Analysis of clamp thread machining technology

Clamp thread processing is one of the basic operating skills that pliers need to master, including tapping threads (commonly known as tapping) and sets of threads (commonly known as sets of threads). The use of taps to process internal threads known as tapping threads; the use of plate teeth set of external threads that is for the set of threads. 

Although the technology is not complex, but in practice, often due to the operation is not standardized, unreasonable, resulting in threads incorrect, rotten teeth, messy buckle and even tap chipped or broken and other issues, so the following thread processing technology has been analyzed and discussed.

Tapping thread operation technology analysis

1. Threading tools

Tap is a tool for tapping threads, the types of organic taps, hand taps and pipe thread taps and so on.

Processing ordinary triangle thread with machine tap and hand tap. A set of machine taps has one tap, and a set of hand taps has 2-3 taps.

Usually, there are two taps in each set of M6-24, and three taps in each set of M6 or M24 or above.

Small tap strength is small, easy to break, so the use of a set of three, and three of the large, medium and small diameter of the same (taper distribution of cutting load), the head of the cone chipped teeth, broken after the two cones or three cones can be regraded into the head of the cone to use.

Large tap tapping laborious, so cutting needs to be divided into several times to complete, and the head taper, two taper of large, medium and small diameter are smaller than the three taper (columnar distribution of cutting load), the work of the load distribution is reasonable, the operation of labor-saving.

Reamer is a tool for clamping taps, divided into two types: ordinary type and D type, each of which is divided into two forms: fixed type and adjustable type.

M5 below adopts fixed ordinary reamer, the length of its handle corresponds to the specification of the thread, the operating force is reasonable, and it is not easy to break the tap.

The adjustable reamer is used for taps above M5, and a reamer with a suitable handle length should be selected according to the size of the tap.

When tapping next to the workpiece steps or inside the box, use the D-type reamer to avoid the workpiece during operation.

2. Determination of the bottom hole of the thread

During the cutting and extrusion tapping process, the greater the plasticity of the material, the more likely it is to be pushed toward the tip of the threaded part.

If the diameter of the threaded hole is the same as the minor diameter of the thread, there will be no gap between the thread crest and the root of the tap teeth, causing the tap to be squeezed by the metal, jammed, and even broken.

Therefore, the extrusion deformation of the material should be considered when tapping, and the diameter of the drilled bottom hole should be appropriately increased to ensure the proper size of the threaded hole.

This can generally be determined by looking up the relevant manuals or by empirical formulas. For plastic materials, D bottom hole = D – P; and brittle materials, D bottom hole = D – (1.05 ~ 1.1) P. Where D bottom hole for the diameter of the bottom hole, D for the thread diameter, P for the pitch of the thread, the unit is mm.

Blind hole tapping, because the cutting part of the tapping can not be complete thread, so the depth of the hole should be greater than the effective depth of the thread, according to the H drilling = h effective + 0.7D selection.

Where H drill hole is the depth of the bottom hole, h effective for the effective depth of the thread D for the thread diameter, unit are mm.

3. Operating methods for tapping threads

There are two methods for tapping threads: hand tapping and machine tapping. Hand tapping is more difficult, relying on both hands to control the center line of the tap and the center line of the threaded hole when tapping, which is easy to produce skew and swing, so the clamping of the workpiece before tapping is very important.

Place the side to be tapped in a horizontal or vertical position, so that it is easy to observe and judge whether the tap is perpendicular to the plane of the workpiece.

In order to make the tap easy to locate and cut into the bottom hole, the hole should be chamfered and the depth of the chamfer should be greater than the pitch of the thread.

3.1 Initial Tapping and Alignment

When starting to attack, put the tap, one hand presses the top of the reaming bar, and presses hard along the axial direction of the tap, and the other hand turns the reaming bar gently.

Tap into 1 ~ 2 turns or so, should be orthogonal to the two directions to observe whether the tap is perpendicular to the plane of the workpiece, if necessary, the use of 90 ° angle ruler for correction.

General tap into 3 ~ 4 turns, the tap direction is basically determined; if the direction is not correct, you can spin out the head cone, the use of two cones for correction, and then tapping with the head cone.

When the tap cutting part of all into the bottom hole, do not apply axial force to the tap, should be two-handed smooth rotation of the reamer.

3.2 Key Considerations for Starting Tapping

Start tapping stage is the key point and difficult, for larger thread diameter can choose glossy nut or special sample plate for correction (as shown in Figure 1 (a), (b));

For small workpiece inconvenience clamping, it is not easy to correct the taper perpendicularity, this time can be used to assist the tapping fixture tapping (shown in Figure 1 (c)) [2].

