Milling a pocket is not a continuous move?

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13 Apr 2018 17:08 #108954 by FernV

Longbow wrote: I wonder if the problem lies in the way that nativeCAM builds up the program code (g-code) subrutines?


Hi

I think the problem is not with NativeCAM.

I tested a normal circle and velocity does drop some times then return back to normal.
I tested again with G61 and G61.1 with same result.
I also tested with G64 commented from default with still same result.

I wrote gcode for a simple circle and added it to custom gcode after deactivating previous circle with the same result :


Here is the code with comment where feed drops :
G0 x-0.5 y0 z0
g2 x0.5 y0 z-0.1 i0.5 ;velocity drops after this line then returns to normal
g2 x-0.5 y0 i-0.5
g2 x0.5 y0 z-0.2 i0.5 ;velocity drops after this line then returns to normal
g2 x-0.5 y0  i-0.5
g2 x0.5 y0 z-0.3 i0.5 ; NO velocity change here
g2 x-0.5 y0  i-0.5

This code could be hand-writen by anyone and I hope someone can test it and tell us about the result he gets.

I do not know why it does this but will keep investigating.

Regards
Fernand
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13 Apr 2018 17:52 #108956 by PCW
I'm not a good gcode reader but it sure seem like the TP thinks there are sharp corners (in Z?)
Heres with g64 p0.001 q0.001:



and with g64 p0.005 q.005:

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13 Apr 2018 18:30 #108958 by andypugh
I thought that this had already been explained? But possibly in the wrong thread (perhaps the forum messed up)

github.com/LinuxCNC/linuxcnc/issues/426

Mentioned here: forum.linuxcnc.org/18-computer/34332-lin...-not?start=10#108809 Which does not really seem to be the thread it belongs in.
The following user(s) said Thank You: FernV

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13 Apr 2018 18:46 #108959 by PCW
Except bug or not, this is a mix of helical and circular moves so would be expected to slow down
at the junctions (and that's just what you see in the first plot, 5 slowdowns at the circle/helix junctions)

There may be another bug but it does not show up on my test setup (inch, 20 IPS/S accel F100)

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18 Apr 2018 11:57 #109242 by Longbow
I tried with g64 p0.001 q0.001 and it slows to a stop 3 times during a circle (the half circle where Z axis is ramping down)

I tried without G64 and it slows down to a stop only once - when the Z axis has finished ramping down to the new Z step.

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18 Apr 2018 13:24 #109252 by Todd Zuercher
Could you share your ini file? The only slow downs I see are the expected ones at the Z acceleration/deceleration points.

What if you tried the move as a true full helix, rather than half helical and regular arcs?
G0 x-0.5 y0 z0
g2 x0.5 y0 z-0.05 i0.5 
g2 x-0.5 y0 z-0.1 i-0.5
g2 x0.5 y0 z-0.15 i0.5
g2 x-0.5 y0 z-0.2  i-0.5
g2 x0.5 y0 z-0.25 i0.5 
g2 x-0.5 y0 z-0.3 i-0.5
g2 x-0.5 y0 i0.5

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19 Apr 2018 12:24 #109293 by Longbow
I tried your Gcode and it moves in a helix with no pauses!:) - I just had to add a feedrate because there was none specified.

Here is a video: ufile.io/mqaz8
(I modified the code a little to mill a larger circle)


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File Name: DMU50M.ini
File Size:5 KB
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20 Apr 2018 11:06 #109331 by Longbow
Here is a video of a circle milling using nativecam code:
ufile.io/jvhdn

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