Draw-Off Nut Live Center (BNN / BNNC): Overview & Specifications
A comprehensive reference for the BNN/BNNC live center with its built-in draw-off nut for tailstock removal, covering working principle, key features, the full dimension table, and selection and application guidance.
Overview
▲ Product appearance (POINTTECH catalog)
The BNN series is a live (revolving) center that concentrically supports a rotating workpiece from the tailstock side. Unlike a dead center, the center point rotates together with the workpiece on integral bearings, so it steadies the end of the workpiece at high speed without the friction heat and wear of a fixed point. The defining feature of the BNN is the draw-off nut (AN nut) at the end of its Morse taper shank, which lets the operator push the center out of the tailstock sleeve and release it easily after a job.
Inside the body, a double angular contact bearing set carries radial and axial (thrust) loads simultaneously, while a high-performance lip seal and a deflected-shaft design keep dust and coolant out of the bearing space to protect bearing life. Both the point and the body are heat-treated for rigidity and wear resistance, making the BNN suitable for both CNC and conventional lathes.
Key Features
- Accuracy guaranteed to 0.003mm TIR (0.0001") — minimizes run-out to preserve concentricity.
- Excellent for both CNC and conventional machines.
- Draw-off nut type — the AN nut helps achieve easy release from the tailstock.
- Heat-treated point to HRc 60 ± 2 for high hardness, wear resistance, and lasting accuracy.
- High-performance lip seal and deflected-shaft design protect the double angular contact bearing space from ingress of dust and coolant.
- Heat-treated body for extra strength, rigidity, and long life.
- Carbide point available (BNNC type).
- Carbide point to HRa 90 ± 5.
Caution: The listed Max R.P.M and Workpiece Weight are rated limits. As speed increases, the permissible workpiece weight and axial load decrease (see the technical-data curves), so always select with a margin for your actual conditions. The 0.003mm-class accuracy and HRc 60±2 heat-treatment performance assume the bearing section is kept free of dust and coolant ingress.
Specifications
MODEL | MT | A | B | C | D | L | Workpiece Weight | Max R.P.M | Max Run Out | AN NUT NO. |
|---|---|---|---|---|---|---|---|---|---|---|
021002 (022002) | 2 | 50 | 25 | 68 | 43.5 | 141 | 500 | 5,000 | 0.003 | AN09 |
021003 (022003) | 3 | 50 | 25 | 85 | 43.5 | 158 | 500 | 5,000 | 0.003 | AN09 |
021004 (022004) | 4 | 69 | 32 | 108 | 55 | 203 | 800 | 3,800 | 0.003 | AN13 |
021005 (022005) | 5 | 88 | 40 | 136 | 70 | 256.5 | 2,000 | 3,000 | 0.003 | AN17 |
021006 (022006) | 6 | 105 | 50 | 189 | 81.5 | 328 | 3,500 | 2,800 | 0.005 | AN20 |
Unit: mm, kg. The model number in parentheses (022xxx) denotes the carbide-tip type (BNNC). Full dimensions (A–G, E, F, H, G, Weight) follow the BNN drawing on catalog page 9.
Carbide-Tipped Point
The BNNC type applies a carbide (cemented-carbide) tip to the center point, providing high wear resistance at HRa 90 ± 5 hardness. It outlasts the standard steel point and better maintains accuracy when machining high-hardness materials, running long continuous cycles, or working in abrasive environments.
MT | Carbide Tipped Point No. |
|---|---|
MT2 | 022002 |
MT3 | 022003 |
MT4 | 022004 |
MT5 | 022005 |
MT6 | 022006 |
Selection Guide
First select the model by your lathe tailstock's Morse taper (MT2–MT6). Then compare your workpiece weight and operating speed against the rated values in the table. MT2/MT3 reach up to 5,000 rpm for smaller, high-speed work, while MT4–MT6 support 800–3,500 kg workpieces for medium-to-heavy turning. When both speed and load are high, choose one size larger to keep a safety margin. If wear resistance and long life are critical, or you machine high-hardness materials, choose the carbide-tipped BNNC type.
Applications
The BNN/BNNC is used on CNC and conventional lathes for OD turning and grinding of shafts, axles, rolls, gear blanks, and other workpieces that require between-centers support. The draw-off nut especially improves productivity in high-mix low-volume production with frequent setup changes, or in any environment where the center is removed from the tailstock often.