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PT thread, NPT thread, G thread, metric thread

KYLT Precision CNC Machining — Wed, 06 Nov 2019 20:10:59 +0000

NPT, Pt, G are pipe threads

What is NPT screw thread?

NPT is the abbreviation of national (American) pipe thread, which belongs to 60 degree taper pipe thread of American Standard and is used in North America. Refer to GB / t12716 for national standard.

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What is PT screw thread?

PT is the abbreviation of pipe thread. It is a 55 degree sealed tapered pipe thread, belonging to the Wyeth thread family. It is mostly used in European and Commonwealth countries. It is commonly used in the water and gas pipe industry. The taper is specified as 1:16. Refer to GB / t7306 for national standards.

What is G screw thread?

G is a 55 degree non thread sealing pipe thread, belonging to the Wyeth thread family. The mark g represents cylindrical thread. Refer to GB / t7307 for national standard.

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In addition, 1 / 4, 1 / 2 and 1 / 8 marks in the thread refer to the diameter of the thread size, and the unit is inch. The insiders usually call the thread size by minute, one inch is equal to 8 minutes, one / 4 inch is 2 minutes, and so on.

G is the general designation of pipe thread (Guan). The division of 55 and 60 degrees is functional, commonly known as pipe circle. That is, the thread is processed from a cylindrical surface.

ZG is commonly known as pipe cone, that is, the thread is processed from a circular cone. The general water pipe joints are like this, and the national standard is marked RC.

What is Metric screw thread?

Metric threads are represented by pitch, while American and British threads are represented by the number of threads per inch, which is the biggest difference between them.

Metric thread is 60 degrees of equal profile, English thread is 55 degrees of equal waist profile, American thread is 60 degrees.

Metric screw threads are in metric units, and American and British screw threads are in English units.

The pipe thread

The pipe thread is mainly used for the connection of pipes. The internal and external threads are closely matched, including straight pipe and cone pipe. Nominal diameter refers to the diameter of the connected pipe. Obviously, the thread diameter is larger than the nominal diameter. 1 / 4, 1 / 2, 1 / 8 is the nominal diameter of inch thread.

Angle of thread:

60 degrees for metric and American threads, 55 degrees for British system, 30 degrees for TM water pipe thread, 60 degrees for SM needle thread and BC thread, 30 degrees for metric trapezoidal thread, 29 degrees for British trapezoidal thread, and table thread (tw29 degrees TR and tm30 degrees).

Common thread:

metric thread M; British system w; American system UNC, une, UNEF

Pipe thread:

British PS, Pt, PF; American NPs, NPT, NPTF, NPSM

Air nozzle thread:

The outer diameter of CTV and TV 1 / 4-20 is 1A: 0.2367-0.2489 (6.012-6.322); 2A: 0.2408-0.2489 (6.116-6.322) 3A: 0.2419-0.2500 (6.1443-6.350)

Inch thread:

according to nominal size and number of threads per inch

For example, 1 / 4 “- 20, 3 / 4” – 10, 1 “- 8, 1 / 4” – 20 means that the nominal size is 1 / 4, that is, the major diameter is 6.35mm (25.4 divided by 4 = 6.35), 20 teeth per inch, and so on.

NPT thread Brief Size

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Tapping problems, REASONS AnALYSIS, solutions

KYLT Precision CNC Machining — Sat, 12 Oct 2019 17:18:31 +0000

Use common type tap, which problems are always happen?

The main problems often occur in tapping process:

Taper broken;
Taper broken teeth;
Tap wear is too fast;
Excessive thread diameter;
Too small thread diameter;
Surface roughness of threads is too high.

CNC machining aluminum workpiece

What cause the tapping problems happen in machining work?

1) Tap breakage

The diameter of the bottom hole is small and the chip removal is not good, which results in chip blockage; the depth of the drill hole is not enough when the thread can not be tapped; the cutting speed is too high and too fast when tapping thread; the diameter of the tap used for tapping thread is different from that of the bottom hole of thread; the selection of the grinding parameters of the tap is inappropriate, and the hardness of the workpiece is unstable; the tap is used for too long and wears excessively.

