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Tube Adapter & Rod End Installation.

Added on 2008-02-21

A few precautions need to taken when correctly installing tube adapters/threaded inserts into tubing.

Prior to fitting any tube adapter, the end of the tube needs to be prepared. The tube also needs to be checked to ensure the adapter is a snug fit inside the tube. If not the next size up adapter needs to be used and the 'spigot' section machined to provide a snug fit.

Highslide JSInstallation of 4130 tube adapters is simple if a few precautions are taken.The next step is to machine the weld chamfer to the end of the tube. I use a 30 degree angle and machine until only around 20% of the original wall thickness remains square. This allows full weld penetration, and a smilar prep. is usually machined into the tube adapter when manufactured.

Following chamfering it is necessary to drill for plug welding (also referred to as rosette welding). I cannot stress how important this proceedure is. The holes are drilled to correspond with the location of the end of the spigot on the tube adapter. For 0.095" wall thickness tube, I use a 15/64" drill bit (6mm). This allows easy access to the bottom of the hole with the TIG torch. Heavier wall tube obviously needs a bigger hole. I drill the hole using a vertical mill, passing right throught the tube to create 2 holes as a minimum. Highly stressed items, may reqire 4 holes.

The plug welding serves two purposes. Firstly it traps the spigot section of the adapter to prevent it 'working' inside the tube, eventually expanding the tube and causing the 'V' butt weld to crack and fail. I have repaired many 4 link arms, where plug welding was not used, and the tube adapters have pulled right out.

Secondly the plug welds preheat the usually heavier wall sections of the tube adapter, prior to the final 'V' butt weld being done. When manufacturing a 4 link arm with a tube adapter at each end, I plug weld both ends first, then return to the first end plug welded to do the 'V' butt welds. The metal flows nicely immediately without any 'cold start' issues.

Highslide JSThreads must be cleaned out after welding, if purging has not taken place. Plug welds are clearly visible.Once cool (and not artificially cooled), the final important step it is clean out the threads with a slightly 'dull' tap. Unless the item has been purged, welding will produce an oxidised surface on the inside of the adapter, usually in the threads, due to lack of inert gas during the welding process. Failure to clean the threads usually ends in tears, with expensive rod ends and 4 link arms becoming a single unit when the threads lock solid from the contamination. The only way I have managed to save customers rod ends when this has happened, is to machine the adapters almost completely away in the lathe, then pick out the remaining thread pieces of the adapter with a steel scribe. The rod end thread is usually damaged, but can most times be salvaged.

Finally any rod end subsequently installed in the finished tube adapter assembly should be liberally coated in zinc based thread anti seize. If this proceedure is not undertaken, similar thread lock up can occur in the months/years ahead due to corrosion. Usually when installed, a portion of the rod end thread is exposed inside the link arm. Over time this section of the thread starts to corrode due to condensation inside the arm. Very rarely can the rod ends be removed, or in some cases even adjusted if this corrosion occurs.

Rod Andrews
Andrews Race Cars