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Why Titanium for Thermal Expansion Cancelling?

Printer Model
Voron 2.4r2
Extruder Type
Cooling Type
I wondered why titanium backers became the thing to cancel out deformation due to the thermal expansion difference between aluminum and steel. So I looked into the Thermal Expansion coefficients of aluminum, steel and titanium. And now I suspect the answer is, "Because it sounds cool and nobody really thought it through."

Steels typical of linear rails have a TEC of right around 9.6. Aluminum and alloys typical of extrusions are right around 13.0. And Titanium is right around 4.8. So putting a titanium backer to combat thermal deformation leaves you with 73% less expansion on the rail side as compared to the extrusion, and only 38% less on the backer side. It should deform roughly half as much, which would be great if there weren't a better solution.

But why the heck is everyone doing this, instead of simply putting another MGN9 rail on the opposite side of the extrusion? It's slightly heavier, but only on the Z-axis. And with 4 motors and not a lot of reason to care about this much weight on the Z-axis, this seems like the obvious solution.

Having ranted, I am ready to hear the secret reason for this and be corrected... Cheers.
the answer is probably more "because it's gucci and looks nice" - my understanding is there's no functional reason for using a fancy titanium backer over a spare steel mgn9 rail.
Weight. Titanium is lighter, which may be important for the X axis if you use a backer there. For Y it theoretically does not matter as much, flying gantry may sag less when motors are powered off. On Trident Y, weight does not matter.
Titanium is easier to anodize into fancy colors and effects, too.
Use what you have :) if you have steel backers or old rails, by all means.
Its because most rails these days are Stainless Steel, the extrusions are aluminum and we need to add a 3rd metal to counteract heat expansion. Titanium is the lightest one of them all with the right properties to function as a backer. the GitHub is full of great tests made by Whooping.