Automatic Hacksaw

1
Automatic Hacksaw
Corey Case
Greg Platz
ME358 Mechanism Analysis
November 21, 2005
Kathryn Carroll
Josh Wheeler
2
Abstract

• An analysis of an automatic hacksaw was
  performed. For the analysis, the automatic
  hacksaw was simplified to a 4-bar slider/crank
  mechanism. Using the simplified model, position,
  velocity and acceleration and were calculated.
  These values were used to determine that the
  mechanism does operate within the specified
  parameters.

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Introduction

• The automatic hacksaw is a tool that utilizes
  a common hacksaw blade to precisely cut material
  with an oscillating motion.

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Assumptions

• As the saw cuts through the work piece, the
  mechanism as a whole rotates. This will slightly
  effect the calculations, however, the effects are
  minimal and are negligible and were not factored
  in.
• Since information for acceptable cutting force
  could not be found, it was assumed that the
  calculated cutting force found in the analysis
  was acceptable.

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Drawing
3D scaled representation of the mechanism.
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Drawing
4-bar slider/crank mechanism with required
dimension.
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Animation
Click on picture to view animation
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Degree of Freedom (DOF)
L 4 J1 4 J2 0 G 1
DOF 3L 2J1 J2 3G
DOF3(4) 2(4) 0 3 DOF1
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Position AnalysisCalculated
?2 (Degrees) Slider Position (m)
2.667 0.215
183.477 0.114
288 0.17
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Position Analysis Working Model Results
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Velocity AnalysisCalculated
?2 (Degrees) Slider Velocity (m/s)
2.667 0
183.477 0.008
288 0.442
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Velocity AnalysisWorking Model Results
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Acceleration AnalysisCalculated
?2 (Degrees) Slider Acceleration (m/s2)
2.667 -4.48
183.477 2.40
288 0.034
Cutting Force(max) Mass Acceleration(max) F
2.27Kg 4.48m/s2 10.17 Newtons
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Acceleration AnalysisWorking Model Results
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Critical Parameters

• Position The maximum amount of blade must be
  used without the mechanism binding. The distance
  the blade travels must be safe for all users of
  the mechanism.
• Velocity The optimal cutting speed for blade
  wear and safety of a hacksaw is 40 to150 surface
  feet per minute, or .20 to .76 meters per second.
  
• Cutting Force Information for cutting force
  could not be obtained.

Position
Safety/Performance
Velocity
Cutting Force
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Results

• Position The maximum allowable object is 12.7
  cm wide due to the vice. The 25.4 cm long cutting
  blade moves a total of 9.98 cm, 4.99 cm from each
  side, and leaves 1.37 cm of clearance on the edge
  of the blade. The calculations show that this is
  utilizing most of the cutting blade.

Blade and object placement
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Results

• Velocity Peak velocity was found to be 0.442
  m/s. From this, the RMS velocity was calculated
  to be 0.313 m/s. The RMS value is at the low
  side of the allowable velocity range. This means
  that the automatic hacksaw will achieve excellent
  blade wear and the mechanism will be safe to use
  because of the lower speed.
• Acceleration The maximum acceleration was found
  to be 4.48m/s2. From this value, the maximum
  cutting force was determined to be 2.27 Newtons.

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Conclusion

• The automatic hacksaw has one degree of
  freedom, thus, for every input there is only one
  output. The blade travels 4.9cm from each side,
  which falls into the safety and performance
  parameters of blade travel. The RMS velocity of
  the blade was calculated to be .313 m/s, which
  satisfies the velocity parameter of performance
  and safety. The acceleration obtained was
  4.48m/s2, from this a cutting force of 20.32
  Newtons was determined.
• The techniques in this report could have
  been improved if the average velocity measurement
  for cutting speed was obtained by integrating the
  position curve given by the working model, rather
  than using the root mean square (RMS) value for
  velocity.
• Since the machine falls into all the
  critical parameters found, there are no necessary
  improvements that need to be performed.

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References

• http//www.jjjtrain.com/vms/other_power_hacksaw.ht
  ml
• Design of Machinery, Norton L., Robert. (2004)
  McGraw-Hill.
• Mr. John Merril