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Jagged Radius into jagged Cuts?

miko_cardenasmiko_cardenas OS Professional Posts: 17
  I am noticing that I am getting jagged lines with larger radiuses vs smaller ones. Is this simply a result of the way Onshape renders as the dimensions change (and does it end there)?  Or will these jagged edges translate directly into how the CNC cuts the material?  

I hope that makes sense- I am a newb here with just a couple of weeks of experience with both Onshape and CAD. 

Best Answers


  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    edited November 2015
    Hmmm, @3dcad - I did not get a perfect circle from sending a dxf from Onshape for profile cutting on the one occasion I tried it - small circles were not faceted, but a large one was (not horrendously, but unmistakably).
    Admittedly this was in June of this year.
    (Process : flame cutting; material, 12mm mild steel, large circle diameter ~ 230mm)
  • miko_cardenasmiko_cardenas OS Professional Posts: 17
    @3dcad did you get a chance to test how the cuts came out?  
  • 3dcad3dcad Member, OS Professional, Mentor Posts: 2,467 PRO
    I tried with drawings but nothing came out when I made 1200x1200 piece with rounded corners and R500 circle groove in the middle. It doesn't fit on paper and it should be 1:1 for cnc.

    I will try from sketch tomorrow(ish)..
  • miko_cardenasmiko_cardenas OS Professional Posts: 17
    Any one else have any other insight into this?  

    Here's an example of this.. All the red circled areas started out as nice clean radius's.  Then as I work through at some point they convert to straight lines.  

     What I am trying to do in this example is add a curved groove to the dark blue horizontal bar.  Whether I start out with a circle (and trim the rest off)  or use the 3-point arc, the result is not a clean line

    Again, the question do these jagged lines (with radius's and circles) translate into jagged cuts from the CNC machine?  Any insight would be appreciated.
  • juan_avilesjuan_aviles Member Posts: 78 ✭✭
    I have not noticed the tessellation transferring to parts when I machine them.  I also do not see it when I export from OnShape into my CAM software.  
  • michael3424michael3424 Member Posts: 624 ✭✭✭
    Run a simple part from OnShape through your CAM program and check the G-code that it generates.  G-code generated to machine a simple disk should be a couple of G2 program lines if the file is propagated correctly.  If not you will probably see a whole bunch of G1 or G2 program lines.
  • miko_cardenasmiko_cardenas OS Professional Posts: 17
    @juan_aviles thanks for sharing your experience.  Obviously as you might have inferred I am a total newb to both Onshape and CAD in general.  Sounds like tessellation is a common occurrence with the rendering in CAD programs...
    @michael3424 I do not have a CAM program.  Do you know of any cloud based options (i.e. like Onshape) which does this?  
  • brucebartlettbrucebartlett Member, OS Professional, Mentor, User Group Leader Posts: 2,121 PRO
    @miko_cardenas the tessellation's in your images seem quite bad for a simple part it might be worth contacting support. 
    Engineer ı Product Designer ı Onshape Consulting Partner
    Twitter: @onshapetricks  & @babart1977   
  • matthew_menardmatthew_menard Member Posts: 96 ✭✭✭
    Is there any way we could get a "regen" command similar to AutoCAD?  AutoCAD would do the same tessellation to circles and arcs as you zoomed in and out of your document, but you could force it to redraw everything at the zoom level you were currently at so that your rounded edges at least looked round until you went zooming in and out again.
  • michael3424michael3424 Member Posts: 624 ✭✭✭
    @michael3424 I do not have a CAM program.  Do you know of any cloud based options (i.e. like Onshape) which does this?  
    If you don't use a CAM program, how do get your CNC machine to make a part from an Onshape file?  You've got me curious because the only ways to generate a CNC program (G-code) that I know of are CAM programs, hand code, and conversational wizards and tesselation in Onshape would only be a problem with the CAM program.  I'm not aware of any Cloud-based CAM programs but there are several PC-installed CAM programs available at prices ranging from free to $20,000 or more.  The free programs generally aren't worth the bother from what I've seen.  Check the partners link that @brucebartlett provided for CAM providers that should work well with Onshape.

  • 3dcad3dcad Member, OS Professional, Mentor Posts: 2,467 PRO
    In woodworking cncs, you can usually open dxf in built-in editor and modify if needed and run without any additional steps. I've been working with cnc for roughly 20 years and during that time I haven't ever needed to read or write g-code nor use CAM. BUT I only use 3ax machines so programming is very simple.

