Compensating chuck

This article or the following section is not adequately provided with supporting documents ( e.g. individual evidence ). Information without sufficient evidence could be removed soon. Please help Wikipedia by researching the information and including good evidence.

The compensating chuck is a special form of a chuck which, in addition to the tool holder , is also intended to eliminate machine-related tolerances and errors.

There are compensating chucks especially for thread cutting and reaming . Both forms differ considerably in structure and function.

Compensating chuck for threaded holes

Compensating chucks for thread cutting have the main feature that they can compensate for differences in length from the working speed and the working feed rate used in relation to the thread pitch and depth by changing the length. This makes it possible to produce threads with taps on mechanical column drilling machines or older, also worn, CNC machines . Since not all, especially older, CNC machines had the necessary computing power and accuracy to reduce the feed rate synchronously when the programmed thread depth was reached and at the same time reduce the spindle speed and reverse it and restart it with the opposite feed rate, this was the application Element, the compensating lining, is unavoidable.

Today these compensating chucks are only used on CNC machines when larger threads have to be produced with extremely small pitches ( fine threads ) and thread milling is not an option due to the machining position . When used on CNC machines, for example, the feed rate per revolution, which corresponds to the thread pitch, is programmed to be slightly smaller (a few 1/10 mm). Thus, after the first cut, the tap pulls itself into the part which is compensated by the compensating chuck. Compensating chucks usually only have a stretching range of around 10–15 mm. It must be ensured that the stretching range of the compensating chuck is not used up 100% when the thread depth is reached. If the difference to the real pitch is programmed too large, the chuck reaches its yield point before reaching the thread depth and the tap tears out the thread or even breaks off in the hole.

Rubbing compensating lining

Compensating chucks for reaming have the task of compensating for machine-related errors, such as the hitting of the work spindle , concentricity errors of the work spindle, geometry errors such as angular misalignment of the Z axis to the work table, and positioning errors in the X and Y directions. There are conceptually two different ways to do this.

For angles and positioning errors

Compensating chucks (*) are used for angle and positioning errors, which have a self-centering effect and are also known as pendulum holders. This means that the reamer , if it has a correspondingly large chamfer and there is sufficient allowance in the hole , centers itself and the compensating chuck allows an axis shift or offset between the center of the hole and the position of the work spindle above the hole. This range can be set on the compensating chuck, but should in no case be more than half the depth of cut. The depth of cut is calculated from the bore diameter of the prefabricated bore and the tolerance center of the fit to be produced by two.

If the compensating chuck is set too far, the resulting imbalance comes into play. In this way, the desired effect is reversed, there is greater wear on the tool and the surface quality can no longer be achieved, and the cylindrical shape and roundness of the fit can come outside of the tolerance range. Another area of ​​application for this type of chuck are cam-controlled multi-spindle automatic lathes. Here, too, it is important to eliminate indexing errors in the spindle drum.

For concentricity errors

This form of compensating chuck is increasingly used when the work spindles no longer have a sufficiently precise runout (deviation greater than 0.02 mm) or when high-performance reamers with indexable inserts are to be used. The tool or the reamer with the compensating chuck is clamped in the work spindle and aligned there for concentricity. This is done with the help of a dial gauge and a key (usually an Allen key ) by placing the dial gauge on the zero ring of the reamer and determining the maximum deviation by turning the work spindle by hand or in jog mode. Then the freely positionable setting ring is turned to the maximum point of the deviation and the concentricity of the reamer is adjusted with the help of the shifting screw. This process is repeated until the runout on the tool itself is less than 1/100 mm or the value prescribed by the tool manufacturer is reached. Since all automatic tool changers always carry out their tool changes in the same angular position, CNC machines only need to be corrected once after the tool has been loaded into the machine. If the tool is changed by hand and it is possible to install the tool in the work spindle in a twisted manner, ensure that it is correctly positioned.