Roll taps are the most commonly used tool for threading. They provide a simple and easy solution for putting threaded holes in a variety of materials. The name roll taps (A.K.A. forming taps) originates because the tool forms threads rather than cuts them. Understanding the basics on how to identify a tap and proper inspection methods is vital for accurate manufacturing.
How to Identify a Roll Tap
Roll taps can be easily identified by their concentric threads going around the cutting tool. There is only 1 relief in the tap for chip evacuation hence the importance of proper feeds and speeds to prevent overloading the tool. For reference, below is a picture of a forming tap.
There is text on the forming tap revealing a few important details:
- OEM name and part number.
- The size and pitch of the tap (8-32).
- The letter ‘B’ denoting internal thread.
- The tolerance of the pitch diameter. Please reference the table below for additional information.
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 Roll 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 Roll 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
For information on the differences between cut and roll taps please check out our article here. STG Machine also had a free drill chart available for download here. If you have any questions or comments feel free to leave a comment down below. Please remember to subscribe to our newsletter for continuous updates and for additional articles.