1. #1
    Hi Everyone !
    my name is Olivier and I'm from Belgium.

    In first place I want to thank you for all the extremly valuable informations your are sharing here. I would never come up with this design without you !
    Also I'm learing English so feel free to correct me when I write nonsense sentences

    For now I'm at the design stage (for the last 2 years actually...), and this is probably the 8th version. Now I want to BUILD this thing. Since a few brains are better than only one, please comment my choises without scruples !

    here are my main requirements :

    - moving gantry (floor space constraint)
    - approx. 1200x750x110mm working area
    - capable of 3D wood and aluminium machining. For aluminium, I've no need for speed but I want quality surface finish, as I expect to machine multipart molds. if I understand well, I need BOTH rigidity and speed for Aluminium ? I will make an effort about resonance by filling most cavity with PU
    - The whole machine have to be moveable easily enought without loosing accurracy, or a least be easy to recalibrate.
    - future option for a second extra light and quick gantry for plasma cutting, scribe, 3D printer, etc..
    -room for improvment as finance make it possible (servo, better spindle, etc)

    Here are the major parts and design choises :

    - 2.2k spindle with VFD, design provision to swap to 3kw spindle in the future
    - 2x rm1605 ballscrew and motor for Xa and Xb
    - 1x rm1605 ballscrew for Y
    - 1x rm2005 ballscrew for Z, probably with gaz spring (I'm thinking about direct belt drive in place of ballscrew for price and compactness, using )
    - anti-backslash ballscrew nut OR dual nuts with preloading setup for Xa, Xb, Y and Z
    - NEMA23 3Nm stepper motor (because I have them, will be swapped for servo when money allow)
    - HTD 5mm 15mm wide belt reduction, swappable between 1:1, 3:1 and 1:3 ratio
    - HGR15 rails for Xa, Xb and Y
    - HGR25 rails for Z

    for electronics I'm thinking of linuxCNC, Mesa card and gecko drives, but since electronics is no problem for me I will concentrate on mechanical aspect of the machine for now.

    there is a lot of things not drawn on this model, like gear reduction, motor bracket, base, etc. but I think this is enought to start think with.

    frame is build mostly with 80x80x3mm steel tube.
    Xa and Xb are 200x80x3mm steel tube with a slot on the outer edge so I can integrate ballscrew inside the tube.
    this is for dust protection only since the slot ruin the rigidity of the tube, the rail will be mounted on some 200x40x8mm angle iron and will be reinforced from the inside of the machine.

    Click image for larger version. 

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    epoxy leveling wiil be done in one pass for Xa, Xb and Y, then Y will be flipped 180 and linear bearing will be mounted directly on the epoxy. I think this method will help me a lot it will come to fine tune everything. the two remaining epoxy channels will be used as datum for tuning the rails, and as straight edge for other uses in the future.

    Click image for larger version. 

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    the Z axis will not be easy to build I know, but i think this kind of design can improve rigidity dramatically. I've make huge effort to keep rails and ballscrew aligned on the same plane to limit levers everywhere.

    for Z axis, in this drawing I use 8x HGH15 linear bearing for rigidity, but i'm considering switching to 4x HGH25 or HGH30 to simplify the build.

    I will come back later with more details as I draw them. this build is going to be slow since I don't have the money to buy critical parts in one pass..

    feel free to comment and thank you to be there

    Olivier
    Last edited by oliv49; 28-03-2018 at 08:39 PM.

  2. #2
    Interesting design, it is ambitious for a first build!

    If the aluminium pieces you need to machine are small then a mill style is a better option. But if the pieces are fairly large then a router is required but be aware it will not be as stiff as the mill. To maximise the stiffness of the route I would avoid cutting long slots in the bed and gantry frames as this will reduce the stiffness noticeably (from a box to a U channel), and even adding the L bracket will not recover much of it. I wouldn't make that choice just to protect the ballscrews. Go for stiffness in the basic structure first, then add external ballscrews, and then add brush covers over the screws if required.

    15mm rails are a bit small on X and Y, go for 20mm instead. On the Z then 20mm is also fine with 4 rails and 8 carriages. If you drop to 4 rails and 4 carriages (I'm guessing you mean mounted around the lowest part of the Y axis box) it will still function but you will have lost a fair bit of the advantage of the box Z structure. I would say either go all out for 4 rails / 8 carriages, or go for simpler conventional Y and Z, not something in between.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  3. #3
    hello oliv,
    You have a challenging design, yet you should improve your y axis saddle. I will upload some pictures for you to do so.
    First of all for the Y axis : 2 linear rail is not enoughhhhhhhh!!

  4. #4
    Check these symetric structure of Z axis pictures. I suggest you to place 2 rails on each side with different directions.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Halbmond; 08-06-2018 at 12:22 PM.

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