Common threads--quiz answers. (Shop Talk).

Did everyone enjoy last month's quiz on threads? If you haven't taken the quiz yet, you still have a chance. Visit the RTSI web site at www.cnc-training.com, take the quiz and then meet us back here to review the answers.

The Answers:

1. A thread has three important diameters, what are they?

Major diameter, minor diameter and pitch diameter

2. Which of these is the most important diameter?

The pitch diameter

3. Explain why you made that choice.

Because the internal and external threads contact at the pitch diameter.

4. What is the difference between the pitch and TPI?

Pitch is the distance between each thread crest and TPI is the number of threads in 1".

5. List three methods for creating OD threads on a turning center.

Single point threading, thread rolling and threading with a die head

6. Which of these methods creates the strongest thread?

Thread rolling produces the strongest thread.

7. List two methods for creating threads on a machining center.

Thread milling and tapping

8. Taps are identified by the length of the tap chamfer. Name the three types of taps.

Taper, plug and bottoming

9. How do you determine the feed rate for a tap?

The feed rate equals the pitch of the thread.

10. What is special about a UNJ style thread?

This thread has a root-controlled radius.

11. When machining an external UNJ style thread what do we need to remember to do?

Use a special UNJ series-threading insert.

12. Why would we select a high spiral, turbo tap?

Use a turbo tap when tapping a blind hole.

13. What is meant by a compound plunge angle?

On a CNC lathe, a modified plunge angle is used when single point threading insert is programmed to approach the part at a certain angled approach.

14. List three advantages of thread milling over tapping.

Size control, ability to cut large diameter threads, minimum clearance between the full thread diameter and blind hold.

15. What is the angle of a National Pipe Taper thread in degrees, minutes and seconds?

1 degree 47 seconds 23.68 minutes

16. What does the term Full Form Threading Insert mean?

This is an insert shape designed to cur a specific thread form including the crest and root radius.

17. List 3 features that are different between a 1/8 BSPT thread and a 1/8 NPT thread.

BSPT has a 55 degree included angle thread, rounded crest and root radius and a different number of threads per inch.

18. A tap can be described as a 3/8-16 GH3 tap. What exactly does the GH3 mean?

The pitch diameter of the tap is 0.0015 above nominal.

19. What is the difference between a 3-4-10 UNF 2A and a 3/4-10 UNF 2B thread?

2A indicates an external thread and 2B indicates an internal thread.

20. Are these two threads the same size?

No, they are not the same size.

21. Explain your answer.

The external class 2B thread must be larger for the class 2A thread to assemble.

22. ANPT stands for Aeronautical National Pipe Taper. How does this thread differ to a NPT type?

This thread conforms to standard SAE AS71051.

23. What does the term NPTF stand for?

National Pipe Taper Fuel

24. Given a M12 x 1.75-6H thread, what is the pitch in inches?

0.06889"

25. What does the term 6H mean?

This is the tolerance class for an internal thread.

Steve Rose is a professional trainer and president of RTSI, Solon, OH, which also offers Internet web site development. Mr. Rose can be reached by phone [phone]; fax [phone]; e-mail [e-mail]; or on the web at www.cnc-training.com