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  1. #1
    Join Date
    Jan 2010
    Posts
    23

    Odd problem making parts

    Hi guys,

    I am a rookie with a new CNC Taig but am having some strange issues pop up.

    I am running gecko 540s and using Mach3 to control. Using Vectrics Cut2d and Cut3d to generate gcode.

    I made several parts and all came out really well - within a few thou. I was cutting on plastic. I moved to aluminum and made a couple of parts and they came out well but I was concerned that the plunging was a bit rough so I thought I would try to ramp in on the plunge depth rather than diving straight in (this is an option in Cut2d).

    Here's where the problem started. Using the ramp to start in on a plunge, my part came out looking like a staircase.

    This problem also occurs if I lay out several parts to run at the same time and also occurs on a single part if I raster in the x axis for the profile.

    I thought maybe it was backlash in the x, but I'm not sure that makes sense. At any rate, I adjusted the backlash nut and put on my dial indicator and my backlash is less than 2 thou and I still have the issue.

    Could it be an issue with Mach3 and the incremental mode?

    Any ideas or help is definitely appreciated.

    Thanks,
    Matt

  2. #2
    Join Date
    Feb 2007
    Posts
    456
    A picture of the stair-stepping might make it more clear what is happening. Since all you changed is the code, it does not make sense that it would be Mach 3. Try this, mount something to your table that you can indicate against. Set your machine zero to that location. Run one part positioned on the table so that the table does not come back into your indicator. then re-zero the machine to see if it is still reading zero. Repeat for each axis. This will let you know if you are loosing steps or if the G-code is screwy.
    Jeff Birt

  3. #3
    Join Date
    Jan 2010
    Posts
    23
    Hi Jeff,

    Thanks for the help. I'll try and run the check and see what happens. I'll also try and take a picture of a part with the stepping. Another check I'm going to try is a different post processor to see if anything comes out differently.

    Matt

  4. #4
    Join Date
    Jan 2010
    Posts
    23
    So I did a lot of troubleshooting. What I found I am not sure I understand yet, but may be pretty interesting.

    In addition to checking the backlash (a thou or so repeatable) I also checked the Mach3 backlash settings (in case they were responsible for strange behavior) - disabled. No problem.

    I checked the stepper motors and their attachment to the lead screws - no problem. Also I switched the steppers from the x to the y screws just to make sure it wasn't a bad stepper. Same issue.

    Then I switched the cables between the x and y axis (so that what the controller thought was the x was the table y axis) which I think would pretty much rule anything mechanical out (the problem has only ever happened in the x axis) or in. The shifting then occurred in the y axis for the first time, so it would seem to be a controller or software issue.

    I tried a few different flavors of g-code (generic g-code, mach2/3 arc in, mach2/3 atc in, etc - I think even Fanuc). All gave me the same issue.

    Here is the really bizarre thing. When I rotate the part 90 degrees in Cut3d, everything works. I can even rotate it 90 degrees and then rotate the raster direction so that it is doing exactly the same cuts (just looking at the part rotated 90 degrees) and everything still works.

    I think this is an issue with Cut3d and how it generates the toolpath. It may also be interacting with my STL files in some way that generates this behavior - I don't know.

    At any rate, I am back to making parts instead of frustration.

  5. #5
    Join Date
    Sep 2006
    Posts
    1738
    This is very good information. I have been a TAIG user for a few years, have a 540, use Cut3d and VCarve-Pro. I have dealt with the exact same problems in the past. Just like you, I have ruined parts like this. A staircase affect was done, the shape was fine but incremented a decent amount every time, but equal. I did the same thing you did, all the mechanical, electronics and computer swapping. I have been though it all, countless threads. The computer seems to have been a better help, but can never be the final word on anything. I questioned Vectrics software, it was very odd sometimes. The intial files; STL were done in Pro-Engineer. At one time, the Cut3d generated the G-code so oddly it did not make sense. I was told to download a new Beta version, problem solved. There is one other issue I will never understand, I won't know if it's software or computer/machine error, but I was cutting a rather 3d part and if the part had mutiple Z movements for RAPIDS it would always mess up in the Z height. It does not make sense, why would the machine run with a small stepover while all three axis are going in a full 3d motion and only on a Z axis rapid to a new position did it mess up. I recently just made a small turtle from wood over Christmas. The file was not to large and the g-code from Cut 3-d generated a minor z aixs rapids, came out fine. I think it only applied to large scale, because when I was making that part with many z rapids, I tested to a %50 reduction and it cut fine.

    Machine has been great over the past few months, I have had it as CNC though for about 2 years.

  6. #6
    Join Date
    Jan 2010
    Posts
    23
    Well I'm glad to hear I'm not the only person who has ever had this happen. I will have to try with some other formats to see if this is perhaps just an issue with STL files. I guess I can imagine how the orientation of the triangles might result in something like this.

    It is pretty strange because the g-code loads correctly and looks right in the tool path window. I also noticed that the shift was occurring in between layers - I suspected the rapid might have been at fault. I limited the rapid in Mach3 but still had the issue. It continues to be pretty baffling.

    I guess until I figure this out I will be air cutting parts before running them.

  7. #7
    Join Date
    Sep 2006
    Posts
    1738
    one huge factor I left out is the fact that I use EMC2 as my controller rather than MACH. Which brings up a really interesting question; two different controllers and the exact same problem. Do you have any idea how many hours I spent trying to solve EMC2 and then buying a new DELL, which has been better.

    It also seems to have been a hit and miss. Sometimes I would load everything, it worked fine, I would test parts for the problem, they worked out ok (These were simple 2d parts, small) and yet sometimes it just staircased on me and actually ruined important parts.

    Although things have been running pretty smooth for about a year now, id say a little less because I actually upgraded my computer this time last year.

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