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

  1. #401
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    Default Re: David A's New 2x3 Bench Top CNC

    From a support point of view you only need the top and bottom clamp on the spindle. This will save you $$$ and weight. More contact area on the rod clamp will be better. Or even a 100% clamp vs the thru bolts. Peter



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

    Outlawtaz, please do.



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

    Quote Originally Posted by peteeng View Post
    From a support point of view you only need the top and bottom clamp on the spindle. This will save you $$$ and weight. More contact area on the rod clamp will be better. Or even a 100% clamp vs the thru bolts. Peter
    Peter, you are correct with just the top and bottom clamp. Effective clamp height would still count as 4".

    However, as the shafts and the clamp plates should act as a single piece, my thought was that four clamp bolts per shaft would provide more stiffness and distribute loads better, particularly on side-to-side loads. 4" high single piece clamp would definitely be better but there are also inside countersunk bolt holes for the shafts required and I did inquire at several shops about machining this spindle mount as a single piece and the cost was way beyond the scope of this machine. I myself do not have the equipment to machine 4" aluminum into this shape with sufficient precision.

    The contact areas on the shafts or the clamp is determined by the open ball bushing specs. I utilized the maximum possible area.



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

    The ClearPath software runs only one servo at a time.

    To try out the Y-axis (two servos, Y/A), I had to
    install only one servo on one side and run that
    single servo. I had to dial down the acceleration
    rate to not stress the gantry too much and then
    let go early to not hit the bumper with the slow
    deceleration.

    This is at 150 ipm:

    .



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

    And this is at 450 ipm:




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

    Hi David - I do quite a bit of contact analysis and I'm sure the top and bottom is all that's needed. The word "should" is not equivalent to will. If you had a bronze bush or roller bearings its the edges that do the work. Keep Making cheers Peter



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

    Quote Originally Posted by peteeng View Post
    Hi David - I do quite a bit of contact analysis and I'm sure the top and bottom is all that's needed. The word "should" is not equivalent to will. If you had a bronze bush or roller bearings its the edges that do the work. Keep Making cheers Peter
    Your analysis is faulty if you think a roller Bearing or bronze bush work like that, it's all about how the bearing or bushing is loaded, what he is doing is for rail support, more than spindle support

    Mactec54


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

    Hi Peter, first of all, thank you for your contribution.

    You are correct with your suggestion of not
    needing the middle clamps for spindle clamping.

    Both conditions provide the same clamping
    height when looked purely for clamping function:
    David A's New 2x3 Bench Top CNC-img_6312-base-s-h-jpg

    David A's New 2x3 Bench Top CNC-img_6312-2-s-h-jpg

    Last edited by davida1234; 03-22-2019 at 05:46 PM.


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

    However, this assembly is also the Z-slide.

    It has to transfer cutting loads from the
    spindle through the clamps to the shafts
    (rails) which in turn run in the ball bushings
    of the X-carriage:
    David A's New 2x3 Bench Top CNC-img_6312-base-jpg

    If you do not connect the bottoms of the
    shafts with each other, you have two
    independently cantilevered (unsupported)
    shaft ends which could move independently
    from each other. With regards to the load
    plane, this would mean a possible twisted
    load plane.

    If you do provide a connection at the
    bottoms of the shafts with each other, less
    twisting will occur as the two shafts and
    the clamp will now begin to act more like
    a Vierendeel truss.

    In that case, the 4-clamp layout would have
    more structural rigidity than the 2-clamp layout:
    David A's New 2x3 Bench Top CNC-img_6312-jpg

    David A's New 2x3 Bench Top CNC-img_6312-2-jpg

    Last edited by davida1234; 03-22-2019 at 05:29 PM.


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

    It turns out that the shortest ball screw
    of them all has a slight bend.

    I could not get the Z-slide to move
    as smoothly and quietly as the other
    ball nuts.

    While waiting for a new screw, here
    is what I have so far for the Z-slide.
    Max. speed would be about 330 ipm
    with the gearing I have but I ran it at
    200 ipm only with the bent screw:





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

    I used to design a lot of gantries for marinas. And once we were asked to build some that were Vierendeel trusses vs the usual diagonal brace truss. This was for aesthetic reasons so various decorative panels could be put into the rectangular holes. I could never get these to work as the vertical baluster connections did not have enough stiffness or strength to support the required live load unless these were made exceptionally large or very many or had large braces in the corners, defeating the aim for a rectangular hole. So that's why you do not see many of these things, they are not very efficient structurally.

    If you consider the stiffness of a bolted connection it is usual to have two bolts per connection so as to provide the connection with rotational resistance, as a connection can rotate around a single bolt connection. Each of the clamp connections in this design relies on a very good preload and a very good fit to prevent this rotation and hence fretting in the joint. I suggest a drop of loctite on these surfaces when you do then up will help. To improve the fit lapping would be good as well but this is going a long way to prevent something that you are addressing by having lots of bolts and parts at this point in the structure. I'm sure it's going to work. I appreciate that all designs are a bunch of compromises and as soon as a decision is made to go a certain way you end up with good and bad aspects around that . Your shafting is huge so I'm sure it will work fine After many hours of router work you will find out how this designs fairs. After 2 years of work I pulled down a router and found the Z linear bearings had some unexpected clearance. Looking at the distance travelled (as UCCNC keeps a record of X,Y,Z travelled) this was very unexpected. So speaking to the supplier about the bearings, preload and utility etc has changed my view on how to spec these in future. The z axis does quite a bit more work then expected especially when it gets bumped and it crashes. It's the first contact area so to speak of the tool loads so needs to be robust. Peter



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

    Quote Originally Posted by peteeng View Post
    it is usual to have two bolts per connection so as to provide the connection with rotational resistance, as a connection can rotate around a single bolt connection.
    Peter, I appreciate your insight.

