Hi dknguyen,
I imagined it was for a helicopter model. You might want to try something different and easier, not less elegant.
This is how i'd do it without lots of tools and machinery: Get two different dia aluminum pipes (20 and 25mm) which you cut to the desired length. Use a piece of pinewood shaped as cone to connect both pieces and use two component glue (Epoxy).
If the drive shaft for the tail rotor has to pass through drill a hole leaving enough space for it.
Supposedly you're going to paint the tail boom and nobody will see the piece of wood between the two sections if you do the job accurately what I assume.
If necessary smoothen the joints using putty.
Depending on the thickness of the aluminum pipes I'd consider glueing stabilizing ribs into it (a lot of work, I know) for maximum rigidity.
Please consider the length of the drive shaft. If it is unbalanced (not 100% straight) it will rip off the tail boom in no time. Plan for intermediate (maintenance free, sealed on both sides) ball bearings, using one at each end and one in the middle of the boom.
The bearings don't have to be pressed into the aluminum pipe. Rather press them onto the shaft and have them fit snug into the pipes.
When finished, don't forget to post a photo of your helicopter.
Regards
Hans