Porthole Tube Fitting - Tip

For the new ROBOT prototype, I needed to fit short tubes, glued horizontally to the (vertical) main airframe tube. 

These are a like the "portholes" on the old Centuri Skylab model, only larger in diameter. 

To see the Centuri Skylab: CLICK HERE

Wrap some 220 grit sandpaper around your main airframe tube.

Sand the tube end against the sandpaper with a back and forth motion, to the left and right. Sand in a straight line.

Try holding the smaller tube still and moving just the larger tube with the wrapped sandpaper.

On the left, the curve sand is about half way through. More sanding is needed until - 

You get the best fit with no gaps.

The outside layer skin will tend to fold under.

Lift out with a fingertip and lightly sand off with some 400 grit. 

 

Here's a good fit of the Robot head on the neck tube.

This technique rarely comes up, but could come in handy one day.