Problem Statement: 

Create an analysis and a model of a machine that uses a lead or ball screw. To solve this problem, my group went with the choice of creating a table vise. This is a somewhat simple machine that incorporates a lead screw and a moving jaw. 

Problem Assumptions:

• The lead screw moves one of the jaws.
• A safety factor of 18 was used with our calculations and selected parts. 
• A grade 2, 3/4 - 6 ACME thread lead screw will be used.
• A - 36 cast steel will be used for the base and jaw.
• 6061 Aluminum alloy will be used for the clamping material of the jaws.

Thought Process:

Lead screws can be used for various applications, from complex machines such as a lathe or a mill, to more simple machines such as a vise. The table vise that my partner and I choose to design was intended to accomplish a few things: Have a large factor of safety, as these types of tools are often pushed way beyond their advertised limits, and be simple to use and maintain. We ended up choosing a lead screw over a ball screw for this very reason. In an industrial, dirty environment where you would most likely find a table vise, a ball screw would have its performance lowered due to metal shavings and various debris. Choosing a simple, cast steel base keeps the cost of production low, while keeping the forces it can withstand within our large factor of safety. One of the other things we considered during this process was the material of the jaws that do the clamping. On a typical vise, the jaws are made of aluminum, to all the material to slightly deform the jaws, giving them the ability to clamp down with more force. We ended up choosing the 6061 aluminum alloy because it is stronger than other types of aluminum, and is also resistant to corrosion. The material of the lead screw is a mild steel, and this interacts with the cast steel of the vise with a 0.4 coefficient of friction (from Dr. Fagan's resources). As stated earlier, a factor of 18 was chosen, due to our material availability and lead screw availability, this safety factor can be easily incorporated to create a strong vise grip that will operate well above the advertised uses. 

Sources:

https://www.mcmaster.com/lead-screws

https://www.engineeringtoolbox.com/friction-coefficients-d_778.html

https://www.designworldonline.com/how-to-correctly-apply-lead-screws/

Partner:

Ian Sullivan

Design Sketches and Equations: