Mech 200 is one of early courses in the CSU mechanical engineering curriculum. It covers the various types of manufacturing processes in use today, and the lab component has students use a variety of them for hands on projects in a machine shop setting.

The flagship project for the course is a clock. It’s made of 5 components students must manufacture themselves: an aluminum base, a brass pencil holder, a brass nut, a steel pen holder, and a plastic clockface. The clock motor is provided. The objective of the clock project was to familiarize students with manual lathe and mill operations, as that is how the bulk of the clock is produced.

Other projects in the course were a trivet manufactured on a CNC mill; a screwdriver manufactured using a CNC lathe, manual lathe, and pneumatic forge; and another optional project for a screwdriver manufactured with injection molded plastic.

We were given the hypothetical questions of how much it would cost to produce one clock, one trivet, and one screwdriver (the non-injected molded one), and how much it would cost to produce 10,000. The scenario for the single item was posed as if we were contracting a machinist to manufacture the item for us.

Using material rates from McMaster-Carr, a 3/8″ thick bar of aluminum can be ordered at a size of 2″ by 12″ for $59.86. A 5/8″ diameter brass bar (1 ft long) can be ordered for $54.92, a 5/8″ diameter steel bar (1 ft long) can be ordered for $8.43. The 1/8″ thick plastic face (6″ by 12″) can be ordered for $4.87, and brass nuts can be ordered pre-made for $14.99 for a package of 25. Materials alone cost $143.07 plus shipping.

It took me about 12 hours to produce the clock as a novice machinist with no experience, and odds are high an experience machinist would manufacture most of the clock components using a CNC mill/lathe, not a manual one, which would dramatically reduce cost of labor times. If the going rate at a machine shop is $75 an hour, I’d wager the labor cost for one clock is $300-400 dollars. Adding materials and other small fees, it would be $450-600 total for one clock.

One trivet would take significantly less time than a clock, though a 6×6″ sheet 3/8″ thick would cost $70 and need to be cut to size. My experience with the trivet on the CNC took about 20 minutes, so I’d imagine the final cost for a trivet would be $100-150. An individual screwdriver is really hard to estimate for, and it would probably be easiest to go to a hardware store than having one manufactured custom. Given the specialty of the types of processes involved, I would imagine it costs $700-1000 for one screwdriver.

Economies of scale do play a role, as it is cheaper to order material in bulk versus individually. That being said, producing clocks on a mass scale would require more time and initial investment, as trying to assemble all these manually would be an inefficient use of time. Mass producing these parts on CNC components would also take a lot of time, as an operator would still have to make sure each piece of raw stock is set up correctly in the machine to avoid crashes. If using CNC machines, it would be easiest to have a mill dedicated to the clock base, and an individual lathe dedicated to the brass and steel parts. The brass nut would be relatively easy to manufacture on a grand scale, as the machine in the CSU machine shop was designed for that exact purpose.

But if I were manufacturing these at a large scale, I would try using diecast/molding techniques to speed up the time required for each part. Casting allows for parts to be produced faster and in greater quantities, though I am unsure of what specific treatments the different metals involved will need (e.g. different cooling times).

Using material rates from McMaster-Carr, a 3/8″ thick bar of aluminum stock does come in 8″ wide bars, but these bars are only a foot long, giving us a maximum 6 clocks per bar at the cost of $121.31 plus shipping/handling. A 2×2 ft bar would require more cutting and manufacturing to properly size the clock bases, and these sheets cost $545.54 plus shipping/handling. It would be simpler to order the 1 foot by 8″ bars, though we would need to order 1667 of these (maybe 1670 to have some spare stock in case), and that would cost us at least $202,590. These are just for the bases, we haven’t even looked at the other parts yet. A 3 ft brass 5/8″ brass rod is $171.63. If each part is 2″ long, we can get 18 per each bar, so we’d need 556 bars total. That would be $95,427. The 5/8″ diameter steel we can get in 6 ft rods for $38.30. Assuming each steel part is 2″, we can get 36 parts per each rod of stock. We’d need 278 bars, at a cost of $10,648. The nuts we can buy premade in packs of 25 for $14.99. That would be about $6000 for 10,000 nuts. The 1/8″ thick PMA faces, assuming they’re 6×6″ would be $4.87 for a 6×12″ sheet. That’s two faces per unit, so we’d need 5000 of those, at a total of $24,350. In total, our materials alone cost $338,915, plus shipping. The labor costs involved would be astronomical if these were being worked on manually.

Producing 10,000 trivets with a CNC mill would be easier than the clock components, as there are less operations involved for the trivet, but it would still take far too long to be efficient. It would still take ~20 minutes per each, though. If each trivet takes exactly 20 minutes, and there are 10,000 to produce, we’re looking at 20,000 minutes, or 3333.3 hours to make them all. That 138.9 full days. Mass producing trivets with a CNC is probably not the best way to do it. The cost of the material is unfortunate here, too, as aluminum isn’t sold in multiples of 5,” meaning that each trivet would have to be cut to size manually, and there would be a lot of wasted material.

The screwdriver would be hardest to create individually, given the variety of parts and processes involved, but on a grand scale it can be done, after all the shelves of Lowes and Home Depot manage to stay full. That being said, trying to mathematically calculate how much it would cost for one person to make 10,000 screwdrivers individually feels the same as trying to complete the task itself: it isn’t worth it. Nobody in their right mind would intentionally do such a thing. Maybe some machinists do manufacture 10,000 tools over the span of their multi decade careers, but intentionally setting off on such an errand isn’t worth the time and labor.

Here’s my advice for future Mech200 students for all of these projects. 1) Start early, as there are only so many machines in the shop, and you’ll need the time to familiarize yourself with setting each one up and operating it. Plus, as the semester chugs along, the machine shop will only get more and more crowded as others try to finish their projects. 2) The adage “measure twice, cut once” is very relevant here, especially given the cost of repurchasing raw stock from the bookstore. It can also be very frustrating to spend a few hours laboring over a piece only to mess up a cut and have to start from scratch. 3) The screwdriver is not nearly as hard to make as it looks.

Things I wish I knew going into Mech 200: that these processes aren’t as intimidating as they look. That doesn’t mean don’t take the machines seriously – they are still very dangerous tools capable of causing tremendous harm if used incorrectly. Safety should always be the first priority when working around anything found in a machine shop, even handheld tools. What I mean is, while a lathe or a mill may look intimidating to operate, like a bicycle, it gets easier the more you use it. Give yourself the chance to use machines and learn how they work, and with time/practice, the fear factor will diminish.