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Conumer Friendly CNC

Discussion in 'Concepts and Ideas' started by Andrew Allen, Dec 31, 2017.

  1. Andrew Allen

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    Why do so few CNC machines have even the simplest creature comforts?

    I see 3D printers that "home" by running against the mechanical stops in all 3 axes, tearing up the tape on the bed in the process.
    If a machine can not even find its starting point, it is not ready for widespread adoption.

    Most CNC machines are run by people who could build them, just like most computers used to be run by people who could build them.

    Computers changed. Now they fix themselves. I wonder: How hard it would be for a CNC to fix itself?

    Home switches would be the first step. Switches cost pennies each.

    Add encoders on the steppers, and modify the software to slow down and then catch up on steps when it looses steps. I see quadrature optical encoder disks and sensors for $2 a set. There was a day when the electronics would have had a hard time dealing with encoder interrupts, but today we get AtMega 2560 boards for $10. The hard part is mounting the encoders. Dual-shaft steppers get pricey. I'm sure there is a way that would work on and NEMA motor of a certain size.of we are willing to give up a quarter inch of the shaft. We just design our CNC frame to not need the whole shaft length.

    Before anyone asks, we still need home switches so we know where home is after a power failure.

    Add a sensor or two to detect vidration, and tell the software to adjust when it senses vibration by slowing the feed rate. I see 3-axis accelerometer boards for $2-$3 each. Most hobbyist CNC boards support IIC and SPI busses. There may be simpler solutions for detecting vibration.

    Add a Z button to detect where the bottom of the tooling really is.

    For 3D printers, detect a loss of fillament and stop. Ruining prints is a sign of a kludged together system. We can do better.

    I also see incompatible systems. I should be able to buy any CNC frame from a company (out of many sizes) and put any tool head on it. A locking cyllindrical collet is not that hard. The hardest part is making sure the driver board can run any head you mount, but that is a few I/O lines for transistors, relays, and/or sensors. Heads should include: 3D printers, routers/mills, foam cutters, draw knives, lasers, and more. Every tool head could include a CAD program that also generates G code.

    I wish Dremel and Lowes would get together and sell usable systems, ranging from 4"x6"x4" to 4'x8'x2'.

    What do you think?
     
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Resident Builder Project Maker Contest Winner! Builder

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    Homing switches are supported by all controllers, as are Z probes (Grbl and Smoothieware also supports XY probing by the way). People just rarely connect those because setting ZERO manually is easy.

    Filament sensor: Easy: filament-detector [Smoothieware]

    On the other hand: re Incompatible Systems: The problem (historically) is this:

    standards.png
    Credit: xkcd: Standards

    Thats why theres no concensus in this, or any industry.

    But its not that hard though. Build your machine using our modular parts, to be just that, then post your design by clicking on the "Post a Build" button to share the design with the world. If its great, it will dominate

    Personal comment (my own view): Closed loop motor control is a "want" because of underpowered drivers, a properly built and spec'ed system DOES NOT LOOSE ITS position even with open loop control of steppers. The problem why this is a problem, is those whoefully underpower and undersized(thermally) pololu drivers that got popular. Run your machine on some DQ542MA Stepper Motor Driver drivers and you wont skip steps, no need to overcomplicate the plan with closed loop control
     
  3. Andrew Allen

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    Thanks for the feedback.

    I agree on everything but the feedback loops.
     
  4. Joe Santarsiero

    Joe Santarsiero OB addict
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    Printer homing sequence should be xy then z. The trick there is for the operator to make sure they don't leave the hotend near the bed after leveling it manually.
     
  5. LordJesse

    LordJesse Well-Known
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    If you want stepper encoding, here you are:
    http://tropical-labs.com/
    A one-board arduino/driver/encoder solution.

    Jesse
     
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  6. Joe Santarsiero

    Joe Santarsiero OB addict
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    Cool.
     
  7. Gary Caruso

    Gary Caruso Master
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    If you want feedback you can get servos, it's easy just a bit more money.. Clearpath servos are one example.
    But like Peter said, good strong steppers and drivers just don't lose steps, I've hit and pushed tight clamps off the part and still not lost a step (and this is with belts!). Only when I've crashed a 1/4" bit have i lost a step without breaking a bit. With screws forget it, you can do serious damage before losing steps.

    Should closed loop steppers or servos be cheaper? Yes they would be if we all demanded them and it was the norm, but the economy of scale is not there for that.. yet..
     
  8. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Resident Builder Project Maker Contest Winner! Builder

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    Thanks for the support (; Gary

    Encoders on DC motors - thats something thats gets me excited (;
    But encoder on steppers... I've been in this game too long, i dont get excited over fads (;
    Case in point: When you buy a car, and you can choose between one that's steering is so horrible (aka weak underpowered stepper drivers in this comparison) that it tends to "go offroad every now and then" but comes with encoders on the wheels that "picks it up and puts it back on the road".... or the other option: A well built car that stick to the road you steer it on?
    By the time you skip steps you have way bigger problems (wrong cutting recipe (also very likely), crappy control/drivers, incorrect acceleration, or worse, mechanical issues (binding etc). Fix the root cause, don't overcomplicate the issue by adding complexity to fix the "symptoms" and leave the problem
     

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