Tubing ordering problem

[mhorowit]

Folks - I ran into an ordering problem and can't see what I did wrong. Was hoping you could spot what happened so I can avoid it in the future.

I'm practicing repair by inner sleeve. I had some 3/4 OD tube from a previous order and planned on ordering the next smaller size to use as inner sleeve material.

Looking at the Dillsburg catalog, we see 3/4 tubing has a published wall thickness of .028 (I measured it at .03, but I'm not using a precision instrument). I figure the ID would therefore be .694 (.750-.028-.028= .694). The next smaller size tube (11/16=.680) should have slipped into the 3/4 tube by .014. It didn't, so I began measuring. The actual OD of the 11/16 tubing was .690 (not .680) and the actual ID of the 3/4 tubing was .670, screwing up the fit by .020.

Question - did I overlook something? Is this problem univeral? Is this what comes from the factory and we need to be able to adjust to?

Question - Ideally this would get turned in a lathe (don't have) I was able to clamp the tube internally and turn it in my drill press, but turning was tedious. Does anyhone have a suggestion for removing the metal more rapidly than with a file? - MikeH

[Guest]

Re: Tubing ordering problem

buy 5/8" tube

[Bob Waldron]

Re: Tubing ordering problem

Mike,

Tubing comes in ALL sorts of thicknesses. Look in Aircraft Spruce and see the dozens of options. I suspect that your 3/4 inch tube is thicker than .028.

Also, 11/16 O.D. tube SHOULD measure .6875 which is pretty close to .690.

I would avoid turning down a tube with a lathe (or drill) because you are giving up strength and changing the metal properties.