Boring

Product overview

Sandvik Coromant offers dampened boring tools for rough and finish boring. The adapters are designed with Coromant Capto backend couplings for best possible clamping and flexibility. This gives you unique flexibility and modularity to build desired tool assemblies. Coromant Capto basic holders are available in all common machine interfaces.

Silent Tools finish and rough boring tools give increased productivity and close tolerances from lengths of 3–10 x BD. When using Silent Tools, you have the opportunity to double the depth of cut. Through coolant is a feature for precise direction of jets to the cutting zone.

Using extension and reduction adaptors are possible on damened boring tools, but the tool will no longer be optimized. However, a dampened tool with extension or reduction still performs better than an undampened tool.

Boring bar adaptor dia, DC

inch

mm

Rough boring	Fine boring
Boring range Ø 25-150 mm (0.984-5.906 inch)	Boring range Ø 23-167 mm (0.906-6.575 inch)	Boring range Ø 150-315 mm (5.906-12.402 inch )
Dampened DuoBore ™	Dampened CoroBore ® 825
Coromant Capto® back-end coupling Coolant through

Radial adjustment of fine boring head: Diameter adjustment of 2 microns Two different diameter setting mechanisms 825 - Nonie scale (dia 23–315 mm, 0.90–12.4 inch) 826 - A click for each diameter increment (dia 150–315 mm, 5.90– 12.4 inch)

^®How to use CoroBore 825

Example of setting: In this example the blue line on the scale disc is a reference since it is aligned to a line on the vernier in the starting position.

Start position	Adjusted position
Scale disc turned clockwise until the line of scale (red) lines up with the second line (green) of the vernier. Diameter increased by 0.002 mm (0.00008“)
Scale disc turned clockwise until the line of scale (red) lines up with the third line (green) of the vernier. Diameter increased by 0.004 mm (0.00016“)
Scale disc turned clockwise until the line of scale (red) lines up with the fourth line (green) of the vernier. Diameter increased by 0.006 mm (0.00024“)
Scale disc turned clockwise until the line of scale (red) lines up with the fifth line (green) of the vernier. Diameter increased by 0.008 mm (0.00032“)
Scale disc turned clockwise until the line of scale (red) lines up with the sixth line (green) of the vernier. Diameter increased by 0.010 mm (0.0004“) = 1 division of scale.

Main considerations

The Silent Tools boring tools reach a maximum of six times the bore diameter into your workpiece. If you need to go deeper, ask for an engineered solution.

Our recommendation is to always use Silent Tools for long overhangs, over 4 x BD.

Tool overhang and diameter of tool

Choose largest Coromant Capto size possible Choose shortest possible basic holder If possible, use a heavy duty basic holder For overhangs over 4 x BD, use dedicated tools, e.g Silent Tools.

		-PR - WM			Conventional Dampened adaptor
Cutting speed in relation to overhang, with different geometries		Cutting speed in relation to overhang, with conventional and dampened adaptors

Insert shape and entering angle/lead angle

Use entering angle 90° (0°) for roughing and 92° (-2°) for finishing. Less force in the radial direction gives less radial deflection and vibration. Triangular-shaped inserts (T-style) are first choice for boring operations. CoroTurn^® 107 inserts meet these requirements and are first choice.

Nose radius

The nose radius, RE, on the insert is a key factor in turning operations. Selection of nose radius depends on the:

• Depth of cut, a_p
• Feed, f_n

and influences the:

• Surface finish
• Chip breaking
• Insert strength

Small nose radius

• Ideal for small cutting depths
• Reduces vibration
• Less insert strength

Large nose radius

• Heavy feed rates
• Large depths of cut
• Stronger edge
• Increased radial forces

Nose radius in relation to depth of cut

The radial forces that push the insert away from the cutting surface become more axial as the depth of cut increases. The nose radius also affects the chip formation. Generally, chip breaking improves with a smaller radius. As a general rule of thumb, the depth of cut should be greater than or equal to 2/3 of the nose radius or half the nose radius in the feed direction.

Feed starting values depending on nose radius

Force direction mainly axial	Force direction both axial and radial

Rough boring

Productive boring

Involves two cutting edges and is employed for roughing operations of holes, with tolerance IT9 or larger, where metal removal rate is the first priority. Feed rate is obtained by multiplying the feed by the number of inserts. (fn=fz x ZEFF)

Productive boring

Step boring

When adding a shim under one of the slides, the insert will only take the inner half of the desired radial cut, and the result is a stepboring tool. Select this method if you want to take a larger radial cut than one insert can take, but remember to reduce the axial feed to what is normal for a tool with only one cutting edge. If the two inserts are set to take the same radial depth of cut, the outer one will always take the largest cutting force, due to higher speed and more chip removal. By doing this right, vibration can easily be avoided and a smooth surface is guaranteed. This set-up will produce a stepped shoulder if it is not going through the workpiece. The feed rate and the produced surface finish is the same as if only one insert is used (fn=fz). Produced hole tolerance is IT9 or larger.

Step boring

Single-edge boring

Single-edge boring is the best option when: You need to reduce cutting forces due to a low power machine You have problems with vibration Close tolerances, accurate roundness or good surface finish is required Produced hole tolerance is IT9 or larger.

Single edge boring

Finish boring

Factors that influence vibration

To reduce vibrations, choose a light cutting insert with a positive cutting geometry and small nose radius. T-style inserts are first choice for boring operations.

High vibration tendency	– Heavy feeds – Large depth of cut – Strong edge security
Less vibration tendency	– Ideal for small depth of cut – Reduces vibration

Information about other vibration influence factors such as the following can be found in the application guide, read more.

• Insert point angle
• Positive geometries
• Wiper inserts
• Edge rounding
• Cutting data and cutting speed.
  

Tips and tricks

• Choose the largest possible tool diameter with the shortest possible basic holder
• The entering angle should be close to 90 degrees to give more axial cutting forces and less radial/tangential forces
• A small nose radius is ideal for small depths of cut and decreases the risk of vibrations. Large nose radii have strong edge security and allow for heavy feeds and large depths of cut. The risk of vibration gets higher the larger nose radius you use. Therefore, triangular, positive style inserts are first choice for dampened boring operations
• In stable conditions, use wiper inserts for high productivity or when high quality surfaces are required

		Conventional
		Dampened adaptor
Less radial forces (Fc) with small radii	Cutting speed in relation to overhang, with conventional and dampened adaptors

Tool assembly and maintenance When using dampened tools in assemblies, care should be taken to hold the tool bodies correctly to make sure that the adaptors are not damaged. These are easily deformed due to the thin wall thickness. Use assembly mounting fixture Check that all units are assembled correctly, with the correct torque Check machine spindle, run-out, wear and clamping force Always use a torque wrench and apply recommended torque on screws for insert and tool assembly Check inserts and insert seats regularly Replace worn or exhausted screws and washers Clean all assembly items before assembly Lubricate all assembly items with oil at least once a year Lubricate the fine adjustment mechanism for fine boring regularly

• Product overview
• Main considerations
• Factors that influence vibrations
• Tips and tricks