    You are right, the Vierendeel truss is an inefficient way for
    a structural shape than triangulation but in this case, it was a
    "free" outcome and besides, hard to triangulate two SS rods.

    And I think four bolts are even better than two.



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

    Electronics and software....... My weakest point.
    It seems that my brain just doesn't work their way.

    Trying to make some progress. I am new to
    UCCNC/UC100 and a lot to understand even
    if it is somewhat similar to Mach3.

    At least the C11G seems fairly simple.

    Installing the triggers for the proximity switches.
    Just a steel bolt / T-nut affair:
    David A's New 2x3 Bench Top CNC-15-img_7770-jpg

    David A's New 2x3 Bench Top CNC-16-img_7773-jpg

    Adjust clearance with the sensor. About 3-4mm:
    David A's New 2x3 Bench Top CNC-17-img_7782-jpg



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

    I am reposting the website info for
    the ball nut drive in case somebody
    is interested in reviewing what is
    involved with it and missed the link.

    Comments and criticism are welcome.

    powerballnuts.com

    Thank you,
    David

    Last edited by davida1234; 03-23-2019 at 09:58 PM.


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

    .

    I NEED HELP!

    All axes individually work fine when connected to
    ClearPath software but nothing moves with UCCNC.

    Have been combing through the manuals for
    CNC4PC's C11G BoB, UCCNC and UC100 all weekend.

    UC100 and C11G powered on.:
    David A's New 2x3 Bench Top CNC-img_7788-jpg

    Last edited by davida1234; 03-24-2019 at 09:30 PM.


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

    X-axis setup. I tried switching step/direction. No change:
    David A's New 2x3 Bench Top CNC-img_7790-jpg

    Y-axis setup. I tried switching step/direction. No change:
    David A's New 2x3 Bench Top CNC-img_7800-jpg

    A-axis setup. I tried switching step/direction. No change:
    David A's New 2x3 Bench Top CNC-img_7801-jpg

    And the Z-axis setup. I tried switching step/direction. No change:
    David A's New 2x3 Bench Top CNC-img_7802-jpg



  17. #417
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    Default Re: David A's New 2x3 Bench Top CNC

    General settings:
    David A's New 2x3 Bench Top CNC-img_7793-jpg

    Diagnostics:
    David A's New 2x3 Bench Top CNC-img_7796-jpg

    And appearance if that makes any difference:
    David A's New 2x3 Bench Top CNC-img_7797-jpg



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

    And an unrelated question:

    Could not figure out how to do keyboard shortcuts for X-Y-Z jogging.
    How do you set it?

    Also, there is no need for the A, B and C axes.
    Makes it cluttered. Can you remove them from the window?

    David A's New 2x3 Bench Top CNC-img_7792-jpg

    Thank you for any help. I am really stuck at this point.



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

    To add hotkeys in UCCNC on the Configuration-I/O trigger-Hotkeys page select one of the empty slots. Press the SET button next to the key code and on the pop up window press the keyboard button you want to use and when you see the key code appearing then press OK.
    Press the SET button next to the Function slot and from the pop up rolldown list select the function name you want to use or type in the function code of the jog function you want to use. (if you know the code).

    I have no idea why your axis not running. I have no experience with those servos unfortunately.



  20. #420
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    Default Re: David A's New 2x3 Bench Top CNC

    Hi David - Each component in your Z assemble that we are speaking of only has one bolt in each connection not 4. A connection is defined by two faying surfaces. Your touching surfaces (faying) only have one bolt in them. The connection depends on the preload of the bolt creating friction in the arched area and the geometry of the arch resists rotation. If it was flat then friction is the only thing stopping rotation under load around a single bolt (friction maybe enough depending on the situation). If the fit is not as perfect as possible (and it will not be unless lapped) then the connection can wiggle slightly thru every load cycle fretting the surface asperities (high spots probably on aluminium side vs the steel side) leading to looseness. The loadpath thru this assm would be complex. The middle parts may not see any load. Don't want to labour this, your connection will work fine it's just a finer point in machine design to understand. To get around this adhesives are now used in joints to improve the connection grip vs friction eg loctite or epoxy. In your assem connection rotation is resisted by the router up the middle holding the single bolt line so in terms of the primary load path it can't rotate but if it frets it can slightly. This is an endurance design issue vs a static load condition issue, time and motion will give us the answer.... This is typical of a bedding in period of a machine. You do everything up run it for a while and find things have loosened up. The machine has knocked off or compressed the asperities and so then you retorque and go this again. After the third reset it won't change for a very long time usually.

    Cheers Peter

    As a general machine design principle we try to keep the loadpath simple and clear (KISS everywhere) to understand so that it is easy to calculate the required performance of the part or connection in question. This also results ina simpler machine and simple is best. In this case if the two middle bits are left out then this is easy to do. If the middle bits are in its very difficult to predict the loadpath unless you use sophisticated FEA. So we'd probably assume that the outers are the primary loadpath and the inners are redundant and along for the ride. Keep at it, great build. There's lots of discussion about software, electronics, dust collection (which is great) etc in the forums but not much detail on mechanical engineering. Always looking for a bright idea if I can't figure one out myself...

    Last edited by peteeng; 03-25-2019 at 01:57 AM.


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