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IndustryArena Forum > WoodWorking Machines > DIY CNC Router Table Machines > Fair strong DIY CNC machine (Wood and Aluminum) - Design Idea
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  1. #1

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    Jun 2021
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    4

    Fair strong DIY CNC machine (Wood and Aluminum) - Design Idea

    Hi Everyone, I have decided to try build my own CNC. What I am looking for is to build a fair strong platform that works with wood mainly and aluminum sometimes. I found a really nice design on internet (I lost link to owner but all credit goes to him), and I started modifying his design to better idea until reached initial design as per photos.

    Items planning to use:
    - 2.2kw water cooled spindle
    - NEMA 34 stepper (4.0N.m / 3.6mH) for all axis
    - SFU1605 ball screw for all axis
    - HGR20 linear guide rail for X and Y axis
    - HGR15 linear guide rail for Z axis

    Workable Area (so far):
    Y > 790 mm
    X > 648 mm
    Z > 125 mm

    Looking forward for your feedback and idea. thank you in advance.
    Attached Thumbnails Attached Thumbnails 1.jpg   2.jpg   3.jpg  

  2. #2
    Member
    Join Date
    Jul 2018
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    3488

    Re: Fair strong DIY CNC machine (Wood and Aluminum) - Design Idea

    Hi Rab -
    1) For that size spindle I would use 20mm cars vs 15mm on the Z. The bottom cars on the Z take a lot of beatings and need to be strong. Especially if you want to take full advantage of 2.2Kw. oK for a 1.5Kw
    2) The base screw bearings mounted on the cantilevered flat plate is a candidate for vibrating. Either mount it lower or web it some how
    3) The large N34 Z motor again is on a cantilever and is a candidate for vibrating stiffen it or support it better
    4) the construction extrusion bolted to the back of the gantry is way too inefficient. Since your cutting up plate make a plate box gantry way better
    5) Its not ideal chopping so much metal out of the Z plate for the drive nut. Its usual and better to do the trench in the gantry so the tool plate is as stiff as can be
    6) The bearings behind the spindle need to be further apart the 2.2kW spindle if used to its max will generate a lot of moment on this area. Especially since you have picked 5mm pitch for the screws, these will move small trucks quite easily so forces will be large
    7) Its coming along... Peter

  3. #3

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    Re: Fair strong DIY CNC machine (Wood and Aluminum) - Design Idea

    Quote Originally Posted by peteeng View Post
    Hi Rab -
    1) For that size spindle I would use 20mm cars vs 15mm on the Z. The bottom cars on the Z take a lot of beatings and need to be strong. Especially if you want to take full advantage of 2.2Kw. oK for a 1.5Kw
    2) The base screw bearings mounted on the cantilevered flat plate is a candidate for vibrating. Either mount it lower or web it some how
    3) The large N34 Z motor again is on a cantilever and is a candidate for vibrating stiffen it or support it better
    4) the construction extrusion bolted to the back of the gantry is way too inefficient. Since your cutting up plate make a plate box gantry way better
    5) Its not ideal chopping so much metal out of the Z plate for the drive nut. Its usual and better to do the trench in the gantry so the tool plate is as stiff as can be
    6) The bearings behind the spindle need to be further apart the 2.2kW spindle if used to its max will generate a lot of moment on this area. Especially since you have picked 5mm pitch for the screws, these will move small trucks quite easily so forces will be large
    7) Its coming along... Peter

    Thank you Peter,

    1) i will change to 20 mm
    2) i will try redesign to make it better
    3) i think i found better mount for N34 motor
    4) now this important, if i do plate box gantry, will not be heavier?? the extrusion is bolted too with the cantilevered flat plate (not showing in photo up) will not be good?
    5) am working on that, i really need as you said to reduce a lot of metal in Z
    6) i will wide the distance between them.

    I have important question, the SFU1605 ball screw. I have been told they will make the movement way slow on X and Y axis with N34 motors, do you suggestion i go for 1610 or 2010 maybe?

  4. #4
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    Apr 2004
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    109

    Re: Fair strong DIY CNC machine (Wood and Aluminum) - Design Idea

    You would want to go with a 10mm lead screw to optimize speed vs a 5mm lead screw. You really do not lose any usable resolution unless the rest of your machine is really robust and tuned in to use that resolution.

    Even with my current 25mm 4 start ball screw, with N34 motors, I am limited to 350 ipm max Rapids running with 78v feeding the controllers, but stay well below that max speed as a safety margin.

    John Z

    Sent from my SM-G991U using Tapatalk

  5. #5

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    Re: Fair strong DIY CNC machine (Wood and Aluminum) - Design Idea

    Quote Originally Posted by JohnZ View Post
    You would want to go with a 10mm lead screw to optimize speed vs a 5mm lead screw. You really do not lose any usable resolution unless the rest of your machine is really robust and tuned in to use that resolution.

    Even with my current 25mm 4 start ball screw, with N34 motors, I am limited to 350 ipm max Rapids running with 78v feeding the controllers, but stay well below that max speed as a safety margin.

    John Z

    Sent from my SM-G991U using Tapatalk
    so do you suggest i stay with NEMA34 and change to 10mm lead screw, or go to closed loop NEMA23/NEMA24 and stay with SFU1605?

    I found NEMA23 3N.m (425 oz.in) 3 phases and NEMA24 4N.m (566 oz.in) 2 phases with good price so money not that big difference now

  6. #6
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    Re: Fair strong DIY CNC machine (Wood and Aluminum) - Design Idea

    I would say to go with the 10mm pitch with either motor frame size. This provides the following benefits...

    Lower RPM of the ballscrew at both cutting and rapid movements. Reduced whip on those long screws. Keeps the stepper motor up in its higher torque curve, minimizes missed steps.

    Cons - reduced resolution per step. This is really only a con when your entire machine can actually use that resolution under cutting forces. Let's look at your 10mm lead with a typical 200 step per rotation motor at 1/8 microsteps. Each microstep gives you 10mm / 200 / 8 or 0.00625mm (or about .00025") of motion. Your gantry plus all other mechanical components combined will flex orders of magnitude more than this. Reduced linear thrust. This might be an issue, but if you look at the torque curve of your motor, then compare the motor torque at the RPM you will be cutting at with a 10mm lead, then compare the torque at 2x that RPM for a 5mm lead, thus usable thrust will be remarkably similar. I know that this is very oversimplified, but the bottom line is that the 10mm lead will be better for your use case than a 5mm lead.

    Regarding N34 vs N23... I'll just say that I regret buying large N34 motors. I would have been much better off with N23 motors with a lower inductance, and more usable torque at the RPM's I actually use. I wasted time and money going from a 12v controller, to 24v, then to 80v controllers, then from generic Chinese controllers to Gecko controllers. I'd have been much better off with good N23 motors and good controller's from the beginning.

    John Z

    Sent from my SM-G991U using Tapatalk

  7. #7
    Community Moderator ger21's Avatar
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    35476

    Re: Fair strong DIY CNC machine (Wood and Aluminum) - Design Idea

    Go with 2010 screws, and find some Nema 34's with much lower inductance, less then 2mH. Run them at 60V.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

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