Parts per Bar and Bar Remnant Calculator for Bar-Fed Lathes
Parts per bar drives bar stock cost, bar changes per shift and how much remnant ends up in the scrap bin. This calculator works the length budget of a bar: usable length, the length each part consumes, whole parts per bar and the drop-off left over.
Your numbers
Mill bars are commonly sold in 12 ft (144 in) lengths. Use your actual stocked length.
Length of the part as it comes off the sub-spindle or catcher.
Parting blade width. 3/32 in is 0.094. Swiss grooving cutoff tools are often 0.5 to 1.5 mm.
Extra length removed to clean up the cutoff face.
Bar end that cannot be machined: collet grip, feed finger and pusher clearance. Check your machine manual.
Extra parts to cover setup pieces, first article and in-process scrap.
Your results
Length-based yield only. It does not include the chips from turning the diameter down, bar straightness losses or mill length tolerance. Confirm the stub length with your machine and bar feeder manuals.
Material yield vs finished part length
Sweeps Finished part length from 0.25 to 4, holding your other inputs fixed.
Compare planned bar yield with actual bar issues
Optional: we can show how to pull actual bar issues and parts completed from your ERP and flag jobs where yield is drifting.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Enter the bar length you actually buy, the finished part length, the cutoff blade width, any facing stock and the stub that stays in the collet and feeder. Then enter the good parts you owe the customer, a scrap and setup allowance, and the price of one bar. The result shows parts per bar, remnant, bars to order and bar cost per good part. The chart sweeps part length so you can see how yield jumps and drops as parts get longer, which is useful when quoting a family of lengths on the same bar.
- Use the stocked length, not the catalog nominal length.
- Measure the stub on the machine, do not guess it.
- Add 1 to 3 percent scrap for stable runs and more for new setups.
The formula behind it
Usable length equals bar length minus stub. Pitch equals part length plus cutoff width plus facing stock. Parts per bar equals the integer part of usable length divided by pitch. Remnant equals bar length minus parts per bar times pitch, which includes the stub. Bars required equals good parts times one plus the scrap allowance, divided by parts per bar, rounded up. All lengths are in inches. This is plain length accounting, the same arithmetic used on screw machine and bar-fed CNC lathe quotes.
Reading the result
A part that fits 61.4 times in a bar yields 61 parts and the 0.4 left over joins the stub in the remnant. Small changes in pitch matter when the count sits near a whole number: trimming 0.01 in of facing stock can add a part per bar, while a wider cutoff blade can remove one. The yield percent shows how much of the bar length becomes finished length. Low yield on short parts is normal because the cutoff kerf and the stub are fixed losses spread across many parts.
Common mistakes
The most common error is forgetting the stub and then wondering why the bar yields two parts fewer than the estimate. The second is using the finished length without the cutoff width. The third is mixing mm and inches. Also remember that bars arrive with a length tolerance, so a 12 ft bar can be a little short. In an ERP such as Infor SyteLine, Epicor or NetSuite the bar usually appears as a raw material item with a bar-to-part yield on the routing or BOM, and a wrong yield silently skews issued quantity and cost.
Frequently Asked Questions
What is the stub in bar work?
The stub is the piece of bar that cannot be machined because it is held by the collet, feed finger or pusher at the end of the bar. It is left over at every bar change and is usually several inches, depending on the machine and the bar feeder.
Does cutoff width really matter?
Yes. Every part consumes its own length plus one cutoff kerf. On a 0.5 in part with a 0.094 in blade, the kerf is nearly 19 percent of the length each part uses, so blade width has a large effect on short parts.
How do I handle bars that vary in length?
Use the shortest length you accept at receiving, or run the calculator at both the nominal and minimum length. For critical long-run jobs, log actual parts per bar for a few bars and use that observed number in the routing.
Can I use this for Swiss machines?
Yes, as a length budget. Swiss bars are often 8 to 12 ft, the cutoff is narrower and the stub depends on the guide bushing and collet. Enter your own cutoff width and stub for an accurate result.
If bar yield and remnant are tracked in spreadsheets today, Netray can help pull actual bar issues from your ERP and compare them with planned yield.
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