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Offline derek

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Stuttering problem with line segments
« on: April 17, 2013, 10:49:27 AM »
I’ve been ignoring this problem for a while now but it’s now bothered me to the point where I need to try and fix it.

The picture I’ve attached  is a cut using a waterline strategy. It was done with line segments as opposed to arcs. This section is where the Z drops down .005” and then proceeds around the perimeter. When it makes this move there is a noticeable thud and the gantry stutters. You can see it in the cut as the chop diminishes in size. The other corners are smooth so it’s only right after it makes a Z move. The Z move is on a line of its own.

If I convert the line segments to arcs the problem disappears.

I’m running a smooth stepper and if I convert any large tool paths to arcs then invariably the smooth stepper will crap out and throw an error at some point during the run. Usually about 15 min after I leave for the night:) So consequently I’ve stopped converting my tool paths to arcs. Nothing worse than setting up for a 12 hour run and you come in the next day and you only made it through an hour of it!

My look ahead in general config is set to 100. I bumped it to 200 with no change.

Here are a couple of links to videos.
The first one is of the line segments. If you observe my patented shot glass vibration meter you will see the jerk that ultimately causes the stutter.
http://www.youtube.com/watch?v=FPwhyXx1aM0

The second video is of the arc segments. Note the lack of shake.
http://www.youtube.com/watch?v=mhibmc2Ah94

Any thoughts on this?

Thanks
Derek

Oh and don't ask why I have a shot glass near my router:)

Offline BR549

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Re: Stuttering problem with line segments
« Reply #1 on: April 17, 2013, 11:34:53 AM »
Derek there is no reason for the SS to crap out just because it uses ARCS.  IF it really is then you need to get with Warp9 and get it fixed.

Mach3 has never really done micro segmented code well. The idea to correct this is to reduce the node counts with arcs instead of micro short lines.

Are you sure that the zigzag is NOT in your gcode?  OR does your machine have a bit of loosness in it that casuses the zig zag when Mach3 runs short line segments and it constantly startstop?

You may be able to tune some of it out with CV but it is mainly a test and tune situation with YOUR secific machine. NO magic numbers for all machines.

Just a thought, (;-) TP

Offline Tweakie.CNC

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Re: Stuttering problem with line segments
« Reply #2 on: April 17, 2013, 11:40:20 AM »
Derek,

I must admit that this is something I have not seen happen but I would suspect it’s a vibration being set up in your cutting bit.

Are you using a single flute cutter ?

Have you tried different RPM or a shorter length cutter ?

Is the front bearing on your spindle OK ?

The problem you are having with the SS and arcs really needs to be resolved as a matter or urgency though.

Tweakie.

btw. That's a man size shot glass  ;D
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline derek

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Re: Stuttering problem with line segments
« Reply #3 on: April 17, 2013, 03:00:23 PM »
Thanks for the feedback guys.
That isn't a Zig Zag. That is the shake on the gantry every time it makes the z plunge and starts it's move. Since I'm profiling and stepping down .005" each pass it cuts the same chop each time so what you're seeing is the culmination of about 75 passes.
But at least it's consistent!


The smooth stepper isn't going to be around much longer as I'm probably going to move towards the Kflop direction or the UC100. I've never been overly happy with the smooth stepper anyway. I bought a Kflop/Kannalog combo for my crusader retrofit and that's probably the direction I'll be going. I'm really in a hold pattern until Mach 4 comes out to see if they implement any kind of jerk control.

As far as mechanics… Well it's a 60" gantry with too much weight and too little support. I was hoping I could get a handle on the clunking and hopefully that would buy me a little more time. This is the first time I was able to accurately document that it's a problem with line segments vs arcs. Terry I agree with you about Mach and line segments. It just really seems to have issues but ultimately it' probably more of a mechanical issue. I just wish Mach wasn't so bangie bangie when processing line segments. I don't have the 2 to 3 weeks it would take to build a proper gantry on my kind of budget.

Derek
« Last Edit: April 17, 2013, 03:07:07 PM by derek »

Offline BR549

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Re: Stuttering problem with line segments
« Reply #4 on: April 17, 2013, 10:15:11 PM »
YOu may try backing down the accelleration number a bit ,it could help with the shaking.

(;-) TP
Re: Stuttering problem with line segments
« Reply #5 on: April 17, 2013, 11:22:42 PM »
Derek,
Are you using an older version of M3?

John Champlain

Offline Fleck

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Re: Stuttering problem with line segments
« Reply #6 on: April 18, 2013, 12:17:31 AM »
I have this issue also, I use Rhino and export to Bobcad 25. I have noticed that when given the the choice of lines or arcs in CAM, if I choose lines it seems to smooth things out. I do not have that choice for all features. I was modeling in Rhino with no regard for control point count for a long time, I am now trying to use few ponts as possible in my drawing hoping this helps with the jerky movements. Hope you find a solution, I still deal with it often.
this is my router, there are many like it but this one is mine

Offline derek

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Re: Stuttering problem with line segments
« Reply #7 on: April 18, 2013, 06:40:19 AM »
Derek,
Are you using an older version of M3?

John Champlain

Hi John
I'm running .056

Quote
I have noticed that when given the the choice of lines or arcs in CAM, if I choose lines it seems to smooth things out.

I read that as the complete opposite of what I'm experiencing. Line segments are smoother for you?


Quote
YOu may try backing down the accelleration number a bit ,it could help with the shaking.

I cut the acceleration in half and it's still quite pronounced. Unfortunately it becomes quite lethargic so I don'y know how that will affect things.

Derek
Re: Stuttering problem with line segments
« Reply #8 on: April 18, 2013, 08:59:25 AM »
Derek,
There have been other odd issues with older versions of M3 in some CV situations, which upgrading M3 have cleared up.  Perhaps you might try upgrading to Ver. .062, which cleared up a problem for me and some others.  

Regards,
John Champlain  

Offline Fleck

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Re: Stuttering problem with line segments
« Reply #9 on: April 18, 2013, 11:27:17 AM »
Sorry, arcs i meant.
 I am going to try turning my backlash comp off today and do some air runs see if that helps. It would be nice to eliminate.  
this is my router, there are many like it but this one is mine