Machining with long overhangs – considerations

When machining with long overhangs, from tool diameter 4×D, vibration will start to become an issue. It is not possible to avoid vibration entirely in metal cutting operations, but there are various ways of reducing it.

Damped boring bars

Vibration is often the limiting parameter in gaining high output in the machine, e.g. turn down speed, feed, and depth of cut. Damped boring bars are designed to minimize vibrations through a dampener inside the tool body.

By using dampened boring bars you can increase the cutting parameters and at the same time get a more secure and vibration-free process with close tolerances, good surface and much higher metal removal rate, which in summary gives you a lower cost per component.

The majority use damped boring bars for long overhangs and poor accessibility. However, great productivity increases and surface quality improvements are to be gained even for shorter overhangs (over 4×D).

Whether you increase your metal removal, improve your surface finish, secure your process or reduce your production costs you will certainly enjoy the silence.

Considerations for cylindrical shanks

• Use holders with at least 4×D clamping using a split boring bar design – preferably with CoroChuck® 935
• Use a split cap clamping on the saddle for at least 4×D
• The moment of the boring bar needs to be considered
• A counterweight might be needed depending on the diameter/overhang

Machining with long overhangs in flatbed lathes

In flatbed lathes, internal machining using a steady rest and long boring bars is typical. Use damped boring bars to minimize vibrations, reducing the need for special boring heads with support pads. Damped boring bars can be mounted on the turret or in the tailstock positions.

Machining with long overhangs in turning centres

In turning centres, long boring bars create extra issues with vibration and also collision risks when other tools are being used. By using damped boring bars these potential problems can turn into a competitive advantage.

For long boring bars, go for the largest Coromant Capto® size possible to get maximum stability from the coupling flange. External clamping units do not need to be the same size as they are different tools anyway.

Machining with long overhangs in horizontal multi-task machines

It is common on larger horizontal multi-task machines to have long bores to be machined. Machines have adopted separate loading stations for longer boring bars than the normal magazine can handle. These boring bars are also available with ATC (automatic tool change) for different cutting heads to be stored in the normal magazine.

Machining with long overhangs in machining centres

With the combination of two lengths of machine interface adaptors and three lengths of dampened arbor milling adaptors, getting the optimized length is simple with this modular solution.

There are three considerations to be made about clearance when using a damped milling cutter.

a

b

c

a) Assembly with oversized cutter: clearance all the way

b) Assembly with nominal cutter diameter and undersized shank adaptor: clearance along the undersized shank

c) Assembly with nominal cutter: no clearance