Cut quality problem


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    Default Cut quality problem

    I post this cut quality question on the Mach3 forum. I'm just cutting a simple cam 2.5d profile, it sounds super smooth while cutting but I get slightly wavy and bumpy cuts. This is answer I received, but don't know how to correct this in Rhino or Madcam? Suggestions?

    Check your Gcode - if the curves are comprised of many straight lines then the answer is with your CAD/CAM and it's Post Processor.

    (Vectric, for example, will enable 'curve fit' to replace the many straight lines in an imported dxf and then the final Mach3 post processor will use 'arcs' (G2, G3) for the toolpath).

    Similar Threads:
    Attached Thumbnails Attached Thumbnails Cut quality problem-20190920_164051-jpg  


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    Default Re: Cut quality problem

    There are two things here I would like to discuss. Or, maybe three when I think about it.
    1. Yes, the default Mach3 post is producing small lines representing the arch. There are a few settings you can adjust to make it good. First make sure the mesh settings are set according to the help file. These settings you can save in your normal template files so it is a make-once-always-set thing if done right. There is also a tolerance setting in the Tools Dialog. The lower you set it, the better result (and larger file). With that said, it is very high precision G-code coming out of MadCam. I've done cuts where the room temperature affects the tolerance.

    2. All 2.5D operations can be transposed to G2/G3 in MadCam, but I strongly believe the Mach3 post is still line based. For older machines it produces a smaller file to process and you can gain some serious speed in modern sturdy machines.

    3. BUT, to me this looks like jitter, your machine is simply not beefy enough to cut like this and in worst case you have material building up. You can experiment with cut depth, go shallow and more rounds, keep cooling with alcohol, soap or water mist and make sure to blow off chips. It will probably give you a better result.

    Also, are you using an ALU specific cutter? That can make a hyyuge difference.



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    Mach3 has some conversational programming options. When I do a circle interpolation the cut comes out perfectly smooth. So I'm ruling out machine and cutting bit for now.

    I've played with the mesh settings, cutter tolerances... they help but problem is still there.

    I really think this is a Rhino drawing problem. I'm using a a 2d curve drawing only for the toolpath. Is a curve affected by mesh settings?
    This closed curve is originally imported into Rhino from 3600 cloud points. I then generate closed curve from points. I then rebuild curve to around 100 points.

    Do I need to extrude curve and use the extruded shapes sides for a better toolpath?

    I do remember testing a circle drawn in Rhino, used Madcam and comparing to the conversational cut circle in Mach3. Mach3 was a beautiful cut. From Rhino/madcam same issue as pic in original post.

    I'm missing something in my Rhino and or Madcam settings

    Thank you for your help!



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    Default Re: Cut quality problem

    What is the cam tolerance you set for the linear motions output? If I set mine at 0.1mm I would get similar results on M3, worst in fact. Although if the motions are set to 0.001mm then the finishes are near perfection (to the naked eye anyway). Likely you'll end up with 10,000+ lines of code at those low tol so set your M3 look-ahead to about 500 and you should be sort-of-okay



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    Quote Originally Posted by Mecanix View Post
    What is the cam tolerance you set for the linear motions output? If I set mine at 0.1mm I would get similar results on M3, worst in fact. Although if the motions are set to 0.001mm then the finishes are near perfection (to the naked eye anyway). Likely you'll end up with 10,000+ lines of code at those low tol so set your M3 look-ahead to about 500 and you should be sort-of-okay
    My M3 look ahead is at 200. I'll try a high number there.

    I don't know what you mean by linear motions output? In my tool cutter tolerance I have it set to .0001" (imperial). I played with this setting. Really didn't seem to make a difference.

    There is a setting to change in machine setup. I'm not by that computer, and I forget what it's called. Is there anything there that would be helpful? There's also 4 separate boxes to check... something 2 toolpaths or 4 toolpaths... what are they for?



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    Default Re: Cut quality problem

    And do I really want jagged seams checked in Rhino mesh settings



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    Default Re: Cut quality problem

    Quote Originally Posted by williamsmotower View Post
    I don't know what you mean by linear motions output?
    By means of post processing points, the cam tool should give you the option to set a tolerance for the linear motions (distance between each points it outputs).
    If that option is not available then that's not a CAM, its a SCAM. Need to look at procuring another CAM with an industry focus (pretty standard option with most cam)

    Attached Thumbnails Attached Thumbnails Cut quality problem-ops-jpg  
    Last edited by Mecanix; 09-22-2019 at 02:34 AM.


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    Default Re: Cut quality problem

    What finishing speed are you using?
    With my Sieg X2 and a 6mm 4fl cutter it only seems to like 1500rpm, 175mm/min, 0.3mm stepover.
    Backlash won't cause that, it'll only cause a flat spot or line at transitions/ change of direction.



