Selecting The Style Of Tap To Use
The First Questions
You need a tap. What information is needed, and how do you choose the right tap for the job?
When you call North American Tool, we will ask for the basic thread description which specifies the diameter, thread pitch or TPI, the Class-of-Fit (for gaging purposes), and the thread type (e.g. 60-degree, Acme, Buttress, Whitworth, Pipe, etc..). All of these features should be called out by the customer, or included on the Part Print.
After that, the following three questions will assist North American Tool in providing the best possible solution, rather than the first available solution.
1. WHAT IS THE MATERIAL BEING TAPPED?
This will help us recommend the proper geometry, and base-material for the tap; Hi-speed Steel (HSS), Premium Steel (HSSE), or Carbide. It will also tell us whether you have the option to cut, or form the threads. And, the material knowledge will help us recommend a coating, or surface treatment, to improve tap performance.
2. HOW DEEP ARE THEY TAPPING, AND WILL THEY REQUIRE EXTRA LENGTH ON THE TAP FOR "REACH'?
The answer to this question will determine tap thread length and shank clearance needed based on depth. It also helps us envision the kind of forces that might come into play, how much torque might be generated on the tap, and whether excessive depth will contribute to a chip evacuation problem. Remember, by industry standards, anything over 1-1/2 times tap diameter in depth is consider excessive, and "depth-of-cut" needs to be a consideration in the tap design.
3. IS THE HOLE BEING TAPPED "THROUGH," OR "BLIND"?
The answer to this question will lead us to a recommendation on flute geometry (straight, spiral, or spiral-point), and chamfer length allowed. A part print, if available, is helpful to determine how much "clearance" is available in a blind hole to accommodate the tap chamfer length potential.
The answers to these three give us a great start on recommending the proper tap. Additional questions about material hardness, machine requirements, fixture limitations as they apply to reach and clearance, coolants and lubricants, and gaging issues will further refine the tooling recommendations.
A wise man once said, "90% of the time that a tool fails, it's not the fault of the tool. It is more likely the wrong tool for the job". All too often, vital information has not been gathered before ordering the tool. Please help yourself by asking the right questions, or working with people like North American Tool who will ask them for you!