BIZOMAT MAKEOS · Manufacturing
Bar Stock Plan for Bar-Fed Parts (Bars, Yield, Material Cost, Machine Time)
How many bars do I need for this batch of bar-fed parts, how much of the bar ends up as parts, what does the material cost, and how long will the run take?
Material and time plan for parts made from bar on a lathe or screw machine: length per part with cut-off and facing allowance, parts per bar, bars to order and stock length and mass (as the screw machine stock tool), material yield, material cost per part, machine hours from the cycle time and bar change time, and shifts needed.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Part length | mm | Finished length of one part. |
| Cut-off tool width | mm | Width of the cut-off (parting) tool. |
| Facing allowance per part | mm | Extra length faced off each part. |
| Bar length | mm | Length of the bar stock. |
| Remnant (unusable end) | mm | Length left in the collet or feeder that cannot be used. |
| Parts needed | Parts to make. | |
| Bar mass per metre | kg/m | Mass per metre of the bar. |
| Material price | $/kg | Price of the bar material. |
| Cycle time per part | s | Machine cycle time per part. |
| Bar change time | s | Time to load a new bar. |
| Hours per shift | h | Hours in a shift. |
| Least material yield accepted | % | Least share of bar that should end up in finished parts. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Part length
- What it is
- The finished length of one part along the bar axis.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25.4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Cut-off tool width
- What it is
- The width of the parting (cut-off) tool: the length of bar turned into chips at each cut.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.57 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Facing allowance per part
- What it is
- Any extra length faced off each part beyond the cut-off, for example to clean up the parted face.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Bar length
- What it is
- The length of each bar of stock as supplied.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3048 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Check whether supplied bars are cut to an exact length or are random lengths.
What this means: Remnant (unusable end)
- What it is
- The length left in the collet, chuck or bar feeder at the end of each bar that cannot be made into parts.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Parts needed
- What it is
- The number of good parts to be made from the bar stock.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 100000000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Bar mass per metre
- What it is
- The mass of one metre of the bar stock, from the supplier’s catalogue or from the section area times density.
- Units and format
- Enter a number in kg/m: kilograms per metre of length. The form accepts 0.000001 kg/m to 1000 kg/m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.2 kg/m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Material price
- What it is
- What you pay per kilogram for the bar material, from the supplier’s quotation.
- Units and format
- Enter a number in $/kg: money per kilogram. The form accepts $0/kg to $10000/kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $3/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Cycle time per part
- What it is
- The machine cycle time to make one part, from the start of bar feed to cut-off.
- Units and format
- Enter a number in s: seconds. The form accepts 0.000001 s to 100000 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 45 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Seconds, not minutes.
What this means: Bar change time
- What it is
- The time to load a new bar and restart, added once for each bar.
- Units and format
- Enter a number in s: seconds. The form accepts 0 s to 10000 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Hours per shift
- What it is
- The number of working hours in one shift, used to convert machine hours into shifts.
- Units and format
- Enter a number in h: hours. The form accepts 0.000001 h to 24 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Least material yield accepted
- What it is
- The lowest share of the purchased bar length that should end up in finished parts.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 75% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Method and formulas
- Length per part = part + cut-off + facing; parts per bar = ⌊(bar − remnant) ÷ length per part⌋; bars = quantity ÷ parts per bar (rounded up) (as the screw machine stock tool).
- Yield = parts × part length ÷ (bars × bar length); material cost per part = bars × bar length × mass per metre × price ÷ quantity.
- Hours = (quantity × cycle + bars × bar change) ÷ 3600; shifts = hours ÷ hours per shift.
- Example: 109 parts per bar need 10 bars (36.576 kg), 83.333% yield, about 0.10973 of material a part and 12.667 hours of machine time.
Limitations
- Whole parts per bar; last-bar remnants and set-up parts are not added.
- Constant cycle time; tool changes and inspection add time.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Order bar stock for a turned-part batch
- Quote material cost per part
- Plan the run time on a bar-fed lathe
Who it is for
- CNC machinists
- Estimators
- Production planners
What you get
- Parts per bar, bars and stock mass
- Material yield and cost per part
- Machine hours and shifts
Interpreting the result
- A thinner cut-off tool and a shorter remnant both raise yield: on short parts the cut-off can be most of the waste.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1175–1176. Topic reference; no source tables or recommended settings are reproduced.
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Open the Bar Stock Plan for Bar-Fed Parts (Bars, Yield, Material Cost, Machine Time) calculator