Handtools

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Chapter 16

• Handtools

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Handtools

• Extend the capability of the hand
• Selection criteria
• What the tool can do
• How the tool is used

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Guideline 1

• Use Special-Purpose Tools
• Benefit Performs well tasks that are repeated
  many times/week
• Costs Capital, maintenance, utility
• Analysis
• Estimate years of use and usage/year
• Divide total cost by usage
• Compare to savings

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Tool Selection

• Whether a tool is expensive depends on a detailed
  analysis, not just capital cost.
• Benefits include savings beyond just labor
  savings (capability, quality, etc.)

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Handtool Selection Steps

• Do a job analysis.
• Identify tool-use issues
• Operating forces
• Repetitions per minute or per shift
• Postures
• Select the right tools.

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Guideline 2

• Design Tools to Be Used by Either Hand
• The tool should be in the users preferred hand.
• Strength, dexterity, and performance are greater
  for the preferred hand.
• Benefits
• Includes the 10 of the population that is
  left-handed.
• Allows nonpreferred hand to be used when the
  preferred hand is engaged or resting.

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Handgrip Strengths
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Gloves

• Protect the hand against abrasion, impact,
  chemicals, heat, cold, cuts, infection,
  vibration.
• May decrease manual dexterity and increase
  assembly time.
• Decrease force grip.

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Guideline 3

• Power with Motors More Than with Muscles
• Mechanical energy is 10 to 1000 times cheaper
  than human.
• Motors extend capability and do not fatigue.
• Motors permit a larger percent of workforce to do
  the job.

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Reducing HandArm Vibration Syndrome

• Use a process with zero or low operator
  vibration.
• Use equipment with low levels of vibration.
• Use equipment with vibration-isolated handles.
• Avoid resonance.
• Furnish vibration-isolated gloves.
• Encourage workers to follow VS-reducing practices.

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Guideline 4

• Use the Proper Grip
• Power grip
• Semipower grip
• Precision grips

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Use Balancers or Wands
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Power grip

• Tool handle perpendicular to the forearm axis.
• Direction of force
• Parallel to forearm
• At an angle to forearm
• Applied as torque about forearm

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Power Grip
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Semipower Grip

• Fingers act as a group but thumb position
  changes.
• Oblique grip thumb aligned along tool axis
• Hook grip fingers wrap around tool, thumb is
  passive
• Hook grips are preferable to pinch grips.

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Precision Grips

• Has about 20 strength of a power grip.
• Internal precision grip (e.g. table knife) held
  inside hand
• External precision grip (e.g. pencil) with shaft
  held outside the hand
• Forearm or tool may be supported.

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Guideline 5

• Make the Grip the Proper Thickness, Shape, and
  Length
• Hand Sizes
• Are larger with gloves.
• Tend to be larger for men than for women.
• Grip Diameter
• For power grip, 35 mm to 45 mm is optimal.
• For precision grip, use 9.5 mm to 12.7 mm.

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Examples Precision tools
Bayonet grip prevents twisting
Variable grip diameter
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Grip Shape

• Section Perpendicular to Grip Axis
• Prevent rotation and slippage.
• Use thumb conoid or noncircular cross-section.
• Improve coefficient of friction of handle.
• Section Along Tool Grip Axis
• Keeps tool from moving forward and backward in
  hand.
• Allows force exerted along tool axis to be
  greater.
• Can act as a shield.

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Grip Shape (cont.)

• Length
• For power grip, all fingers must make contact.
• For external precision grip, shaft must be
  supported.
• For internal precision grip, tool must extend
  past palm but not as far as wrist.

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Guideline 6

• Make the Grip Surface Smooth, Compressible, and
  Nonconductive
• Smoothness reduces pressure points.
• Compressibility minimizes pressure on the hand.
• Nonconductivity reduces heat and cold problems
  and risk of electric shock.

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Guideline 7

• Consider the Angles of the Forearm, Grip, and
  Tool
• Angle
• Keep the wrist in neutral position.
• Best angle varies with posture.
• Consider changing the job to improve angle.
• Consider pistol-grip or bent tools.
• Clearance
• Increase distance from hot surfaces to reduce
  burns.
• Provide shield from heat.
• A narrow neck reduces heat transfer.
• Avoid pinching risk with repetitive-use tools.

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Guideline 8

• Use the Appropriate Muscle Group
• Muscle Direction
• Strengths and ranges of motion differ.
• Consider normally-open tools.
• Give muscle something to push against.
• Muscle Size
• Consider moment arm.
• Provide power grip.

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Guideline 8 (cont.)

• Use the Appropriate Muscle Group
• One versus Many
• Use fingers in combination.
• Pinch types vary greatly in strength..
• Consider trigger strips instead of buttons.
• Consider alternate types of triggers.
• Rotate Inward
• Hand and arm can rotate 70º clockwise, 150º
  counterclockwise.
• Muscle Time
• Reduce time the muscle is used.
• Use clamping tools, locking triggers, discrete
  controls, straps.
• Consider guides or funnels for positioning.