Screwdriver Project

The MECH200B Screwdriver Project involved the fabrication of forged and injection molded screwdrivers using the CNC lathe, manual lathe, and injection molding press.

Forged Screwdriver

The forged screwdriver required the use of the manual mill to face and knurl, the CNC lathe to turn and chamfer, and the drop forge to form the tip.

What I Learned

Once we began the screwdriver project, I was pretty confident in my skills on the manual lathe, so the facing and center drilling in preparation for the CNC lathe was no problem. Using the CNC lathe itself was also pretty straightforward, and we had TAs to help us through the setup process. They told us at the beginning of the project that about one in every ten screwdriver blanks ends up with a cavity from air trapped inside during the casting process, and I got to see this for myself with my first blank. Once I'd finished my second one (no pockets this time), I moved on to the knurling process, and achieved good symmetry on my first attempt. Next, I used the drop forge and torch to form the tip, and really took my time grinding down the excess material to stay in tolerance. Once I was happy with that, I moved on to the heat treating process, which like the rest of the project, went pretty smoothly.

My Advice For Future Students
- The first part you have to start paying attention is the knurling. I would suggest lining up the knurling wheels at least five times, including one of which you thought was perfect. I have one of my classmates to thank for forcing me to redo it even when I thought it was fine, and it was definitely worth not having to do it again.
- As far as the mistake of getting the brush stuck in the knurling wheels when applying the cutting oil, I found it hilarious how many brushes were destroyed even after our multiple warnings. I didn't have a problem holding it on the opposite side, but maybe I just got lucky. Regardless, it's worth pointing out, don't stick the brush in the wheels.
- Don't be scared to measure twice and cut once when grinding off material after forging. I didn't realize how much finish work was still needed after the actual drop forging process. Luckily, it's pretty fun to see the shape progress as you go.

Injection-Mold Screwdriver

The injection-mold screwdriver only required the use of the injection mold press to form the handle over the shank of the screwdriver.

What I Learned

There isn't a whole lot to the injection-molding process, I came in and finished in about 10 minutes thanks to a TA that helped me through the process: Fill the hopper flush with plastic beads, place the screwdriver shank in between each die, place in the machine, take out, and remove screwdriver. The only finishing required is cutting off the sprue (the tiny nub left where the plastic enters the die).

My Advice for Future Students

Only sand the necessary part of the screwdriver. The handle can start to peel if you try to cover the entire thing, and you aren't graded on it anyway.

Cost of a Single Screwdriver

As of December 2024, the cost for one forged screwdriver is about

$219.65.

Materials
- Steel shank
  - $6.97
- Aluminum for casting
  - ~$5.00
Labor
- The average pay for a machinist in Colorado
  - $25.96/hour
- Hours required
  - 8 hours

Modernizing the Process

To streamline the production of the screwdriver, one might consider different alternatives to the custom machining process.

To produce mass amounts of screwdrivers quickly and efficiently, most companies use presses on an assembly line to form steel wire into the shape of a screwdriver head. The shanks are then hardened by heat treating in a large oven. Once the shanks are finished, the handles are created by injection molding, which as we saw in lab, is fast and minimalizes material waste.

Mass Production - 10,000 Units

A worthwhile comparison would be to see how the costs and time of mass production compare to custom production in the CSU EMECH.

Method of Production - Pressing, Heat Treating, Injection Molding
- Cost
  - Assuming a 15% discount for bulk orders, the cost of 10,000 screwdrivers is about $288,320
- Time
  - Assuming it takes 1 minute to press, 12 hours to heat treat 1,000 screwdrivers, and injection molding can produce 1,000 screwdrivers per hour, the total time would be around 17,800 minutes, or 6 work weeks.
Method of Production - CSU EMECH
- Cost
  - Assuming one screwdriver at a time, the total cost would be $339,200.
- Time
  - Assuming 8 hours per screwdriver, the total time would be about 5 million minutes, or 400 work weeks.

Screwdriver Project

Forged Screwdriver

What I Learned

Injection-Mold Screwdriver

What I Learned

Max Coulter