BIZOMAT MAKEOS · Materials
Ring Blank Plan (Rolled Ring or Cut from Plate, Mass and Cost)
For this machined ring, is it cheaper to buy a rolled (forged) ring blank or to cut the blank from plate, and how much material does each waste?
Comparison of blank routes for a rectangular-section ring: finished ring volume and mass, and the rolled-ring blank with machining allowance, by Pappus’s theorem (area of the section × path of its centroid, as the Pappus surface and volume tool), against a square plate blank of the same thickness with its offcut credited as scrap; mass, cost and material yield for each and the cheaper route, checked against your budget.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Finished outside diameter | mm | Outside diameter of the finished ring. |
| Finished inside diameter | mm | Inside diameter of the finished ring. |
| Finished height (thickness) | mm | Axial height of the finished ring. |
| Machining allowance per surface | mm | Material left on each machined surface. |
| Extra on the plate square (cutting edge) | mm | Extra added to the square plate blank for flame or saw cutting. |
| Density | kg/m³ | Density of the material. |
| Prices | ||
| Rolled ring price | $/kg | Price per kilogram of a rolled or forged ring blank. |
| Plate price | $/kg | Price per kilogram of plate. |
| Scrap credit | $/kg | Value per kilogram of the plate offcut and centre disc returned as scrap. |
| Budget per blank | $ | Most you will pay for the blank. |
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 outside diameter
- What it is
- The outside diameter of the finished, machined ring, from the drawing.
- 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 400 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Ring and blank masses rise with it, and the plate square grows with it, so plate cost rises quickly.
- Get it right
- Enter the finished size; the tool adds the machining allowance itself.
What this means: Finished inside diameter
- What it is
- The inside (bore) diameter of the finished, machined ring, from the drawing.
- 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 300 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger bore reduces the ring mass and rolled blank mass but not the plate blank mass.
- Get it right
- It must be smaller than the outside diameter; enter the finished bore, not the blank bore.
What this means: Finished height (thickness)
- What it is
- The finished axial height of the ring, its thickness between the two flat faces.
- 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 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- All masses and costs rise roughly in proportion to the height.
- Get it right
- Enter the finished height; the blank is made thicker by the allowance on both faces.
What this means: Machining allowance per surface
- What it is
- The material left on each machined surface of the blank (outside, bore and both faces) for machining to the finished size.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger allowance increases both blank masses and lowers material yield.
- Get it right
- It is per surface: the tool adds it twice to each diameter and twice to the height.
What this means: Extra on the plate square (cutting edge)
- What it is
- The extra added to the side of the square plate blank for flame or saw cutting, on top of the outside diameter and allowance.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger edge makes the plate blank heavier and costlier; it does not affect the rolled ring.
- Get it right
- Enter the total added to the square’s side, from your cutting supplier or process.
What this means: Density
- What it is
- The density of the ring material, used to turn every volume into a mass.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 20000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7850 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- All masses and both blank costs rise in direct proportion to density.
- Get it right
- Take it from the material data sheet for the grade.
Prices
What this means: Rolled ring price
- What it is
- The price per kilogram of a rolled or forged ring blank of this material, from a supplier 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 $3.5/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The rolled ring cost rises in direct proportion to this price.
- Get it right
- Use a quoted price for a ring of about this size; small orders often carry set-up charges per piece.
What this means: Plate price
- What it is
- The price per kilogram of plate of this material and thickness, from a supplier quotation, including cutting if it is bought cut.
- 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 $1.5/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The plate blank cost rises in direct proportion to this price.
- Get it right
- Use the price for the thickness you need; thick plate is often priced differently.
What this means: Scrap credit
- What it is
- The value per kilogram you are paid for the offcut corners and centre disc of the plate blank when they go back as scrap.
- 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 $0.3/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher scrap credit lowers the plate blank cost.
- Get it right
- The tool credits plate blank mass minus rolled ring blank mass at this rate; use the scrap merchant’s price for that grade.
What this means: Budget per blank
- What it is
- The most you are prepared to pay for one blank, against which the cheaper route is checked.
- Units and format
- Enter a number in $: an amount of money; use one currency for every money input. The form accepts $0 to $100000000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $120 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Compare like with like: both blank costs here exclude machining and freight.
Method and formulas
- Ring volume = section area × 2π × radius of the section centroid (as the Pappus surface and volume tool).
- Rolled blank: section (OD + 2a − ID + 2a) ÷ 2 × (h + 2a) on its centroid radius; cost = mass × ring price.
- Plate blank: square of side OD + 2a + edge, thickness h + 2a; cost = mass × plate price − scrap × scrap credit; yield = finished mass ÷ blank mass.
- Example: the finished ring weighs 21.579 kg; a rolled blank costs 94.74 $ against 99.411 $ from plate.
Limitations
- Rectangular ring section; contoured rings need their own section area and centroid.
- Plate offcut assumed sold as scrap, not reused.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose between a rolled ring and a plate cut-out
- Estimate material for a large machined ring
- Quote a ring part
Who it is for
- Estimators
- Buyers
- Manufacturing engineers
What you get
- Finished ring and rolled blank volume and mass
- Plate blank mass and scrap
- Cost, yield and the cheaper route
Interpreting the result
- Thin, large-diameter rings waste most of a plate blank, so rolled rings usually win as the ring gets thinner.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 66–67. Topic reference; no source tables or recommended settings are reproduced.
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Open the Ring Blank Plan (Rolled Ring or Cut from Plate, Mass and Cost) calculator