How Do I Calculate Helicoil Pull Out Strength?

Helicoil inserts provide a saving grace for mechanics and engineers who accidentally destroy a machined screw cavity in metal. When the cavity threads get stripped, no new screw or bolt can be inserted and tightened until the cavity is repaired. Inserts save the day. A mechanic can input the new Helicoil insert, twist into place and insert a new screw or bolt. The working feature of the Helicoil involves its strength to stay in place when the new bolt is tightened. This strength depends on the metal into which it is inserted, the type of new bolt put in the Helicoil, and how much torque is applied to tighten the bolt.

Instructions

1

Determine the type and size of Helicoil insert that has been used or will be used. Identify the type of metal into which the insert will go carbon metals tend to be stronger than soft metals such as aluminum. Reference the bolt torque that will be applied when tightening by looking at the corresponding repair manual for the application.

2

Drill a hole into a test piece of metal matching the same metal as your application on which the Helicoil will eventually be used. Use a power drill and metal drilling bits to make the cavity.

3

Obtain a Helicoil insert kit with a tang tool included at a hardware store. Purchase the kit that matches the cavity you need to test they come in different sizes. Insert the matching Helicoil insert per the products instructions in the kit. Break off the Helicoil tang with the tang tool once the Helicoil is fully inserted in the test metal.

4

Insert a new bolt that fits inside the Helicoil insert now in the test metal. Tighten the bolt until it is snug in the Helicoil insert, using a socket wrench or crescent wrench. Change out the socket wrench or crescent wrench with a torque wrench for the next step.

5

Set the torque wrench dial for half the pressure strength to which the bolt should be tightened in the given metal. For example, if the value should be a tightening pressure of 50 lbs per square inch, start with 25 pounds per square-inch first. Reference your repair manual for the specific torque settings necessary. Change the torque setting when you have tightened the bolt to 50 percent of the torque value and you hear a click from the torque wrench tool. Use a calculator to figure out the percentage value.

6

Attempt 75 percent pressure next performing the same action in step 4. Attempt a 100 percent torque value in the subsequent test. Test the Helicoil insert at 125 percent and then at 150 percent, going further in increments until the Helicoil insert finally slips in its hole. Use the last successful tight value as the strength of the Helicoil insert before it fails.