Cutting by use of rotating axially moving tool – Means to drive tool – Including means to move tool along tool-axis
Reexamination Certificate
2000-06-05
2001-07-10
Bishop, Steven C. (Department: 3722)
Cutting by use of rotating axially moving tool
Means to drive tool
Including means to move tool along tool-axis
C408S222000, C470S096000, C470S101000, C470S198000
Reexamination Certificate
active
06257809
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an improved apparatus and method for threading holes in material.
DESCRIPTION OF THE PRIOR ART
Current methods of tapping, or forming threads in a hole, generally use a hard steel tap with a tapered threaded first end that cuts the threads as it is rotated at a second end. Longitudinal grooves, or flutes, which may be straight or helical, interrupt the threads to generate cutting elements, and to carry the chips generated by the cutting elements. They reduce, but not entirely eliminate, the binding effect that the chips have on the revolving tap. Binding of the tap requires increasing torque at the driving end to advance it. The increased twisting of the tap may break it, often leaving the broken end stuck in the hole. This not only results in loss of the tap, but also often means scrapping the part due to the cost of removal of the broken tap. Taps bind at the cutting end, and are driven at the opposite end. The torque of the driven end twists the tap, and this twisting is what causes the tap to break. The longer the tap, or the distance between the driven end and the cutting end, the greater the twisting action and the threat of breakage. If this distance could be shortened, it would reduce tap breakage. After a hole is tapped, the tap is removed by reverse rotation. This is time consuming, and may damage the already formed threads by going over them a second time with other cutting edges. An exception is the nut tap that puts short threads in nuts. These are made with a long cylindrical shaft between the thread cutting portion and the squared driver end. As each nut is threaded, it advances onto the cylindrical shaft, pushed there by the next nut. After many nuts are threaded and collected on the shaft, the driver end is disconnected and the accumulated nuts removed. It would be useful in many operations to be able to remove a tap from the hole after the thread is cut without reverse rotation of the tap, or disconnection of the driver end. When a tap has been driven part way through the hole, resistance to rotation builds up. Because of the danger of tap breakage, it is common practice to periodically reverse rotation at these times to break off the chips. This increases tapping time and effort. It may also increase tap breakage, because starting friction is greater than sliding friction. It would be desirable to have a tapping system with reduced threat of breakage, because the hole may then be threaded with one continuous rotation.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide apparatus that will reduce the distance between the cutting elements of the tap and the rotational driving force. The apparatus and method of the invention comprises means for rotationally driving the tap at a driving location intermediate its two ends, and for automatically adjusting the driving location to maintain a minimum distance between the driving location and the actively cutting portions of the tap as the tap progresses through the hole. Since this reduces tap breakage, it makes it possible, in many situations, to continuously rotate the tap without periodic reversals. When there is no stopping of the rotation, there is no starting friction as it is started up again. This further reduces tap breakage. It is another object to provide a tapping system that will enable the tap to pass through the threaded hole and be removed from the other side of the workpiece, either automatically or manually, so as to avoid having to unscrew the tap to remove it. It is yet another object to provide a tapping system that maintains a correct position of the tap orthogonal to the workpiece surface for enhanced quality of operation and reduced tap breakage. These and other objects, features, and advantages of the invention will become more apparent when the detailed description is studied in conjunction with the drawings in which like elements are designated by like reference characters in the various drawing figures.
REFERENCES:
patent: 899916 (1908-09-01), Smith
patent: 1111413 (1914-09-01), Smith
patent: 3945069 (1976-03-01), Cecil
patent: 5529442 (1996-06-01), Jorgensen
patent: 5797710 (1998-08-01), Sawabe
patent: 5876158 (1999-03-01), Beiter
patent: 6012878 (2000-01-01), Hicks
MSC Industrial Supply Co Catalog Melville, NY 11747 page Describing Nut Tap HSH3 Part No. 0468023 2 pages total.
Bishop Steven C.
Blum Alvin S.
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