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Threads provide a helical groove or projection on cylindrical or conical metal parts like screws and bolts, enabling the joining and fastening of components in assemblies. But successfully cutting threads into these parts requires specialized thread-cutting tools known as taps.
There are several different types of thread taps, and all of them have specific purposes. Knowing exactly which tap to use when can be a bit confusing sometimes. Therefore, we’re here with this definitive guide.
This guide will cover the diverse array of 10 essential thread tap varieties machinists rely upon to produce precision threaded elements.
1. Bottoming Taps
Bottoming taps include only 1-1.5 tapered leading threads. This allows cutting threads to completion at the very bottom of blind holes. The absence of tapering eases, producing full-depth threads down, shouldered, or shallow holes where excessive taper contact area would hinder operation.
2. Plug Taps
With around 3-5 tapered front threads, plug taps balance taper and bottoming variants. The shortened taper allows reaching the full thread depth faster but with manageable axial force. Plug taps conveniently tap holes to completion in fewer turns.
3. Taper Taps
Featuring 8-10 gradually tapered starting threads, taper taps slowly establish the thread form to reduce friction and threading torque as more of the chamfered cutting area engages. The gradual engagement makes taper taps the easiest to start tapping holes manually.
4. Spiral Pointed Taps
Resembling hand taps, spiral point taps incorporate spiral cutting edges for improved chip ejection and can operate at moderately higher speeds. The spiral pointed tip helps facilitate smooth initial thread cutting. However, they push chips forwards into holes, unlike hand taps. It’s easier to eject chips in through holes, but should be avoided in blind holes.
5. Spiral Flute Taps
An open upward spiraling flute characterizes this tap variety. The spiral cavity actively extracts chips away from the cutting interface up and out of holes instead of pushing them in deeper. This proves advantageous for blind holes and maintaining uninterrupted cuts through hole intersections. The spiral flute has a disadvantage of being the weakest flute geometry. In many blind hole applications, spiral fluted taps are being replaced by form taps.
6. Interrupted Thread Taps
These taps feature spaces between threading teeth instead of a continuous sequence. Removing alternate teeth improves chip clearance by providing space for efficient chip breaking and lubricant penetration. However, the incomplete thread form requires careful handling to avoid compression or deformation issues under axial loads.
7. Pipe Taps
As the name suggests, pipe threading taps help generate tapered or straight internal screw threads needed for sealing pipe connections to exacting tolerances. Tapered pipe taps must cut increasingly deeper from top to bottom of untapered holes and endure far greater wear and tear. So, using a piloted reamer first to correctly pre-taper holes saves significant tap effort.
8. Form Taps
Instead of shearing away metal through cutting, form taps displace and mold ductile materials into finished female thread contours through high-pressure compression. This cold thread-forming technique leaves no chips while generating precise, intact, stronger internal threads that can handle demanding specifications. Different feed rates, hole sizes and optimal materials warrant consideration before deployment.
9. Nut, or Nib, Taps
These taps are specifically designed for special tapping machines for the fastener industry. These taps are also know as bent-shank taps because of the the drive methods. They often have taper chamfers for extended tap life and are specialized because the tap never reverses.
10. Carbide Taps
These are taps manufactured from carbide instead of high speed steel. The carbide material provide extreme hardness that is good for applications that are very abrasive or at very high speeds. Despite these benefits, industry data indicates that about 2% of the taps sold in North America are carbide. The reason is that carbide has many disadvantages. These include very high costs, increased breakage due to the brittleness of carbide, and the inability to remove broken taps.
Summary
The comprehensive guide above covers the 10 fundamental thread tap categories that machinists require to optimally produce every threaded component, from rugged aerospace screws to miniature medical device fasteners.
Mastering this diverse range of cutting, forming, and milling taps for thread generation remains pivotal to accommodating the vast application space flexibly, relying upon high-precision, repeatable threading solutions every day.
Whether shops machine a few specialty threaded parts or mass produce catalog standard screws, investing in a judiciously equipped thread tap arsenal promises order growth.
