bent guide rail...

[mino]

I bought a (second!) TS 55 about two months ago and had some oddball trouble doing some very easy cuts. i found that the 55" rail was bowed out at the center by about 1/16".  !
...

The rail you got was clearly faulty. Such a deviation is NOT OK nor normal. Even for a used rail.

Hard to say if it was damaged on transport or slipped through a QA check.

I am pretty sure such a rail would not pass a QA - unless something was missed by someone.
The Festool FS/2 series seem to have a pretty high accuracy standard. All rails I saw were within 0.2 mm (0.01") across the length when stress-free checked against a DIN Class 0 straight edge (deviation

 

[newellj]

The rail you got was clearly faulty. Such a deviation is NOT OK nor normal. Even for a used rail.

Hard to say if it was damaged on transport or slipped through a QA check.

I am pretty sure such a rail would not pass a QA - unless something was missed by someone.
The Festool FS/2 series seem to have a pretty high accuracy standard. All rails I saw were within 0.2 mm (0.01") across the length when stress-free checked against a DIN Class 0 straight edge (deviation

 

[mino]

I was wondering about which was the reference edge.  Thanks for your post.  On the MFT/3 rail I mentioned, the reference side is nearly perfect; it's the other (outside) edge that's somewhat curved.

I know nothing about extruding aluminum but it seems a little odd that one side would be laser-straight and the other bowed?

The big problem with extrusions is thermal stress during making - it is hard to maintain consistent thickness across the piece for this reason. You can however force/make a part which will have one surface straight with (most) imperfections "moved" to the other surfaces via post-extrusion cold pressing. You cannot really improve the thickness variance as easily without a milling step - which can negatively affect temperature stability with thin material in turn so is better to avoid it.

Just to confirm, by "inner" I meant the surface pointing to the center of the whole rail - i.e. the one closest to the splinter guard/cut line.

 

[newellj]

Just to confirm, by "inner" I meant the surface pointing to the center of the whole rail - i.e. the one closest to the splinter guard/cut line.

Interesting and thanks, yes, that's how I understood your post - and that is the surface that was straight on the rail in question.