Machine Shop Disaster

Performance test was the only thing racing through my mind as I walked slowly to my CAD and CNC programming class, computer controlled machine tools, Friday afternoon. I was in no hurry for the test, but the slower the pace the more anxiety built in me. I opened the door to the class at two o’clock and was struck by the smell of oil and cutting fluid. I kept out of the way of the running machines and entered into the computer room. It looked more like a surgical operating room: clean, swept, and all the tools placed in order for the tasks of the day.

Then I placed my book bag by my computer and grabbed a piece of butter board, a block of plastic, and sat back in a chair waiting for my turn at the machine. I ran my fingers up and down the smooth yellowed butter board trying to calm myself. The mini mill, a small computer controlled mill, would only take fifteen minutes to complete the part, but it felt like an eternity sitting in front of the blank computer screen. The minute hand slowly ticked by.

After staring at the black screen, I went over the operating procedure in my head a thousand times, forwards and backwards. The machine was going to cut a rectangular journal, shave the right side of it down by two inches, and then drill four quarter inch holes in the short side. I had studied the procedure religiously the night before and asked my teacher every question about the mini mill imaginable. Still nervous, I cycled through the procedures and checked them again for accuracy, just like one of these computers in the room.

Soon as the clock read two fifteen, the teacher called for the next student. I entered the mini-mill room and heard the door close shut. A man could have heard a pin drop in the room. I was completely isolated from the entire class with the machine.

At the same time as the door shut, I swept the surgically cut pieces of butter board form the keyboard of the computer. The pieces littered the floor and air. I placed the block tightly in the vise and inserted the cutting tool into the collet (tool holding device). I opened my file on the computer and slowly pressed the go button, but the mini-mill sat there lifelessly for a moment.

“Error!” the computer shouted in bold red letters.

Immediately, I shoved my face right up to the screen to read the remark. The computer had found unreadable code in line ten. I had already checked the program but scrolled to line ten and saw the problem. Two plus signs sat at the end of the code. I had put them there by accident when I added lengths to find the origin of the part. I deleted them and went on. It was odd that marks meaning positive accomplishment were causing me trouble. The machine started again. Two twenty ticked by on the clock.

At the same time, the whistle of the cutting tool echoed through the room, and the machine hummed to life. I thought “finally success.” The arm of the mini-mill slowly moved the cutting tool in small increments towards the part. The bit began slicing the correct pattern, but it was just trimming air. The mini-mill had moved the cutting tool seven inches off the block. I slapped the emergency stop button, and scrolled through the code again, but my untrained eye found nothing wrong. I looked at the clock over my shoulder and saw two fifty, ten minutes left of class. Simple mistakes had devoured priceless time.

Meanwhile, my heart raced, and sweat rolled over my face fogging the lenses of the safety glasses. I took them off and looked at the block without the film of anxiety. With shoulders hunched, I lowered my head.

“Okay,” I thought nervously, “Let’s reset the cutting tool’s starting position.”

I carefully redid the math and set the bit back in position. The clock stated 2:55, five minutes remained of class. Again, I slowly pushed the start button.
For the second time, the machine buzzed and rapidly moved the cutting tool to the right side of the block to mill the first journal. My pride rose then suddenly fell with the mill’s next movement. The tool bite into the part like a dog on a bone and sliced through the middle of the block. I punched the emergency stop. My body was drained and limp. I stood in the mini-mill room staring at my deformed block. It was three o’clock, and class was over. I wandered out of the room with the deformed block in my hand towards the teacher’s desk.

“Finished?” he asked.

I looked him in the eye and confidently stationed my misshapen part on his desk.


By Jarad Williams