Max, I noticed that some of my capillary tubing is not arrow-straight - has a slight bow in it (like it was unrolled from being spooled, but not totally straightened out. It is probably ok for sleeves less than 0.5-1.0", but anything longer will have a wobble.
A new fly in the ointment!
Yes, my 36" long piece of 1.5mm OD, 1.0mm ID that I got has a "bow" of about 3/16" if you place it on a flat surface and measure how much it deflects in the middle.
How much runout is that in a piece 1/2" long...
Well, if it's linear, and the center of the long piece is 3/16" out, that's 3/16" in 18". So for 1/2", that would be 3/16 / 36 = .005"
That's more than I'd like.
In my example, my tubing was only about 1/4", so it would have a maximum runout of .0025", and I would be happy with that. And given that about half of it is pressed on a straight motor shaft, that would cut the error in half again, to about .00125".
Comparing it to a piece of Albion brass tubing that is 12" long, I can see that the Albion is REALLY straight, observing it next to a steel straight edge.
So the choice is yours! Perfectly straight? Or somewhat stronger? It doubt it makes any difference for the level of precision and forces we are talking about in N Scale.
