Update Rationale.md

docs/machines/desktop_cnc/Rationale.md

@@ -65,7 +65,7 @@ To do so the X carriages should be a little closer, and also the Z axis more com
 
 The X left bearing should be less than 32mm diameter (eg the 3001 is 28mm) to have stronger bearing lock part. Otherwise it could easily collide with the Z axis middle plate.
 
-Maybe the X backplate can entirily be fit inside a pocket of the shoulders. A risk involved is to machine the X backplate in thickness is order to make a good fit. If not pieces will not fit or fit loose.
+Maybe the X backplate can entirily be fit inside a pocket of the shoulders. A risk involved is to machine the X backplate in thickness is order to make a good fit. If not pieces will not fit or fit loose. The X backplate should also be made a little less than 600mm in lenght for easiness of production.
 
 The Y 8mm front and back plates seems too thin to properly hold the bearing and the axial force coming from the ball screw.May is the case to design special bearing holders OR to investigate the ready made solutions(here is more space to play with).