Universal Screwdriver
Design Team
Sean de Laforcade , Katey Farel
Matt Lapinski, Josh Peterson
Design Advisor
Prof. Andrew Gouldstone
Abstract
Current screwdrivers use mating surfaces between the driver and screw head to apply torque. For installing
and removing screws. While this method is successful for screws and drivers with matching geometries,
users require multiple screwdrivers to access the wide range of screw sizes and shapes used in consumer
goods. The objective of this project was to explore the design space of materials and geometries that would
allow low torque application to a range of household screw sizes and shapes with a single tip. An explored
preliminary design space included granular packed cells, magnetism to increase normal force and friction
between driver and screw head, and malleable heads to increase surface-to-surface contact between driver
and screw head. Experimental testing and design iteration led to the final product, a malleable head
reinforced with a metal plate.The malleable element of this design will allow the driver to mate with the
recessed geometry of the screw, while the reinforcement plate will give the driver strength to apply the
required torque for inserting and removing screws. The composite geometry allows mating with a range of
screw heads, and sufficient torsional stiffness to insert or remove that range of screws.
For more information, please contact a.gouldstone@neu.edu.
The Need for Project
The screwdriver is one of the most common tools in the world.
No single screwdriver tip is
capable of providing torque to Despite its useage, no screwdriver currently exists that has the ability to
a wide variety of screw sizes apply torque to a wide range of screw sizes and geometries. Users need
geometries. Such a to buy multiple screwdrivers or a kit that has removable tips for each
screwdriver, if created, could screw. A single screwdriver that could work on a large variety of
replace an entire set of drivers. common screw types and sizes will hold a competitive advantage over
the ‘universal’ screwdriver kits currently on the market. The team is
creating a product that will appeal to hobbyists and people who like
DIY projects.
The Design Project Objectives and Requirements
Design an inexpensive Design Objectives
The screwdriver must be able to effectively drive common
universal screwdriver that can
apply torque to a wide variety household screw types and sizes. Common household screws include
of household screws with a hex, Torx, Philips, flat, and Pozidriv and range from machine screw
single tip. sizes 0 to ¼”. The screwdriver must apply torque easily and
consistently, without damaging itself and/or the screw not requiring
excessive applied pressure. The product may be sold on the market in
two forms. The first is a full screwdriver including the handle, shank,
and tip. The second is a hex style tip for use with universal screwdriver
and ratchet kits currently on the market. This will allow customers to
buy either a complete universal screwdriver, or supplement an existing
universal screwdriver kit.
Design Requirements
The screwdriver must apply at least 30 in-lbs of torque, which
is comparable with the torque an average human can apply with other
hand held screwdrivers on the market. During torque application, the
rotational position of the handle, shaft, and head must be maintained.
This means that the head, shaft and handle must rotate evenly under
torque.
Design Concepts Considered
The team explored multiple
The screwdriver should not damage the screw, so torque may
methods of torque
only be applied through the interaction of the exterior surface of the
transmission from screwdriver
screw and the screwdriver tip. The team decided that this interaction
to screw. The preliminary
could be a result of mating surfaces (like conventional screwdrivers),
concepts were based on
magnetism, enhanced friction, or a combination of the three.
surface to surface interaction
Conventional screwdrivers rely solely on mating surfaces to
between the driver and screw.
transmit torque. Since a truly universal screwdriver must be able to
drive screws with different recessed geometries, its tip must be
malleable in order to conform to different screws. Pressure-dependent
strength and stiffness would allow the tip to be malleable, but with the
application of normal force, exhibit the ability to effectively transmit
torque.
Solid rubber and tightly packed granular material exhibit
pressure-dependent
properties
suitable
for
preliminary
testing.
Polyurethane rubber was chosen for the solid geometries due to its high
tear strength, high elastic modulus, and low cost. Stock polyurethane
rods of durometers 40A, 60A, 80A, and 90A were purchased and cut to
shape using an ultrasonic cutter. The most successful durometer was
determined through experimental analysis. 80A was found to easily
conform and the effectively apply torque. Tightly packed granular
material was tested by filling rubber membranes with coffee grounds.
