Mechanical Dexterity Testing

Ever seen a new guy from across the shop and ask yourself where the heck did they find this person? Watching them at a distance for even a few minutes tells an experienced eye a lot about a persons skills in a completely non verbal way. Lack of experience is not something a person can camouflage with good speaking skills like you might be able to do in a purely verbal interview. Any decent salesman or politician can do it all day long. I don't care as much about what you say you can do as much what you actually can do. You cant hide out in the shop for long under the watchful eyes of journeymen.

There are many unique ways to get things done with your hands, so what is that we are actually seeing when we are watching? My thoughts are its the telltale movements of long muscle memory and self confidence that what we see from across the shop. The question is how can we get this kind of insight during an interview?

Recently I headed up a committee to hire several entry level mechanical technicians. I decided early on that it was important to watch them do something for a few minutes than to try to discover the right skills by just asking questions and listening to answers tailored for our approval. The hope as that even a short demonstration would give us an idea of basic skill and mechanical abilities. I had a little bit of a hard  sell on the idea of testing to the rest of the team, but in hindsight they are seeing the value of what this simple evaluation provides. The process has provided some interesting insight into how mechanical minds work and approach different kinds of problems. We have definitely seen some unique methods to complete the tasks we have the candidates demonstrate and learned some things ourselves. The second benefit of the testing was it gave us a way to take some basic measurements to help compare the candidates quantitatively.

The goal in any hiring scenario is to find the best skills and attitude that fit the job requirements from the available pool of talent. I believe that if you hire tough then you can manage easy. What this means is the interview is harder and more intimidating up front but exposes potential weaknesses early. To be clear this is only one tool of many we use to help us make better hiring choices. This evaluation  is put on the scale with the rest of the interview process and adds or subtracts some weight to help us make more enlightened selections.

Meet the busy box

After doing some research into what kinds of tests are out there I devised this busy box to evaluate simple mechanical dexterity and problem solving abilities. Each of the surface patterns has a specific task associated with it. Some appear at first glance to be quite simple but when you add in the stress of the interview and a stopwatch the tasks quickly become more challenging. The tasks are not intended to be devilishly difficult, quite the opposite. Our intent was that the task be generic and simple enough that anyone with even a modest skill level would have encountered at some point in their work experience. 

The first task is really a warm up for things to come. It is the easiest task for most people to do. We give some verbal instructions which is actually first part of the test. Great skill but no comprehension of the instructions is not a good way to start. The plate is bushed with threaded inserts. Behind the inserts is a plate which limits how far the fastener can be inserted. We ask the subject to start in a particular place and insert fasteners in a simple pattern. Starting with their strong hand they insert the fasteners in the requested pattern. When they complete the pattern, they remove them in the reverse order with the weak hand. You might ask what could we learn from this really simple exercise?

The first thing we learn is can the subject follow basic instructions. Then we see how they handle the fasteners. Do they drop them, are they fast or slow, do they miss the pattern, do they double check to see if they are all seated. On removal do they drop the bolts into the tray roughly or do they set them in. Do they ask any questions or require clarification. Quite a few things come out of this innocent task that takes a shade over a minute to complete. We get to watch them do something they might have to do on their first day on the job just like we would be watching them from across the shop. The test is stressful for several reasons. In the interview are typically at least four interviewers all watching intently as the subject works. The second stress amplifier is a stopwatch. This gives us some insight into how the subject handles stressful situations. Can they work through it? Are they confident and steady, or nervous and shaky? Its no more stressful than your first day at a new job which is what were trying to do.

The large dexterity is just a warm up for the next exercise. In this task the subject is not allowed to touch the pins with their fingers, they must use the tweezers. The task is to pick up a pin and insert it into the upper pattern of drill bushings. There is a stop plate below the bushings that keeps the pins from falling through. The fit is fairly loose so no pressure is required to get the pin in the bushing. What makes this task difficult is the tool we provide.

These ESD safe plastic tweezers are really difficult to use on the polished drill blank pins. It takes the lightest of touches to grasp the pin tight enough to pick it up, but not so tight the pin squirts out of the jaws. The pin needs to be picked up in the center of gravity or very carefully from one end. This task shows us how quickly the subject adapts to the crummy tweezers and finds the right technique. In the tray there is a shallow depression that gives some clearance under the pin that makes it easier to pick up. Most of the people we tested figured this out within a few tries.

The pins are inserted into bushings in a particular pattern. We have the subject install the pins with their strong hand and remove them with their weak hand in reverse order the pins were installed. It looks simple but its not.

The second exercise with the pins is to install them by hand in bushings that are quite snug on the pins. This shows us how the subject handles subtle fits and alignments. You have to be dead straight and gentle to get the pins to align and slide into the bushings. Similar to using a gage pin to measure a bore accurately. We check to see it all the pins are seated to the same depth and whether the subject checks the installation height. This task is actually a relief after the pins with tweezers test.

This task is similar to the first one. The fasteners are smaller which evaluates finer dexterity and manipulation and the ability to follow verbal instructions. We watch for dropped fasteners and rough handling as well as spinning techniques in particular during removal.

The last task is an access problem. The hole in the center of the box is used for the final test with the busy box. In the four corners are holes. In these holes we install a cap screw with a washer on the top side of the plate and underneath a spacer, another washer and a nut are assembled all through the limited access of the Tupperware hole.

  We get to see how the subject handles the nut and washer without being able to see them. It requires some dexterity to hold the washer, spacer and nut with one hand and get the nut started. All this through a hole and no vision. There are four holes so we also see if there is a favorable side and if they use the same hands or are able to switch as they move to each of the corners. We added the plastic window so we could see some of the more creative underneath techniques during the test.

The last task is an attention to detail exercise. The subjects are asked to sort the pile of screws into alike piles in the pockets of the tray. I warn them it is an attention to detail task and to make sure they pay attention. Looks simple enough right? The screws were carefully selected from inch and metric sizes to be rather difficult to see the differences.

Not much difference. The screws on the right are metric and if you look carefully you will see the heads are slightly larger.

Some of the smaller socket head screws. Screws on right are metric and English on the left.

Different finishes added in to mix it up. Once again metric on the right side.

All the screws correctly separated and segregated. There are more types than pockets which shows us how the subject handles the unexpected problem. The screw sort has proven pretty tough even with subtle hints like, its an attention to detail problem and a second chance with "are you happy with that?" if they finish too quickly.

That sums up the mechanical dexterity testing we did. It was very enlightening for us to watch these folks work the problems. The value in getting to see them perform actual work for a short time told us quite a bit about the person and their experience and how they handle stress.

After I created the busy box it tested it on a group of volunteers to collect some baseline data. It helped to refine the instructions and see how established people under low stress performed. The volunteers consisted of people that do this kind of thing every day like technicians, to office people and engineers. I'm looking forward to making a new one up for more advanced level evaluations. It may be interesting to add something that has no solution. Kind of like the Kobayashi Maru test from Starfleet.