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  1. #1

    Join Date
    May 2020
    Posts
    4

    Chinese cnc not square

    I just purchased a Chinese cnc, it my first CNC, so I quickly found myself craving expensive software. I've since purchased hopefully all the software I'll ever need.
    And now I'm finding flaws of a Chinese cnc
    The work bed is t-slot aluminum. And isn't square to the Gantry ever so slightly with about .7mm difference over the span of 14"
    I'm considering milling the t-slot into submission, it feels like there is or should be a better way. I'm hoping to get some advice from everyone
    Googling "Chinese 3040 CNC" will show what machine I'm up against

  2. #2
    Registered
    Join Date
    Dec 2003
    Posts
    591

    Re: Chinese cnc not square

    Does the longitudinal axis have a single ballscrew or is there one each side?

  3. #3

    Join Date
    May 2020
    Posts
    4

    Re: Chinese cnc not square

    The gantry, has one ball screw, and two guide rails near the edge of the machine

  4. #4

    Re: Chinese cnc not square

    Quote Originally Posted by Razrburn View Post
    I just purchased a Chinese cnc, it my first CNC, so I quickly found myself craving expensive software. I've since purchased hopefully all the software I'll ever need.
    And now I'm finding flaws of a Chinese cnc
    The work bed is t-slot aluminum. And isn't square to the Gantry ever so slightly with about .7mm difference over the span of 14"
    I'm considering milling the t-slot into submission, it feels like there is or should be a better way. I'm hoping to get some advice from everyone
    Googling "Chinese 3040 CNC" will show what machine I'm up against
    Maybe try to adjust the screws of machine's feet.
    http://cncmakers.com/cnc/controllers/CNC_Controller_System/CNC_Retrofit_Package.html

  5. #5
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    Join Date
    Dec 2003
    Posts
    591

    Re: Chinese cnc not square

    I would be surprised if fiddling with the screws at the base of the gantry achieved very much.When doing the cut that revealed the defect,was the machine conventional cutting or climb cutting?I would suspect the drift was due to a cumulative amount of play from the base of the gantry and the Z axis combined with some cutter flexing.It would be interesting to know whether running the cut in the opposite direction resulted in an equal and opposite inaccuracy.

  6. #6

    Join Date
    May 2020
    Posts
    4

    Re: Chinese cnc not square

    I wrote a simple gcode file to just around and pause, and I used a plastic card and tried to slide it under the bit in the spindle while off. I didn't try to flex the machine while doing it. The gantry seems rather solid I didn't visually notice any flex while moving (taking out of the box). I'm talking about .7mm so maybe I need to try and lift on the gantry and see if I can find slop in the accuracy first

  7. #7
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    Join Date
    Jun 2013
    Posts
    40

    Re: Chinese cnc not square

    Use a spoilboard, flycut it then check to see if everything is level. If not then tram the spindle. I would not expect that the aluminum base it going to be flat. Mine wasn't but it does not matter because you should be using a spoilboard anyway.

  8. #8

    Join Date
    May 2020
    Posts
    4
    Quote Originally Posted by milo30 View Post
    Use a spoilboard, flycut it then check to see if everything is level. If not then tram the spindle. I would not expect that the aluminum base it going to be flat. Mine wasn't but it does not matter because you should be using a spoilboard anyway.
    I'm trying to avoid a spoil board at all cost
    In the future im going to attempt some aluminum milling and I'm worried about a spoil board melting from heat, or expanding from cutting coolant. I still have a ways to go but I've been sitting with this issue. So far my best solution seems to be placing some aluminum flat stock down as close to the bolts that hold the t slot to the frame. Clamping and cutting it down to a shim. After the set of shims are cut install them under the t-slot between the frame. And see how/if any better it made it. Maybe give it a few days to see if flycutting the t-slot would be worth anything, not sure if the clamps will rewarp the aluminum.
    I've been glancing at solid steel t-slot slabs. Maybe that is the long term solution

    I've been a little busy, had my Chinese cnc control box apart. It Seems to have unused functionality under the hood.
    Shipped with pirated software, and chinsy cloned a planet CNC mk1 board
    Seem like the PCB is ready for Xyz limit switches.
    Found unpopulated contacts for spindle pwm control but I think it's for the mach3/lpt port. Same board has minor changes and is wired for USB only but has a lpt connectorfor giggles.
    It be a while but I'd like to integrate
    Coolant pump, and spindle control. Eventually I'll probe the mcu to see if it's packing some support at the firmware level. If not I have some ideas that maybe I can monitor a stepper motor such as a-axis and listen to a specific steps to activate coolant, and tune pwm.
    I could let the spindle board see a digital pot and have a mcu monitor the user speed setting, and read a switch to allow manual or auto speed. I could go a bit further and add rpm feedback too ensure x rpm is really x rpm. A feedback sensor would create better cuts and help visualize spindle load percentage

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