All threading tools are unique and they each serve a different purpose. Cut taps and roll taps are not always interchangeable, and knowing when to use each is very important. In this article we will discuss the details of a cut tap and how to identify one. For information on the differences between taps please check out our article here.
How to Identify a Cut Tap
Cut taps will usually have 4 individual thread sections with relief for chip evacuation. Cut taps are available with 3 different chamfer configurations: bottoming, plug and taper. Below is an example of a cut tap with a plug chamfer. The tip at the top of the tap is a feature put on by the manufacturer. We prefer taps with sharp tips because it allows us to easily touch off our tools and relate our pre-drill depth to our tap depth.
Notice the text near the back of the tap. This text will help you identify the size, material and pitch of the tap along with a few other tidbits of information.
The tap pictured above is a ⅜ diameter tap with 40 threads per inch (pitch) and it is a NS (American National Special Thread) form. The tap is made of high speed steel (HS) and it falls within the GH-2 pitch diameter class.
Pitch Diameter Limits for taps:
L1: Nominal to Nominal minus .0005’’
H1: Nominal to Nominal plus .0005’’
H2: Nominal plus .0005 to Nominal plus .0010
H3: Nominal plus .0010 to Nominal plus .0015
H4: Nominal plus .0015 to Nominal plus .0020
H5: Nominal plus .0020 to Nominal plus .0025
H6: Nominal plus .0025 to Nominal plus .0030
Coated Vs Uncoated Taps
Most taps are available with a coated feature made of titanium nitride. The coating helps prolong tool life by increasing chip flow inside of softer materials. Some reports have indicated that the coating allows you to run your taps at higher feed rates. Coated taps are by no means required, but if you are experiencing short tap life they may be an option to consider.
Inspection of Taps
All types of tools wear out and taps are no exception. Taps should be inspected prior to use and checked with a thread gauge to ensure conformance. When inspecting a tap, start at the top and work your way backwards inspecting for:
- Chipped or broken flutes
- Heavy wear on the beginning flutes
- Lack of coating (if applicable)
- Sharpness of the flutes