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Author Topic: PLEASE HELP - How to set feedrate for mixed linear and rotary axes?  (Read 17556 times)

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Hi all!

I have connected a CNC system built around Mach3 .042, to a machine which has 2 linear axes and 2 rotary axes. The linear axes have velocity set in mm/min and the rotary axes in degrees/min.

If I use G1 with an F-word, while invoking a linear axis, I know I'm talking of mm/min. When I invoke motion in a rotary axis alone, I know I'm talking of degrees/min. But how do I reconcile the F-word in multi-axis motion? For example, how do I make sense of this G-code scrap:
G1 X100 Y102 A23.2 B35 F100
where X and Y are linear axes; A and B are rotary axes.

How does the F-word work here? What does it mean in the above scrap? How do I generate Gcode from a CAM software for this?


Offline Graham Waterworth

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Re: PLEASE HELP - How to set feedrate for mixed linear and rotary axes?
« Reply #1 on: June 05, 2010, 05:24:23 AM »
The linear axis will be mm/min and the rotary will be deg/min and the movement blended so all start and stop at the given points.

Without engineers the world stops
Re: PLEASE HELP - How to set feedrate for mixed linear and rotary axes?
« Reply #2 on: June 05, 2010, 06:20:01 AM »
Thanks Graham, but how would you write such G-code by hand? For example, if I wanted to move XYAB axes simultaneously from any arbitrary position to any other at a known tool feed-rate, can you give me an example of how I would write the code? Let's assume the A & B pivot points are both 100mm away from the distal end of the axis arm and the tool-tip respectively.

My client, who is using this machine, uses it to engrave tyre mould segments. He later bolts the segments together on to a former to give the full tyre mould. He uses a CAM system to generate the G-code, but that doesn't seem to work ok with my controller. A Siemens 802D system installed a few years earlier on a similar machine, required 2 months and an expert to fly in to work exactly this problem out, so that the CAM system could effectively be used with the machine.

Do you think, we could work out the circumference described by the distal ends of the rotary axes, and convert the rotary axes to linear and map the circumference calculated, to linear motion, in effect carrying out a Mercator's projection of a globe on to plain paper?  ;D The Siemens system has specified all axes as linear - is there something in that?

Offline RICH

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Re: PLEASE HELP - How to set feedrate for mixed linear and rotary axes?
« Reply #3 on: June 05, 2010, 11:55:49 AM »
FWIW, my sanitized notes on motion and feedrate.

Co-ordinated Linear Motion  (Section 10.1.5 in manual)
Co-ordinated linear motion - each axis moves at constant speed and all axes move from their starting positions to their end
                                        positions at the same time, also defined as control the axes so that, at all times, each axis has completed
                                         the same fraction of its required motion as the other axes
                                            - IE; any two axes ( x,y or z ) produces motion in a straight line
                                            - the motion can be done at prevailing or rapid feedrate and may default to the slower axis feedrate
FEEDRATE ( unless G93 is used ) Section 10.1.6 in manual
1. X, Y, Z  + A, B, C         - without simultaneous rotation -  F =length / minute  ( along the linear path )
2. X, Y, Z  + A, B, C         - with simultaneous rotation -       F =length / minute  ( for the XYZA combination linear path ~ modified F
                                                                                                                   based on a diameter)
3. X, Y, Z  + A or B or C  - with simultaneous rotation -       F= Degrees / minute of  A or B or C
3. X, Y, Z  + A B C                                                                    F= Degrees / minute  using a blended ABC / conceptual angular motion
                                                                                                        for total time

3 Feed Rate Modes - ( Section 10.7.25 in manual )
G93        - inverse time feed rate -            F = 1/F#  minutes ( if the F number is 2.0, the move should be completed in half a
                                                                 - if active, an F word must appear on every line which has a G1, G2, or G3 motion
                                                                 -  an F word on a line that does not have G1, G2, or G3 is ignored.
                                                                 -  does not affect G0 (rapid traverse) motions.
                                                                    It is an error if: inverse time feed rate mode is active and a line with G1, G2, or G3
                                                                    (explicitly or implicitly) does not have an F word

G94        - units per minute feed rate         F= inches / minute, mm / minute, or degrees / minute, determined by length  units are  being used and which axis or axes are moving

G95          units per rev feed rate               F= number of inches / mm / degrees per spindle revolution, determined by what length  units are being used and which axis or axes are moving. 


Offline ger21

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Re: PLEASE HELP - How to set feedrate for mixed linear and rotary axes?
« Reply #4 on: June 05, 2010, 11:56:20 AM »
I believe that if you enter the A and B axis radius on the settings page, all the feedates will be in mm/min.

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