Have you ever had a tapping job that was so troublesome that it caused heartburn or acid indigestion due to broken taps, bad finish, short tap life, over or under size threads etc?
Getting a good understanding of the definitions of the parts of a tap will help you to better understand the functions of tap designs. Special thanks to North American Tool for letting us share their short and simple explanations!
Minimum clearance between two mating parts; the prescribed variations from the basic size.
ANGLE OF THREAD
The angle included between the sides of the thread measured in an axial plane.
The imaginary straight line that forms the longitudinal centerline of the tool or threaded part.
A gradual decrease in the diameter of the thread form on a tap from the chamfered end of the land towards the back which creates a slight radial relief in the threads.
BASE OF THREAD
The bottom section of the thread; the greatest section between the two adjacent roots.
The theoretical or nominal standard size from which all variations are derived by application of allowances and tolerances.
The tapering of the threads at the front end of each land of a tap by cutting away and relieving the crest of the first few teeth to distribute the cutting action over several teeth; Taper taps are chamfered 7-10 threads; plug tapsare chamfered 3-5 threads; semi-bottoming (or modified bottoming) taps are chamfered 2-2.5 threads; bottom-ing taps are chamfered 1-2 threads; taper pipe taps are chamfered 2-3.5 threads.
The gradual decrease in land height from cutting edge to heel on the chamfered portion, to provide clearance for the cutting action as the tap advances.
The top surface joining the two sides or flanks of the thread; the crest of an external thread is at its major diameter, while the crest of an internal thread is at its minor diameter.
The leading side of the land in the direction of cutting rotation on which the chip forms.
The longitudinal channels formed in a tap to create cutting edges on the thread profile, and to provide chip spaces and cutting fluid passages.
The edge of the land opposite the cutting edge.
HEIGHT OF THREAD
The distance, measured radially, between the crest and the base of a thread.
The angle made by the advance of the thread as it wraps around an imaginary cylinder.
The undercut on the face of the teeth.
The inclination of a concave cutting face, usually specified either as Chordal Hook or Tangential Hook.
INTERRUPTED THREAD TAP
A tap having an odd number of lands with alternate teeth along the thread helix removed. In some cases alternate teeth are removed only for a portion of the thread length.
The part of the tap body which remains after the flutes are cut, and on which the threads are finally ground. The threaded section between the flutes of a tap.
The axial distance a tap will advance along its axis in one revolution. On a single start, the lead and the pitch are identical; on a double start, the lead is twice the pitch.
Commonly known as the “outside diameter.” It is the largest diameter of the thread.
Commonly known as the “root diameter.” It is the small-est diameter of the thread.
PERCENT OF THREAD
One-half the difference between the basic major diameter and the actual minor diameter of an internal thread, divided by the basic thread height, expressed as a percentage.
The distance from any point on a screw thread to a cor-responding point on the next thread, measured parallel to the axis and on the same side of the axis. The pitch equals one divided by the number of threads per inch.
On a straight thread, the pitch diameter is the diameter of the imaginary co-axial cylinder...the surface of which would pass through the thread profiles at such points as to make the width of the groove equal to one-half of the basic pitch. On a perfect thread this occurs at the point where the widths of the thread and groove are equal. On a taper thread, the pitch diameter at a given position on the thread axis is the diameter of the pitch cone at that position.
The angular relationship of the straight cutting face of a tooth with respect to a radial line through the crest of the tooth at the cutting edge.
RELIEF (or Thread Relief)
The removal of metal from behind the cutting edge to provide clearance and reduce friction between the part being threaded and the threaded land.
The bottom surface joining the sides of two adjacent threads, and is identical with or immediately adjacent to the cylinder or cone from which the thread projects.
A flute with uniform axial lead in a spiral path around the axis of a tap.
The angular fluting in the cutting face of the land at the chamfered end; formed at an angle with respect to the tap axis of opposite hand to that of rotation. Its length is usually greater than the chamfer length and its angle with respect to the tap axis is usually made great enough to direct the chips ahead of the taps cutting action.
A flute that forms a cutting edge lying in an axial plane.
In producing a tap to given specifications, tolerance is:
(a.) the total permissible variation of a size;
(b.) the difference between the limits of size.
First things first, what is the root of a tap?
