Some customers ask about the difference between inner gantry rail and outer rail. Inner rail is harder to clean/reach. When the rail is not straight, the mirror will be at a larger angle than using outer rail.
As shown above, if the two rails have a height difference, the inner rail structure will create a large angle error because the two rails are close together.
One good thing about the rod type rail gantry is that when it becomes loose overtime, we can use the adjustment screw to make it tight again. HIWIN type linear rail is good for heavy laser head, but when it becomes loose, we will have to replace the entire cartridge. Also, the cartridge type has lubricant inside. Avoid mixing different types of lubricants; there may be unwanted chemical reactions.