Still struggling with CV settings

[Derek]

So I'm trying to get smooth motion out of my rack and pinion stepper router. As I said in an earlier post it has spent it's life doing basic point to point work and it did it really well. Now I'm trying to use it as a 3D carver and the results are less than wonderful. My main complaint is I cant get any kind of smooth motion when transitioning between arcs and line segments. This is kind of the same issue that I have with the bridgeport but I find it hard to believe that this is normal motion. I'm willing to sacrifice some accuracy for smooth motion but I have tried all kinds of settings in the CV section and nothing seems to make a difference.
Units are inches
Here is a snip of the code:
Feed is set to 100 ipm

Screen shot of settings for this test:

Code: Select all

N1 G20
N2 G0 G17 G40 G80 G90
N3 G64(CONSTANT CONTOUR OFF OR TURN ON W/G64)
N4 G54

N672 G01 X-12.0428 Y14.7786
N673 G02 X-11.9666 Y15.0742 I3.4524 J-0.7329
N674 G02 X-11.8121 Y15.5098 I3.8949 J-1.1364
N675 G02 X-11.6829 Y15.7905 I4.0958 J-1.7150
N676 G01 X-11.6589 Y15.8339
N677 G02 X-11.4733 Y16.1556 I3.5632 J-1.8406
N678 G02 X-11.3030 Y16.4013 I4.9988 J-3.2829
N679 G02 X-10.9968 Y16.7662 I3.7765 J-2.8585
N680 G01 X-10.8412 Y16.9228
N681 G01 X-10.7593 Y16.9981
N682 G01 X-10.6774 Y17.0716
N12457 M30

When it transitions from line 672 to 673 the feed drops from 100 ipm to 24 ipm. It also drops to like 42 ipm transitioning from 676 to 677

Here is a slow motion video of the screen:
https://youtu.be/YeyidvkZG1g

Is this how everyones machines are running? The tool path isn't that complicated.

Thanks
Derek

[cncdrive]

line 672 to 673 moves from current point to 673. line point since 672. line is your first movement in your g-code file.
On your video moving to 672. line and moving from 672. to 673. has about 180 direction change in the movement vector,
so ofcourse the feedrate has to drop, the machine must deccelerate to change axis direction.
If the axis would not deccelerate down just change direction would make your axis to loose steps and your motor to stall.

On the other 2 lines 676 to 677 I can make it to make the transition without much slowdown, but I don't know what are your job requirements, so I have no idea if it would fit your needs.
But it is possible to set the CV up to move those lines without visual decceleration ( I had no time to measure it, just visually inspected.). It can be that your linear addition and unify length are too short and so then the controller is not allowed to interlink that line... but making those settings high can cause other issues. So everything depends on the job and your requirements...

[Derek]

On the other 2 lines 676 to 677 I can make it to make the transition without much slowdown

What did you change and what values. This will help me get a feel for it.

[cncdrive]

I changed those two mentioned parameters, the linear addition and unify length to some high values 10 and 20, but I don't know if that will cause any other issues with your project.

[Derek]

Well I changed them to 10 and 20 and videoed it again in slow motion and it dropped to 42 ipm between 676 and 677 which is no change at all on my machine.

I drew an single arc based on the start, end and general radius of the test code and ran it. It did the entire move with no slowdown.

I plotted out the arcs and the line at 677 and there is only about .001" transition from the natural path of one arc to the next arc.

In order to not have any noticeable slowdown with the test code I have to reduce the feed rate to 22 ipm.

Basically the same problem I have with all the machines. It can track along an arc just fine but throw in a line and it has to slow down a lot to make the transition. I guess the nature of my work being a lot of 3D carving is pushing things.

Better figure out how to have more arcs:)

[cncdrive]

Try to higher the accelerations of the XY also if possible that could help even if a decceleration has to happen.

And I don't think the transition is 0.001 units only. I did not measure it, but now I had some time to test with your settings and as soon as the linear and corner error values are changed to 0.05 from the 0.005 then no decceleration happens, so the transition has to be somewhere between 0.005 and 0.05.

[Derek]

I'll give that a try in the morning.

Although I remember changing them to .1 and it seemed to be the same.

[cncdrive]

Hmm, when I loaded your profile today and changed those 2 values from the mentioned 0.005 to 0.05 then it does not deccelerate down at me is why I think the transition is probably larger than 0.005.
But again, I did not measure any signals, I just visually observed the feedrate with F100 I saw it dropped to around 99 only with those tolerance settings changed, so it seems the transition is larger than you think is why the decceleration. With 0.005 tolerance I saw the same as you, that decceleration happens, the feedrate could be visually seen to be dropped and it is because there is a complete decceleration at the transition point.