CNC ROUTER - Frame Layout

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    About

    Valide CSS!
  • First of all, it's important to chose the right DOF's. I want to be able to mill and also foam cutting. It will be the best to have X1 & X2 solid on a base frame and have 2 different sub frames: one for milling and one foam cutting. Propably the best configuration:
  • solid: X1, X2 support (stiff connected to an open frame/window)
  • milling: strong Y1, Z1 support
  • foam cutting: ligth Z1, Z2 support

  • There are a lot of different way to build up an 3D Frame. Here I showed 6 basic designs, where X & Y lay in horizotal level and Z vertical. Also the order of X,Y,Z could be changed, which could lead to more leading supports.
    Concept:123
    Schematic:
    Tool:ZX,YX,Y,Z
    Product:X,YZ-
    Application:MillingSTL printingMeasuring devices
    Pro's:StrongProduct hardly movesFixed product
    Con's:
    Concept:456
    Schematic:
    Tool:X,Z-X
    Product:YX,Y,ZY,Z
    Application:MillingMilling-
    Pro's:Robust
    Con's:Product movesProduct movesNot realistic

    A lot of milling machines are based on concepts 1 (heavy duty), 3 (routers) & 4 (compact routers). For building RPT or measurement machines, you don't want to move the product. So the most logich choise would be concept 3.
    Here are some pictures of different machines:

    Concept 1Concept 2Concept 3
    (no picture)
    This is the first concept I could think of. There is a X1, X2, Z1, Z2 and a removable Y1. The second idea, is a frame wich has a X1, X2, Y1 and Z1. The Y1 could be changed to an Z2. In this concept, the Y1 & Z1 must be indentical! The third concept, is a normal router (like concept 3 above), with an extra light version Y2 & Z2 mounted on the end of the table.
    5 motors4 motors5 motors (2 light)
    Concept 4
    This is also a nice concept! It's modulair, where X1 & X2 are always mounted. You can taken of the Y1 & Z1 and replace this with light Z1 & Z2. You can also position the y-axes up-side-down (normal router).
    6 motors (3 or 4 active)

    There are some different ways of lineair guideways:
    • Linear ball guideway
    • Supported linear ball guideway
    • Linear rail guideway
    Beside this choice, also the support is important for getting the right stiffness. Here you could find an impression of different options. Below you could find a cost price calculation.

    The inertia of the profile that is used, has a liniear influences on bending stifness. Here the inertia of one single tube with outer diameter of 25 [mm] and different inner diameters are compared. Also because of decreased cross section, the relative weight decrease is shown.
    D [mm]d [mm]I [mm^4]Inertia [%]Weight [%]
    25019175100100
    2551914410096
    2510186849784
    2515166908764
    2520113215936
    30252058610744
    Here you can see a tube with inner diameter of d=10 [mm], where stifness is decreased with only 3% and saves 16% in weight. Or when outer diameter is changed to 30 [mm] with inner diameter of 25 [mm], the stiffness is increased with 7% but weight is decreased with 56% !! This is a good way for finding the right stiffness/weight combination, when using tubes.

    The second important issue is rod support. There are different methods of clamping the rod, see picture below.

    I will add stiffness numbers later on, but made alread a decision for creating some kind of support like #8. (Likely 2 symectrical supports.)

    First of all, one single round rod will not support axial moments, therefore you need 2. In picture above with rod support #8, it's obvious to create a more stiff system with smaller rod dimensions and this means lower costs for those components!
    R1: R2: R3: R4: R5:
    R6: R7: R8: R9:
    P10: P11: P12: P13: P14:
    S1: S2: S3:
    Score different supports:

    The costs of a new linear guideway:
    • 2 Linear ball guideway: 174 euro
    • 2 Supported linear ball guideway: 217 euro
    • 1 Linear rail guideway: 328 euro