steel Fasteners
All calculations are for non-lubricated, non-galvanized fasteners.
| Size | Major Diameter [in] | Minimum | Nominal | Do Not Exceed | Notes |
|---|---|---|---|---|---|
| #2-56 | .086 | 2.1 | 2.5 in-lbs | 4 in-lbs | |
| #4-40 | .112 | 4.4 | 5.2 in-lbs | 8.7 in-lbs | |
| #6-32 | .138 | 8.2 | 9.6 in-lbs | 16.3 in-lbs | |
| #8-32 | .164 | 16.8 | 19.8 in-lbs | 33.7 in-lbs | |
| #10-24 | .190 | 19.4 | 22.8 in-lbs | 41 in-lbs | |
| 1/4-20 | .25 | 63.9 | 75.2 in-lbs | 143 in-lbs | |
| 5/16-18 | .313 | 112 | 132 in-lbs | 295 in-lbs | |
| 3/8-16 | .375 | 201 | 236 in-lbs | 528 in-lbs |
Motor Case Bolt Torque Specifications
This will provide an example on how to calculate the optimal bolt torque, using calculations for the bolt torque specification of the Hermes 3 motor case.
While the upper section table provides more general information, this section will provide specifics to get a more optimal value of bolt torquemore specific calculations.
Max Tensile Load
First we must calculate the maximum tensile load of the bolts being used. This is the measurement of the maximum amount of tension force the bolt can withstand before it fractures. In the case of Hermes 3, we are using 5/16-18 by 5/8" Grade 8 Steel Bolts.
...
30.5 ft/lbs is now our final value for the optimal torque. This is necessary to guarantee that the bolt is not too loose (which would cause our seal to not be as strong), or too tight (which would deform our bolts and potentially damage the material being clamped).
...