KEVOS® MAKEOS · Threads
Acme Nut Bore Inspection (Minor Diameter Limits, Drill Choice, Measured Bore)
For an Acme nut, what are the limits on the minor diameter of the bore, which fractional drill falls between them, and does my measured bore pass?
Inspection and drill choice for the minor diameter of an internal Acme thread: the smallest and largest minor diameter for general-purpose or centralizing classes, and the drill size range allowing for the drill cutting oversize (as the Acme tap drill tool), the nearest fractional (64ths) drill within that range, and the measured bore against the minor diameter limits.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Basic major diameter | in | Basic major diameter of the Acme thread. |
| Threads per inch | Threads per inch. | |
| Class | choice | Class of thread (general purpose or centralizing). |
| Probable drill oversize | in | How much larger than its size the drill is expected to cut. |
| Measured bore diameter | in | Measured diameter of the bore (the nut minor diameter). |
Method and formulas
- Minimum minor = D − p (general purpose), D − 0.9p (centralizing 2C–4C) or D − 0.025√D − 0.9p (5C–6C); maximum = minimum + 0.05p (as the Acme tap drill tool).
- Drill range = minor limits − probable oversize.
- Fractional drill = smallest 64th at or above the lower drill limit, used if it is within the upper limit.
- Example: the bore must be 0.8 to 0.81 in; a 0.79688 in drill fits; 0.805 in passes.
Limitations
- Drilled or bored holes; reamed or bored holes do not need the oversize allowance.
- Fractional drills only; number and letter drills give more choices.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose the drill for an Acme nut blank
- Inspect the bore of an Acme nut before threading
- Check a centralizing Acme nut bore
Who it is for
- Machinists
- Inspectors
- Toolmakers
What you get
- Minor diameter limits
- Drill range and fractional drill
- Measured bore decision
Interpreting the result
- The band for an Acme minor diameter is only a twentieth of the pitch wide, so boring is often safer than drilling.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 944–947, 1921–1946. Topic reference; no source tables or recommended settings are reproduced.
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Open the Acme Nut Bore Inspection (Minor Diameter Limits, Drill Choice, Measured Bore) calculator