    I don't even like to use dxf import since it usually tries to create also holes with router though there is bunch of drills available. I have found it faster to mark points (coordinate dimensions) in cad similar to cnc editor so that I can just copy coordinates. And very often I like to use parameters for quick modifications.
  • michael3424michael3424 Member Posts: 624 ✭✭✭
    @3dcad - Interesting, does your editor generate any G-code or does it also handle the CNC control function?  It's hard for me to imagine working with a CNC system that doesn't let you look at the motion control commands (G-code).

  • 3dcad3dcad Member, OS Professional, Mentor Posts: 2,467 PRO
    @michael3424 It does generate the gcode, it just happens in background and there is no reason for viewing in normal work. Sometimes I have checked something from generated gcode, like what tool is used for a specific hole (if there is multiple tools with same dia) - but this is rare and happened only few times in my history.
  • michael3424michael3424 Member Posts: 624 ✭✭✭
    @3dcad - OK, if the OP uses the same sort of system, he should be able to inspect the generated code in a text editor to see if the tesselation shows up in the tool paths.  Or just machine a simple circle or arc from the Onshape part and inspect it visually.
  • don_howedon_howe Member Posts: 109 ✭✭
    The image quality or tessellation is an issue with OS and I have had a help ticket in regarding the poor image quality for several months now. It's quite disconcerting to see holes in my model with large radii. @brucebartlett pointed to my thread https://forum.onshape.com/discussion/comment/11409#Comment_11409

  • miko_cardenasmiko_cardenas OS Professional Posts: 17
    matthew_menard I like that idea -  sounds like it might be an  easy fix and would help assure us when need be.  
    michael3424 I wish I had a CNC machine let alone CAM... I am new to all of this along with Onshape and CAD in general.
    brucebartlett  Thanks for providing the links to the other threads addressing this.  Would submitting a help ticket even address this?  I ask because if it is based on my graphics card I am perplexed as to how Onshape might help. (@don_howe seems to confirm this- thanks for chiming in.).  As far as purchasing a CAM program as much as I'd like to, and as a lean startup, I am definitely not in a position to consider taking on learning CAM...
    3dcad thanks again for the insight.  What are 3x machines?  (my best guess are CNC machines capable of cutting and moving in 3 axis...)
  • 3dcad3dcad Member, OS Professional, Mentor Posts: 2,467 PRO
    Your guess is right, 3 axis machines move only in x, y, z. If you need more complex working, 5 axis machine can do that but then cam is the way to go.. Axis 4 and 5 are for tool angle and rotation.
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    Strictly speaking, a 3 (or 5) axis machine is capable of interpolating (making continuous changes of position) on three (or five) axes simultaneously.

    So an old school overhead router with an x-y CNC table is really only 2 axis, even though it may be capable of automatic moves in the z axis to multiple positions, established against dead stops.

    Sometimes something along these lines would be informally classed as a "2.5 axis" machine.
  • michael3424michael3424 Member Posts: 624 ✭✭✭
    @miko_cardenas - OK, it sounds like you are doing designs that will be fabricated by someone else, using their own machine and programming method so you have no way to verify whether tessellation is an issue or not in your machined parts.  Others here are more expert, but I'd think that your local graphics card will have no effect at all on the accuracy of the data in your model or the file that you export for your fabricator.  If it would help, I can run one of my models through my CAM software and see if there is any tessellation on the resultant G-code, though it sounds like @juan_aviles has already confirmed that.

  • miko_cardenasmiko_cardenas OS Professional Posts: 17
    michael3424  thanks for the offer.  It sounds like I should be fine but if you get a chance I wouldn't mind hearing the type of output you get in running the test.  I would assume that you experience tessellation issues as well? 
  • michael3424michael3424 Member Posts: 624 ✭✭✭
    miko - I just ran a quick test and designed a 2.185-in diameter disk that was 0.25-in thick.  Onscreen, the disk was mildly tesselated, perhaps a 30-sided polygon.  I exported the part as an IGES file and then imported that into my CAM program, where it looked like a perfectly round disk with no tessellation.  I created a contouring toolpath in my CAM program (SprutCAM) to cut the disk out of solid material and then generated the G-code for machining the part.  The G-code cut the disk in a single G2 command, which is an arc, that specifies a center location, radius, and start and end points for the cut.

    So, in summary, the parts exported from Onshape that will be used to CNC machine the parts result in geometries with no tesselation, just as @juan_aviles found.

  • miko_cardenasmiko_cardenas OS Professional Posts: 17
    michael3424 Awesome!  Thanks for confirming the issue of tessellation being more an issue experienced from my end as opposed to what the CNC shop would experience.  Out of curiosity what material were you cutting? 
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