Tap Drill & Tapping Speed — UNC 1/4"-20 in Aluminum
Tap-drill size, RPM and synchronized feed for UNC 1/4"-20 in Aluminum (75%-thread rule with material-specific speed).
The inch equivalent of D−P: 0.250 − 1/20 = 0.200" — the #7 drill (0.201") in every chart. The calculator works in mm; 5.11 mm rounds to the 5.1 mm metric stock drill at ~73% engagement.
Formula
Note: Catalog starting values only — always confirm against your tool maker's data sheet and cut a test part. Machine rigidity, coolant and workholding shift real-world numbers.
Tap-drill size, RPM and synchronized feed for UNC 1/4"-20 in Aluminum (75%-thread rule with material-specific speed). A free cnc machining: speeds, feeds & tool wear tool — no sign-up, no upload, instant results in your browser.
About Tap Drill & Tapping Speed — UNC 1/4"-20 in Aluminum
Tap Drill & Tapping Speed — UNC 1/4"-20 in Aluminum computes the governing relationship drill ≈ D − (P × %engagement / 76.98) · vf = n·P live as you type. The inch equivalent of D−P: 0.250 − 1/20 = 0.200" — the #7 drill (0.201") in every chart. The calculator works in mm; 5.11 mm rounds to the 5.1 mm metric stock drill at ~73% engagement. Defaults are pre-filled with realistic values for this exact scenario, and the worked example substitutes your numbers step by step so the math is never a black box.
How to use Tap Drill & Tapping Speed — UNC 1/4"-20 in Aluminum
- 1Enter your values — Thread major diameter, Thread pitch, Tapping speed Vc, Thread engagement (sensible defaults are pre-filled).
- 2Read the live results: Tap drill diameter, Tapping RPM, Feed (locked to pitch).
- 3Check the "with your numbers" line to see drill ≈ D − (P × %engagement / 76.98) · vf = n·P substituted step by step.
- 4Adjust inputs until the scenario matches yours, then copy or share the result.
Why use Tap Drill & Tapping Speed — UNC 1/4"-20 in Aluminum?
- ✓Instant, free and private — every calculation runs client-side in your browser; nothing is uploaded
- ✓Built on the stated formula drill ≈ D − (P × %engagement / 76.98) · vf = n·P with authoritative sources cited on the page (Machinery's Handbook, 31st ed. — Speeds and Feeds; ISO 2306 — Drills for tapping holes)
- ✓The inch equivalent of D−P: 0.250 − 1/20 = 0.200" — the #7 drill (0.201") in every chart.
- ✓SI ⇄ Imperial toggle converts your inputs in place, so you can work in the units your drawings use
Frequently asked questions
What formula does the tap drill & tapping speed — unc 1/4"-20 in aluminum use?+
It evaluates drill ≈ D − (P × %engagement / 76.98) · vf = n·P, exactly as published. Sources: Machinery's Handbook, 31st ed. — Speeds and Feeds; ISO 2306 — Drills for tapping holes. The substituted worked example on the page lets you verify every step against the textbook.
How should I read the result — and how far can I trust it?+
The inch equivalent of D−P: 0.250 − 1/20 = 0.200" — the #7 drill (0.201") in every chart. Catalog starting values only — always confirm against your tool maker's data sheet and cut a test part. Machine rigidity, coolant and workholding shift real-world numbers.
When is this calculator the right tool for the job?+
Tap-drill size, RPM and synchronized feed for UNC 1/4"-20 in Aluminum (75%-thread rule with material-specific speed). A free cnc machining: speeds, feeds & tool wear tool. The calculator works in mm; 5.11 mm rounds to the 5.1 mm metric stock drill at ~73% engagement. For neighbouring scenarios, the related tools below cover the same engine with different presets.
Does it support both metric and imperial units?+
Yes — the SI ⇄ Imperial toggle converts the values already in the fields, preserving the physical quantity, so you can flip mid-calculation without re-entering anything.
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