BIZOMAT MAKEOS · Manufacturing
Bar Stock for Screw Machine Parts
How many parts does each bar give, and how much bar stock do I order for this quantity?
Parts per bar and bar stock required for automatic screw machine or bar-fed lathe work, from the part length, cut-off tool width, facing allowance, bar length and the remnant lost to chucking, with the handbook’s feet-per-1000-parts estimate for 10-foot bars.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Finished part length | mm | Overall length of the finished part. |
| Cut-off tool width | mm | Width of the cut-off blade (wider for larger bar). |
| Facing allowance per part | mm | Extra length per part removed by facing. |
| Bar length | mm | Length of the bars supplied. |
| Remnant (chucking) allowance per bar | mm | Bar end left in the collet or bar feeder. |
| Parts required | Number of good parts needed (add your scrap allowance). | |
| Bar mass per metre | kg/m | Mass per metre of the bar (from a stock-mass calculation). |
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: Finished part length
- What it is
- The overall length of one finished part as it comes off the machine, before any extra for facing or the cut-off.
- 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.
- Get it right
- Use the drawing length; the cut-off width and facing allowance are added separately.
What this means: Cut-off tool width
- What it is
- The width of the cut-off blade: bar consumed by each parting cut and lost as chips.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 50 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.
- Get it right
- Use the actual blade fitted; wider bar usually needs a wider blade.
What this means: Facing allowance per part
- What it is
- Extra bar length per part removed when the end is faced, on top of the finished length and the cut-off width.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 50 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.
- Get it right
- Leave at zero if the part is not faced after parting.
What this means: Bar length
- What it is
- The length of each bar as supplied by the stockist, before any remnant is left in the machine.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 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 the supplied length; nominal bar lengths are often imperial, such as 10 feet.
What this means: Remnant (chucking) allowance per bar
- What it is
- The length of each bar that cannot be made into parts: the end left in the collet or bar feeder when the bar is changed.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 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.
- Get it right
- Measure a few real remnants from your machine and bar feeder rather than guessing.
What this means: Parts required
- What it is
- The number of good parts the order needs. The tool works out how many whole bars give at least this many.
- 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.
- Effect on the result
- Bars to order rise in steps as the quantity crosses each multiple of parts per bar.
- Get it right
- Add your own scrap and setup allowance; the tool does not include start-up parts.
What this means: Bar mass per metre
- What it is
- The mass of one metre of the bar, used to turn the stock length into a mass to order and a material mass per part.
- Units and format
- Enter a number in kg/m: kilograms per metre of length. The form accepts 0 kg/m to 10000 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.
- Effect on the result
- Stock mass and material per part are directly proportional to it.
- Get it right
- Work it out from the bar section and material density, or take it from the stockist’s table.
Method and formulas
- Length per part = part length + cut-off width + facing allowance.
- Parts per bar = ⌊(bar length − remnant) ÷ length per part⌋; bars = ⌈quantity ÷ parts per bar⌉.
- Handbook estimate for 10-ft bars: feet per 1000 parts = (L + W) × 84, with L and W in inches.
- Example: 25.4 mm parts with a 1.57 mm cut-off give 109 parts per bar and need 10 bars.
Limitations
- Start-up and setup parts are not included.
- The handbook estimate assumes 10-foot bars and its standard chucking allowance.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Order bar stock for a screw machine job
- Quote material cost per part
- Compare bar lengths and remnant allowances
Who it is for
- Screw machine setters
- Estimators
- Production planners
What you get
- Parts per bar
- Bars to order
- Stock length and mass
Interpreting the result
- Shorter remnants (bar pullers, remnant-less feeders) can save a bar in every few on short parts.
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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