Tapping Tool Core-Diameter Cutting Edges for Lower Torque Threading
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Solution Overview
Problem
Existing tapping tools experience high tool load during the tapping process due to the large cutting length of pre-drilling cutting edges, which results in increased feed force and torque, and chips can damage the thread raw profile.
Innovation Solution
The tapping tool incorporates core diameter cutting edges between the thread producing section and the countersink cutting edge, which produce the core diameter independently of the pre-drilling diameter, allowing these edges to guide within the thread profile and remove the diameter allowance in a free-cutting stroke, reducing the load and preventing chip entry into the thread raw profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pre-drilling cutting edge extends to the pilot diameter to create the pilot hole, then the pilot hole is formed during the tapping stroke, but the cutting edge length increases resulting in high cutting edge load and increased feed force and torque
Solution Approach 1:
The cutting edges are segmented into three distinct types with different functions: pre-drilling cutting edges (frontal) for creating the pilot hole, core diameter cutting edges (lateral on drill bit web back surfaces) for defining the core diameter and guiding within thread pitches, and thread-generating machining teeth for forming the internal thread. This segmentation allows each cutting edge type to have optimized geometry for its specific function, reducing overall cutting edge load.
Solution Approach 2:
The core diameter cutting edges are extracted as a separate functional element from the traditional pre-drilling cutting edge. By positioning these core diameter cutting edges on the back surfaces of the drill bit webs and extending them radially outward, the patent separates the core diameter formation function from the pilot hole creation function, allowing the pre-drilling cutting edges to have shorter effective cutting length.
2Ease of manufacture
If the pre-drilling cutting edge has large cutting edge length to create the pilot hole, then the pilot hole is formed, but chips can damage the thread raw profile
Solution Approach 1:
The core diameter cutting edges act as an intermediary protective element between the pre-drilling cutting edges and the thread-generating machining teeth. During the tapping stroke, these core diameter cutting edges are guided within the thread pitches and protect the thread raw profile from chip damage while allowing the pre-drilling cutting edges to perform their function.
3Force
If core diameter cutting edges are added to independently generate the core diameter, then the tool load is reduced and chip damage is prevented, but the device complexity increases
Solution Approach 1:
The core diameter cutting edges serve multiple functions simultaneously: they define the core diameter during the tapping stroke, guides the tool within the thread pitches, protect the thread raw profile from chip damage, and participate in material removal during the free-cutting stroke. This multi-functionality justifies the added complexity by consolidating several protective and formative functions into a single cutting edge element.
Data Source
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AI summary
The invention relates to a tapping tool (23) for producing a workpiece threaded hole (1), the internal screw thread (9) of which has a screw-thread major diameter (dA) and a screw-thread minor diameter (dk). According to the invention, the tapping tool (23) has a number of minor-diameter cutting edges (34) between a thread-producing portion (29) and a countersinking cutting edge (49). In a tapping stroke (G), the minor-diameter cutting edges (34) are guided in the screw-thread turns (15) of the internal-screw-thread raw profile (8). In a cut-out stroke (F), the minor-diameter cutting edges (34) remove the diameter excess (Δd) on the radially inner screw-thread vertex (21) by machining down to the screw-thread minor diameter (dk).