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Chapter 14

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

● Tool Selection– Base on detailed analysis, not just capital cost.– Benefits include savings beyond just labor savings (capability, quality, etc.)

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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.

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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 non-preferred 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.

● Decrease force grip.● May

– decrease manual dexterity– increase assembly time.

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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 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.

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Guideline 4:Use the Proper Grip

● Power grip● Semipower grip● Precision grips

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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 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.

IE 366Guideline 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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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.

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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.

IE 366Guideline 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.

IE 366Guideline 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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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

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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

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.

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Examples

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Knives

Source: Intercodev, http://www.intercodev.com/knives.htm, last accessed 19 May 04

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Knife with upright handle

Source: Intercodev, http://www.intercodev.com/knives.htm, last accessed 19 May 04

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Knife with upright handle

Source: Intercodev, http://www.intercodev.com/knives.htm, last accessed 19 May 04

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Ergonomic Pliers

Source: Wiha Quality Tools, http://www.wihatools.com/300seri/328_inomic.htm,last accessed 16 Nov 09

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Wire Stripping Pliers

Source: MichaelHoligan.com, http://www.michaelholigan.com/Shopping/Product.asp?pfid=CHA957,last accessed 19 May 04

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Scissors

Source: Intercodev, http://www.intercodev.com/scissors.htm, last accessed 19 May 04

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Scissors

Source: Intercodev, http://www.intercodev.com/scissors.htm, last accessed 19 May 04

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Handles

Source: Intercodev, http://www.intercodev.com/handles.htm, last accessed 19 May 04

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Ratchet Screwdriver

Source: Lara Specialty Tools, http://www.lara.com/cgi-bin/store/commerce.cgi?product=workshop, last accessed 19 May 04

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Ratchet Screwdriver

Source: Pro’sKit, New Product Release …, http://www.prokits.com.tw/english/new_dm/pk-3018ab/pk-3018ab.htmlast accessed 19 May 04

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Hammers

Source: ContractorsTools.com, http://www.contractorstools.com/barco.html,last accessed 19 May 04

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Coiled-Handle Hammer

Source:NIOSH/Ergonomic Interventions in Ship Building/Coiled Hammer Handle, http://www.cdc.gov/niosh/ergship/coilhamm.htmllast accessed 19 May 04

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Ergonomic Hand Tools Links

● humantech Vendorweb– http://vendorweb.humantech.com/

● NIOSH Guide– http://www.cdc.gov/niosh/docs/2004-164/pdfs/2004-164.pdf