Issues with consecutive arc motion

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14 May 2026 07:48 #346390 by winterkills
Issues with consecutive arc motion was created by winterkills
Hello all, I picked up a machine from someone else with axis 2.7.15 and am trying to make a countersink by ramping down in a spiral. For clarity, I am using an end mill and going in a CCW helical spiral. Sample code is as follows:

G03 R0.168 X0.168 Y0.000 Z0.0043
G03 R0.168 X0.000 Y0.168 Z0.0035
G03 R0.168 X-0.168 Y0.000 Z0.0028
G03 R0.168 X0.000 Y-0.168 Z0.0020...

The issue is as follows. The first arc will look correct, the second arc will drive more left before driver down so the arc will be incorrect (it's almost as if the Y is lagging), the third arc will be correct, the fourth arc will drive in the x first and the y seems to drive late like it's lagging. I've used halscope to look at some outputs and these are them: ibb.co/b5WTfCH3

The secondary issue is that the machine stops or slows between arcs and I don't want that to happen.

For the life of me I can't figure out why it's happening. 
Previously I changed the .ini file to increase the lookahead and the arc blending because the segments were stopping between every arc and I wanted a more continuous motion. I get the R is slightly off if the Z is included BUT then I would expect all four arcs to have the issue not just two of them.

(I don't need any help with the gcode as that is not the problem I am having - also I am well aware that *technically* ramping down each line will produce a slight inaccuracy in the machined dim - but that is within the req tolerance of the feature I am machining) 

Thanks for your help

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