Forging billet allowance and stock cut calculator

What this model answers

Finished-part volume is not always the same as starting billet volume. A flash allowance adds material around the net part, while a proportional process loss removes part of what enters. Their arithmetic order matters: a loss percentage is reversed by dividing by the retained fraction.

The resulting billet length is then used in a stock-cut budget. That makes the page more specific than a mass-from-volume conversion: it asks how many identical billets can be cut after end cropping and saw loss, and how many stock bars the order needs.

The Tap drill thread percentage calculator handles a later machining geometry question. A billet volume budget does not specify the drill diameter or establish finished thread tolerances.

Measure the right inputs

Use net finished volume in cubic centimetres and material density in kilograms per cubic metre. Round-stock diameter and all cutting lengths are millimetres. The conversion between cubic centimetres and cubic millimetres is applied before dividing by stock cross-section.

Flash percentage is additional volume relative to the net part. Process loss is the fraction of the pre-loss blank volume that is not retained. The entered density is assumed identical for all volume terms; thermal expansion and material-specific forming behavior are not inferred.

Read the result in context

Cropping applies at both ends of every stock bar. Kerf applies only between neighboring billets in the remaining length. If your cutting process also needs an extra trim cut, include it in the appropriate crop allowance rather than assuming it is already modeled.

One billet must fit before any bar count can be returned. A very small finished volume combined with a large bar diameter may produce a theoretically short cut that is impractical to handle. Geometric fit alone does not establish a usable forging blank.

Work through the numbers

A 100 cm³ finished volume with ten percent flash and no process loss needs 110 cm³ of billet volume. At 7800 kg/m³ that is 0.858 kg, and a 50 mm round bar needs a theoretical cut length of about 56.023 mm.

After cropping ten millimetres at each end of a one-metre stock bar, 980 mm remains. With two-millimetre internal kerfs, sixteen such billets fit, so one hundred billets require seven stock bars.

Where the model stops

Uniform cylindrical stock and volume accounting only; no die-fill, deformation force, scale prediction, hot expansion, tolerance or forgeability analysis.

Flash and loss allowances are supplied assumptions, not recommended percentages. Confirm actual process allowances, cutting practice and material suitability with the responsible manufacturing team.