Clock
The clock project was my introduction to manual machining processes, laser cutting, and CNC machining.
This project gave me a feel for how much your decisions at the design and setup stage ripple through the entire machining process. Probably the biggest takeaway was the importance of specifying the largest tolerance you can actually get away with. It's tempting to tighten everything up, every zero you shave off your tolerance every zero you shave off the price. If a feature doesn't need to be held tight, letting it float saves you money and the machinist a ton of grief.
Closely related to that is the finish lesson: avoid sanded finishes whenever possible. Sanding is brutally time-consuming and it ate up more of my project hours than I expected. It feels like it should be a quick "just clean it up" step, but it absolutely is not, and the results aren't even that consistent compared to a good machined finish. The hours spent sanding to 600 grit then re-starting after there were extrusion marks left on the base really hammered this home.
Material choice was another eye-opener. Aluminum and brass are just so much nicer to machine than steel. They cut clean, chip nicely, don't fight you on the boring and tapping, and let you run faster without babysitting the tool. The steel pencil holder, by comparison, was slower and less forgiving across the board. It made me appreciate why material selection isn't just an afterthought; it changes how the whole part comes together.
Finally, the project really hammered home the general importance of attention to detail, and especially when it comes to metrology. A part is only as good as your ability to actually verify it, and sloppy measuring will burn you whether you machined it well or not. Taking the time to measure carefully and consistently is what separates a part that fits from one that's almost right.
Cost Estimate:
RAW STOCK:
3/8" x 2" Aluminum Rectangle Bar 6061-T6511-Extruded
-$14.05
ALUMINUM:
Steel:
5/8" 1018 Steel Round Bar
-$8.79
5/8" Brass Round Bar 360-H02 Extruded
-$25.39
Brass:
Acrylic Sheet 12 x 12 inches, Clear, 1/8 inch
-$8.95
Acrylic:
Material Cost:
-$57.18
LABOR COST:
Hours Sent: 30
Machinist hourly wage in Colorado:
-$26.95
Total Labor Cost:
$808.50
Total cost: -$865.68
Potential Improvements:
-
Stock cutting — Instead of a horizontal band saw, use an abrasive/cold saw with an automatic stock feeder. Same basic operation (cutting raw aluminum, brass, and steel to length), but the auto-feed removes the need for the machinist to reposition and re-clamp stock between cuts, which matters more as batch size grows.
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Pen/pencil holder turning — Keep the CNC lathe, but add a bar feeder so the lathe can pull in and index new stock automatically between parts instead of the operator loading each piece by hand. Keep the in-process sanding/finishing tool as-is; this doesn't change the operation, just removes idle time between cycles.
-
Aluminum body milling — Instead of a standard 3-axis CNC mill requiring a manual re-fixture to machine the second face, use a CNC mill with a 4th-axis trunnion or pallet-changer setup. This lets the machine rotate the part itself instead of the operator manually reorienting it, which was the exact tradeoff flagged as "not worth it yet" in the prior revision — at higher volume, the fixture cost pays for itself in labor time saved.
-
Surface finishing — Instead of a manual disk sander, use a vibratory/tumble finishing station for the aluminum pieces after milling. This can run unattended while the operator works on other steps, rather than requiring hands-on sanding time.
-
Engraving and face slot — Keep this combined with step 3 as before (same orientation, same setup), but if the CNC mill has live tooling or a secondary spindle, this can be run as a continuous operation immediately after facing without any tool change pause.
-
Nut production — Instead of a manual turret lathe, use a CNC Swiss-type lathe. This is the natural production-scale replacement for turret lathe work on small-diameter parts like this bolt — faster cycle times and tighter repeatability with less operator involvement per part.
-
PMMA face — Keep the CNC drill-then-fixture-off-center-hole strategy, but use a vacuum fixture plate instead of a custom mechanical vice fixture. This gives faster part changeover (no manual clamping adjustment between pieces) while still using the center hole for alignment reference.
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Finishing and assembly — Instead of manually spraying finishing coats, use an automated spray booth with a rotating part holder, so coating thickness and coverage stay consistent across parts, then hand-assembly remains the same since assembly is inherently a manual verification step.
Cost Estimate for Various Mass-Production Methods
Manual-EMEC Method:
Cost per clock:
-$865.68
Cost for 10,000 clocks:
-$8,656,800
Hours per clock:
-30 hrs
Hours for 10,000 clocks;
-300,000 hrs
Automated Method:
Cost per clock:
~$100 (electricity + labor + raw materials)
Cost for 10,000 clocks:
-$1,000,000
Hours per clock:
~10 hrs (mainly from tumble finishing)
Hours for 10,000 clocks;
-100,000 hrs (can tumble many clocks at once so isn't effectively this high)
Clock Base GD&T
Functional Requirements:
1. The counter bore bust be deep enough such that the nut doesn't protrude from the bottom of the base.
2. the counter sync mush be deep enough to the martini head on the bold doesn't protrude form the bottom the base.
3. the holes mentioned in 1 & 2 must be at the correct diameter so the respective threaded features do are able to pass through the base.
4. The slot for the clock face must have the correct width, length, and be sufficiently deep to retain the clock face.
- Clock Base Drawing With GDT&T