Student Material 001: Precision Measurement and Safety Quick Reference
Material ID: U8M4-MAT-001
Purpose: Quick reference for measuring instrument usage, tolerance interpretation, and shop safety
How to Read an Outside Micrometer
- Sleeve reading: Count the large numbers (each = 0.100") and small lines past zero (each = 0.025")
- Thimble reading: Read the thimble line aligned with the sleeve index line (each = 0.001")
- Vernier reading (if equipped): Find the vernier line that aligns with ANY thimble line (each = 0.0001")
- Add all three: Sleeve + Thimble + Vernier = Total reading
Example: Sleeve = 0.275" (2 large + 3 small lines), Thimble = 0.013", Vernier = 0.0004" → Reading: 0.2884"
Measuring Instrument Selection Guide
| Dimension Type |
Instrument |
Resolution |
Accuracy |
Best For |
| External diameter/length |
Outside micrometer |
0.0001" |
±0.0001" |
Final inspection |
| External (quick check) |
Digital calipers |
0.0005" |
±0.001" |
In-process checks |
| Internal diameter |
Telescoping gauge + mic |
0.0001" |
±0.0005" |
Bore measurement |
| Internal (quick) |
Inside calipers or caliper jaws |
0.001" |
±0.002" |
Rough checks |
| Depth |
Depth micrometer |
0.001" |
±0.001" |
Counterbores, steps |
| Runout/alignment |
Dial indicator |
0.001" |
±0.001" |
TIR, centering |
| Fine alignment |
Dial test indicator |
0.0005" |
±0.0005" |
Vise, spindle alignment |
| Height |
Height gauge |
0.001" |
±0.001" |
Scribing, comparison |
Tolerance Interpretation Quick Reference
| Drawing Notation |
Meaning |
Acceptable Range |
| 1.000 ±0.005 |
Bilateral tolerance |
0.995 to 1.005 |
| 1.000 +0.002/-0.000 |
Unilateral (oversize OK) |
1.000 to 1.002 |
| 1.000 +0.000/-0.003 |
Unilateral (undersize OK) |
0.997 to 1.000 |
| .995 / 1.005 |
Limit dimensions |
0.995 to 1.005 |
Fit Types Summary
| Fit Type |
Shaft vs. Hole |
Assembly |
Example Use |
| Clearance (RC) |
Shaft < Hole |
Slides freely |
Bearings, pivots, loose pins |
| Transition (LT/LN) |
May be either |
Light press or slip fit |
Locating pins, alignment |
| Interference (FN) |
Shaft > Hole |
Press fit, permanent |
Press-fit bushings, gears on shafts |
Machine Shop Safety Quick Reference
The 5 Non-Negotiable Rules
- Safety glasses: ALWAYS on in the shop
- Chuck key: REMOVE immediately — never left in
- No gloves: Near ANY rotating machinery
- No loose clothing: Short sleeves, hair tied, no jewelry
- Stop before touching: Stop the machine before measuring, adjusting, or cleaning
Emergency Equipment Locations (Fill In For Your Shop)
| Equipment |
Location |
| Emergency stop buttons |
_____ |
| Eyewash station |
_____ |
| First aid kit |
_____ |
| Fire extinguisher |
_____ |
| SDS binder |
_____ |
| Emergency exit |
_____ |
| Emergency phone |
_____ |
End-of-Session Checklist
- [ ] All machines OFF, controls neutral
- [ ] Workpieces removed or secured
- [ ] Chips cleaned from machines
- [ ] Cutting tools stored properly
- [ ] Measuring instruments cleaned and stored in cases
- [ ] Ways wiped with light oil
- [ ] Coolant levels checked
- [ ] Floor swept, no slip hazards
- [ ] Shop lights and ventilation per protocol
Last Updated: 2026-03-19