The root of a tap is the surface at the bottom of the thread-form that connects adjacent thread flanks and is expressed as a width or as a diameter. The term root diameter is also called minor diameter, it’s one of those things, you say rain and I say precipitation, meaning the same thing...
North American Tool realizes how confusing the painstaking math is to get preplate part limits and a Tap “H” limit, but don’t worry, all you have to do is contact us with your thread information, and we will do the work. Call us at 800-USA-TAPS.
If you want to know how it's done, we’ve included the formulas for the engineer in all of us.
Recently we had an application question at North American Tool. A customer had opened up the drilled hole to 55 percent of thread in hopes of reducing wear and increasing tool life. Instead, it lead to the cut tap breaking at the first full thread of engagement. That prompted a engineering discussion and is the basis of this technical article to address this very common misperception.
If a tap doesn’t create the hole, why is the hole size so important?
This leaves the good machinist to select a drill that is more or less than 75%. If 75% is good, then a higher number is better, right? WRONG (in many cases). On page 115 of the current North American Tool catalog a range for percentage of threads from 50% to 85%, with the recommended range between 65% and 75%. This guideline range to use is a reflection of several factors:
In higher tensile steels, larger hole sizes (less percentage of thread) may work better to reduce torque in tapping. When using oversize hole diameters, the tap should also have an oversize chamfer point diameter so all threads in chamfer are cutting and not just dropping in a hole.
Such was the case with the application porblem. As was stated above the operator thought that by increasing the drill diameter size would lead to better tool life. Instead, because the diameter was of the hole was so large the cut tap did not engage the threads along the chamfer length and instead engaged at the first full thread at the end of the chamfer. The caused premature wear and stress on the that thread in the flutes and eventually to catastrophic failure. The solution was a modified tap from North American Tool.
Summary: You've got to use the correct tap for the application!
At the end of the day, taps are made to very strict tolerances, often much more so than the piece parts they are called on to machine, and the first place one might want to find blame is with the tap.
What if one manufacturer makes a tap that works and another one made by a different company doesn’t work at all?
In all likelihood, the “general purpose” of one is closer to the correct geometry for the application. One might get a completely different result if another material were being machined. Therefore it is always best to order a tap for the specific application.
Marcus Schellinger, a rising senior in a Rock County High School (WI) on track to graduate at the end of the 2019-20 school year has spent the last six weeks working at North American Tool in South Beloit, IL.
Marcus had to take the initiative to apply online to the Rock County 5.0 program (in its second year) a part of the Rock County Economic Development Committee.
Marcus was assigned to work a CNC Mill and a CNC Lathe in the Bar Steel A department of North American Tool Corporation. This is where the making of a tool begins and Marcus proved more than capable. “It gave me insight into the methodology behind working that I can take and apply to school” said Marcus.
“I was given responsibilities that enabled me to apply the knowledge and skills I have learned in school course work” reports Marcus. Jeff Sherman, the Director of Manufacturing at North American Tool said he was extremely impressed with Marcus and his work ethic and willingness to learn.
Marcus worked with Flint Hansen day to day and “got to develop some faster methods to operate the machine”. The Rock County 5.0 program did a nice job at matching the skill set of the student with the opportunity available.
The program was conceived and overseen by James Otterstein the Economic Development Manager of the Rock County Economic Development Committee. The idea was to “accelerate personal, as well as professional skills and career related exposure. This structured paid internship model will provide students like Marcus with a meaningful career pathway experience that will serve as a foundational element of their Academic & Career Plan.
When asked what he would say to future students considering an internship at North American Tool , Marcus replied “I would tell them to ‘go for it’ and they would regret nothing.”
If you have a shop (or a customer) that machines aluminum and aluminum alloys as its go-to substrate, why are you selling/buying general purpose tools?
You are working with the most popular-to-machine material. How does your company stand out from your competitors who machine aluminum? Isn’t the advantage of aluminum that it is already free-machining and more desirable to work with in the first place? Isn’t it likely your competitors have reached the same conclusion? If you are using general purpose tools, you are likely getting similar results to your competition. Here’s a suggestion on how to make a competitive advantage.
Application specific tools like the TMAL series from North American Tool allow you to optimize the tool you use for the aluminum you machine. Take advantage of a more aggressive geometry, a micro-grain carbide substrate and the ZrN coating to give you a performance advantage over general purpose tools.
What makes these North American Tools application specific and how are they different?
