CNC BF16 - Mechanics


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    Valide CSS!
  • The 4th rotation axis is working.

    Created some tool holders for the turning table. The cutter will make it more easy to turn some pockets and with the proxxon tool holder, it's possible to create some nice sleeves for circlips.

    My new spindles & couplings are arrived! So it's time for new speed measurements. Total layout of the X-axis:

    I was not really convinced of the maximum speeds with the DIY spindle setup, basically because of some tolerance issue's due to my 'sloppy' turning & milling capabilities. There are still some strange sounds coming from some of the couplings, probably due to small misalignments. Currently, with the arduino and using ball spindles RM1605, stepping delays are down to 100 [us/pulse]. This means 10 [kHz] pulse frequency. Having a step size of 5, the maximum speed will be 3 [m/min], with a 0.005 [mm] theoretical precision. While the current arduino Bressenham code could run up to 62 [us/pulse] max, there is still a lot of friction in the dovetail guide, which is reducing speeds. Also the acceleration algorithm could be improved. For now, I'm satisfied. :)

    I did some vibration analyses on the BF16. I'm not sure what kind of cast material is used, so a guess: Iron Cast G40 - Emodules of 140 [GPa]. Here a list of the first 6 modes:
    Mode 1 - 31 Hz
    Mode 2 - 45 Hz
    Mode 3 - 170 Hz
    Mode 4 - 195 Hz
    Mode 5 - 390 Hz
    Mode 6 - 440 Hz

    It's clear the column is the weakest point of the construction. Also the stiffness is not very high:
    K_x = 3.2 [N/mm]K_y = 2.9 [N/mm]K_z = 6.8 [N/mm]

    Time for some re-enforcement!
    K_X = 9.4 [N/mm]:
    K_Y = 43.5 [N/mm]:
    K_Z = 47.6 [N/mm]:

    New improved vibration analyses:
    Mode 1 - 83 Hz
    Mode 2 - 105 Hz
    Mode 3 - 230 Hz
    Mode 4 - 370 Hz
    Mode 5 - 510 Hz
    Mode 6 - 520 Hz
    Conclusion: by adding an additional support, stiffness could be optimized a lot! Another nice option: bolt the column against the wall.

    The BF16 is a very light milling machine. So vibrations are very noticeable and could possibly optimized. Sources for resonances:
    • Play of lead screw (backlash) & play of guidance:
      • X axis
      • Y axis
      • Z axis
      • Spindle axis
    • Stiffness total construction:
      I will do some measurements and calculations later.
    • Stiffness tool.

    After receiving the RM1605 spindles from Chai, it was time to turn the shafts. That material was a little harder then I suspected. In the end, I managed to create 3 spindels and made also 3 flexible Oldham couplings myself.

    After installing the spindles and motors, it made some strange noises at maximum speeds. It is obvious, that aligning & using thigh tolerances are very important! Some advice: For only a few $'s more, it's not worth to turn the shaft ends yourself.

    Time to convert the steel molecules into a virtual electronic representative CAD file.

    Latest BOM:
  • BF16 Milling head & HBM Cross table (stepfile)
  • Bearings (SKF: 6301-2Z)
  • Couplings (MCOG38-10-14)
  • X Shaft: spindle, fixed bearing block, floating bearing block, motor shaft & spindle block
  • Y Shaft: spindle, fixed bearing block, motor shaft & spindle block
  • Z Shaft: spindle, fixed bearing block, motor shaft & spindle block
  • Old couplings: obsolete1, obsolete2