1ISE 311 - 15

Handtools

Extend the capability of the hand Selection criteria:

What the tool can do How the tool is used

Selection process:1. Do a job analysis.

2. Identify tool-use issues: Operating forces Repetitions per minute or per shift Postures

3. Select the right tools.

2ISE 311 - 15

Guidelines (LIST EXAMPLES BELOW …)

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 __________________

3ISE 311 - 15

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 Selection1. Whether a tool is expensive depends on a detailed analysis,

not just capital cost.

2. Benefits include savings beyond just labor savings (capability, quality, etc.)

4ISE 311 - 15

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.

5ISE 311 - 15

Handgrip strengths

6ISE 311 - 15

Gloves

Protect the hand against abrasion, impact, chemicals, heat, cold, cuts, infection, vibration.

May decrease manual dexterity and increase assembly time.

Decrease force grip.

7ISE 311 - 15

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.

8ISE 311 - 15

Guideline 4: Use the proper grip

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

9ISE 311 - 15

Examples

10ISE 311 - 15

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.

11ISE 311 - 15

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.

12ISE 311 - 15

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.

13ISE 311 - 15

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.

14ISE 311 - 15

Examples

15ISE 311 - 15

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.

16ISE 311 - 15

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.