The versatile 391.37A/B system can be used for both fine boring and face grooving applications. It allows precision adjustment in microns to achieve close hole tolerances. Build modular assemblies with Coromant Capto® or HSK for increased tooling flexibility.
Fine-adjustable heads and sleeves
Benefits
- Choose between conventional (.37A) and high speed (.37B) fine-adjustable heads
- Flexible solution for a broad diameter range
- Excellent surface finish with wiper inserts
- Close hole tolerances of IT6
Features
- Diameter adjustment by 0.002 mm (0.00008 inch) for high accuracy
- The high-speed fine boring heads have an adjustable counterweight, which enables runs at 20,000 rev/min
- Reduction sleeves available from size 20 to 16
- Internal coolant supply / cutting fluid through the tool
Application
- Fine boring for small diameters from 3 mm (0.118 inch)
- For conventional fine boring and face grooving
ISO application area
R429U boring and face grooving bars
| R429U bars | Boring | Face grooving |
| Diameter range | 3–36 mm (0.118–1.42 inch) | 14–50 mm (0.551–1.97 inch) |
| Insert choice | 3–11 mm solid carbide bars 8–36 mm CoroTurn 107 indexable inserts | CoroCut MB-09FA |
| Application |
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Recommendations
- The recommended first choice is the light cutting knife edge geometry (L-K) with nose radius 0.2 mm (0.008 inch)
- Choose a light cutting insert with a positive geometry for best surface finish and close hole tolerance.
- Choose a small nose radius to minimize vibrations and cutting forces.
- Choose a nose radius smaller than depth of cut
- Wiper inserts can be used with small L/D ratios at high feeds under stable conditions to increase workpiece quality and productivity levels.
Product range
 |  |  |  | |
| With adjustable counterweight | Solid carbide bar | Steel bar | Carbide bar with brazed steel head | |
| Boring range mm (inch) | 14–50 (0.551–1.97) | 3–11 (0.118–0.433) | 8–36 (0.315–1.417) | 8–32 (0.315–1.260) |
| Hole tolerance | IT6 | IT6 | IT6 | IT6 |
Precision adjustment
Single-edge fine boring tools have adjustment possibilities to accurately pre-set the cutting edge within microns.
- One full turn of the scale will move the insert 0.25 mm (0.010 inch) radially.
- Adjustment with nonius scale (0.002 mm (.00008 inch) on dia.)
- One full turn of the scale will change dia. by 0.5 mm (0.020 inch)
- Each division of the dial has 50 divisions, representing 0.010 mm (0.0004 inch)/diameter. The vernier has 5 divisions, making it possible to adjust the diameter by 0.002 mm (0.00008 inch).
Sleeves
- Sleeves are available to decrease the diameter range from 20 to 16 mm (0.787 to 0.630 inch)
- Example: From diameter 16 mm (0.630 inch) bars in heads to dia. 20 mm (0.787 inch) bars
Starting recommendations for fine boring
| Material | Designation |
Vc m/min (ft/min) |
Ra 0.8 µm (31 µinch) | Ra 1.6 µm (63 µinch) | ||||
| Insert |
ap mm (inch) |
fn mm/rev (in/rev) |
Insert |
ap mm (inch) |
fn mm/rev (in/rev) |
|||
| Steel | 46MnVS6 | 180 (591) |
TCEX 110302-L-F 1125 | 0.2 (0.008) |
0.25 (0.010) |
|||
| TCMT 110304-PF 4325 | 0.4 (0.016) |
0.09 (0.004) |
TCMT 110304-PF 4325 | 0.4 (0.016) |
0.13 (0.005) |
|||
| Super Duplex | F55 | 130 (427) |
TCMT 110304-MF 1125 | 0.4 (0.016) |
0.07 (0.003) |
TCMT 110304-MF 1125 | 0.4 (0.016) |
0.13 (0.005) |
| Titanium | Ti6AI4V | 50 (164) |
TCGX 110204-ALH10 | 0.4 (0.016) |
0.10 (0.004) |
TCGX 110204-ALH10 | 0.4 (0.016) |
0.13 (0.005) |
| Aluminum | ALAS9U3Y40 | 270 (886) |
TCGX 110204-ALH10 | 0.4 (0.016) |
0.09 (0.004) |
TCGX 110204-ALH10 | 0.4 (0.016) |
0.13 (0.005) |
| Cast iron | K3.2.C.UT | 225 (738) |
TCMT 110304-PF 4325 | 0.4 (0.016) |
0.03 (0.001) |
TCMT 110304-PF 4325 | 0.4 (0.016) |
0.13 (0.005) |
Tool holding
Bending stiffness and torque transmissions are the most important factors when choosing a tool holder for boring operations. For best stability and hole quality, use Coromant Capto or the Coromant EH system.