The packed cells held the shape of the screw geometry after insertion,
and the area of the packed cell that was inside the geometry of the
screw took the shape well. However, the rubber membranes tore easily,
and the concept was abandoned due to its inability to withstand cyclic
loading.
The second preliminary concept, magnetism, was eliminated
for a few reasons. Firstly, magnetism itself would only be applicable to
ferrous screws. Any non-ferrous screw would require another form of
surface to surface interaction to drive. Secondly, the space inside the
shank is limited, making it difficult to create an inductor that produces
a strong enough field to ‘hold’ a ferromagnetic screw enough to drive
it. Finally the cost and difficultly of assembly lead the team to discard
this concept.
Enhanced friction is still a concept being considered, as it is
easy and inexpensive to embed both polyurethane and metal with a
particles of aluminum oxide. This would provide extra grip between
screwdriver head and screw geometry without cosmetically damaging
the screw.
Recommended Design Concept
The recommended design
The results of the preliminary experimental analysis showed
concept is a thin stainless steel that transmission of torque from driver to screw is more successful with
reinforcement plate with a stiff and strong material reinforcing one that conforms to the recessed
polyurethane cast on front and geometry of the screw. Experimental analysis also proved that torque
back faces. is most effectively transmitted via sharp corners, due to locally high
stiffness and strength of nonlinear elastic materials under loading.
Design Description
Since conforming fully to the recessed geometry is no longer
the main goal of the design, a rigid plate may be used to reinforce
malleable material. To design this plate, dimensions of each screw size
and geometry were evaluated. Common geometry was identified by
superimposing Phillips, Torx, hex, and flat geometries, the four most
common geometries (see Figure 1). End points of the greatest common
diameter can be referred to as “torque points”. The plate is dimensioned
Figure 1
with the width of each step determined by the distance between torque
points of each screw size, and the vertical distance between these steps
determined from the ANSI standard for depth of each screw size. The
thickness of this plate was chosen to fit the smallest screw size within
the scope. Two side plates were also designed to prevent the main plate
from deforming during torque application. 304 stainless steel was
chosen for its stiffness, strength, ease laser cutting, and ease of laser
welding for prototyping and production. An opening through the plates
Figure 2
allows polyurethane rubber to be cast as a single piece around the plate
(see Figure 2). The geometry of the polyurethane rubber replicates the
most successful solid rubber tips from preliminary testing, maximizing
contact with as many screw head geometries as possible.
The
polyurethane rubber does provide any additional torque points until
screw size 4 so that it will not interfere with small slotted screws. All
screw sizes above 4 will be contacted by the polyurethane rubber to
allow for more torque points (see Figure 3).
Figure 3
Analytical Investigations
Computer simulated FEA shows an increase of stiffness and
strength on corners of solid polyurethane rubber under loading. Under
loading conditions expected from a hand held screwdriver, localized
stiffness at these corners increased by about 2.5 times.
Experimental Investigations
Experimental analysis of recommended concept was
successful. The tip was able to effectively transmit torque to hex,
Philips, and slotted screws from sizes 2 – 12. Design iteration is
required for use on ¼” screws.
Key Advantages of Recommended Concept
Screwdriver will be price competitive in current market.
Although not proven yet, side reinforcement plates improve fatigue
resistance allowing for long life. This product allows users to have a
single screwdriver for common screw sizes and types with a single tip.
Financial Issues
Production costs will initially include tooling required for the
Good for mass production.
Estimated COGS under $8. casting and turning of the handle, welding of the reinforcement plates
Tooling will be relatively to stock, and mold for casting polyurethane rubber. However, piece
expensive. prices will be very low, especially at production volumes. The hex bit
version of the product will be less expensive to manufacture than the
full screwdriver.
Recommended Improvements
Design could improve by
To improve this design, the reinforcement plate could taper to
optimizing polyurethane be thicker as the width increases. A better polyurethane rubber
rubber geometry as well as design/mold could increase the number of torque points with many
improving the reinforcement screws. During the project, the team was limited by the resolution of
plate with varying thickness. the fused deposition modeling 3D printing. Ideally the reinforcement
plate would be thicker in the sections designated for the larger screws
and thinner in the areas for smaller screws. This could be achieved in
the future by casting the reinforcement plate.