Pipe/Tubing Fit

For “1 1/4” aluminum Schedule 40 PIPE, it supposedly has a 1.660 OD and a .140 wall. This would make for a 1.38 ID. Now, I can get TUBING spec’d with a 1.375 OD. Will the tubing fit precisely in the pipe? Not like a press fit but able to slide well but not wobble. I have no idea what the tolerances are on these materials and I don’t have time to go to the metal store to actually measure/try it. Thanks.

Dave,

I say go for it. We bought a bunch of tubing last year, and most of it was within +/- .005" of the specified dimension. Also, if the fit is too tight, you can always take some scotch-brite pad to take a thousanth or two off the od of the aluminum pipe.

It’s worth a shot.

Andy B.

Thanks for the quick reply. You say the tubing was in good tolerance, but what about pipe. Is it made to the same tolerances? An online metal store says they guarantee OD and wall dimensions but not ID. However it is impossibe to guarantee two without guaranteeing the other. My tubing OD can’t be more than about .008 under the size of the pipe ID and if it is oversize by a lot, that is okay if I can turn it down. The tubing is going to be a bit over 2 feet long. I’ve never tuned anything that long before. But I would definitely try scotch brite and/or sandpaper before I put it in the lathe.

Also, on turning long stuff, I will be needing to do a slight bit of work on the pipe. I need to turn about 1 inch of one end from the 1.660 to 1.615 and cut like a 1/8 or 3/16 slot down the side. What would be the best way to do each of these operations? Again, the pipe will be a little over 2 feet long.

Thanks.

My materials prof loves talking about this. Basically, you can get 2 of the 3, but not all three. OD and thickness means you get a minimum wall thickness all the way around, but the inside can end up kind of wavy. I definitely wouldn’t expect it to hold a .005 tolerance without some machining. But then, I’m still an engineering student, so I could be wrong.

As for turning down one end, most lathes have a chuck that will allow the material to be passed through the entire machine. If the lathe you hope to use has the capability to handle the diameter you are using, this is probably the easiest method. Be very careful with the extra tubing that is spinning outside the lathe…it can be easy to forget but will remind you that it’s there very quickly! For the slot, I would use a V-Block set-up in a standard vise to hold the pipe on its sides allowing you to run an endmill through one side of the tube.

Sanddrag,
It depends on what you plan on using it for. Outside, in the elements, those tolerances will quickly close down and you won’t be able to pull stuff apart. It also will depend on what you use to cut the tubing to length. A hacksaw or tubing cutter will distort the cut end where a cutoff saw might not. A slight bend in the tubing will also close down the tolerance and since this pipe is not handled with care in hardware stores, expect a few dings here and there.
The ARRL Radio Amateurs Handbook has a table on aluminum tubing standard sizes for 6061-T6 tubing and good discussion on telescoping tubing sections for antennas. The current book should be on your library shelf. The table is in the chapter on antenna projects and will also show methods of joining sections and calculations for sag, overlap and windload if you need that info.

Turning this could be a little tricky. My lathe at home will not allow a 1-1/4" diameter piece thru the head stock so I wouls have to turn it on centers. You will have to make plugs for the end of the pipe to provide support for the dead/live centers.