Coromant Capto coupling is the only modular tooling system designed for all metal cutting operations, including all hole making methods. The same cutting tools and adapters can be used in different applications and machines. This makes it possible to standardize one tooling system for the entire workshop. Remember the following:
Coromant Capto coupling is the only modular tooling system designed for all metal cutting operations, including all hole making methods. The same cutting tools and adapters can be used in different applications and machines. This makes it possible to standardize one tooling system for the entire workshop. Remember the following:
- Choose the shortest possible adapter
- Choose the strongest possible adapter
- If reduction is needed, use tapered version if possible
- For long overhangs (>4 x DCON), use dampened adapters
- For long overhangs, ensure rigid clamping with flange contact to spindle if possible
The Coromant EH system delivers great tooling flexibility – Choose from an extensive variety of heads, adapters, and shanks.
- Reduced tool inventory with standardized tools, minimizing machine downtime
- For boring operations requiring long reach, such as in large machining centers in the diameter range of 1–36 mm (0.039–1.42 inch). Deep pockets are a typical application where the Coromant EH system offers the required reach without limiting process security
Choice of adapters/chucks for boring
| | Adapter and chuck systems | ||||
|---|---|---|---|---|---|
| Choose coupling/chuck first, then adapters/chucks |
Coromant Capto | CoroChuck 930 |
Shrink fit
adapter
|
Collet chuck
adapter
|
|
| +++ Very good | Torque transmission | +++ | +++ | +++ | +++ |
| ++ Good | Run-out | +++ | +++ | +++ | +++ |
| + OK | Balance | +++ | +++ | +++ | +++ |
| Boring tool couplings | | | | | |
| CoroBore 820 | Coromant Capto | 1 | | | |
| DuoBore | Coromant Capto | 1 | | | |
| CoroBore XL | Coromant Capto | 1 | | | |
| CoroBore 825 | | | 1 | 2 | 3 |
| | Cylindrical | 1 | | | |
| | EH | | 1 | | |
| Fine boring head 391.37A/B | Coromant Capto | | | | |
| CoroBore 824 XS | Coromant Capto | 1 | | | |
| CoroBore 824 XS | EH | | 1 | | |
| | | | | | |
| | | 1 | = First choice | | |
| | | | | | |
| | | 2 | 3 | = Complementary choice | |
| | | | | | |
Coromant Capto® system – First choice
|
First choice should always be tools with Coromant Capto coupling, which offers excellent repeatability and the best stability characteristics on the market.
|
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|
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| | CoroBore 820 | ||
|
 |
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| Coromant Capto basic holders and adapters | CoroBore 825 | ||
 |
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| | DuoBore | ||
| |
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| | Fine boring head | ||
| |
 |
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| | CoroBore XL | ||
| | |
CoroChuck™ 930 – First choice for boring tools with cylindrical shanks.
| CoroChuck 930 precision chucks have a very good run-out precision and high torque transmission thanks to the latest Fulcrum technology. This technology delivers the best pull-out security on the market. |
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| HD version | CoroBore 825 Cylindrical shank | ||
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| ||
| Slender version | | ||
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| CoroBore 824 XS EH | |
Complementary adapters
| Shrink fit adapters can be used for accessibility purposes. However, CoroBore 825 with an integrated dampening mechanism is preferable if accessibility is required. |
 |
|
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| Shrink fit adapter | CoroBore 825 Cylindrical shank |
| |
|
|---|
| Collet chucks can be used together with CoroBore 825 cylindrical shanks. However, it is not the optimal solution due to lower clamping forces and larger run-out compared to HydroGrip. Furthermore, it is not individually balanced. |
 |
|
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| Collet chuck adapter | CoroBore 825 Cylindrical shank |
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