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    Default Re: Cut quality problem

    Backlash shouldn't be the issue, I do have .001" on each axis, but have backlash compensation on in Mach3. My manual programming yields no issues with backlash. My Madcam post shouldn't turn off backlash compensation?



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    Default Re: Cut quality problem

    Quote Originally Posted by williamsmotower View Post
    My Madcam post shouldn't turn off backlash compensation?
    Lets have a look at your program/gcode. Your CAM may in fact add both 'counter-backlash' & 'backlash' every now and then, which is what I've been suspecting from the start (tol).
    If you upload that program that'll make it much easier for us to debug remotely



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    Default Re: Cut quality problem

    Here is the gcode in attachment. I used this to skim the part .002" to see if the cut quality was better. Finish turned out exactly like original

    Attached Files Attached Files


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    Default Re: Cut quality problem

    are these settings correct?

    Attached Thumbnails Attached Thumbnails Cut quality problem-madcamoptionsjpg1-jpg   Cut quality problem-madcamoptionsjpg2-jpg  


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    Default Re: Cut quality problem

    I just set up a dial indicator to check my X,Y. Backed off indicator a known amount, re zeroed and ran file. Went back to my known offset via MDI move.... both axis back to exact zero (on a .0005" indicator)



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    Default Re: Cut quality problem

    Seems a lot of lines there to me.
    Try un checking the radius comp and see how it looks.

    Myself for a finish pass I'd drop Z to full depth a minimum of 0.6mm away from the surface.
    Then lead-in for a pass from there.

    In theory there should only be a few lines afaic.
    The usual lead-in etc bits at program start - the starting cut position - the arc R and the next position at 90 degrees - the next arc R and the 180 degree position - lead out - program finish position - end.

    That's what I get anyway. Looks like it's compensating at every move for some reason as was suggested by mecanix.

    I don't do inches



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    Quote Originally Posted by dazp1976 View Post
    Seems a lot of lines there to me.
    Try un checking the radius comp and see how it looks.

    Myself for a finish pass I'd drop Z to full depth a minimum of 0.6mm away from the surface.
    Then lead-in for a pass from there.

    In theory there should only be a few lines afaic.
    The usual lead-in etc bits at program start - the starting cut position - the arc R and the next position at 90 degrees - the next arc R and the 180 degree position - lead out - program finish position - end.

    That's what I get anyway. Looks like it's compensating at every move for some reason as was suggested by mecanix.

    I don't do inches
    This code is a fairly complex cam shape.



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    Default Re: Cut quality problem

    A reply from the Mach3 forum for this problem....


    Gazillion of short segments, no arcs.
    Even setting lookahead sky high will not help you having better part.
    Your CAM is not generating G2/G3 code, only G1, which is linear interpolation versus circular interpolation.
    I have no knowledge on madcam, I use Aspire (as is Tweakie) where I can do a curve fit.



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    Default Re: Cut quality problem

    Quote Originally Posted by williamsmotower View Post
    I have no knowledge on madcam, I use Aspire (as is Tweakie) where I can do a curve fit.
    Had a look at your gcode and was right on the tolerance between linear motions. I count 895 lines into your program where ideally you'd need a good 10,000 lines to get a half-decent edge/surface finish with linear motions output. That program would be perfectly fine for roughing the part, perhaps not so much at finishing it though.

    RE your latest question. Try to see if you can find a setting within the CAM doc where is say "Output Arcs, or IJK"
    Quick search returned this link also where member dcd121 described ideal settings for curves for your CAD/CAM, see if this can be of any use to you:
    https://www.cnczone.com/forums/madca...s-circles.html



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    Default Re: Cut quality problem

    Mechanix, unfortunately I already have my settings like in the link you posted. But, you gave me an idea. I'm going to rebuild this shape with 10k points. It may make the lines so small I won't have any chopiness.

    Did you look on page 1, I posted 2 screenshots of Madcam settings that I don't know if I should leave or change



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    Default Re: Cut quality problem

    Quote Originally Posted by williamsmotower View Post
    Did you look on page 1, I posted 2 screenshots of Madcam settings that I don't know if I should leave or change
    Missed that, sorry. The only option of interest seems to be "Convert Curves to Arc and lines" (in the first screengrab/bottom). Although not exactly sure what this do because Arcs & Lines are two very different motions.
    Worth trying postprocessing to see if you are getting IJK (arc) output in the program with the option enabled?

    Quote Originally Posted by williamsmotower View Post
    I'm going to rebuild this shape with 10k points. It may make the lines so small I won't have any chopiness.
    That is certainly an option I'd tryout if option above fails.



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    Default Re: Cut quality problem

    How would I know if I'm getting arc output by looking at the gcode?



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