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IndustryArena Forum > GENERAL MANUFACTURING PROCESSES > MILLING > Big difference between the drawing and the work piece.
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  1. #1
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    Big difference between the drawing and the work piece.

    Hi Everybody,

    I have tried to find the solution to my problem, but I found only a part of it.
    When I have used multiple depths of the contour milling, the wall of the workpiece wasn't straight, it was like a staircase. I found a loose screw at the end of my X-axis based on one of the posts, thank you for this!

    My other problem looks a bit more serious.

    - when I mill only contour or pocket, the dimensions of them are perfect
    - when I drill holes, the distances between them are perfect too
    - when I want to combine them in one workpiece, they are shifted relative to each other.

    If I swap the X and Y axes, the shifting will be on the other axis. You can see it on the shifted pocket contour.jpg, there is 6pcs sample. When the depth is only one step (0.25 - 0.5mm), it looks everything is perfect (perfect.jpg). There is a pocket in the centre of the workpiece and there is a hole in the centre of the pocket or workpiece.
    When the depth is 2-4mm, still ok (perfect.jpg). When it is 8-10mm, they are shifted.

    As I saw the deeper the cutting (more steps, multiple depths, or longer code??), the bigger the shifting. Sometimes there is a big shifting (big shifting.jpg)

    I have tried the adaptive clearing but I have cried after I saw the finished workpiece. I have no idea what happened and I don't know is there any connection between this and the previous problem or not.

    So you can see the problem in the pictures (adaptive input.png and adaptive output.jpg)
    The cutting is not inaccurate, it is horrible.

    The distance between the holes (points) are perfect on the workpiece and the outer dimensions are perfect too.

    On the other workpiece, I have tried the adaptive clearing, but 1mm is missing from the left side of the left component and the pocket isn't exactly in the centre of the right component (adaptive.jpg).

    I'll upload more photos about the problem to my Google drive, the code if you need, setup of the milling software, I hope they will help more.
    https://drive.google.com/open?id=1YC...7Qo5Uvb6UGbLEh

    I have a Chinese CNC4030Z with 800W spindle and bl-usbmach 2.31 motion controller. At the moment I try only to draw the shape of the drawing to the paper with different setups, but my ideas don't work.

    What I have tried so far:
    - if I change of the cutting speed, the lines between the 5pcs workpiece are straighter, but still far from the 90 degree
    - I have tried to connect the motion controller card to the laptop with shorter USB cables and in different USB connectors, didn't help
    - I have tried to reduce the micro-steps from 1/8 to 1/2 (in the software and on the driver's PCB as well), didn't help
    - I have decreased the acceleration and speed of the servos in the software, didn't help
    - I have increased the numbers of look-ahead in the software from 20 lines to 200 lines, didn't help
    - I have checked the stepper drivers, now there is (enough) grease between the chip and the heatsink (...), didn't help. I also checked the screws between the axes and stepper motor, they are tight.
    - I think it doesn't affect anything, so I only mention that I got the machine without any grounding, therefore I have grounded all the part of it and connected to the ground for safety reasons.
    - I have tried with another version of the software.
    - I have replaced stepper motor drivers, but there isn't any change.


    Many thanks in advance for helping with my problem!


    Kind Regards,
    Rob
    Attached Thumbnails Attached Thumbnails adaptive input.jpg   adaptive output.jpg  

  2. #2
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    Re: Big difference between the drawing and the work piece.

    Can you post a photograph of your machine?It might be useful to see what kind of tracks your machine has and whether there are drive belts that may be flexing.I would be almost certain that the root of the problem is mechanical in some way.

  3. #3
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    Thank you for your answer Routalot.

    There is a photo of the machine on the link, but I can upload here too.

    I think if there was a problem with the mechanics every workpiece would be different, but I can draw exactly the same (incorrect) draw many times.
    But I don't have too much experience in it.

    I think my next step will be to replace the motion controller card if there won't be a better idea this weekend.
    Attached Thumbnails Attached Thumbnails cnc 3040.jpg  

  4. #4

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    Re: Big difference between the drawing and the work piece.

    Do not replace the motion controller yet; you claim the motions are correct ("When the depth is 2-4mm, still ok (perfect.jpg). When it is 8-10mm, they are shifted.")
    Therefore it is not a motion control issue but more or less related to excessive force applied to it (guessing remotely here)

    There must be a motion that requires an excessive amount of force at that depth somewhere in your program (e.g. radius of the same size of the tool) and the stepper(s) are most likely losing a step or more during this move.
    Investigate if the WCS position is the same as it was originally after the shift. If different pos then your steppers can't handle this force (lost steps).

    Q: what is the biggest radius on your part and tool size used?

  5. #5
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    Re: Big difference between the drawing and the work piece.

