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##### General Mach Discussion / formula not following in G02
« on: December 20, 2010, 12:09:41 AM »
Hello All, I am new to cnc  and gcode.  I am impressed with Mach 3 and the Hobby cnc gear.   I am building a custom machine.   I am finding that the formulas don't follow the X and Y Axis.  The machine has only two axis.  A rotary table (A axis)  and an linear axis (B axis)on that rotary table(A axis).  The tool is on that linear axis( B) and is constrained to a line that passes through the center of the  of that rotator (axis A).   A axis is the rotate and B axis is the linear arm. X and Y axis are active but are not connected to any motors.  This will be a plasma torch. It looks a little like a Banjo.  All axis (X Y A B) are homed to the center of the rotory table. It is in the R and D phase.
Idealy it will use just X and Y in the g code.
The formulas are as follows.
Rotate      A= arctan(y/x)*57.2957795    ( it took me a bit to understand the default is in Radians. )
Radius on the arm    B=((x^2)+(y^2))^.5  ( simple Pythagorean theorem)

For any given point the formulas work great.   I have scaled the both axis and they run well, don't lose any steps, and return to home with very little backlash.

When I run gcode. ( my test has be a 5 inch square).  I am using 2dnc to  generate the gcode.  No tooling off set.  My machine will draw the square.  The corners are square and at right angles.   The sides of the squares are cutting as slight arcs. ( Coming off the line .25 or so) All 4 sides of the square have this  and the crown is away from the origin.  Opposing sides are parallel at the  5 ".  I have the same results any place I have where ever I cut this on the table.   The  A and B axis seem to follow in G00 And G01. with the error mentioned . But will not follow in any G02.  The A and B axis just drop out and stop. When the tool path progresses  back into G01 after G02, Mach 3 will pick A and B back up ( in the correct coordinates ).  If you "Hold the feed " and restart It will move the A and the B. This will only last for that block only.  Is this a bug?  Is it processing problem in my computer?  Is this a ABS or Inc (G90/91) issue.  I have tried it  both ways. Or even the G90.1/91.1 issue ( I think I have tried all combos)

Here are some questions.

Does any one know why the G02 drops the formulas?
Do formulas process in ABS (Machine Co) ?
Will Mach 3 be able to process the feed rate?
Will I be able to use offsets with this or will  Xand Y all ways have to homed at the origin ( center  of the the rotate)?