QuotedPartCost guides · Updated 2026-10-30
How much does it cost to machine 4140, annealed vs pre-hard?
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A stepped 4140 pre-hard drive shaft, 1.25 in bar, 6 in long, with a groove, a keyway and a cross-drilled pin hole, prices at $412 for one, $80.13 each at 10 and $30.33 at 100, at US small-shop rates with a 30% markup. Pre-hard 4140 at 28-32 HRC cuts at about a third of 6061's rate in our catalog, but on a small shaft the turning is 4.9 minutes, so setup and the bar dominate. The one-bar list price, $8.42/lb, is what makes a 4140 one-off expensive; at 100 pieces the shaft is mostly machine time. Machining annealed 4140 and sending it out for heat treat is its own route, priced on the pre-hard vs annealed page.
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The shaft and its routing
The part is a drive shaft turned from 1.25 in round bar: a 1.25 in diameter 2 in long, a 1.0 in diameter 3 in long with a 1/4 in keyway 1.5 in long, and a 0.75 in end 1 in long with a retaining-ring groove. A 0.257 in pin hole is drilled through the large diameter. General tolerance is ±0.002 in; no ground diameters.
The lathe turns it in two operations. The keyway and cross hole need the mill, so the shaft gets a second setup there. That mill setup and the lathe setup are most of a one-piece price, whatever the grade.
| Operation | Work center | Rate | Setup min (lot) | Run min (part) |
|---|---|---|---|---|
| CAM programming | CAM programming | $95/h | 30 | 0.0 |
| Turn, 2 ops | CNC lathe | $90/h | 81 | 4.9 |
| Mill secondary, 2 features | 3-axis VMC | $95/h | 45 | 3.5 |
| Deburr | Deburr / bench | $55/h | 5 | 0.8 |
| Inspect | Inspection | $75/h | 16 | 0.6 |
Five steels, same shaft
Read the material and machining columns separately. Machining is set by how fast each steel cuts: our catalog rates 4130 at 0.5 of 6061's removal rate, 8620 at 0.48, 1045 at 0.42, 4340 at 0.35 and 4140 pre-hard at 0.33. On this small part that is a minute or so of turning between the best and the worst.
The material column needs a caution. 4140 and 1045 carry audited one-bar list prices that fall toward a distributor price at volume. 4130, 4340 and 8620 carry a single starting price in our catalog, closer to a distributor's volume price, so at 1 and 10 pieces they look cheaper than a cut piece really costs. Get a cut-piece quote for those before you send a one-off.
| Steel | Condition | Turning min | Material at 10 | Material at 100 | Machining at 100 | Price at 1 | Price at 10 | Price at 100 |
|---|---|---|---|---|---|---|---|---|
| Steel 4140 pre-hard | pre-hard, 28-32 HRC | 4.9 | $20.87 | $6.32 | $17.01 | $412.15 | $80.13 | $30.33 |
| Steel 4130 | annealed or normalized | 4.0 | $5.95 | $5.95 | $15.66 | $374.35 | $58.98 | $28.09 |
| Steel 4340 | annealed | 4.7 | $7.68 | $7.68 | $16.71 | $379.89 | $62.60 | $31.71 |
| Steel 8620 | carburize and harden after machining | 4.1 | $5.46 | $5.45 | $15.81 | $698.35 | $91.04 | $31.50 |
| Steel 1045 | plain carbon, for comparison | 4.3 | $10.37 | $4.54 | $16.11 | $385.61 | $65.31 | $26.85 |
Annealed vs pre-hard, and 8620
Pre-hard 4140 (sold quenched and tempered to about 28-32 HRC) is machined once and shipped. Annealed 4140 cuts faster and tools last longer, but if the print calls for hardness the parts go out for quench and temper, may move, and often need a finish pass after. For hardness under about 32 HRC, pre-hard is usually the cheaper route on small lots because it skips the outside lot charge and the second trip to the machine.
8620 is different: it is carburized for a hard case and a tough core. The case-hardening lot charge of $250 lands on whatever lot you have, which is why the 8620 shaft is $698.35 for one but within a few dollars of the others at 100.
