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IndustryArena Forum > MetalWorking Machines > CNC "do-it-yourself" > Yet another gantry cnc design
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  1. #1

    Question Yet another gantry cnc design

    Hey guys!

    After acquiring of chinese 3018 CNC and playing around it little bit (installing new 500W 100V 12,000 RPM Spindle, limit switches, more stiff springs in anti-backlash mechanism, etc) I started to think about rebuilding it from scratch. I honestly don’t know why those chinese engineers have put the axis with the longest travel (X) on the gantry. They could easily design X travel of 180 mm and Y travel (table itself) of 300 mm without breaking the bank, thus making the gantry much stiffer. But they've chosen more floppy way and as the result whole Z carriage has a play of 2-5 mm just by twisting it by hand, let alone cutting.
    (However, I managed to get good result on the PCB making side of things though). But I wanna be able to cut & mill aluminum and for this some changes HAVE to be done.

    Let's start with basic specs for the new machine:

    Small table top footprint.
    Gantry type - fixed (for more rigidity).
    X travel - 180 mm.
    Y travel - 300 mm.
    Z travel - 95 mm.
    Table - Z carriage clearance - 125 mm (for accommodating using of 4-th axis with 100 mm chuck or basic 3" milling vise with height of 70 mm).

    Spindle.
    Two options can be installed:
    a) 500W 100VDC 12,000 RPM air cooled spindle with diameter of 50 mm (0.49 Nm).
    b) 800W 220VAC 24,000 RPM water cooled spindle with diameter of 65 mm (0.33 Nm).

    After several design iterations I came up with following hardware:

    X axis (gantry):
    2xHGR15 280mm rails. 2xHGH15CA blocks;
    SFU1204 ball screw (4 mm pitch, 10 mm minor diameter). Belt driven;
    Bearings - motor side - fixed, FK10. Opposite side - supported, FF10;
    Motor - NEMA23 57HSE2N-D25 closed-loop stepper, 4.2A, 2Nm torque. Driver - HSS57.

    Y axis (table):
    2xHGR15 420mm rails. 4xHGW15CA blocks;
    SFU1204 ball screw (4 mm pitch, 10 mm minor diameter). Direct coupled;
    Bearings - motor side - fixed, FK10. Opposite side - supported, FF10;
    Motor - NEMA23 57HSE2N-D25 closed-loop stepper, 4.2A, 2Nm torque. Driver - HSS57.

    Z axis:
    2xHGR15 160mm rails. 2xHGH15CA blocks;
    SFU1204 ball screw (4 mm pitch, 10 mm minor diameter). Direct coupled;
    Bearings - motor side - fixed, FK10. Opposite side - supported, FF10;
    Motor - NEMA23 57HSE2N-D25 closed-loop stepper, 4.2A, 2Nm torque. Driver - HSS57.


    Structure materials:
    Aluminum profiles (20x40, 20x60, 20x80, 40x40).
    Structural steel plates with thickness of 8 and 10 mm.
    Connection type - bolted.

    Several screenshots of the inventor project in the current state using 3018 original table (belt and pulleys for X axis are not yet added to the model):









    So, what do you think about the design? What aspects could be improved for milling light metals?
    Would steel plate give enough rigidity or better stick to the full aluminum structure?
    Thank you!

    Happy New Year!
    Phil.

  2. #2
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    Re: Yet another gantry cnc design

    It seems you have joined the ranks of those who bought tiny machines in the hope of producing useful parts.It isn't impossible,but it won't be quick....

    They are quite useful for getting to grips with the processes of CNC machining and maybe producing small parts from soft wood.The design you have put forward will be a big step up once its working.I would be a little concerned about the leverage on the spindle bracket and might go as far as sawing it in half with each smaller section moved as far apart as is practical.

    It looks as though you intend to use a fairly tall machine and this complicates things as far as rigidity goes.I suggest you add to the spindle in your design a collet nut and a tool and then take a look at how close the machine will approach a vertical wall in all directions without fouling,it might surprise you.It will also give an idea of how steep a slope is feasible if you try 3D surfacing.Good luck with the project.

  3. #3

    Re: Yet another gantry cnc design

    Thank you! I hope this design would work too!


    Quote Originally Posted by routalot View Post
    It seems you have joined the ranks of those who bought tiny machines in the hope of producing useful parts.It isn't impossible,but it won't be quick....
    Oh yeah..

    Quote Originally Posted by routalot View Post
    ...
    They are quite useful for getting to grips with the processes of CNC machining and maybe producing small parts from soft wood.The design you have put forward will be a big step up once its working.I would be a little concerned about the leverage on the spindle bracket and might go as far as sawing it in half with each smaller section moved as far apart as is practical.
    Unfortunately, it's placed as close to gantry as its fan can fit. (see screenshot). Now the fan clearance is 1.0 mm. Horizontal distance between spindle CL and face of the Z blocks is 49.25 mm, and between spindle CL and face of the X blocks is 87.25 MM. As the matter of increasing rigidity of the Z carriage to gantry connection I can install additional 15mm rail with 1xblock on the top of the gantry (see screenshot).

    Quote Originally Posted by routalot View Post
    ...
    It looks as though you intend to use a fairly tall machine and this complicates things as far as rigidity goes.
    Yeah. Right now uprights are 350.5 mm tall, thus I've reinforced them with 2 vertical gussets and 1 cross-member and base plate. I'll run some FEA on major machine assemblies and post results here.

    Quote Originally Posted by routalot View Post
    ...
    I suggest you add to the spindle in your design a collet nut and a tool and then take a look at how close the machine will approach a vertical wall in all directions without fouling,it might surprise you.It will also give an idea of how steep a slope is feasible if you try 3D surfacing.Good luck with the project.
    I'll definitely add them, as well as a vise and 4th axis assy.

    Thank you!
    Phil.

  4. #4
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    Re: Yet another gantry cnc design

    My suggestion for a change of spindle mount would involve sawing one of those in half and moving each half nearer the ends of the spindle body.The physics improves and the rigidity of the bearing support plate just about eliminates the possibility of flexing.I hope my screenshot has attached to this post.

  5. #5

    Re: Yet another gantry cnc design

    Quote Originally Posted by routalot View Post
    My suggestion for a change of spindle mount would involve sawing one of those in half and moving each half nearer the ends of the spindle body.The physics improves and the rigidity of the bearing support plate just about eliminates the possibility of flexing.I hope my screenshot has attached to this post.
    Oh, I see now what you mean! Nothing beats good visual explanation
    Yeah, this definitely gives less freedom in vertical axis. Gonna put it in the model.
    Thanks!

  6. #6

    Re: Yet another gantry cnc design

    Quote Originally Posted by routalot View Post
    My suggestion for a change of spindle mount would involve sawing one of those in half and moving each half nearer the ends of the spindle body.The physics improves and the rigidity of the bearing support plate just about eliminates the possibility of flexing.I hope my screenshot has attached to this post.
    Hmm, I forgot, that spindle mounting plate is just 62 mm height and bracket is 40 mm. So after sawing it I can only get about 62 - (40/2-3(width of cut)) = 25 mm spacing between 2 halves.
    I'll add them to the model to show this visually.

  7. #7
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    Re: Yet another gantry cnc design

    Buy two?

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