What I do is acquire a .125" wall thickness tube of aluminum the diameter of the tube I am going to sleeve; next I cut a .060" slot through and lengthwise the tube on a mill. Now I cut a piece of .063 sheet aluminum 1.00" longer then the tube and .375" wide, I then slightly taper one edge of the aluminum strip so it can be easily inserted into the slot of my tube expanding it by .003". In most cases I have had to sand the strip just so slightly for the desired fit. Now I seal all the aluminum tooling with Freekote FMS, and apply Freekote 700 NC mold release. I then place the strip in the slot flushing it to the OML (outer mold line) of the tube and layup my fiberglass sleeve/tube. After the cure cycle is complete I remove the strip of aluminum by the 1.00" extra of length I previously spoke of allowing the tube to spring in just a little while self de-molding the tube. Here are a couple of pictures of an untrimmed 5" diameter tube, and with mounting flanges manufactured with this process, I have also manufactured up to 8' long tubes molded this way and in smaller diameters as well. Note: Aluminum tubes spring in when cut through span wise, steel spring outwards making it a non suitable choice for this application.
Bob
