CNC / machinist calculator
Parts Per Bar Calculator (Bar Stock Yield)
Before you order bar stock or quote a run, you need to know how many parts each bar actually makes. It is not simply the bar length divided by the part length: every part loses a parting-tool kerf, you usually face a little stock off each one, and the chuck has to grip a remnant at the end that never becomes a part. This calculator takes all of that and gives you the honest number of parts per bar and how much stock is left over, so your material cost and yield are right.
How it works
Each finished part consumes its own length plus the width of the parting cut that separates it, plus any facing stock you take to clean the end. The bar also gives up a remnant at the tail, the length the collet or chuck needs to hold, which cannot be turned into a part. So the usable length is the bar length minus that remnant, and the number of parts is the usable length divided by the length one part consumes, rounded down to a whole part.
Keep the units consistent, all inches or all millimetres. The leftover figure is the unusable bar end: the gripping remnant plus whatever partial length was too short for one more part, which is the drop you pay for and scrap or return. (Kerf and facing stock are also lost, but they are counted inside the length each part consumes, not in the leftover.) Cutting the part length, tightening the parting kerf, or reducing the remnant all raise the yield.
Worked example
A 144 in (12 ft) bar making 2 in parts with a 0.1 in parting kerf and a 3 in chuck remnant yields 67 parts, using 140.7 in and leaving 3.3 in of drop. Cut the kerf or remnant and the count climbs.
Frequently asked questions
How do I calculate parts per bar?
Subtract the chuck remnant from the bar length to get the usable length, then divide by the length each part consumes, which is the part length plus the parting kerf plus any facing, and round down to a whole part.
Why is it not just bar length divided by part length?
Because every part also loses the width of the parting-off cut, you often face a little stock off each one, and the chuck must grip a remnant at the end. Ignoring these overstates the yield and understates the material cost.
What should I use for the kerf?
Use the width of your parting or cutoff tool, since that much material turns to chips between each part. A typical parting insert is roughly 0.04 to 0.12 in (1 to 3 mm) wide for common bar diameters, wider on large bars; use your actual tool width for an accurate count.
What is the remnant?
It is the length the collet or chuck needs to hold the bar safely, plus any end that cannot be reached, which never becomes a part. On a bar-fed lathe this is the fixed drop at the end of each bar and is worth entering so the yield is realistic.
Related calculators
Sources
- Parting off - insert width by bar diameter (Sandvik Coromant)
- Bar Feeder Basics - common remnant lengths (Production Machining)
- Bar stock (Wikipedia - the parting-off process, no numeric values)
Every formula on this page is shown and sourced. See how we verify.
These calculators are for planning and as a starting point. Recommended speeds and feeds are published starting values that vary with your specific tool, coating, machine rigidity, workholding and coolant. Always start conservative, listen to the cut, and follow your tool maker data sheet.