Joint Overlap for Tube Inserts

[MiME]

I will be installing an aluminum threaded tube insert in a 1.125 ID tube. The insert will be bonded to the inner wall of the tube with epoxy. Is there a minimum recommended length for the insert to extend into the tube for proper adhesion?

I will also be installing an aluminum connector over the outer wall of the same size tubing and have the same question about the minimum overlap between the carbon fiber tube and outer aluminum connector for a good bond.

[John Kimball]

On 5/12/2023 at 3:44 PM, MiME said:

I will be installing an aluminum threaded tube insert in a 1.125 ID tube. The insert will be bonded to the inner wall of the tube with epoxy. Is there a minimum recommended length for the insert to extend into the tube for proper adhesion?

I will also be installing an aluminum connector over the outer wall of the same size tubing and have the same question about the minimum overlap between the carbon fiber tube and outer aluminum connector for a good bond.

Welcome to the forum.

The basic rule of thumb for inserts is about 1x to 1.5x the diameter of the tube. So a 1.125" ID tube would be at least 1.125" and 1.7". It also depends on the use of the tube. If it's just a static load and you just want it stay in place, a shorter insert will be fine. But if you will see some shear, torque, or flex loading, you will want a longer insert.

And as always, prep of both bonding surfaces is key to good adhesion. lightly abrade both surfaces (remove any shine so both surfaces are dull) and thoroughly clean with isopropyl alcohol.