Guides · 23 October 2026
Bar stock cost per turned part: parts per bar, cut-off and the bar end
On a lathe the material cost of a part is not the weight of the part, or even the weight of its blank. It is a share of a whole bar: the blanks, the cut-off between them, and the end of the bar the chuck or bar feeder cannot use. That difference is easily 10 percent of the material line, and on small batches it can be most of it.
Length per part: blank plus cut-off
Start from the finished length, add a facing allowance for each end you face, then add the width of the parting tool, because that slice turns into chips:
length per part = finished length + facing allowance + cut-off width
A 80 mm part faced on both ends with 1 mm each, parted off with a 3 mm blade, uses 85 mm of bar.
Parts per bar, after the bar end
Every bar leaves a piece you cannot machine: what the collet or chuck holds on the last part, or the remnant a bar feeder ejects. 100 to 300 mm is common; measure yours. The parts a bar gives are:
parts per bar = ⌊(bar length − bar end) ÷ length per part⌋
Round down: a part that does not fit is not a part.
A worked example
1045 steel, Ø40 mm, bought in 3 m lengths at A$3.10 per kg. Part 80 mm long, faced both ends (1 mm each), 3 mm parting blade, 150 mm bar end.
| Step | Value |
|---|---|
| Weight of Ø40 steel bar (π ÷ 4 × 0.04² × 7,850) | 9.865 kg/m |
| One 3 m bar | 29.59 kg · A$91.74 |
| Length per part (80 + 2 + 3) | 85 mm |
| Parts per bar ⌊(3,000 − 150) ÷ 85⌋ | 33 |
| Material per part, whole bar shared | A$2.78 |
| Material per part, blank weight only (85 mm) | A$2.60 |
The bar end alone adds 7% here; with a 250 mm bar end it would be about 10% (32 parts per bar).
Small batches pay for whole bars
If the job is 20 parts, you still cut into a full bar. Unless you will use the other 13 parts' worth of bar soon, the honest material cost is the bar:
| Quantity | Bars | Material | Per part |
|---|---|---|---|
| 20 | 1 | A$91.74 | A$4.59 |
| 33 | 1 | A$91.74 | A$2.78 |
| 100 | 4 | A$366.96 | A$3.67 |
The 100-off line is the one that surprises people: 100 parts need 3.03 bars, so you buy 4, and 32 parts' worth of steel goes on the rack. Whether you charge for it depends on how often that size moves. If it sits for a year, charge for it, or quote the quantity break at 99 and 132 so the buyer can choose.
Things that change the numbers
- Bar feeder or not. Bar feeders usually leave a longer remnant than hand-loaded short bars. Use the figure for the machine the job will run on.
- Cut-to-length service. If the supplier cuts blanks, you pay a saw charge per piece instead of the bar end, and each blank needs its own facing allowance.
- Scrap credit. Brass and copper chips are worth something; steel chips rarely are. Only count a credit you actually receive.
- Yield. Start one or two extra on a new job; they use bar too. The material cost guide covers yield and kerf for plate as well.