[jetski]

As far as thermal expansion. When you are running in the upper rpm range on similar machines (cost wise). They all have this problem. If they tell you they dont watch for their nose to grow. The only thing that will minimize it is less temp or no temp change. If they can prove it with a Renishaw laser or a ball bar. The closest machines I have seen have liquid cooled spindles, ball screws, and in some cases castings. I would run the machine and find the hot spots like the spindle motor, axis drive motors, ball screws. Run the thing at there recomened top rpm at the recomended rapid rates in a helical path for 8 hours and bring the sales man/ sales engineer in and ask him if he agrees heat causes thermal expansion. If he is dumb enough to say no, or to say their machine stays cool and stable. Touch his bare nether reigons to the spindle or ball screw and see if he now understands heat transfer. The problem is they are going to tell you to warm it up. In the time it takes to load the program and/ or zero the z axis. Your machine has changed. I have seen some shops run a complete 2 hour program empty to get the machine settled in and then run the real part. Oh I forgot to mention, when you change spindle speed the temp will change too. The heat the spindle puts off changes from 1000 rpm to 8000. If they sold you this and you spicificaly asked about thermal expansion. Some sales man or application engineer is in deep do do. and you have a leg to stand on. Or I have seen literatue state thing that are tighter than they can do also. Sorry for the early confusion.