Thread: New to CNC

  1. #1
    Hello all.

    New Member hoping to get into the world of DIY Self Build CNC machines, primarily a router initially.
    I have no practical experience of CNC Machines but did some Coding simulation in Auto Desk Inventor during my Mechanical Engineering HNC course several years ago.

    I have a new project coming up next year where I will be converting a VW Van to a Camper. The furniture units can be made or bought as a flat pack and installed but you get a generic layout unless you commission a bespoke build which can cost 1000's.
    So, being the inquisitive type I am, I am looking to make my own cabinets from 15 mm Lightweight Furniture Plywood myself on a Gantry type CNC Router.
    The biggest piece of board I will have to work with is 1300 mm by 800 mm.

    So I have ordered the following from China to get me going and to aide my design. I have a spare 32 bit PC to use with the CNC Software and will use Autodesk Inventor on my 64 bit PC.

    2pcs SBR16 - 350mm linear rail
    2pcs SBR16 - 1000mm linear rail
    2pcs SBR16 - 1500mm linear rail
    12pcs SBR16UU block
    1pc* SFU1605 - 350mm ballscrew with ball nut* *(BK12/BF12 end machined)
    1pc* SFU1605 - 1000mm ballscrew with ball nut*(BK12/BF12 end machined)
    2pcs SFU1605- 1500mm ballscrew with ball nut* (BK12/BF12 end machined)
    4pcs BK/BF12 Support
    4pcs 6.35*10mm coupling
    4pcs Nut housing

    I am planning on having 2 X-Axis Ball Screws to avoid rake, I just don't know at this stage how the 2 screws will be driven. Belt driven form 1 NEMA 23 motor or each screw with its own motor (I have ordered 4 motors/couplers/drivers).
    I'm not sure yet how the X-Axis rails will be mounted but I want to investigate the possibility of the rail supports (maybe 10) being initially setup using a multipoint water leveling system where it will allow many support blocks, all of exactly the same size to be set and levelled on a set of connected water towers (110 mm Plastic Pipe) before they are fixed in place by some means.
    I have worked with casting polyester resins in the past, so I want to explore the possibility of casting the Gantry in one piece. So, the 2 X-Axis side supports and one pierce with eh Y and Z -Axis main back plate.
    So, I would like the thoughts of the community on my plans and welcome any feedback even if negative.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. thanx for sharing.......

  3. #3
    Very interested in your project. I myself am a machinist, having worked for last 50 years on lathes, milling machines etc. in tool and die building work. Never worked with cnc though.

    I've been thinking of building a cnc router for quite a while but ended up purchasing a router from auction. It's a Rye model MG2420. with a bed big enough to take on a full size 8x4 or 1x2 meter board

    I'm in South East Kent, near Margate. CT10 area. What parts are you in?

  4. #4
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 15 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 8-9 years. Has a total post count of 6,259. Received thanks 1,031 times, giving thanks to others 45 times.
    Bobby think I'm probably too late saying this as you say ordered and cannot believe none of the other experienced builders haven't piped up.!

    The parts you have shown are all wrong for the machine your wanting to build.
    5mm pitch screws are too slow for cutting wood and larger machine. This is made worse by the cheap motors and drives probably combined with low voltage psu.

    To cut woods correctly so your getting good finish and tool wear you'll need feedrates higher than what 5mm pitch screws and those electrics will allow.
    Let me explain little better why.
    If those motors/ drives and psu are what i think they are then you'll be limited on the usable rpm the motors can produce.
    Cheap motors often have high inductance rating, inductance affects the speed that can produced for a given voltage before torque drops away. So if you have low voltage psu coupled with high inductance motors the motors stall low down the rpm range.
    This combined with high pitch screw affects the feeds you can achieve.
    To give some idea of how slow I'm going to guess a few details based on experience.

    So lets say using 36v psu with inductance around 12mh which is typical for cheap nasty motors, then you'll be lucky to reach 900rpm before motors run out of usable torque and stall.
    Given 5mm pitch then your maximum velocity will be 5 900 =4500mm/min.
    Not that bad you may be thinking, but it gets worse because the drives are analog and highly likely to be affected by resonance which affects motors causing them stall even lower down rpm range.
    Then factor in other power robbing affects like missalignments etc and you'll be down in the 3500mm/min area. In reality you'll leave a safety margin when tuning motors so your realistic max velocity will be 3000mm/min.
    Now this is maximum velocity or rapid speed which can't really be used for cutting because your very close to maximum torque and extra forces cutting requires will stall motors.

    In real world use you'll be limited to maximum cutting feed of around 2500mm/min which isn't any where near fast enough to cut woods.

    For a router you really need 10mm pitch running motors at least with 60vdc and ideally with digital drives to help massively with resonance. Or at least with good analog drives.

    Know it's like shutting gate after horse bolted but it's biggest mistake often made by new cnc builders rushing out buying parts before knowing whats required to give a good setup.



    Sent from my SM-T580 using Tapatalk

  5. To get an accurate idea of what your setup might do, you can use this calculator made by another forum member:

    http://www.mycncuk.com/threads/1524-...tor+calculator

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