BIG KAISER Tooling Today

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balanced cutting, but tooling innovations are changing that. In theory, a stepped cutting tool requires that the inside insert (smaller diameter) is leading the outer insert (larger diameter) by at least

A fine boring tool is not designed producing a square shoulder. When fine boring to a square shoulder, we have designed the insert to have the 3-degree negative lead so that the insert can stay off the shoulder. The tool thereby only needs to ‘kiss’ or blend into the existing corner radius.

half of the feed per revolution. Older twin bore heads that used cam screws or height adjusting screws could not adjust enough height difference to use square inserts. Our new SW heads are capable of up to .016" height separation so it is possible now to use them for stepped cutting methods. In other words, a tool with a step of .008" should not exceed .016"/rev feed or else the outer insert will be cutting at the same diameter as the inside insert. With a tool at 6° lead, this ratio is no longer valid, and a larger step is necessary to enable each insert to bore the diameter it’s set to. This is an instance where thin chips are a good thing. The positive lead angle reduces thrust forces upon exit, avoiding the ‘punch out ring’ and breakout where the bore ends. Stack plate weldments, where the boring tool enters and exits layers of steel plates welded together, are another example of where SC inserts come in handy because they do not produce discs or rings that can get trapped between the layers and cause catastrophic tool failure.

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When it comes to fine boring, the lead angle generally does not influence part quality. When we consider that the depth of cut rarely exceeds half of the radius of the insert, the angle is almost negligible to cutting forces or chip formation. However, there are two choices of insert holders for fine boring tools as well. The standard insert holder uses a triangular insert. In addition to three cutting edges, there are far more geometries, radii, and grades than any other insert. The lead angle is 87 degrees or negative three degrees. The common mistake is to disqualify this insert holder and choose the 90-degree type when boring to a shoulder. In reality, it should always be applied for both square shoulder boring and through hole operations. A fine boring tool is not designed or practical for producing a square shoulder. The square shoulder feature should be left alone after the rough boring operation is completed by a twin bore or a circular milling tool. When fine boring to a square shoulder, we have designed the insert to have the 3-degree negative lead so that the insert can stay off the shoulder. The tool thereby only needs to ‘kiss’ or blend into the existing corner radius and we usually recommend to ‘stay off’ the bottom by about .002" to be sure. The same rules of engagement apply to the CC type of insert holder, even though it can create a true 90-degree shoulder. Only under very strict requirements of workpiece integrity, where blends are not allowed, such as some flight-critical aerospace parts, should the practice of creating the bore and shoulder together be used. And if this is the case, the programmer should back off on the feed rate about 75

Type TC

Type CC

The standard insert holder (Type TC) uses a triangular insert. In addition to three cutting edges, there are far more geometries, radii, and grades than any other insert. The lead angle is 87 degrees. The common mistake is to disqualify this insert holder and choose the 90-degree type when boring to a shoulder. In reality, it should always be applied for both square shoulder boring and through hole operations.