Ty, it works!
But I have a second problem. This fix works only with tile mode : bug with the expand function, adaptive mode and z rotation.
1) I wanted to use the expand to cut properly my tiles before the shell modifier, but I can't use it (see my image for better explanation). For information, ghost tiles already appaer with 0.01%.
Update 24/04 : With an Optimize modifier (not ProOptimizer), the railclone object is cleaned before the shell and it works without mesh glitch. Good to know for simple segment,
2) I don't need adaptivity for the x axis. So no problem with the ghost tiles in adaptive mode, I'll go with tile mode.
However, I want to adjust my railclone in the y axis manually. But the extract of the y/xsplinelength doesn't work with clipping spline (arithmetic).
3) I use "z rotation" to turn my tiles by 90 degrees, and it works great if I stay perpendicular. So it's ok, I don't need oblique tiles. With 45 degrees, the bug shows that Railclone internally calculte its x/y length before cut it with the spline. Can we extract these values ?
I created a manual length variable as a workaround to adjust the gap between the tiles "automatically" (see my file). It isn't practical because I often modify my spline.
On a side note, can the rounding function in arithmetic operator choose average integer automatically ? 15,543 -> 16 // 15,436 -> 15. I think my nodes are uselessly too complicated.
Thank you for the speed of your last reply.