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Thread: big budget cnc

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  1. #1

    I am peter 30 from belguim.
    first of all sorry about the bad english i don't typ it a lot.

    I am thinking of building a cnc and i hope you can help me with the design.

    The idea i have is a machine of about 3000x 1600.
    Why this big ? because i have a small company and i make kitchens ,dressings,TV cabinets etc.
    this way i can lay down a sheet of MDF of melamine and cut the pieces .

    But the thing thats special about the machine is the next thing:
    i want the gantry to be 3000 mm, so basicly a big gantry and smaller X axes then normal.
    i was thinking for the gantry 160 mm high and 80 mm deep.
    is this enough or do i need to make it bigger so it do's not flex?

    Instead of linaire rails i was thinking a strip of steel or alu and then ball bearing rolling on the alu or steel rail.
    the reason why is simple.
    I want to start with a budget machine and later in the future upgrade it with better linaire rails like hiwin etc but for know i don't have the money to spend on expensive linaire rails.
    for now i will use a bosch router but also in the future a spindle.

    For the drive i was thinking rack&pinion module 1 is this enough or do i need to use 1.5 or 2?
    the motors and R&P will be mounted on the rails on top.

    i was thinking to use these motors.
    Nema 23 stepping motor 57BYGH627

    is this strong enough or not?

    i made some drawings in sketchup.

    Sorry for the many questions but i just want to be sure before i start building.
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  2. #2
    Your machine has so many mistakes I don't think your kitchens will fit together very well.

    Have you considered copying someone else's working design and fixing their mistakes rather than inventing your own?

  3. #3
    what are the mistakes?

    and do you reccomend someone else's design?

  4. #4
    mekanik's Avatar
    Lives in Barrow in Furness, United Kingdom. Last Activity: 15 Hours Ago Has been a member for 9-10 years. Has a total post count of 660. Received thanks 85 times, giving thanks to others 128 times.
    Hi pet30
    Welcome to the forum
    I can't see any logic in having your gantry that long the machine would normally have the gantry spanning the shortest width.
    trying to construct a gantry that length you are on a hiding to nothing, have a look through some of the build logs.
    Enjoy the forum.

  5. #5
    Forget the round rails and bearings.
    I tried it circa 2006..

    Steel frames, sand for smoothness / non-binding,
    increase section sizes 2-5x,
    glue in with industrial goops and bolt if you want, ..

    For accuracy, a steel or granite machinists reference edge/plate, vertex 1000 mm is cheap to 0.04 mm / m,
    sand with wide belt sander to remove most of the bend/curve.
    Then assemble/build, with non-binding free-running linear guides.

    You probably cannot make a good commercial-level cnc router for cheap --
    no-one can.
    Look at mechmate. 8-10k for parts.
    I will likely make one for a local business for full-sheet 2.5 x 2 m size .. and will charge 20k or so.
    It MUST have a toolchanger to be useful/profitable.
    Likely, it will be horizontal, like the more productive modern CNC machining centers.

    Most likely, the 20k cost is paid in 1-2 months.

  6. #6
    and if i was to change the gantry to 1600 mm so just flip the design?
    could i then use ball bearings etc?

    is not my fulltime job , i make kitchens etc after hours. so the machine do's not need to get super fast speeds.

    and could i use the same system as this machine? he uses rack&pinion and round rails


  7. #7
    Strength is not the issue.
    Rigidity is.

    All machine tools are loaded, at max, to == 2% of their strength ie yield point.
    Machine tools today are lightly loaded stressed-skin structures.

    You can make a router with the ball bearings, and it will work. Yes.

    It will not be productive vs others, and cannot use modern carbide cutters, due to flex/vibration/chatter, effectively.
    Your proposed solution will work fine at 5-10 ipm, feed, where real machines run 100-200-800 ipm.
    So about 20x less productivity.

  8. #8
    It will not be productive vs others, and cannot use modern carbide cutters, due to flex/vibration/chatter, effectively.
    Your proposed solution will work fine at 5-10 ipm, feed,
    This is 100% not true.
    Do not listen to Hanermo, who tells everyone that they need to spend $20,000 on a 10,000 lb machine.
    I built a machine 13 years ago, out of wood, using skate bearings on round pipe for the linear bearings. It still runs today, and I can cut at 200ipm, with carbide cutters. With better motors and drives, It could cut much faster.

    Having said that, your design does have some serious flaws.

    Not sure what material you plan on building from, but it looks like a simple aluminum tube?
    If you want to use 80x160 for a gantry, it really needs to be a heavy extrusion, not just a tube. That tube you have modeled will easily flex and twist.

    While skate bearings can be made to work, there are some things you need to be aware of.
    They need to be in very tight contact with what they are riding on, in order to have a rigid structure. And on a flat surface like that, they are not very tolerant of dust and chips, and will bind if dust builds up under them.
    You also are only showing bearings in one direction in each carriage. You need additional bearings to constrain the carriages in the other direction.

    This is a very large machine. It's easy to build a fairly rigid small machine. But as the machine gets bigger, it gets much more difficult. Everything needs to be bigger and stronger, to achieve rigidity. And rigidity is of the utmost importance.
    I think that you will be very disappointed if your first machine is this large. I would recommend building a much smaller machine, which will teach you where you need to improve your design. If you build something similar to what you've shown, it likely won't be worth upgrading in the future. Build a small, inexpensive machine to learn with, and a larger, more expensive machine when you can afford to.

    You can not direct drive the pinion on the stepper shaft. you'll have poor resolution, and not enough power.
    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CAM for Woodworking Joints

  9. #9
    Morning, do you have a budget in mind for this?
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  10. #10
    Your idea is riduculous. Be realistic and prepare a budget of 6k for simple machine this size or better 8k for a Ferrari

    Just copy my second machine and it will do whatever job you throw at it. No need for the heavy duty Z, just 3kw spindle. I have plans for it that i sell to people that know what they want and i offer one to one support for the build.

    Tool changer is not needed for kitchen jobs and it costs 3k at least and you need a controller that could do the job.

    20k machine will NOT pay for a month. You need to have factory and at least 10 people working for you for that to happen. But then you will not be looking at DIY machine, right.

    Maybe a second hand machine around 10k is better for you and will start making money at day 1. You will need 1/2 year at least to build your machine, even if you have the detailed plans of my machine or any other. Its not a one day job. Most people here like what they do and its their hobby, side business or similar so they take their time. Even if i have all pieces i will need a month to build it.

    That may answer all your questions. And yes, crappy machines not with proper linear bearings will make you pull your hair off and will be total waste of time and money. MONEY.
    project 1 , 2, Dust Shoe ...

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