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  • Choose a light-cutting insert with a positive geometry for best surface finish and close hole tolerance.
    • Recommended first choice is the light cutting knife edge geometry (L-K) with nose radius 0.2 mm (0.008 inch).
  • 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 at high feeds under stable conditions to increase workpiece quality and productivity levels.
  • Fine boring heads CoroBore 825/826
    • Always adjust from smaller diameter to larger diameter to avoid back lash.
    • Unlock locking screw before adjustment, tighten afterwards



Product range

Boring range mm (inch) 150-315






Overview of assembly parts: 

CoroBore 825/826 XL, 825D/826D XL,
dia 150-315 mm (5.906-50.197 inch)

Conventional adaptor
Damped adaptor

1. Cartridge
2. Fine boring head
3. Slide
4. Counterweight
5. Adaptor​

1. Cartridge
2. Fine boring head
3. Slide
4. Counterweight
5. Damped adaptor​

CoroBore 825/826 XL,
dia 298-540 mm (11.732-21.260 inch)
CoroBore 825/826 XL,
dia 538-1,275 m m (21.181-50.197 inch)
1. Cartridge
2. Fine boring head
3. Slide
4. Bridge
5. Counterweight
1. Cartridge
2. Fine boring head
3. Slide
4. Counterweight
5. Bridge extension
6. Bridge​


Precision adjustment

Single-edge fine boring tools have adjustment  possibilities to accurately pre-set the cutting edge within microns.

CoroBore 825 XL - Diameter adjustment with new scale

  • Each line, adjusts diameter 0.01 mm (0.00039 inch)
  • 360° turn changes diameter by 0.5 mm (0.01968 inch).  
CoroBore 825 XL - Diameter adjustment with old, nonius scale
  • One full turn of the scale will move the insert 0.25 mm (0.010 inch) radially.
  •  Adjustment with nonius scale (0.002 mm (0.00008 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).
  • Adjustable radial stroke on fine boring head 7.5 mm (0.295


​CoroBore 826 XL
  • Each increment adjusts the diameter by 0.002 mm (0.00008 inch), felt by a click.
  • One full turn of the scale will change dia. by 0.1 mm (0.0039 inch)







Cartridge design

CoroBore 825 XL / CoroBore 826 XL have the same coupling design between cartridge and cross slide, with an elliptical male/female part taking up tangential forces and a face part taking up radial forces.

CoroBore 826 HP has a rigid interface between the fine boring head and cartridge to ensure a stable machining process.

Note: Cartridge for CoroBore® 826 XL and CoroBore® 825 will not fit the CoroBore® 826 HP tool body. The CoroBore® 826 HP cartridge interface is rotated 90 degrees. 

Cartridges for CoroTurn 107 and CoroTurn 111 inserts:
CoroTurn 107:
TC.. 06, 09
(TC.. 1.2, 1.8)
CoroTurn 107:
TC.. 1103
CoroTurn 111:
(TC.. 1.2, 1.8, 22)
CoroTurn 107
CC..06, 09
(CC..1.2, 1.8)

CoroTurn 107 positive basic-shape inserts are the first choice for fine boring applications as they provide lower cutting forces than negative basic shape inserts. Large assortment of insert geometries available.

Use CoroTurn 111 positive basic shape inserts when an extra positive cutting edge is needed.



Tool holding

The CoroBore XL holders are developed with a unique tool side interface, optimized for large diameter boring. The holders have a large support area which generates stability and takes up axial forces with large flat driving keys to take up the high torque.

Internal coolant both centre and flange. Possibility to rotate driving keys and bridge by 90 degrees.
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 adaptors can be used in different applications and machines. This makes it possible to standardize on one tooling system for the entire workshop. Remember the following:
  • Choose shortest possible adaptor
  • Choose strongest possible adaptor
  • If reduction is needed, use tapered version if possible
  • For long overhangs (>4 x DCON), use damped adaptors
  • 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, adaptors and shanks.
  • Reduced tool inventory with standardized tools minimizing machine downtime
  • For boring operations requiring long reach, as in large machining centres in the diameter range of 1–36 mm (0.039–1.42 inch). Deep pockets is a typical application where the Coromant EH system offers the required reach without limiting process security
Choice of adaptors/chucks for boring 
​ ​ Adaptor and chuck systems​
Choose coupling/chuck first,
then adaptors/chucks​​
Coromant Capto​ CoroChuck 930​
Shrink fit
Collet chuck
+++ 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​
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. ​
CoroBore 820​
Coromant Capto basic holders and adaptors​ CoroBore 825​
Fine boring head​
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.​ ​
HD version​ CoroBore 825 Cylindrical shank​
Slender version
CoroBore 824 XS EH
Complementary adaptors


Shrink fit adaptors can be used for accessibility purposes. However, CoroBore 825 with integrated dampening mechanism is preferable if accessibility is required.​
Shrink fit adaptor​ 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. ​
Collet chuck adaptor​ CoroBore 825 Cylindrical shank​​
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