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Thread: David A's New 2x3 Bench Top CNC

  1. #49
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    Default Re: David A's New 2x3 Bench Top CNC

    With the main assemblies of the machine mostly finished, time to move onto the details.

    First, the weight of the Z-Slide will be balanced with springs to provide an equilibrium.

    I use four small springs. Unfortunately, I could not source SS springs with the required properties:
    David A's New 2x3 Bench Top CNC-b5-img_7408-jpg

    Slip two of them onto the 3/16 spring pin and drop in place:
    David A's New 2x3 Bench Top CNC-b6-img_7409-jpg

    David A's New 2x3 Bench Top CNC-b7-img_7411-jpg

    That's how it looks like from the side:
    David A's New 2x3 Bench Top CNC-b8-img_6715-jpg



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    Default Re: David A's New 2x3 Bench Top CNC

    Next, bend a small hook at one end of a 12ga wire and push it up from the bottom:
    David A's New 2x3 Bench Top CNC-b9-img_7413-jpg

    Catch the loop of the inside spring:
    David A's New 2x3 Bench Top CNC-b10-img_7412-jpg

    Pull down the spring and place it onto the inside position of the spindle mount bar:
    David A's New 2x3 Bench Top CNC-b11-img_7414-jpg



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    Default Re: David A's New 2x3 Bench Top CNC

    Pull down the same way the second spring:
    David A's New 2x3 Bench Top CNC-b12-img_7416-jpg

    And place it on the outside position of the bar:
    David A's New 2x3 Bench Top CNC-b13-img_7418-jpg

    Repeat the same on the other side for the remaining two springs.

    The four springs balance the weight of the Z-Slide and the spindle nicely at about half way of the Z travel.
    If equipment weight changes, there are simple spacers that can be placed under the top pin:
    David A's New 2x3 Bench Top CNC-b14-img_7419-jpg

    David A's New 2x3 Bench Top CNC-b15-img_6896-jpg



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    Default Re: David A's New 2x3 Bench Top CNC

    So you not only lifting the weight of the spindle, but that massive mount for it and the those heavy steel round bars. A lot of extra weight compared to others of the same size.

    Last edited by wmgeorge; 02-25-2019 at 06:56 PM.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router Mach4 Kimber 1911 45ACP


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    Default Re: David A's New 2x3 Bench Top CNC

    Good point wmgeorge. The complete setup with everything including spindle, weighs about 25 pounds.

    I don't know how that would compare to a conventional, fairly heavy duty Z-slide, with the linear rail part,
    the spindle mount, the extension plate which usually is necessary, screws/bolts, spindle, etc.
    David A's New 2x3 Bench Top CNC-weight-z-axis-jpg

    Also, please note that the mount provides a full 4" of spindle clamp height for a firm hold of the spindle
    body which very few mounts would provide, I would think.



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    Default Re: David A's New 2x3 Bench Top CNC

    Another point I would like to make is the leverage on the Z-Slide.

    From what I saw on conventional Z-slides, the spacing of bearing points of the
    Z-axis are usually fairly close to each other to provide for max. vertical movement,
    thus creating a large cantilever of the Z-slide.

    On this layout, the bearing points are much farther apart, with the spacing
    of bearing points being larger than the cantilever distance (B) even at the
    bottom of travel:
    David A's New 2x3 Bench Top CNC-leverage-jpg

    The point I am trying to make is that this is a test mule where this new layout
    has nothing proved yet. Right now, the shafts are 30MM. Once I get to the
    cutting phase, maybe it turns out that the shafts are over sized, maybe 25MM
    or even 20MM would be sufficient which would reduce the weight even further.



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    Default Re: David A's New 2x3 Bench Top CNC

    I do a lot of 2.5 D work and V Carving. I also cut MDF board so I need speed on the Z for one yet heavy duty for the other. I have a NEMA 34 motor driving the Ball screw and running on linear rails. My Z is maybe 10-15 Lbs. I have the speed for the carving, and durability for the MDF.

    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router Mach4 Kimber 1911 45ACP


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    Default Re: David A's New 2x3 Bench Top CNC

    That's great info, thank you. The servo I have is a lower power Teknic.



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    Default Re: David A's New 2x3 Bench Top CNC

    On your drawing above you show both A & B having the same direction of force. Actually when cutting or engraving but not so much, a twisting action force is present, on the Z carriage which is transferred to the gantry as well. Perhaps thats the reason most builders are using the flat linear rail and bearings?

    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router Mach4 Kimber 1911 45ACP


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    Default Re: David A's New 2x3 Bench Top CNC

    wmgeorge, of course you are correct and have a keen eye. The upper blue arrow is actually the other way and the lower blue arrow is almost the fulcrum. This was more to show the spacing of the two bearing points (A) relative to the distance (B) of the cutting force and the two blue arrows opposing the cutting force looked more descriptive to me.

    I have to be more careful next time I paste a quick sketch!



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    Default Re: David A's New 2x3 Bench Top CNC

    Quote Originally Posted by davida1234 View Post
    wmgeorge, of course you are correct and have a keen eye. The upper blue arrow is actually the other way and the lower blue arrow is almost the fulcrum. This was more to show the spacing of the two bearing points (A) relative to the distance (B) of the cutting force and the two blue arrows opposing the cutting force looked more descriptive to me.

    I have to be more careful next time I paste a quick sketch!
    You are on the right track the design is good I have a similar but quite different design same idea and principle just waiting for a patent on the design before I show it here

    Mactec54


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    Default Re: David A's New 2x3 Bench Top CNC

    Thank you for the encouragement mactec54. This prototype was planned to have a
    slightly different approach to some of the conditions on a conventional CNC.



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