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IndustryArena Forum > WoodWorking > WoodWorking Topics > Why is this happening?
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  1. #1
    Join Date
    Sep 2009
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    72

    Why is this happening?

    Hello, i have just finished my homemade cnc router (JGRO), and im trying to make a flat surface so i can carve something, so i made a facing operation in order to get the flat surface.

    But it seems that when the machine is traveling lets say positive X, the cut is like 1mm higher than when the machine is traveling in negative X. There are some pics that explain better.

    What could be the reason of these? is it like a backlash or something between the rails?

    Thanks
    Attached Thumbnails Attached Thumbnails DSC00713.JPG   DSC00716.JPG   DSC00717.JPG   DSC00718.JPG  

    DSC00706.JPG  

  2. #2
    Join Date
    Dec 2004
    Posts
    1137
    Looks like climb versus conventional milling. The bit is climbing up the work and is causing the Z to deflect.

    What size bit, what speed, feed and depth of cut? Looks to me that you are pushing the machine beyond what it can do and the wood is flexing under the cutting pressure.

    Oh, and what does the cutting path look like ... is it zigzag, or spiral?

    FWIW,
    Jay

  3. #3
    Join Date
    Sep 2009
    Posts
    72
    Hi Jay, thanks for the reply, im using a 1/4 inch flat endmill, the feed rate was like 20 ips and the depth 2mm, i just wanted to make a flat surface, to carve something out.

    It is a straight cut, a square, it moves along X axis, then steps up in the Y axis 1/4 inch(tool diameter), and cuts again in the X axis.

  4. #4
    Join Date
    Dec 2004
    Posts
    1137
    Yeah, that's what I thought. for best results, you need to cut in one direction. Conventional is best if your machine is not real rigid (something I read about the JGRO's). So you will need to modify your tool path to either spiral in a clockwise direction from the inside out, or if you use a linear path, you will have to cut left to right and when you reach the end, raise the Z and return back tot he left hand side before you cut the next swath.

    Like this:
    [ame="http://www.youtube.com/watch?v=QKNLsytyJYk"]YouTube- CNC #2 Cutting a level surface[/ame]
    If you need a spiral path, just tell me the dimensions and how deep you need/want to cut and what depth per pass and I can whip one out for you on Cut2D.

  5. #5
    Join Date
    Sep 2009
    Posts
    72
    Quote Originally Posted by Jay C View Post
    if you use a linear path, you will have to cut left to right and when you reach the end, raise the Z and return back tot he left hand side before you cut the next swath.
    i didnt do this because it takes much more time to be finished, but as you say my machine may not be rigid, so i think ill need to do as you say.

    Quote Originally Posted by Jay C View Post
    in the video the cuting path is like spiral but in squares right, i think this will take less time than a conventional straight cut and raising the z

    Quote Originally Posted by Jay C View Post
    If you need a spiral path, just tell me the dimensions and how deep you need/want to cut and what depth per pass and I can whip one out for you on Cut2D.
    ok that will be helpful, its a square, 200mm, 2mm depth, depth per pass 3mm (is depth per pass the stepover of the tool?)

  6. #6
    Join Date
    Dec 2004
    Posts
    1137
    Quote Originally Posted by absolutepoker01 View Post
    ok that will be helpful, its a square, 200mm, 2mm depth, depth per pass 3mm (is depth per pass the stepover of the tool?)
    Ok, .25" (6.35mm) is tiny and you are right, it's going to take a while. When I get home I'll post a job. What feed rate (mm per minute)? Step over is how much overlap each tool path with have with the previous. 40% is typical.

    See the attached picture and let me know what you'd like me to use.

    Jay
    Attached Thumbnails Attached Thumbnails toolbit.jpg  

  7. #7
    Join Date
    Dec 2004
    Posts
    1137
    Attached. Hope it works for you. I went with 48% step over to try and help it go a bit faster.
    Attached Files Attached Files

  8. #8
    Join Date
    Sep 2009
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    72
    Hey thanks Jay, im gonna check it out. Ill coment later the result.

  9. #9
    Join Date
    Sep 2009
    Posts
    72
    Hi Jay, forgot to tell you im using metric, so it doesnt work, but thanks for all your help.

    Im going to make one out.

  10. #10
    Join Date
    Oct 2006
    Posts
    669

    Repent!

    It's because God hates you and is trying to show you your wicked ways.

    It is not because of backlash, it is because your z-carriage is out of tram. It is not square and parallel to the surface. Which might involve tweaking the gantry as well. Which of course means you might have to check the squareness of your table.

    Quote Originally Posted by absolutepoker01 View Post
    Hello, i have just finished my homemade cnc router (JGRO), and im trying to make a flat surface so i can carve something, so i made a facing operation in order to get the flat surface.

    But it seems that when the machine is traveling lets say positive X, the cut is like 1mm higher than when the machine is traveling in negative X. There are some pics that explain better.

    What could be the reason of these? is it like a backlash or something between the rails?

    Thanks

  11. #11
    Join Date
    Sep 2009
    Posts
    72
    Mmmmm, how did u check yours?

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