North American Tool's Thread Mill Brochure
Check out our Thread Mill Brochure below and find the tool that was created for your job.
Keep in mind all diameters specified are just the shank the pitches are ground on. Your hole size should be large enough to allow for the circular interpolation to take place on your CNC equipment.
It is generally recommended (call it a guideline, not a rule) that the tool diameter should not exceed 80% of the hole size for which it is used.
We offer programming information on page 16 and troubleshooting info on page 17 for your convenience.
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To get step-by-step instructions on how to get started once you have downloaded the App, visit our video library.
You may think of North American Tool as a custom builder of taps, but they are also very experienced in thread milling as well!
If you deal with exotic alloys like Inconel, titanium, Hastelloy, etc., this blog post is written especially for you.
Exotic alloys are alloys designed for high temperature applications (think aerospace), perform in corrosive environments (think underground), or have the highest strength to weight ratios (think earth moving applications). The machinability of these materials is NOT the first consideration. As much as it would be nice to have an aluminum firewall in a helicopter from the machinist’s viewpoint, as the pilot or passenger you want flame retardant and strong.
Some exotic materials can ignite spontaneously when machined and exposed to the atmosphere. It is likely these alloys were created to perform in applications where traditional materials would fail. Also, these alloys are typically more expensive than traditional steels machined in most shops.
So now, you are faced with machining (more specifically threading) these kinds of alloys. What’s an operator to do? Application specific tools have been designed with these considerations in mind. Thread mills made from solid carbide specifically for exotic metals are manufactured in the USA by North American Tool and a handful of other providers.
You may ask why is a company that makes special taps informing you about thread mills?
The answer is North American Tool is the industry leader in designing and manufacturing SPECIAL TAPS FOR EXOTIC MATERIALS as well.
This is an alternative tool to the special taps we design every day in case your shop has at least a three axis spindle and deals with these alloys.
Because the tool is coated with AlCrN, the tool has greater heat and wear resistance in the high heat, higher abrasive applications one confronts when machining exotic alloys. The threads are milled, rather than cut, typically producing a better quality thread in the piece part.
As an operator, when you select the correct tool for the job, you use the right substrate (carbide in this case), the right geometry and the right coating (AlCrN) and you avoid the issues others face when they try to apply a general purpose tool to a difficult opportunity. It will make your shop stand out from the competition since you produce better results at a reduced cost.
If you are working with exotic materials and need a thread mill or special tap, contact our Customer Service team by email at email@example.com or by phone at 800-872-8277.
The intent of defining a list of tools as "Standard" is to provide uniformity in manufacture, integrity, and use. This "uniformity" allows for ease of service, and provides interchangeability of common parts for the user, and ultimately for the consumer. It is also meant to assure quality of function for which the thread is intended.
In the United States, there are three primary organizations that contribute to those definitions. The descriptions of the entities below are meant to be simple for the purpose of illustration to show basic scope of involvement.
USCTI (United States Cutting Tool Institute) is a tooling manufacturers group that provides recommendations on general dimension and design for its members in the manufacturing of the tools themselves. Tool blank dimensions, flute configuration, and tool nomenclatures are usually defined here.
ANSI (American National Standards Institute) represents our Government to coordinate US Standards with International Standards to meet worldwide markets. This is the recognized stamp of approval for standards adopted by USCTI and ASME.
Certainly there are other standards; DIN, British Whitworth, SAE, etc ......., but there is an overlooked “standard” that may cause blurring of the lines between Industry Standard and Special.
We know this standard as “Popular Specials”. When a tap becomes used with consistent regularity, the manufacturer may decide to include it as a stocked tap in their product offering. Most recognized examples are Extensions, Left-hand, and .005 oversized for pre-plate. In reality, the marketplace itself is another source for setting a standard in someone’s product catalog.
It is common to receive inquiries for quote, or even orders that leave out a few details. Frequently, when asked for clarification on the customer’s needs, the response is “Oh ......, whatever’s standard”. The question then becomes, “Who’s standard?” Without clarification, the decision can be a shot in the dark at a moving target. North American Tool, without further clarification would default to USCTI and ANSI.
If you are forced to use a default setting on your phone or computer, the result is not always an outcome that was desired. So it is when choosing defaults in Tool Design. As a “Specials” manufacturer, we would prefer the customer specify his need.
We've compiled the latest news and technical information about our principals and our market that we hope you find informative!