Author Topic: Mach3 Tool Display "squashed" for 4-axis Gcode??  (Read 6625 times)

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Offline dwneumann

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Mach3 Tool Display "squashed" for 4-axis Gcode??
« on: December 24, 2012, 03:54:17 PM »
I am using a licensed Mach3 with a Taig 4 axis Milling profile (generally with the 2010-4 screenset but this problem exists with the 1024 screenset as well). 
When I load a 2D or 3D Gcode file everything appears at correct scale in the toolpath display window.  But whenever I load a file which has A axis moves, the file appears "squashed" in the toolpath display window.  I have attached a screen capture of one of my files as it appears in Mach3 and as it appears in another simulator.   Why does Mach3 "squash" the display this way?  I have no axis scaling enabled.

If someone is willing... could you load the attached Gcode into a 4-axis Mach3 profile and let me know if it displays correctly for you?

Thanks....

Offline Hood

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Re: Mach3 Tool Display "squashed" for 4-axis Gcode??
« Reply #1 on: December 24, 2012, 04:02:52 PM »
Sounds like your rotation radius is set wrong on the Settings page.
Hood

Offline Hood

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Re: Mach3 Tool Display "squashed" for 4-axis Gcode??
« Reply #2 on: December 24, 2012, 04:05:18 PM »
Here what it looks like if you set the A Axis rotational radius to zero.
Hood

Offline dwneumann

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Re: Mach3 Tool Display "squashed" for 4-axis Gcode??
« Reply #3 on: December 24, 2012, 04:35:57 PM »
awesome... thank you Hood.

Offline Greolt

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Re: Mach3 Tool Display "squashed" for 4-axis Gcode??
« Reply #4 on: December 25, 2012, 04:54:57 AM »
Rather than "Rotation Radius"  I prefer the term "Origin Offset"

The value that should be entered in to the Rotation Radius DRO is the distance that the Z axis origin is offset from the centre of A axis rotation.

In your case the origin is at the centre of rotation, or the origin is NOT offset at all.  So the correct value is zero.

Often users will have the Z axis origin at the outer circumference of the job.  In this case the Rotation Radius (or origin offset) would be the distance the origin is offset from centre.

Mach needs to know this offset so as to display the toolpath correctly.  It is also used to determine the Rotary Axis Feedrate Compensation, but that is another topic. :)

Greolt
« Last Edit: December 25, 2012, 04:56:52 AM by Greolt »

Offline dwneumann

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Re: Mach3 Tool Display "squashed" for 4-axis Gcode??
« Reply #5 on: December 25, 2012, 11:35:43 AM »
thank you Greolt.  I do remember setting the rotation radius some time ago (a suggestion I read on the web) to make the ratoray table spin faster.  I did not realize it would have an efect on the display.

If I set the rotation radius to zero and the steps per inch of the A-axis motor to the manufacturers specifications, the display is correct but the A-axis rapids and feedrate is about one tenth of the specified feedrate.  I suppose the correct adjustment is the A-axis velocity in Motor Tuniing....
Regards,
Dean

Offline Greolt

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Re: Mach3 Tool Display "squashed" for 4-axis Gcode??
« Reply #6 on: December 25, 2012, 08:42:25 PM »
Dean

If you are going to be doing 4th axis work it is definitely worth getting a good handle on the Rotary Axis Feedrate Compensation feature.

The following is a copy of some info I posted in the past

====================================================================================

All axis move in units per min. With a rotary axis those units are degrees.

So what is 120 ipm on the linear axis (desired speed of the tool in the work), is 120 degrees per min for the rotary.

That 120 degrees per min angular feedrate will make the tool move through the work at a speed dependant on the distance the tool is away from the centre of rotation. (in your case, very slowly)

So Mach has a feature to compensate the rotary axis feedrate, to accommodate differing radius that the tool is cutting at.

It is activated via the Toolpath Setup menu. Check "Use Radius for Feedrate" All the other settings in this box are to do with the toolpath display window.

On the Settings page there are three DROs labelled "Rotation Radius". IMO they would be better labelled "Origin Offset"

They are to tell Mach the distance that the relevant axis (Z in this case) origin, is offset from the centre of rotation. (A axis in this case)

So if you are machining on the outer surface of a 10 unit diameter job and Z axis origin (zero) is set on that outer surface, then the correct value for the "Rotation Radius" DRO is 5. The distance that Z origin is OFFSET from centre of rotation.

If, on the other hand, the Z axis origin is at the centre of rotation (my preferred method for most jobs) then the correct value for "Rotation Radius" DRO is zero. The distance that Z origin is OFFSET from centre of rotation is zero.

Mach takes the Z axis DRO value and the "Rotation Radius" DRO value and adds them together to ascertain at what radius the tool is cutting at any one time. Then compensates the angular feedrate to have the tool move through the material at the desired speed.

Maximum velocity as set in motor tuning is honoured, so that will always be the upper feedrate limit.

Now there is one little "Gotcha". A zero value in the "Rotation Radius" DRO will automatically disable the entire feedrate compensation feature. This is a known bug and is being addressed by Artsoft at this time. Hopefully it will be fixed soon.

The workaround for this, is to use a very small value (eg. 0.001) in the "Rotation Radius" DRO when zero is the correct and desired value. Small enough to have no measurable effect on feedrate, but not zero.

=====================================================================================

The issue mentioned in the last two paragraphs was fixed in a later version of Mach3. I don't remember when.

Hope this is of some help.

Greolt

Offline dwneumann

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Re: Mach3 Tool Display "squashed" for 4-axis Gcode??
« Reply #7 on: December 25, 2012, 10:06:59 PM »
Thank you Greolt...
I have now set things up as you suggest. 
I wish your post could be pinned or the info captured in a FAQ for the benefit of everyone!

Regards,
Dean