Due to the correct machine being out of action we put a part onto our GR510 even though it is not really a suitable machine. The part has a hole and a circular profile that we like to keep within a two thou range but which can be allowed to drift up to twice this; using the gantry was pushing it because Haas claims: Positioning (±) 0.0020 " and Repeatability (±) 0.0010 " .
More than 99% of the parts came off within two thou and the lower flange face which is done in three passes with the tool lifting clear between each pass was smooth to the touch between adjacent toolpaths indicating the machine was holding a better tolerance than spec at least in repeatability of the Z axis. Each load was 16 parts and an interesting thing was that a bad part could be between two good parts.
Also interesting was the feature shown in the picture. The profile is a series of blended radii with a straight front that is not tangential to the curve on either end. In the picture it is possible to see ripples where the X axis stops at the transition from G02 to G01 and then again much more obvious at the G01 to G02 transition where X has to accelerate. This is not really surprising because the X axis is the entire gantry structure which I estimate weighs around 6000lb; obviously something this massive needs a healthy push to stop and start. The pattern of ripples was consistent from part to part and as the picture shows at 60 ipm they are smaller than at 100 ipm.