Need Help! Mach3 Motor Tuning, Undercut With 3D


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Thread: Mach3 Motor Tuning, Undercut With 3D

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    Default Mach3 Motor Tuning, Undercut With 3D

    Good Day Everyone,

    Background....

    I built a Mechmate about 6 months ago. For those you are not familiar with it. They are a gantry type machine that run on linear v rails. All axes are gear driven. Mine was designed with all induction hardened rails and wheels. All racks are 20dp with 30 tooth pinion. It is a stepper machine, not servo. The steppers are Oriental Motor PK296A2A-SG7.2. My HMI is Mach3 with 2 parallel ports (one from motherboard and a rosewell pci card). They are connected to a PDMX-126 + PDMX-134. All inputs are 24VDC based with the exception of the touch off sensor to set my tool height (my Z zero and table are 0). I am using Gecko 203V drives powered by Antek PS-5N38 (steppers wired bipolar). Water cooled 2.2kW spindle powered by Hitachi WJ200 VFD controlled by modbus. I use Vectric Aspire.

    Question?
    First and foremost. Sometimes I have a hard time putting to paper what is in my brain, if you need more information please ask as I will try to post the best question and/or answer possible but I do not always do that.
    I am thick headed at times but I am having a hard time understanding how motor tuning velocity and acceleration corresponds with good cut quality with complex 3d cuts. I know this should be simple to understand but somehow my brain is locked. I need it in layman's terms. I have posted elsewhere but everyone says this is where you get the best advice. I did my first finish toolpath with the Area Machine Strategy as Raster. I am getting ghost lines and not a clean dish carving with the cut. Here is a link to the carving. I have used Offset in Aspire before for finish machining but have noticed that it creates a notch on the upswing of the dish cutoff. I have seen most threads and videos use raster. So I have played and played and played with the velocity and acceleration but still have the problem areas. They look undercut on the approach of the 3d model. I have been able to minimize it by moving my acceleration down to 10 on my Z axis but it is still there. It is there at 20 ipm and there at 80 ipm. Programmed feedrate does not change it. The only thing that changes the size of it is the acceleration. So here I am, I could play with these numbers until I get it and waste hours and hours of carving time but I feel if I understood what exactly is happening it would help me correct this problem the correct way. Sorry for the novel.

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    What is your 'Look Ahead' set to in Mach3?



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    Look ahead is 200 lines and cv angle is 50°



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    it looks like it overshoots on the downstroke, is there any flex or backlash in the Z, how is the z drive configured, is it a screw, rack or belt, and what kind of spindle is it, axial play in the spindle (like with a dremel tool) might do that

    www.signtorch.com


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    Signtorch,

    The z is rack and pinion also. The spindle is for ugracnc. 2.2kw wc round spindle. I understand what you are saying but I only see it in a dish cut. Not on a raised 3d model on a flat surface. If I understood how the tuning affects the motors, I would be able to almost eliminated it as I have brought it closer to the model by more than half the distance. I checked the pinion yesterday for looseness.



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    Are you doing a tool change in between the two different cuts? Or is it that Your Z axis raises between the craving and the cutout?

    Which could be a simple drop in the head due to the slippage of the motor not supporting the weight from moving it downwards. Most of the people building a Z axis will use a screw drive system to keep the Z axis true. Since they are not as easy to drop by them self.

    Last edited by dodger889; 11-28-2012 at 10:20 AM.


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    Have you tried zeroing to the top of the workpiece, rather than the table? material thickness is critical in situations like this. I'd be inclined to set Z zero slightly above the workpiece, as CV mode can cause rounding that will dig in around the edges of the dish.

    What is your acceleration set to?

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

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    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

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    Dodger, it is an pinion driven rack with a air spring matched to the weight.
    Gerry, I have not tried to set from top of work piece. Acceleration is 10 in that image.

    This is what I have found so far.

    The steppers I use have a gearbox, me not thinking, all gearboxes have backlash. They have to or they will destroy themselves. I should have thought of this because of my occupation. I checked for backlash with a dial indicator. Found 0.010" backlash. I should have remembered this from the specs when I spoke with Oriental Motors. I vividly remember him saying 0.9° of play. That is roughly 0.0118" across my 1.5" pinion when drawn up in cad. I set up the compensation backlash in mach and tried the piece again. All the ghosting and flats are removed. Not used to seeing a stop-go machine but in the end the parts will be better. The only problem is the first bump compensation is almost 0.003" but the moves are dead on after that. With standard V-carving I never noticed it and with raised models I never saw a problem. Must have just been the way the programs were generated. Sometimes you need to remember your basics.

    Last edited by pblackburn; 11-28-2012 at 12:48 PM. Reason: spelling


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    Does the artwork itself have undercut areas? Also what CAM are you using? Since the artwork probably has quite a few sharp turns in the X-Z and Y-Z planes you might want to consider raising the CV angle; it's possible that the bit is pulling into the material on hard stops.... maybe try 90 deg.



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    Vectric Aspire. I have tried 5° increments up from 90 to 35. No change in ghosting. Only using backlash compensation removes it.

    Quote Originally Posted by louieatienza View Post
    Does the artwork itself have undercut areas? Also what CAM are you using? Since the artwork probably has quite a few sharp turns in the X-Z and Y-Z planes you might want to consider raising the CV angle; it's possible that the bit is pulling into the material on hard stops.... maybe try 90 deg.




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    I did ask another question between the time of the craving and dishing. Does the z axis raise and then lowers? I'm just trying to understand the order(tool path) that you setup in your cut. Because what I see is that the craving is setup for a flat piece and then you are adding the dish shape to it. This will put you on two different plains unless you do some trimming of the tool path of the craving itself.



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    Sorry, it 3d raster rough along X and finish raster x. The complete path is the oval. So yes, the Z does raise and lower was X is in constant motion from left to right and then back again. The top portion of the dish was my mistake of not setting the BOV for the tool. I used a 0.5" ball nose for rough and 0.125 taper ball nose for finish. The problem was not in the rough only the finish. The rough is plenty of distance left for the finish.

    Quote Originally Posted by dodger889 View Post
    I did ask another question between the time of the craving and dishing. Does the z axis raise and then lowers? I'm just trying to understand the order(tool path) that you setup in your cut. Because what I see is that the craving is setup for a flat piece and then you are adding the dish shape to it. This will put you on two different plains unless you do some trimming of the tool path of the craving itself.




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    Problem identified and resolved. It was backlash in the Axis. I was using a gearbox but have replaced it with belt reduction drive. Hard to believe that 0.009" would show up so bad. Thank you all for your suggestions.



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Mach3 Motor Tuning, Undercut With 3D

Mach3 Motor Tuning, Undercut With 3D