Workpiece support for Buffing, Grinding, and Sanding Operations (University of Pittsburgh)

Andrea Sundaram, Karl Kemmerer, Vince Schiappa, Tim Sanchez

Hands-on work – such as prototype fabrication in engineering, or labs in the natural sciences – is a critical part of learning in the STEM disciplines, but the lack of adaptive devices can limit the accessibility of this aspect of education for students with disabilities. In this paper, we interview a model client to identify specific barriers to access, design a device to assist with holding the workpiece during some common metalworking tasks, test the device with our client, and refine the design to better meet her needs. Additionally, we propose that are workpiece support device could be beneficial to individuals with a variety of upper limb functional limitations.

Accessibility to laboratory and machine shop equipment can be a challenge for those with disabilities. Whether inhibiting successful completion of tasks, decreasing independence, or introducing real or perceived safety concerns, such barriers can prevent students with disabilities (SWD) from fully participating in hands-on learning activities. Section 504 of the Rehabilitation Act of 1973, together with Title II of the Americans with Disabilities Act of 1990, establishes the legal framework for ensuring equal access to education to all students, regardless of disability, and is applicable to all educational institutions receiving federal funds (1). Still, barriers to participation do exist, and may disproportionately limit the number of SWD who enter the Science Technology Engineering and Mathematics (STEM) fields (2).

Opportunity Identification
Our project was to improve access to the machine shop for a specific client, Jessica, who has a primary diagnosis of cerebral palsy (CP). Secondary to CP, Jessica uses a wheelchair, and has had the bones in her left wrist fused, which severely restricts strength and range of motion in that hand. Further, it was desired that the product be designed in such a way that it can improve access for individuals with a variety of similar disabilities. To guide the project, our team developed the following mission statement:
“Design a product that allows individuals with impairment of one upper limb in a wheelchair to safely and effectively use machine shop equipment with the dominant hand to enable these individuals to more fully and safely participate in the shop experience.”
The primary stakeholders were identified as individuals with functional impairment of one upper limb and the machine shop staff. Although the context for our project was equal access to educational opportunities, the eventual product could serve to make the same machining tasks accessible in the working environment.
User Needs
An interview with our client regarding her previous shop experiences and the common tasks she found most difficult to perform was distilled into the following user needs:
1. Allows manipulation of workpiece with one hand
2. Has only moderate dexterity requirements for the hand used
3. Is a permanent fixture, or is easily and quickly set-up, disassembled, and transported with one hand
4. Can be used with the belt Sander, bench grinder, and buffing wheel
5. Allows the machine to function normally
6. Can be used from seated height without repositioning the chair during machine operation
7. Maintains or increases safety of machine operation
8. Requires minimal force to operate
9. Withstands shop conditions – e.g. dust and debris – while still operating effectively

Concept Selection
Various early concepts were presented to our design class and our client, and a workpiece support was selected as meeting the greatest number of user needs. The design consisted of a cubical base containing a ball, out of which protruded a shaft and trough. The ball could be oriented at different angles in the base, have its orientation fixed with a clamp, and the trough would be used to support a workpiece.

Refined User Needs
The user needs changed relatively little throughout the initial design process. The requirement for the device to be moved from machine to machine with only one hand was relaxed to, instead, require only minimal assistance. It was intended that our client, Jessica, who has some use of her other hand, would be able to independently move the workpiece holder among the machines, but a user who is truly limited to one hand may require some assistance. It was still maintained that, once set up, a user limited to single-handed use can use the device fully. As no machine controls are being adjusted, the most safety-focused user need was reworded to express the way in which the product will improve user safety. Further interviews with our client and the shop staff established parameters for the workpieces that our device need support.