    By looking at your photos your drawing Zero points in your drawings are different

    So when you Draw something like this make sure that the X Y Zero point is at the same point for the Drawing also when you make the Cam side of it also check the X and Y are in the same Zero start Position, once it is processed you can also check your code that the start X Y zero point is the same

    Cut and past your code here this may show you have a different work offset for the 2 operations
    Mactec54

  6. #6
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    Hi Mecanix,

    Thank you for your reply.
    Yes, I was thinking about the force too. I could increase the steppers' current, but when I use only a pen, there isn't any force.
    When the unit is off, I can move the axes easily (by turning the steppers), so I think if it is easy for me, it will be easy for the stepper motors as well.

    The gap between the components is 5.5mm, the tool's diameter is 4mm and the stock to leave is 0.5mm. If I count well, the radius will be quite small, 0.25mm.
    I don't have the experience, but am I think well, that even if this radius is so small, it should work perfectly isn't it?

    Based on your idea (force), I'll remove the machine from the box, and I'll check all its screws. Maybe I'll find another lose screw...
    And okay, I'll send back to the zero after drawing and see it is the same point as the start point or not.

    A: I think the biggest radius is 0.25mm (the edges' 0.2mm) and the tool's radius is 4mm as I mentioned.

  7. #7
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    Hi Mactec54,

    Thank you for your answer!
    Sorry, I'm quite a newbie in this field, it is not clear what do you mean.

    If I don't count with the 15pcs holes in the five workpieces, I use only one code for the adaptive clearing (see adaptive one step.PNG, in the drive the resolution is bigger), which means (for me) I can setup the X, Y and Z axes 0 points only once, at the beginning of everything. After I have started the milling, I can't do anything else, only wait for the end of the milling.

    I do these steps always individually (drill holes and adaptive clearing), so they don't affect each other. I get this tilted cuts without making holes. the code is in my drive (https://drive.google.com/drive/folde...7Qo5Uvb6UGbLEh).
    The height in this case only -0.5mm (instead of -10mm) because I test it only on a paper with a pen.
    Attached Thumbnails Attached Thumbnails adaptive one step.jpg  

  8. #8
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    I have a sneaking suspicion.
    I have uploaded the "sneaking suspicion.jpg" to my drive in a big resolution.
    If there is a problem, it is always on the shorter (X) axis. It looks, the head can't move to the exact position, it starts to mill always "earlier". I mean, earlier if I suppose that the spindle comes from the right side of the pictures/workpiece...

    But unfortunately, there is something different from the other workpiece where I have 5 small components. I'll try to think about it in my dream... Goodnight!

  9. #9
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    Re: Big difference between the drawing and the work piece.

    If the connections between your controller and the machine are in good shape-(have you checked them on the X axis?),I would suspect either flexing or working the machine too hard and thus causing it to lose steps.It may be that the power supply isn't giving enough power to the X axis when you are using adaptive machining strategies.Have you checked that the power supply is correctly set for your local supply voltage and frequency?Your location isn't obvious and we have no way of knowing what you should be receiving at the wall socket.

    The first post says that results when cutting contours or pockets are good,so the basic accuracy of the machine seems to be reasonable.One thing that might just be the angle of the photograph,the cutting area seems to be a long way above the rails and it isn't easy to determine what sort of rails they are.Can you describe the rails and the number of cars on them please?It might be that if they are unsupported rods,like the Z axis,and if there isn't good and well separated support that you have an amount of flex being magnified by the height of the gantry sides.

  10. #10
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    Re: Big difference between the drawing and the work piece.

    Quote Originally Posted by B77 View Post
    I have a sneaking suspicion.
    I have uploaded the "sneaking suspicion.jpg" to my drive in a big resolution.
    If there is a problem, it is always on the shorter (X) axis. It looks, the head can't move to the exact position, it starts to mill always "earlier". I mean, earlier if I suppose that the spindle comes from the right side of the pictures/workpiece...

    But unfortunately, there is something different from the other workpiece where I have 5 small components. I'll try to think about it in my dream... Goodnight!
    Post your program will soon see if it is your program do this as a text file
    Mactec54

  11. #11
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    Quote Originally Posted by mactec54 View Post
    Post your program will soon see if it is your program do this as a text file
    I can't post it here because it is longer than the uploadable limit, but the code is in my google drive from the beginning. adaptive 1000 0-4mm.txt in the code folder.
    https://drive.google.com/drive/folde...7Qo5Uvb6UGbLEh

  12. #12
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    Re: Big difference between the drawing and the work piece.

    Quote Originally Posted by B77 View Post
    I can't post it here because it is longer than the uploadable limit, but the code is in my google drive from the beginning. adaptive 1000 0-4mm.txt in the code folder.
    https://drive.google.com/drive/folde...7Qo5Uvb6UGbLEh
    Can not down load it
    Mactec54

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