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How to Use a Toolmaker's Microscope
Guide · Updated October 28, 2026
A toolmaker's microscope magnifies a small part on a moving XY stage. You line a crosshair up on one edge, read the stage micrometer, move to the other edge and subtract. A protractor in the eyepiece measures angles.
Check the stage
Check the stage micrometer with a gage block. The free Gage Block Calculator builds the stack.
Step by step
- Clean the stage glass: Dust shows up as edges at 30×.
- Place the part: Set the part on the stage glass, square to the X travel.
- Choose lighting: Transmitted (from below) for outlines; surface for features on top.
- Focus: Focus the eyepiece on the crosshair first, then focus on the part.
- Align: Rotate the part or the protractor so one edge is parallel to the crosshair.
- Measure: Put the crosshair on the first edge, read X; move to the second edge, read X; subtract.
- Measure angles: Line the crosshair with one edge, read the protractor, rotate to the other edge, read again.
Specs (Mitutoyo TM-505B / TM-1005B)
Standard optics: 15× eyepiece and 2× objective for 30× total; 10×, 20× eyepieces and 5×, 10× objectives optional. XY stage range 50 × 50 mm (TM-505B) or 100 × 50 mm (TM-1005B, with an optional 50 mm gage block to cover the full range). Stage glass usable area 96 × 96 mm. Maximum work height 115 mm (TM-505B). Eyepiece protractor: 1° graduation, 360°, vernier minimum reading 6′. Micrometer head resolution depends on the head; the digital 2 in head is 0.00005 in / 0.001 mm (Mitutoyo TM catalog).
Worked example: slot width
A small slot. Crosshair on the left edge, X reads 12.345 mm. Move to the right edge: 20.871 mm. Width = 20.871 − 12.345 = 8.526 mm (0.3357 in). Measure both edges approaching from the same direction so backlash does not add error. Repeat 3 times and average.
Covering more than 50 mm
The TM-1005B stage travels 100 mm but the micrometer head is 50 mm. Mitutoyo uses a 50 mm gage block between the head and the stage: measure the first point, insert the block, and add 50.000 mm to the second reading.
Angle example
Line the crosshair with one flank of a 60° thread form; protractor reads 0° 0′. Rotate to the other flank: 60° 6′. The included angle measured is 60° 6′, inside a typical tolerance for a thread tool check.
Common problems
Edge looks fuzzy: focus or use green filter on transmitted light. Readings vary: backlash; always approach from the same side. Part not square: the X travel does not follow the edge; rotate the part first.
Tips
- Gage blocks: build a stack.
- Threads: three-wire threads.
- Mic heads: check micrometer heads.
FAQ
What magnification?
30× standard on Mitutoyo TM (15× × 2×).
How much travel?
50 × 50 mm or 100 × 50 mm.
How are angles measured?
With the eyepiece protractor; vernier reading 6′.
How do I avoid backlash?
Approach every edge from the same direction.
Which lighting?
Transmitted for outlines, surface for top features.
Related guides and calculators
- How to Build a Gage Block Stack
- How to Measure Threads with Three Wires
- How to Check a Micrometer with Gage Blocks
- How to Use a V-Anvil Micrometer on 3- and 5-Flute Tools
- How to Use a Blade Micrometer
- How to Use Dividers for Layout
- How to Use Outside and Inside Spring Calipers
- All free machinist calculators
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