Best Gantry Linear Rail Configuration ?

[Dec0y]

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[Dec0y]

Interesting..
280+ views and no opinions on what would be the better gantry rail configuration.
Maybe I made the question to hard or confusing..

[asuratman]

I use no. 4 design on all my cnc router based on force work vertically or horizontally ...

[pippin88]

There is no "best" in machine design.

Ever decision is a compromise.

4/5/6 have advantage in resisting torsion. Downsides include more difficult to machine and align. And you have to make sure the carriage mounted to bearings is appropriately rigid.

[Andreiir]

Interesting point with torsion , but why 3 is not better tan 3 or 4 , why in industrial machines there is aproximatley all time used 3 ? How can be more resistant to torsion 456 than 3 or 2 or 1 ? Because there are same dinamic range , and same boxes .

[Dec0y]

Thanks for your feedback

[peteeng]

1) Is good because the "crank centre ie the line of action of the resulting car reaction moment" is through the shear centre of the section so will resist torsion well. Its bad because its harder to machine opposing surfaces and the rails are mounted on "air" so they can vibrate
2) Same reasons as 1) but now they are mounted on long thin surfaces so will vibrate worse. Plus the forward car makes the stack height of the Z more then 1)
3) common arrangement easy to machine rail lands. Poor because the crank centre is not through the shear centre so resisting torsion and bending is not efficient
4) & 5) not easy to machine lands, no advantage in Z stack,
6) rails on edges is better then in middles of flats, crank center is near shear centre. Move bottom rail to bottom of section, near fwd edge and it will be better again as the rails are then furthest apart. Peter