Pneumatic Vise

Going into this project, we knew clamping our workpieces in the CNC machine without any human input would be a significant challenge. We brainstormed several possible ideas to address this, including using the robotic arm to operate a manual vise and or using a vacuum table, but we decided that the best solution was a pneumatic vise due to its relative simplicity and low cost. We initially hoped to purchase a fully assembled pneumatic vise, but due to the budget limitations we faced we decided to convert an old machine vise (which the Olin Shop was nice enough to give us) instead.

The design for our pneumatic vise was based on a converted machine vise we saw at the Boston University makerspace. The general principle of the design is very simple - the leadscrew mechanism is replaced by a pneumatic cylinder (which is controlled by a solenoid valve), and threaded rod and nuts are used together to fine-tune how much the vise is allowed to open and close. Our final design is shown below:

Once our vise was designed, we then manufactured all the parts we needed, starting with the two backstop pieces and the mounting plate for our pneumatic cylinder. We also had to modify the body of our vise to mount our pneumatic cylinder properly, which made for a fun workholding challenge

In our initial design, we had planned to make an entirely custom adapter between the pneumatic cylinder and the movable jaw of the vise (which was threaded to accept the leadscrew). However, when we started to try and make the adapter, we realized that the thread used by the leadscrew was very difficult to replicate - it was a very unusual size and was left handed! Because of this, we decided to instead modify the existing leadscrew to have a tapped hole, and designed and machined an adapter piece to connect the pneumatic cylinder to the leadscrew.

When we assembled and tested our vise, it was able to close very consistently and effectively, but it struggled to open. We realized that this was due to the single-acting pneumatic cylinder we were using. This cylinder had a spring retract mechanism to return to its initial position, but the spring was not strong enough to actually move the movable jaw back to the open position. Therefore, we swapped out the single-acting cylinder for a double-acting cylinder, which allowed both the open and close mechanisms to be pneumatically powered.