In order to gather information about the product landscape, the group performed some informal benchmarking by conducting web searches and consulting our shop staff, who have significant experience working with individuals who have a variety of functional limitations. Many products exist to help support workpieces or tools; one of the most common was a tool support that could be used with a wood lathe, and similar products were available for other machines. The majority of these products were jigs for very specific operations. Others, such as a large L-shaped bracket of three-quarter inch steel that is used as a makeshift jig for many operations in our shop, did not look to provide adequate control of the workpiece or were not easily moved. Bearing this in mind, the group decided to continue with the workpiece support design.
Concept Screening
Based on the initial concept, a number of embodiments were drafted: a sliding design which allowed for translation along an x-axis, a clamp-mounted design which fixed the device to a table, an adjustable “long-arm” design that could be mounted on an individual’s wheelchair or other surface, and a rolling design that stood on the ground. These designs were put into a Pugh matrix to facilitate a systematic comparison of their features. The Pugh matrix was used to determine which aspects of the various designs were most valuable and would be included in further development.
Prototype Testing
An initial prototype of the ball joint concept was constructed primarily using 3-D printed parts. Due to safety concerns of the shop staff, the prototype could not be used with the machines active. However, members of the team, and our client, used the prototype in front of the inactive machines to mimic the motions required for grinding and buffing operations. Our client was generally pleased with the function of the prototype, but she did identify some shortcomings. These were reinforced by our own experience with the prototype device.
Defining the x-axis as proceeding from left to right in front of the machine, the y-axis as into the machine, and the z-axis as vertical, rotation about the x-axis was deemed most important. Translation along the y-axis could be accomplished by sliding the workpiece along the trough, but rotation about the y-axis was found to be of minimal importance. Rotation about the z-axis was thought useful, but, as implemented in the initial concept, brought the end of the workpiece out of contact with the grinding or buffing wheel. Additionally, our client felt the end of the support trough was in too close proximity to the machine, and felt there should be some means of constraining the workpiece from flying off the trough.
Since we could not test our prototype with the machines on, the group also designed a test fixture to measure the forces that would be exerted on the workpiece holder during grinding and buffing operations. This testing found that the magnitude of force directed into the grinding and buffing wheels could be expected to range from approximately 5 N to 50 N. While some of the clamping arrangements considered for the ball may have been able to resist the generated torque, it was thought unlikely they would meet a suitable safety margin.

Based on the necessary degrees of freedom identified in user testing, and the locking force requirements, the team undertook a complete redesign. The current design consists of an arm that pivots about a point directly under the front edge of the grinding and/or buffing wheel – providing z-axis rotation, while keeping the end of the workpiece in contact with the machine. A vertical member is pivotally attached to the other end of the arm – providing rotation about the x-axis – and the trough is attached atop this structure. A spring pin is used to maintain the vertical member at the desired angle. Another pin locks the radial arm straight on to the machine, or it can be rotated about Z, with speed regulated by a rotary viscous damper. Straps on the trough provide some security for the workpiece while still allowing it sufficient movement to carry out machining operations. The base plate, which remains attached to any particular machine, is fabricated from steel to provide strength to the pivot shaft, while most of the rest of the device is 6061 aluminum, to reduce the weight of the arm to 0.61 kg. Cost of materials for the workpiece support was about $50.
Final Design Testing
For this test, the base plate was installed on the grinding wheel support. After the device had been used by the shop staff to satisfy safety concerns, we conducted a test of the final design with our client. She was instructed on the methods for removing and replacing the device on its base plate and for locking the axes of rotation. She first familiarized herself with the motions of the device, then used it to successfully deburr a tubular aluminum workpiece that had previously been cut. Our client felt comfortable using the device, and stated that it helped her to control the workpiece better than the flat support she had used before.

Workpiece Support in Use
Future Work
Future work includes creating a new locking mechanism for Z rotation that is accessible from the user end of the radial arm and incorporating a second rotary damper for X rotation. We will also fabricate additional base plates for the other targeted machines. We will investigate other means of securing the workpiece instead of/addition to the velcro straps.
In this paper, we have identified a barrier to educational and vocational opportunities for individuals with a particular range of disabilities, gathered specific information from a model client, designed an initial prototype, tested it with our client, and redesigned the device based on those tests. The final design was also tested with our client, and found to meet most of her needs.
Though the design was focused on a particular client, the group feels that the solution would be applicable to individuals with a variety of similar functional limitations – enabling independent participation in the hands-on portion of design work. We offer the design to the RESNA community in hopes that it may have a wider impact on improving accessibility.
The group would like to thank our client, and colleague, Jessica, for her insights on the product design, and patience with testing our prototypes. The machine shop staff at the University of Pittsburgh’s Human Engineering Research Laboratories provided many recommendations on both design and construction of our device. Occupational therapist, Sherin Heric, was a valued member of the team during the first semester. We would also like to thank our instructors for the assistive technology design class – Dr. Jonathan Pearlman, Dr. Mary Goldberg, and Mahender Mandala, as well as our fellow students, for their guidance and suggestions throughout the design process.

1. Section 504: Protecting Students with Disabilities. Retrieved from
2. 2. Duerstock, B. And Shingledecker, C. (2014). From College to Careers: Fostering Inclusion of Persons with Disabilities in STEM. Science, 344(6185), 765. doi: 10.1126/science.344.6185.765-c
Corresponding Author Contact Information
Vince Schiappa
6425 Penn Avenue, suite 401
Pittsburgh, PA 15206

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