Machining Speeds & Feeds Card
One page. Speeds, chip load and drill feed, imperial and metric.
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RPM & Feed Rate for Any Material
Enter your bore diameter, material, and bar type to get recommended RPM, feed rate, and depth of cut instantly.
A boring bar is a single-point cutting tool used on a lathe or boring mill to open up an existing hole to a precise diameter and finish — it is the right tool when a drill leaves too rough a surface or cannot hold the tolerance you need. Running the wrong RPM or feed rate on a boring bar costs you finish, accelerates tool wear, and produces the chatter that ruins a workpiece you may have hours of setup time in. Enter your parameters above to get the numbers before you cut.
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⚙️ Boring Bar Sets & Indexable Tooling
Five indexable boring bar sets and SCLCR bars from the live catalog — matched to the RPM, feed, and L/D outputs above
Top Pick
OSCARBIDE 3/4" Shank Indexable Boring Bar Set
- 8-piece 3/4" shank set
- Indexable carbide inserts
- Typical lathe bore coverage
- Stiffer than 1/2" bars
- Shop starter boring kit
1/2" set
Accusize 4-Pc 1/2" Round Shank Boring Bar Set
- 4-piece 1/2" round shank
- Indexable insert pockets
- Smaller-diameter bores
- Lathe and boring mill
- Steel and aluminum work
6-pc set
iCarbide 1/2" Shank Indexable Boring Bar 6-Pc
- 6-piece 1/2" shank set
- Multiple insert geometries
- Compact bore reach
- Roughing and finishing bars
- Indexable carbide tooling
Accusize 1/2" × 7" RH SCLCR Boring Bar
- 1/2" × 7" SCLCR bar
- 80° diamond CCMT/CCGT inserts
- Shorter stick-out, lower L/D
- Finishing and light roughing
- Right-hand lathe boring
Accusize 1-1/2" × 14" RH SCLCR Boring Bar
- 1-1/2" × 14" heavy bar
- Long-reach production bores
- Stiffer than 1/2" shanks
- SCLCR insert pocket
- Cuts chatter on deep bores
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Boring Bar Setup — What You Need to Know
What Is Boring and When to Use a Boring Bar
Boring is the operation of enlarging an existing hole using a single-point cutting tool, typically to achieve a diameter tolerance and surface finish that drilling or reaming alone cannot deliver. You reach for a boring bar when you need a non-standard diameter, better roundness than a drill provides, or you are fitting a bearing or bushing to a specific class of fit. Boring also corrects position errors from the drilled hole — something reaming cannot do. If your tolerance is tighter than ±0.002", boring is likely the right operation.
How to Read and Use Your Results
RPM is the spindle speed to set before cutting — always round down on a boring bar if your machine lacks the exact speed. Feed Rate (IPR) controls how far the bar advances per revolution; too light a feed on stainless or steel causes rubbing and work-hardening. Depth of Cut is shown for both roughing and finishing so you have both values available. The L/D Ratio and Chatter Risk output is the one most machinists skip — do not skip it. It tells you whether your current setup is physically capable of producing a clean bore.
Chatter: Causes, L/D Ratio, and How to Fix It
Chatter happens when cutting force exceeds bar stiffness, creating a resonant vibration cycle that marks the bore wall. L/D ratio — bar overhang divided by bar diameter — is the key variable. Under 3:1 is stable. Between 3:1 and 4:1, reduce feed and depth of cut. Above 4:1, shorten stick-out, move to a larger diameter bar, or use an anti-vibration damped boring bar. Counterintuitively, too light a feed can cause chatter by letting the insert rub rather than cut — if you see chatter, try increasing feed slightly before reducing RPM.
Boring Bar Tips for Better Finish and Tool Life
Tool height is non-negotiable — the boring bar tip must be exactly on the bore centerline. Even 0.010" high creates conditions that promote chatter and poor finish. Always leave 0.010"–0.030" for a dedicated finishing pass and follow it with a spring pass at zero additional infeed — the bar deflects under load and the spring pass picks up 0.001"–0.003" the first pass left behind. Match your insert grade to the material; a wrong-grade insert chatters at any RPM. Use cutting fluid aggressively on the finishing pass to prevent chip welding on the insert face.
Boring Bar Calculator FAQ
What SFM should I use for boring stainless steel with carbide?
Use 150–250 SFM for stainless with carbide inserts — the calculator uses 200 SFM by default. Stay toward the lower end if you are seeing rubbing or built-up edge. Sharp positive-rake inserts and aggressive cutting fluid matter more than chasing the top of the SFM range on stainless.
My machine doesn't have the exact RPM — which way do I round?
Always round down on a boring bar. Excess speed amplifies chatter far more than it improves productivity. The difference in surface footage between adjacent speed steps is modest; the difference in chatter risk is not.
The calculator shows high chatter risk — what is the fastest fix?
Shorten your bar stick-out first. Pull the bar in as far as your boring depth allows. If you cannot shorten it, move to a larger-diameter bar if bore clearance allows, or source an anti-vibration damped bar for that diameter. Reducing RPM 15–20% and increasing feed rate slightly can also break the resonant frequency cycle.
What depth of cut should I leave for the finishing pass?
Leave 0.010"–0.030" for the finishing pass — enough that the insert is making a real cut, not rubbing. After the first finishing pass, take a spring pass at the same setting with no additional infeed. The spring pass picks up 0.001"–0.003" the bar deflected on the first pass.
Related Calculators & Guides
When the Bore Still Fails — Diagnose or Pick the Right Bar
Chatter, poor ID finish, size drift, insert chips, or packed chips: Boring Bar Troubleshooting. Solid vs indexable vs boring head vs damped: Boring Bar Types — Which for the Job.