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Handtools

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  1. Handtools • Extend the capability of the hand • Selection criteria: • What the tool can do • How the tool is used

  2. Guidelines • 1: Use Special-Purpose Tools __________________ • 2: Design Tools to Be Used by Either Hand __________________ • 3: Power with Motors More Than with Muscles __________________ • 4: Use the Proper Grip __________________ • 5: Make the Grip the Proper Thickness, Shape, and Length __________________ • 6: Make the Grip Surface Smooth, Compressible, and Nonconductive __________________ • 7: Consider the Angles of the Forearm, Grip, and Tool • 8: Use the Appropriate Muscle Group __________________

  3. 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 • 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.)

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

  5. Guideline 2: Design Tools to Be Used by Either Hand • The tool should be in the user’s 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.

  6. Handgrip Strengths

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

  8. 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. • Reducing Hand–Arm 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.

  9. 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 Semipower grip Fingers act as a group but thumb position changes. Oblique or hook grip Hook grips are preferable to pinch grips. Precision grip About 20% strength of a power grip. Internal (table knife) or external (pencil) precision grip Forearm or tool may be supported Guideline 4: Use the Proper Grip

  10. Examples

  11. 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.

  12. 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. • 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.

  13. Guideline 6: Make the Grip Surface Smooth, Compressible, & Nonconductive • Smoothness reduces pressure points. • Compressibility minimizes pressure on the hand. • Nonconductivity reduces heat and cold problems and risk of electric shock.

  14. Guideline 7: Consider the Angles of the Forearm, Grip, & 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.

  15. Examples

  16. 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.

  17. 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 • Right 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.

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