CNC plasma cutter

Project CNC plasma cutter
Status	Initializing
Contact	[[Project Contact::Walter, Smeding, Gori, Yotson, Semafoor]]
Last Update	2014-04-09

After acquiring a plasma cutter at the space, it seemed only logical to try and fabricate a CNC version eventually.

This goal is still a while away for now, but as always, we are full of Ideas and this is a convenient place to put them.

CNC plasma cutter based on VSL X-Z table

X-Z traversing unit before any modifications

The working mechanics

Once upon a time, three consecutive interns at VSL made a X-Z traversing unit to automatically measure wind speed velocity distribution of one of VSL's primary standars. This traversing unit was put out of use over half a decade ago, and was finally put on the scrap metal list. If it wasn't for a hackers intervention, it would have been there by now. Luckily it can now have a second life in the spark shack.

The X-Z traversing units has a DC motor for each direction of travel. These motors are coupled to a gearbox and a rotary encoder. A toothed belt then transfers the rotational motion into a linear motion.

Hardware that works

Control electronics with DC-motor controllers and Mitsubishi PLC

The motors work when operated by the joystick controller. Speed is adjustable by means of knobs inside the contol cabinet. The two motorcontollers work [[1]]

Hardware that needs to be sorted

• The onboard RS-232 PLC (Mitsubishi something or other) may or may not work. If it still works, we need a way to program it. Possibly it's easiest to take out the PLC and put an Arduino or Rpi in there instead
• Interface with the plasma cutter (relay, some cable and a plug to match the plug that's already on there)
• mounting for the plasma cutter head
• some rig to reliably hold the sheets of steel vertical (very important for thin sheets that may bulge or buckle otherwise)
• a PC that will survive the Spark Shack

Software that needs to be sorted

• Program for the hardware controller
  • Motion control
  • Speed control
  • Plasma cutter on/off
  • position feedback
  • ...
• CNC software to draw/cut
  • Perhaps use the software from the laser cutter?

Original Ideas

Specs

• 3x3 m working area
• movement speed of 1000mm/s
• Calibrated accuracy and precision of +/- 0.1mm

Axis motors

smeding is going to design and build a proof of concept linear (synchronous) motor for use in the X- and Y-axes. This test rig will be used to determine whether a DIY LSM is at all useful for our application and to finalize the design if we choose to go with the concept. Specifically, this involves figuring out:

• How the attainable accuracy compares to the wanted specifications
• How the attainable movement speed compares to the wanted specifications
• A final design for the drive electronics
• Coil and armature geometries
• Rail geometries (magnet size, spacing and orientation pattern and any backing)
• Optimal control schemes

After this, we'll be ready to construct the three rails (2x X and 1x Y) that make up the bulk of the CNC machine.

prototype BOM

• angle extrusion, probably aluminium for the prototype
• skate bearings (we already have some)
• magnets
• copper wire (we already have some)
• electronics:
  • Microcontroller ([[2]]?)
  • MOSFET drivers (half-bridge or BLDC)
  • MOSFETs (N-channel, high current)

Some rough ideas by Yotson

• 1.5 x 3.0 Meter max. material size. Spec of plasma cutter mentions 12mm as max thickness.

    Table should manage to hold the weight of a 1.5m x 3.0m x 20?mm sheet of steel.

• weight of plasma nozzle + hoses/wires?

• length of nozzle + hoses/wires?

• speed of nozzle over material > 10 cm per second. (non cutting)

• nozzle placement accuracy: < 1mm

• transportable. Able to fit through 'standard' door (on its side, obviously)

• Maybe:

'upgradeable' by placing rotary cutting tool, pencil, knife, spray can, .... ???

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Transport axes: x, y: angle iron and skate wheels + bearings?

linear motors? threaded rod, DC motors, encoders?

z  : ? + threaded bolt, manual adjustment between height of 0mm and 50mm.

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Threaded rod info

ISO standard. From HTTP://en.wikipedia.org/wiki/ISO_metric_screw_thread

Diameter in mm.	Pitch (fine)	Pitch (coarse)	Rotational speed 10 cm/s lin. motion (coarse)	Rotational speed 10 cm/s lin. motion (fine)
20 or 22	2.5	1.5 or	40rps, 2400rpm	50rps, 3000rpm
		2		66.7rps, 4000rpm
30 or 33	3.5	2	28.6rps, 1714rpm	66.7rps, 4000rpm