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4th Axis Right hand rule question
« on: February 11, 2015, 10:27:45 PM »
In trying to get Mach3 setup to run my 4th axis I have been struggling with the Right Hand rule definition.  Is the rotation relative to the tool or not.

It seems Mach3 defines +A to be relative to the tool.  I have attached a screen shot of the tool path view in mach3 with a simple z down, rotate positive 90.  The resultant tool path is RH rule as seen by the tool.  What confuses me is that the consensus seems to think that mach3 should be doing the opposite. Also the default output from VisualCAM shows up mirrored in the tool path viewer.  

Can anyone provide a clear answer on this?  Is mach3's tool path viewer conventional or not?
« Last Edit: February 11, 2015, 10:31:50 PM by wantmys2000 »
Re: 4th Axis Right hand rule question
« Reply #1 on: February 13, 2015, 01:48:34 PM »
I used this reference among others when setting up my 4th on the vertical mill -

http://www.cnccookbook.com/CCCNCGCodeCoordinates.htm

I have my machine set up "conventionally" and correctly modelled in my CAM system, the Mach3 tool path view displays it perfectly,

 - Nick

Offline Greolt

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Re: 4th Axis Right hand rule question
« Reply #2 on: February 13, 2015, 06:36:54 PM »
Explaining a visual aid with words is easy to get wrong or be misunderstood

Example, I quote from the first paragraph of the link posted above

Hold up your right hand with the index finger extended and the thumb up, like you're simulating a gun.
Now extend your second finger at right angles to the index finger.
Those three fingers are now pointing in the directions of positive X (second finger), Y (index finger) and Z (thumb).


Do the action as described and it becomes obvious it is incorrect.   

I prefer pictures.  Maybe I am just a visual sort of person. 

Here is one that describes all axis.
Re: 4th Axis Right hand rule question
« Reply #3 on: February 13, 2015, 07:46:03 PM »
I am comfortable with the right hand rule as it applies to X,Y, and Z.  Its the rotational axis that has me a bit confused.  I have read that the rotational axis's  don't follow the same rules as X,Y, and Z in that it describes the table movement.

So to simplify, if i hold my hand like the picture Greolt attached, with my thumb pointing in +x away from the rotational chuck, does +A move the CHUCK in the direction of my curled fingers, or does the chuck move the opposite direction so the apparent TOOL movement is the direction of my curled fingers?

Based on the picture I originally attached, it seems like Mach3 is interpreting it as TOOL movement.  I am just confused if that is conventional or not.
« Last Edit: February 13, 2015, 07:48:25 PM by wantmys2000 »
Re: 4th Axis Right hand rule question
« Reply #4 on: February 13, 2015, 08:04:55 PM »

............ does +A move the CHUCK in the direction of my curled fingers, or does the chuck move the opposite direction so the apparent TOOL movement is the direction of my curled fingers?

Based on the picture I originally attached, it seems like Mach3 is interpreting it as TOOL movement.  I am just confused if that is conventional or not.

The top surface of the chuck would be turning AWAY from you, the relative movement of the tool would be coming TOWARD you ... the direction that your curled fingers are pointing.

Tool movement YES, and it IS conventional.
Re: 4th Axis Right hand rule question
« Reply #5 on: February 13, 2015, 08:41:30 PM »
Awesome!  Thanks for the clarity.  It makes sense that everything is related to the tool movement.

FWIW, If anyone else is using VisualCAM for Geomagic Design, by default it is opposite to that convention and there is a bug in the -X rotational machine setting that messes up tool path generation.  I ended up having to have a negative scale in the mach3 post, but all is working now.

Thanks for the help!