Pneumatic tool disassembly

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Pneumatic tool disassembly

• Ben Hill
• High Impact
• 9/24/03

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Mastergrip 3/8 Air Ratchet Wrench
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Purpose

• Uses Reversible- As a nut runner for assembly
  or disassembly of autos, aircraft, trucks,
  tractors, furniture, and appliances -from
  product manual

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How does it work?

• Incoming high pressure air
• Vanes conform to cylinder
• Expansion turns core in one direction
• Ratchet section

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History

• Not a new idea
• Trace evolution of tool by tracing patent history
• Current design patent

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Ancient History

• Patents for the basic concept date back to the
  1800s
• About as old as this guy?

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Published Specifications

• 220 RPM RPM of output shaft
• Torque 61-68 Nm Torque of output shaft
• Air Pressure 620 kPa
• Air Consumption 0.00257 kg/s
• -from product manual

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Calculations- air consumption

• Input pressure is gtgtPatm, so it is a choked flow
• Rate of change of mass
• Inlet is four holes with diameter 2mm
• Vsound 344 m/s
• kg/s
• Compare to published value (0.00257 kg/s)

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Calculations- speed

• The area filled with high pressure air is the
  area in orange
• The mass of this air divided by the choked flow
  rate yields the time necessary to fill the area,
  which is the time for ¼ rotation
• Compare to 220 RPM for output shaft

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Calculations- air pressure

• Pressure equals force/area
• Force equals torque/radius
• Compare to 620 kPa

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Calculations- Torque

• Torque equals force radius
• Force equals pressure area
• Compare to average 64.5 Nm for output shaft

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Explanation of discrepancies

• Value computed for speed 130x higher than the
  actual output shaft speed
• Value computed for torque 150x lower than actual
  torque on the output shaft
• Differences come from gearing between motor (what
  we studied) and output shaft (published
  specifications)
• Output shaft spins much slower than motor, but
  with much more torque (by about the same factor)
• Different pressure is a consequence of different
  torque

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Lessons

• Patent searching
• SolidWorks
• Physics
• Math
• Design
• Carbide saw can cut just about anything

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Sources

• Theory and Design of Mechanical Measurements
  Figliola Beasley
• Mastergrip instruction manual
• www.uspto.gov
• Physics with modern physics 3rd edition Wolfson
  Pasachoff
• Brian Storeys packet
• Google calculator