CoroGrip® and HydroGrip® for minimum run-out
The run-out at the front of a CoroGrip or HydroGrip chuck is less than .0001 inch.
At a distance of 3 × tool diameter from the front, the run-out is less than .0002 inch using an h6 tolerance shank.
An individual measuring report is enclosed with each chuck, containing:
- Balance quality code.
- Rotational speed at balance quality.
- Radial run-out at a distance of 3 × Dc from the front.
- Measured clamping power (Nm).
Balancing of tool holders
Balancing becomes a critical factor as spindle speeds rise. Centrifugal forces act on tool holder and cutting tool. Any imbalance creates vibrations. Individually balanced tool holders are critical when spindle speeds approach those of high speed machining.
What can cause unbalance?
- Mass misalignment (grooves, slots etc).
- Eccentricity (distance between the rotational center and center of gravity for the tool).
- Additional components (e.g. a tool that is unbalanced).
- Fitting and tolerances between the spindle and the coupling of the tool.
Within the industry, the level of balance is often specified with a balance quality class (a G-value) calculated according to ISO standard 1940/1.
Sandvik Coromant tool holder balance qualities
All ISO (7/24 inch) taper tool holders have AT3 taper tolerance. Coromant Capto system, HSK and metric solid ISO taper tool holders are “Balanced by design"; ISO 40, HSK 63 and CAT 40 can normally be used up to 15,000 rpm in a modern CNC machine without extra balancing.
For the Coromant Capto system, the maximum recommended spindle speed is reduced to 8,000 rpm when extensions and/ or reductions are used between the basic holder and adapter.
Calculation of unbalance G-value ISO 1940/1
Example: A taper 40 tool holder with a cutting tool
m = 1.0 g
r = 20 mm
u = m x r = 20.0 gmm
Mass of tool = 1.25 kg
e = u /m tool = 16.0 μm
n = 15.000 rpm
G value at 15.000 rpm = e x n / 9549 = G 25
G 2.5 is often requested for tool holders without considering:
- The total weight of the tool holder, including the cutting tool.
- The spindle speed at which the assembly should run.
- That the total unbalance mass in the example above should be only
0.1 g, and unbalance u = 2 gmm, which is difficult and expensive to measure and repeat.
Balanced by design basic holders and adapters
All Coromant Capto coupling sizes C3-C5, HSK 63, solid ISO 40 taper and CAT 40 tool holders marked with the “Balanced by design” symbol are designed as solid 3-D CAD models and the mass and the position of the unbalance is calculated for the tool holder.
The controlled removal of material from exactly the correct locations allows imbalance to be counteracted. Special consideration of the way the holder is clamped during manufacture allows the different surfaces to remain concentric around the rotational center.
Measured pre-balance levels achieved for an adapter clamped in a 40 taper basic holder vary for the different Coromant Capto coupling sizes. Total weight and material movements in the heat treatment process also cause some fluctuations in the values achieved.
40-taper basic holder with an assembled adapter
The values result in a balance value of approximately G 16 at 10,000 RPM according to ISO 1940/1.
Unbalance values for an adapter
The balance values in gmm for an individual balanced by design C3-C5 adapter fluctuate between these values.
Use CoroGrip or HydroGrip chucks, which are individually balanced, for
high speed machining.
Balanced CoroGrip® and HydroGrip® tool chucks for High Speed Machining
Modern machines and tools place greater demands on tool holders. This is particularly true when cemented carbide endmills and drills are used at very high speeds, where a very low run-out is required to achieve long tool life. CoroGrip and HydroGrip fulfill all the demands on a tool holder for HSM.
Three requirements have to be fulfilled when using holders with cemented carbide endmills or drills at high speed:
Low run-out provides high precision.
1. Low run-out. A rule of thumb is that the tool life decreases by 50% if the run-out is increased by .0004 inch.
High clamping forces provide high transmission torque capability.
2. High clamping force. Both tool and component can be destroyed if the tool is moving in the holder during machining. Many holding concepts can’t be used at high rpm because centrifugal forces reduce the transmittable torque to unacceptable levels.
Balanced holders required for high rpm.
3. Balanced holders. Too much imbalance creates vibrations which can negatively influence tool performance and spindle life.
For spindle speeds over 15,000 rpm, individually balanced holders are recommended.
All CoroGrip and HydroGrip high precision power chucks are individually balanced to a quality of G 2.5 at 25,000 rpm for small sizes (40 taper, HSK 32-40-50-63, Coromant Capto coupling sizes C3-C6), and G 2.5 at 14,000 rpm for larger sizes (50 taper, HSK 100, Coromant Capto coupling C8). All tools for use with CoroGrip and HydroGrip are required to be symmetrical and well balanced.
CoroGrip also fulfills demands when it comes to excellent run-out and high clamping force. Due to the very high clamping force, it is possible to clamp tool shanks with h7 tolerances, which is not recommended for shrink fit holders.
CoroGrip and HydroGrip chucks are individually balanced to specified balance quality levels. However, an unbalanced tool, collet or retention stud will influence the total balance of the assembly. Complementary balancing can be required for very high speeds.