ergo-drill-basic

OVERVIEW

My investigation into how people drill began with the Ryobi 3/8 in. D42.  I looked at a number of online reviews and found that many people who were compelled enough to share their experience with others were satisfied with the drill for the price they paid.

Of the factors considered in good hand-tool design, I determined the following were relevant to my understanding of the ergonomics of this drill:

  • The rotation of the wrist is important, as it is ideally in a neutral position while working with hand tools for an extended period of time.
  • It is necessary to look at both right and left handed persons.
  • The angle between the torso and the upper arm in relation to the horizontal axis of the bit is a good indicator of the physical strain felt by the user, as the further away the arm is from the body the more difficult it feels to use the drill.
  • The resistance of the trigger as well as how difficult it was to hold down influences the risk of developing “trigger finger”.
  • A handle that is too short creates uncomfortable “palm compression”.
  • A bent handle with a pistol grip is ideal when the force moves in a straight line in the same direction as the forearm.

 

 


user-testing-graph2

FIRST ROUND OF USER TESTING

Knowing that, I decided to test the drill by asking 8 users to drill a hole in a 1 in. thick sheet of MDF and rate the following on a scale of 1 to 5 (with 1 being the most comfortable/easiest and 5 being the most uncomfortable/difficult):

  • Wrist comfort
  • Shoulder strain
  • Ability to steadily hold the trigger
  • Feeling supported while drilling into a horizontal piece of material
  • The sense of being aligned with the tool while in use

 

 


self-assessment

TAPED USER TESTING

The drill scored most often as “OK”, so to get a more thorough understanding of what was specifically affecting user perception of the drill I needed to see what exactly was happening while the drill was in use.  I set up a camera and tripod in a workshop with sheets of MDF and filmed participants drilling 1 in. holes.  Afterwards, I had them fill out a self-assessment survey.  I then used the video to measure the following and compare it to the self-assessments to find any relationship between perception and posture:

  • Shoulder Angle (torso-upper arm)
  • Elbow Angle (upper arm-forearm)
  • Wrist Angle (forearm-hand)

RESULTS

I measured the posture angles of each participant and plotted the numbers against the perceptions gathered from the self-assessment, and found a number of interesting relationships.  The first was the relationship between wrist angle and experience.  As seen in the graph to the right, an increase in experience level meant a decrease in wrist angle.  This suggests that more experienced drill users are more likely to attempt to neutralize wrist position, as ergonomic research recommends. This could be due to familiarity with the effects of using a drill for an extended period of time or past experiences in which a bent wrist quickly became uncomfortable.

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wrist-angle-experience (1)

Regarding palm compression, most participants rated the stress they felt on their palms was significant, all rating as a 6 or higher.  However two participants rated the stress as 1.  These two participants were adult men over 60 years of age, which leads me to believe that the lack of stress felt was due to their hands simply being larger and more able to grip the handle comfortably.

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palm-tightness4

A third trend showed a link between the position of the shoulder (angle between the torso and the upper arm) and pressure needed to use the drill.  Participants who rated the pressure they needed to use as higher usually had a higher shoulder angle.  This may be a reflection of the difference in the source and direction of force as the arm moves away from the body.  Instead of using one’s body weight to push the drill forward, participants with a larger shoulder angle appeared the be primarily pushing with their arms.

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shoulder-pressuretopush (1)