Gravity and Jerk, which is the greater force in 3D printing?

I'm modifying a CoreXY kit and will use a single linear rail as X axis. I hope to print rather fast as the build volume is large.
Should the rail be on it's edge "vertical" to give more stiffness against gravity, or horizontal to take the shock during corner jerk?
The acceleration is probably not so much, but the hard stop before turning worries me more. Gravity has the benefit of being static.

Thus by gut instinct I'd put the rail horizontally / flat guesstimating gravity to be the lesser evil.
On the edge the rail has the benefit of being more compact in the Y direction, which could gain a couple of cm print volume.

Anyone with more insight care to share?

(didn't do in detail on the print head, lets consider it mostly balanced, I target that. Direct / Bowden / rail size doesn't change the forces relation AFAIK.)

Edited 3 time(s). Last edit at 02/15/2018 05:38AM by orea.

You are creating a compromise between bowing and jerk? Why?

Why not just design it to have the best of both worlds? There are many compromises in 3D printing, but this doesn't have to be one of them.

Mainly because the heavier the moving gantry is, the bulkier everything else has to be, and living in a small flat with limited tools I prefer targeting weight reduction. I already have a heavy direct drive machine in the shape of an evolving FT5, this new one's focus is to be light and fast.

Even when building a tank it is good to know where the energy goes in order to optimise.

Edited 6 time(s). Last edit at 02/15/2018 11:49AM by orea.

I imagine that jerk will be more about rigidity and how you mount your components, rather then its orientation. You can have no (or limited) bowing and still have a lightweight gantry. Don't forget coreXY is more forgiving with weight as it is using 2 motors for most moves and its belt arrangement means that rapid jerk is absorbed by the belts, rather then your structural components.

Printing forces are more concerning than gravity, because the constant force of gravity won't produce visible artifacts whereas jerk produces ringing and other similar patterns in the print.

I think the most important thing you can do is try to line up the center of gravity of the extruder assembly with the centerline of the rail. If the extruder sits too low or too high on the rail any movement will also impart a twisting force to the rail which will be amplified by the distance between the nozzle and the rail.

Thanks for your comments Origamib and 691175002 , I sort of suspected it would be that, especially the gravity being static.
I'll try as slim as 9mm (quite lighter than 12mm) over 450mm span and see what it gives. Hoping to reduce print head weight as much as possible.
Will post results if anything noticeable.