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Enhance hand tool performance by understanding selection criteria and grip guidelines. Discover how to choose special-purpose tools, design for both hands, and use motor power effectively. Explore grip techniques based on hand sizes, shapes, and strengths. Implement forearm, grip, and tool angle considerations for optimal usage. Learn to reduce Hand-Arm Vibration Syndrome and select the right muscle group for various tasks.
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Handtools • Extend the capability of the hand • Selection criteria: • What the tool can do • How the tool is used
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 __________________
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.)
Handtool Selection Steps • Do a job analysis. • Identify tool-use issues: • Operating forces • Repetitions per minute or per shift • Postures • Select the right tools.
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.
Gloves • Protect the hand against abrasion, impact, chemicals, heat, cold, cuts, infection, vibration. • May decrease manual dexterity and increase assembly time. • Decrease force grip.
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.
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
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.
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.
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.
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.
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.
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.