2) Tap thread broken

The front angle of the tap is too large; the cutting thickness of each tooth of the tap is too large; the quenching hardness of the tap is too high; the tap is used for too long and wears seriously.

3) Tap wears too fast

When tapping threads, the cutting speed is too high; the parameters of tap grinding are not appropriate; the cutting fluid is not selected properly and the cutting fluid is not enough; the material hardness of the workpiece is too high; the burns occur when tap grinding.

4) Excessive thread diameter

Improper selection of taper diameter accuracy grade; unreasonable cutting choice; too high cutting speed of tapping thread; poor coaxiality between taper and workpiece thread bottom hole; inappropriate selection of taper grinding parameters; burrs in tap grinding and too short length of tap cutting taper.

5) Thread diameter too small

Improper selection of taper diameter accuracy grade, unreasonable selection of taper grinding parameters, taper wear, and inappropriate selection of cutting fluid.

6) Excessive Surface Roughness of Thread

The selection of grinding parameters of tap is not appropriate; the hardness of workpiece material is too low; the grinding quality of tap is not good; the selection of cutting fluid is unreasonable; the cutting speed is too high when tapping threads; the use time of tap is too long and the wear is too large.

How to solve the tapping problems in machining process?

1) Choose the diameter of the bottom hole of the thread correctly when the tap breaks; the inclination angle of the edge grinding or the selection of spiral groove tap; the depth of the bottom hole should meet the specified standard; reduce the cutting speed appropriately and select according to the standard; correct the tap and the bottom hole when tapping the thread to ensure that its coaxiality meets the requirements, and select floating tapping chuck; increase the front angle of the tap to shorten the length of the cutting taper; and ensure the workpiece. Hardness meets the requirements and safety chuck is selected.

2) The breaking teeth of the tap should be reduced properly; the length of the cutting taper should be increased properly; the hardness should be reduced and the tap should be replaced in time.

3) Too fast wear of the tap reduces the cutting speed properly; reduces the front angle of the tap, lengthens the length of the cutting taper; chooses the cutting fluid with good lubricity; carries on the appropriate heat treatment to the processed parts; correctly grinds the tap.

steel machined part

4) Choose the taper diameter of the reasonable precision grade when the thread diameter exceeds the general one; Choose the appropriate cutting fluid and reduce the cutting speed properly; Correct the coaxiality of the taper and the bottom hole of the thread when tapping the thread, adopt the floating chuck; Reduce the front angle and the rear angle of the cutting taper properly; Clean the burr produced by the grinding taper of the edge, and increase the cutting taper length appropriately.

5) Choose the appropriate taper diameter with small thread diameter; properly increase the front angle and cutting taper angle of the taper; replace the worn taper; select the cutting fluid with good lubricity.

6) Excessive surface roughness of threads properly enlarges the front angle of the tap and reduces the cutting cone angle; heat treatment is carried out to properly increase the hardness of the workpiece to ensure that the front face of the tap has a lower surface roughness value and select a lubricating cutting fluid; cutting speed is properly reduced; and worn taps are replaced.

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SCREW THREAD KNOWLEDGE

KYLT Precision CNC Machining — Sat, 12 Oct 2019 00:03:04 +0000

In machining process, tapping method normally used to making screw thread for machined workpiece. So, as a machining operator, who should got more knowledge about screw thread making.

Screw thread Shape (standard metric thread)

screw thread shape

1.From the picture, we can see that:

P indicates that the pitch is the distance from the tooth to the cusp or the base of the tooth.

Usually the expression is M3 x 0.5, which is pitch in mm.

(M stands for Metric system) and 3 stands for nominal size. The so-called size is the maximum diameter of the screw teeth or the maximum diameter of the internal thread.

2.General standard screw teeth, large diameter (or root diameter) must conform to the nominal size of the screw teeth, while the diameter (internal thread is the same) and small diameter (internal thread is called internal diameter) must conform to the figures found in the specifications as follows (metric standard rough thread).

screw thread Comparison table

screw Thread control table

If it is a fine thread, the clearance will become smaller, and its large, medium and small diameter will change accordingly.

3.British thread are the same, but the pitch is expressed by the number of teeth in an inch, such as: 1/4-20UNC, that is, the outer thread 1/4 “big diameter (6.35mm) has 20 teeth per inch.