What changes a 4140 quote
The shaft is a simple one. On a real print, watch these:
- Ground journals. A diameter held to ±0.0005 in or tighter goes to the cylindrical grinder: another setup and a few minutes a part.
- Hardness over 40 HRC. Machining after hardening needs CBN or ceramic inserts, or hard turning; quote it as a separate, slower operation.
- Length. A long, thin shaft needs a tailstock or steady rest and lighter cuts; stock over about 20 lb adds handling time.
- Bar size. Large-diameter 4140 is sold cut to length by weight, and the minimum cut charge can exceed the material in a short part.
- Black oxide after machining is an outside lot charge: $85 a lot plus $1.50 a part in this catalog.
Engine assumptions
- • Part: fictional 6 in shaft from 1.25 in bar; Ø1.25, Ø1.0 and Ø0.75 steps; one groove; 1/4 in keyway; Ø0.257 cross hole; ±0.002 in.
- • Steel 4140 pre-hard: $8.42/lb for a small lot, falling toward $2.10/lb from about ten full bars; removal rate 0.33 × 6061-T6.
- • Steel 4130: $2.40/lb for a small lot; removal rate 0.5 × 6061-T6.
- • Steel 4340: $3.10/lb for a small lot; removal rate 0.35 × 6061-T6.
- • Steel 8620: $2.20/lb for a small lot; removal rate 0.48 × 6061-T6.
- • Steel 1045: $4.18/lb for a small lot, falling toward $1.60/lb from about ten full bars; removal rate 0.42 × 6061-T6.
- • 8620: case harden, $6 a part on parts of about 46 in² and up, $250 lot charge, 8 days.
- • CNC lathe: $90/h, 65 min standard setup (US catalog default, editable).
- • 3-axis VMC: $95/h, 45 min standard setup (US catalog default, editable).
- • CAM programming: $95/h (US catalog default, editable).
- • Deburr / bench: $55/h (US catalog default, editable).
- • Inspection: $75/h (US catalog default, editable).
- • Stock: at least one 1 ft cut piece per lot.
- • Markup: 30% on cost; $65 minimum line charge. No freight, tax, certs or expedite.
| Steel | Condition | Turning min | Material at 10 | Material at 100 | Machining at 100 | Price at 1 | Price at 10 | Price at 100 |
|---|---|---|---|---|---|---|---|---|
| Steel 4140 pre-hard | pre-hard, 28-32 HRC | 4.9 | $20.87 | $6.32 | $17.01 | $412.15 | $80.13 | $30.33 |
| Steel 4130 | annealed or normalized | 4.0 | $5.95 | $5.95 | $15.66 | $374.35 | $58.98 | $28.09 |
| Steel 4340 | annealed | 4.7 | $7.68 | $7.68 | $16.71 | $379.89 | $62.60 | $31.71 |
| Steel 8620 | carburize and harden after machining | 4.1 | $5.46 | $5.45 | $15.81 | $698.35 | $91.04 | $31.50 |
| Steel 1045 | plain carbon, for comparison | 4.3 | $10.37 | $4.54 | $16.11 | $385.61 | $65.31 | $26.85 |
Sources and limits
Claims are dated where they can change. Product calculations are examples from the stated inputs, not a promise about a customer's quote. Competitor wording is attributed to the source shown.
- Prices, minutes and material lines are computed by QuotedPart's pricing engine from the stated shaft and the US catalog defaults.
- 4140 and 1045 small-lot prices are OnlineMetals' one-bar list prices as recorded in QuotedPart's catalog audit; 4130, 4340 and 8620 carry the catalog's single starting price. — source (checked 2026-10-21)
Questions
Is 4140 hard to machine?
Annealed 4140 machines reasonably well, a little slower than 1045. Pre-hard 4140 at 28-32 HRC is slower again and wears inserts faster, but it is still routine work for carbide on a rigid lathe.
Why is a single 4140 part so expensive?
Mostly setup and the minimum cut piece. One shaft pays for two setups and a foot of bar at a one-bar list price ($8.42/lb in our catalog), even though the part itself uses a fraction of it.
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