Why its better to use 8 linear carriages instead of 4 per axis

Why its better to use 8 linear carriages instead of 4 per axis

If you haven't noticed by now, Samurai Machine tools likes to innovate in every area when it comes to technology. The linear rails on the Samurai 120 have generated the most controversy out of all innovations so its worth explaining the physics in this article. 


The most common complaint with the linear rails is 'they are too small and won't be rigid enough', so lets break this statement down. The word 'small' is a relative term, something can only be small if its compared with something else. The same goes for 'rigid enough', a better statement would be rigid compared to 'x' machine.

The Samurai 120 out performs every other machine in its class, here's why:


There are two methods for determining if a component is suitable for an application. It starts with using the manufacturers data sheet to calculate if the component can withstand the forces and for how long. But math's can only get you so far in this universe, so real world testing is required to gain a true understanding of how the components perform.

The Samurai 120 has been developed in a real job shop, where it has been forced to tackle a huge variety of work. This multi year long testing period has given us all the information needed to determine which components are weak spots in the design, here we will focus on the linear rails.


This diagram shows the traditional design used by our competitors:




This diagram shows Samurai's innovation:


Samurai innovation



These diagrams make everything clear, its very apparent that Samurai's design not only improves the axis motion, but also has downstream effects that improve the entire machine, and even the shipping process! 

 Here is a list of factors positively affected by this linear rail design:

  1. Component cost
  2. Frame material cost
  3. Shipping cost
  4. Easier handling / assembly of frame
  5. Lower moment of inertia - Better performance at high speeds, more accurate interpolation
  6. Faster accelerations
  7. Lower Z plate mass
  8. Bow risk removed
  9. Increased travels
  10. Increased rail life
  11. Lower leverage disadvantage on frame


In terms of forces, a HGR rail has two rows of ball bearings to handle higher loads whereas MGN only has 1 row. However there are 4 MGN bearings and only two HGR, so this cancels out making the translational forces on each bearing roughly similar.

The rotational forces cancel slightly differently, because 2 MGN are closer to center from side view, however from the top view the MGN are wider, which benefits the machine in its weakest direction, X.

The positioning of the carriages overall is as wide as possible to create a strong triangle structure which better withstands moment forces.


The key here is you gain all the downstream benefits listed above, making the smaller rail design significantly better when the entire machine is considered.




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