This week’s fail is an attempt to retrofit a PCB cutting shear with a geared motor. The project was undertaken by [David Cook]. Incidentally he’s very near and dear to us as his bookRobot Building for Beginnersgot us started with hacking in the first place.
This $200 shearing tool is hand-operated and can cut through boards up to 1/16″ thick. But [David] really had to crank on the thing to make a cut. This often resulted in crooked board edges. He decided to do the retrofit in order to achieve higher precision. He sourced a high-torque motor from eBay for around $50 delivered.
The stock handle interfaces with a square axle coming out of the shear’s gearbox. He figured this would be the easiest way to interface the motor. After removing the gearbox cover he was able to machine in some holes to attach the motor on the outside. This involves some interesting tips, like not using lubricant when machining cast iron, and one technique for machining that square hole he needed to interface with the shear.
Despite looking so slick the tests with the motor resulted in a total failure. A loud “BAM” was heard and the motor started rotating. All of the screws connecting the motor case to the motor mount had sheared off. He thought his machined parts were okay, but that was not the case. Trying to remove the screws resulted in a twisted hex key. Even worse, the torque of the motor actually twisted its own shaft and the set screws from the coupler dredged deep groove in the steel. That’s a lot of force!
Sheared off screws
Twisted hex key
Damaged motor shaft
Thanks to [Tomás] for sending in the link to [David’s] fantastic fail write-up.
Fail of the Week is a Hackaday column which runs every Wednesday. Help keep the fun rolling by writing about your past failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.