guide shafts 62 and 64 similar to guide shafts 38 and 40 are fastened to support blocks 66 and 68 thus a first carriage is provided comprising the elements 58 60 62 64 66 and 68 pillow blocks 58 and 60 provide close fitting sleeves receiving guide shafts 38 and 40 therethrough respectively to translate this first carriage along a first path defined by guide shafts 38 and 40 thus the first carriage is limited in its travel so that it can only traverse machine 20 via guide shafts 38 and 40 pillow blocks 58 and 60 are one example of a linear motion device other linear motion devices are also contemplated for example other linear motion devices might include support blocks and rails other slide assemblies roller bearing pillow blocks and ball bushings shaft support blocks 66 and 68 suspend guide shafts 62 and 64 below guide shafts 38 and 40 guide shafts 38 and 40 therefore define a plane above and parallel to a plane defined by guide shafts 62 and 64 a second carriage 70 is slidably mounted to the first carriage via guide shafts 62 and 64 similar to the sliding interface between guide shafts 38 and 40 and pillow.