G02 problem

A sincere thank you to all that responded. In response to some
questions: I am using Gecko g201 stepper drivers. with 400oz\in 4
wire motors. Linear movement is great, actually arc movement is
great, in that it is smooth and steady, the only problem is it moves
the z axis up as it is cutting the arc ( i believe this is called
helical rather than circular interpolation?)
this is a quick example af an arc that the machine trys to cut,
however at line 3 the z axis will drop more than 0.050 then as it is
running line 4 it will raise the z axis to a depth of 0.050

G00 Z1.000000
G00 X4.901788 Y-1.700087
G01 Z0.050000
G03 X6.625787 Y2.844460 I-2.901788 J3.700087
G00 Z1.000000

I have tried to run the code with the r instead of i and j same
results. The machine is set up for plane x,y

Thanks
Dan