Sunday, 28 February 2010

Gaining too much weight ?

How heavy is that gantry going to be ? It's an important question leading up to the selection of stepper motor(s). My y-axis shafts are 600mm. Before reading on, take a guess now....

Using my digital kitchen scale, I scientifically determined the weight of 16mm MDF wood to be 11.2kg per square metre.

Small parts add up...

For mdf, the estimated total area will be (without an actual design plan):
  1. Gantry sides: 300mm x 600mm x 2
  2. Gantry bridge: 600mm x 300mm
  3. Gantry bridge rigidity support: 600mm x 150mm
  4. z-axis base mounted to y-axis bearings: 500mm x 250mm
  5. z-axis base rigidity support: 500mm x 150mm
  6. z-axis sledge: 400mm x 250mm
  7. z-axis sledge rigidity support: 400mm x 100mm
Total area: 1.045m2 = 11.7kg of 16mm mdf

  1. MDF: 11.7kg
  2. Bearings & shaft mounts (measured): 2.3kg
  3. y-axis motor (est): 1.5kg
  4. y-shafts x 2 (measured): 3kg
  5. y-thread (est): 1.2kg
  6. z-axis motor (est): 1.5kg
  7. z-shafts x 2 (measured): 0.7kg
  8. z-thread (est): 0.6kg
  9. Other Stuff (est): 1kg
  10. drill mount: 0.2kg
  11. drill (est max): 3kg
Total for gantry: 26.7kg

This might come down a bit, for example, with smaller motors, a lighter mdf design, or a smaller drill. My Bosch Power Drill weighs over 2kg, but the Dremel is much lighter. But even with conservative figures, it won't go below 21kg. On the other hand, I might decide to go with 18mm mdf, so it would up the weight.

So, to be on the safe side, I'll be taking 30kg as the moving gantry mass when selecting steppers. Quite a surprise.

Just to round it off, the static weight for base and x-axis would add:
  1. Base board (mdf, 1200mm x 700mm): 9.4kg
  2. Base board rigidity (mdf, 700mm x 150mm x 4): 4.7kg
  3. Base board rigidity (mdf, 1200mm x 150mm x 2): 4kg
  4. x-axis shafts x 2: 5kg
  5. x-axis thread (est): 1.5kg
  6. x-axis motor: 1.5kg
Static total: 26.2kg.

All total: 52.5kg.

Gulp! Well, looks like this is not going to be a small gadget that I can take to weekend cnc-parties:
  1. This needs a proper permanent place in the garage.
  2. Instead of making it portable, I might as well build it on a solid table and possibly mount that to the brick wall for added support.
  3. I might have to give some thought to "easy assembly and disassembly".

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