1. User friendly lawn mower blade Demetri stamas

2. Initial thoughts • While trying to come up with a solution there were a few design challenges to overcome. It would be easy to design a blade that essentially just locks into place with no tools required. However, this may not be safe, considering if the blade were to come loose it could be catastrophic. • Whenever I’ve changed mower blades myself it seems like the most difficult challenge is removing the old blade. I have to use a block of wood to keep the blade from rotating while I turn the socket. Even then, the nut is so difficult to budge that many times I need to use a ‘cheater bar’ to get it loose.

3. MY DESIGN This is a crude mock-up of my design. The idea behind it is essentially to use a bolt to transmit torque from the shaft to the blade, but to run the bolt parallel to the blade to make removal easier.

4. EASE OF USE • There are a couple of things that make this blade easy to change. Instead of having to use a block to prevent the blade from rotating when removing the old blade, simply remove this nut with a 3/8 inch socket. Removing this nut will not cause the blade to rotate since the torque of the wrench is not being transmitted axially along the shaft. Also it will not tighten over time with use, so it should remain easy to remove after using the mower.

5. EASE OF USE CONT’d • You can see that the box end of the bolt has a square indent on the blade assembly that it sits into. This is so the consumer doesn’t need two wrenches to tighten the blade onto the shaft. This end will stay in place as the nut is tightened. • Lastly, I designed the axis of the bolt to run at a 90 degree angle to the axis of the blade so that when the customer is removing the nut there is less danger of them cutting their hands on the blade if they were to slip. Having this set up helps prevent them from busting their knuckles.

6. ASSEMBLY Here’s the exploded view diagram.