Hello everyone, i have some issue while machining a workpiece from two sides (top/back). I use Fusion 360 for CAM and in the simulation, everything looks perfectly matched. But in practice, when i cut the second side, i always have an offset (about 0.2-0.5mm), so the model is not perfectly mirrored. This is my trial guitar neck for example: On the left you can see the top side. On the right you can see the back side. The gaps in the back side should be equal. But they are not. The left one in the picture is larger because the endmill had an offset to the left (x-axis). I dont understand why?!? My procedure: 1) I did the CAD in Fusion 360 and also CAM. The back side setup is based on the previous top side setup. WCS=1 on both.Starting points are always the on the top middle of the workpiece. 2) I start machining the top side. Besides the guitar neck, I also add two holes above and beneath the neck-modell (perfectly symetrical to the middle axis of the neck). 3) i take away the workpiece and mill the two holes into my spoilboard. Afterwards i put two pegs into the spoilboard holes, flip the workpiece and fit it on the pegs. So now the back of the model should be perfectly matching. 4) I start running the back side machining and boom: i got the offset Since i cant find an issue in Fusion360 or in the accuracy of my cnc machine, i guess there could be something wrong with the G-Code. Sadly i cant read G-Code at the moment. Can you guys may help me check if there is a problem?? What i found is that there are different X values at the G0 line (orange coloured). Is this where the problem comes from? Top Side: (1 Operation (1 : 2D-Kontur7) ( Work Coordinate System : G54) ( Tool 8: Schaftfrser 2 Flutes, Diam = 6mm, Len = 23.00mm) ( Spindle : RPM = 5000) ( Machining time : 0h:4m:28s) G90 G94 G17 G21 (When using Fusion 360 for Personal Use, the feedrate of) (rapid moves is reduced to match the feedrate of cutting) (moves, which can increase machining time. Unrestricted rapid) (moves are available with a Fusion 360 Subscription.) (Operation 1 of 1 : 2D-Kontur7) G54 (This relies on homing, see Search Results for Query: G53 fusion | OpenBuilds ) G53 G0 Z-5 G0 X-13.188 Y702.265 M3 S5000 G4 P1.8 G0 X-13.188 Y702.265 Z15 F2000 Z5 G1 Z1 F667 Z-2.4 X-13.189 Y702.258 Z-2.494 F2000 Y702.236 Z-2.585 X-13.19 Y702.2 Z-2.672 X-13.192 Y702.151 Z-2.753 X-13.193 Y702.09 Z-2.824 X-13.195 Y702.018 Z-2.885 X-13.198 Y701.938 Z-2.935 X-13.2 Y701.851 Z-2.971 X-13.203 Y701.759 Z-2.993 X-13.206 Y701.666 Z-3 X-13.223 Y701.066 X-13.218 Y700.972 Back Side: (1 Operation (1 : 2D-Kontur9) ( Work Coordinate System : G54) ( Tool 8: Schaftfrser 2 Flutes, Diam = 6mm, Len = 23.00mm) ( Spindle : RPM = 5000) ( Machining time : 0h:11m:37s) G90 G94 G17 G21 (When using Fusion 360 for Personal Use, the feedrate of) (rapid moves is reduced to match the feedrate of cutting) (moves, which can increase machining time. Unrestricted rapid) (moves are available with a Fusion 360 Subscription.) (Operation 1 of 1 : 2D-Kontur9) G54 (This relies on homing, see Search Results for Query: G53 fusion | OpenBuilds ) G53 G0 Z-1 G0 X11.989 Y702.231 M3 S5000 G4 P1.8 G0 X11.989 Y702.231 Z10 F2000 Z5 G1 Z1 F667 Z-1.4 Y702.223 Z-1.494 F2000 X11.99 Y702.201 Z-1.585 X11.991 Y702.165 Z-1.672 X11.992 Y702.116 Z-1.753 X11.994 Y702.055 Z-1.824 X11.996 Y701.983 Z-1.885 X11.998 Y701.903 Z-1.935 X12.001 Y701.816 Z-1.971 X12.003 Y701.725 Z-1.993 X12.006 Y701.631 Z-2 X12.023 Y701.031 X12.034 Y700.938
your setup origin for BOTH sides must be one of those pins. on side 1 set at the top of the stock in the middle of the pin. on side 2 set it at the surface of the table (actually the same stock surface as the first side, just upside down now), in the middle of the same pin DO NOT reprobe X and Y after turning the stock, only Z I would set X and Y where I want the alignment pin, mount the stock, drill the holes through the stock into the spoilboard, then run side 1, turn the stock, set Z at table surface, run side 2
Thanks for the reply. I define my x and y before starting. Just as you mentioned and only reprope z. As far as i understand it should not matter if i take a pin for origin or the points like in my picture since those points are also in line with the pins.
The GCode will only reflect what Fusion360 shows that it is doing. If you are going to use the same X & Y position on the machine for the origin on both sides, the CAM origin points for each setup either need to be exactly on the centre line of the pins, or exactly symmetrical on opposite sides of the centre line, otherwise you will get an offset. I can't tell from the pictures whether that is the case. You won't see this in the F360 simulation.
@Nephsol, it would help if you could upload your Fusion file so we can see exactly what you have done. Alex.
OMFG! I´am such a donky ! You are totaly right! Fusion is putting the Neck center to the workpiece but what i forgot to think about: The neck cetner line is not identical with the center line of the workpiece because of the asymmetrical headstock. So i have a sligth offset to the pinhole: Thank you so much for the advices! This forum is epic . The following neck will be perfect . This realy makes my day guys!
