Chapter 14 Handtools
Handtools Extend the capability of the hand Selection criteria: What the tool can do How the tool is used
Guideline 1: Use Special-Purpose Tools IE 366 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 Base on detailed analysis, not just capital cost. Benefits include savings beyond just labor savings (capability, quality, etc.)
Handtool Selection Steps 1.Do a job analysis. 2.Identify tool-use issues: Operating forces Repetitions per minute or per shift Postures Workpace 3.Select the right tools.
Guideline 2: Design Tools to Be Used by Either Hand IE 366 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 non-preferred hand to be used when the preferred hand is engaged or resting.
Handgrip Strengths IE 366
Gloves Protect the hand against abrasion impact chemicals heat, cold cuts, infection vibration. Decrease force grip. May decrease manual dexterity increase assembly time.
Guideline 3: Power with Motors More Than with Muscles IE 366 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 IE 366 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.
Guideline 4: Use the Proper Grip IE 366 Power grip Semipower grip Precision grips
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
Power Grip IE 366
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.
Precision Grip Has about 20% strength of a power grip. Internal precision grip (e.g. table knife) External precision grip (e.g. pencil) Forearm or tool may be supported.
Guideline 5: Make the Grip the Proper Thickness, Shape, and Length IE 366 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 (tab) 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.
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.
Guideline 6: Make the Grip Surface Smooth, Compressible, and Nonconductive IE 366 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, and Tool IE 366 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.
Joint Angles Source: Canadian Centre for Occupational Safety and Health, OSH Answers: Ergonomics, http://www.ccohs.ca/oshanswers/safety_haz/power_tools/ergo.html, last accessed 19 May 04
Guideline 8: Use the Appropriate Muscle Group IE 366 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 IE 366 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.
Examples IE 366
Knives Source: Intercodev, http://www.intercodev.com/knives.htm, last accessed 19 May 04
Knife with upright handle Source: Intercodev, http://www.intercodev.com/knives.htm, last accessed 19 May 04
Knife with upright handle Source: Intercodev, http://www.intercodev.com/knives.htm, last accessed 19 May 04
Ergonomic Pliers Source: Wiha Quality Tools, http://www.wihatools.com/300seri/328_inomic.htm, last accessed 16 Nov 09 27
Wire Stripping Pliers Source: MichaelHoligan.com, http://www.michaelholigan.com/shopping/product.asp?pfid=cha957, last accessed 19 May 04
Scissors Source: Intercodev, http://www.intercodev.com/scissors.htm, last accessed 19 May 04
Scissors Source: Intercodev, http://www.intercodev.com/scissors.htm, last accessed 19 May 04
Handles Source: Intercodev, http://www.intercodev.com/handles.htm, last accessed 19 May 04
Ratchet Screwdriver Source: Lara Specialty Tools, http://www.lara.com/cgi-bin/store/commerce.cgi?product=workshop, last accessed 19 May 04
Ratchet Screwdriver Source: Pro skit, New Product Release, http://www.prokits.com.tw/english/new_dm/pk-3018ab/pk-3018ab.htm last accessed 19 May 04
Hammers Source: ContractorsTools.com, http://www.contractorstools.com/barco.html, last accessed 19 May 04
Coiled-Handle Hammer Source:NIOSH/Ergonomic Interventions in Ship Building/Coiled Hammer Handle, http://www.cdc.gov/niosh/ergship/coilhamm.html last accessed 19 May 04
Ergonomic Hand Tools Links humantech Vendorweb http://vendorweb.humantech.com/ NIOSH Guide http://www.cdc.gov/niosh/docs/2004-164/pdfs/2004-164.pdf 36