3.3 Swarf Removal and Tapping Speed Control

During the tapping process, each time the reamer is rotated 12~1 rounds M5, the following taps should not be rotated more than 12 rounds each time), it should be reversed 1/4~112 rounds in order to cut off and remove the swarf, to avoid swarf clogging, resulting in damage to the taps and breakage.

When tapping deep hole threads, the reversal stroke should be larger, and should be repeated several times.

The speed of reamer rotation should be adapted to the material to be tapped, brittle material such as cast money can be faster than plastic material (such as steel).

3.4 Balanced Force and Handling Resistance

The strength of both hands turning the reamer should be balanced, avoid excessive force and shaking. .

In the event of resistance is large, not strong trigger, should be reversed first chip, and then continue to tap; or switch to the second cone tapping a few rounds, reduce the load and then use the head taper tapping.

When you hear the tap and metal friction “cluck, cluck” sound, you should immediately stop tapping, and invert the tap, check the reason, otherwise continue to tap the tap may break.

3.5 Transitioning Between Taps

The first tap is tapped, change to the next tap, the hand should be screwed into the turn, and then use the reamer operation, this is to prevent the back of the tap in the absence of alignment of the front threads, due to improper force and chaotic buckle.

When the end tap is tapped and the tap is withdrawn, the reamer is first used to rotate smoothly in the reverse direction, and when the tap can be rotated by hand, the reamer is stopped to prevent the reamer from driving the tap out of the tap, which will produce swinging, vibration and damage the surface roughness of the threads that have already been processed.

3.6 Special Considerations for Blind and Through-Hole Tapping

When tapping blind hole threads, mark the depth on the tap and exit the tap frequently to remove chips from the hole to prevent chips from clogging the effective thread depth. The chips should be removed thoroughly after tapping.

When tapping through-hole threads, the calibrated part should not be all out of the head to avoid damaging the last few threads.

To facilitate chip removal, for through-hole threads, use a special left-hand fluted tap (chips are discharged downward); and for blind-hole threads, use a right-hand fluted tap (chips are discharged upward).

3.7 Cutting Fluid Selection for Improved Tapping Performance

In order to improve cutting performance and thread accuracy, appropriate cutting fluid should be selected according to the nature of the material, so as to reduce cutting resistance, reduce the surface roughness of the screw hole, and prolong the life of the tap.

Generally, the composite cutting fluid containing both oily agent and extreme pressure agent should be used.

Set of thread operation technology analysis

1. Tools for Threading

Set of threads of the tool plate teeth is a set of threads of the tool, types of round plate teeth, square plate teeth and live tube plate teeth, etc. Plate teeth on both sides of the cutting part, one side of the wear and tear, can be changed to use the other side. Plate tooth outer circle has 4 cone pit and a deep groove.

The center line of 2 cone pits through the center of the plate teeth, used to locate and fix the plate teeth; the other 2 cone pits center line does not pass through the center of the plate teeth, when the plate teeth are worn, sawing through the deep groove can be used to tighten the plate teeth of the 2 cone pits, so that the diameter of the threads become smaller, so that the plate teeth can continue to be used.

Plate rack is a tool for clamping plate teeth, there are three kinds of round plate teeth rack, adjustable plate teeth rack and pipe plate teeth rack.

2. Determination of the diameter of the round bar before threading

The same as tapping threads, plate threads set when there is extrusion, so the diameter of the round bar should be smaller than the thread diameter, the size of the manual or according to the empirical formula to determine.

The formula is d rod = d-0.13P, where d rod is the diameter of the rod, d is the diameter of the thread, P is the pitch, the unit is mm.

3. Threading operation method

3.1 Chamfering and Cleaning Before Threading

In order to facilitate the plate teeth cut into the workpiece, the end of the round rod should be chamfered before the set of threads, and the diameter of the chamfer should be smaller than the small diameter of the thread. Clean up the chip groove of the plate teeth and the cutting eyebrow inside the thread.

3.2 Proper Clamping for Stability

Cutting torque is large when setting thread, round rod workpiece should use hardwood V-shaped clamping block or thick copper plate liner clamping fixed in order to firmly clamp.

3.3 Initial Threading and Alignment Check

The method of starting the set is the same as that of tapping, use one hand to hold down the center of the plate tooth frame and apply axial pressure, and the other hand to cooperate with the light turn, while observing the end face of the plate tooth and the axis of the round rod is perpendicular.

In the plate teeth into 2 ~ 3 turns, check the plate teeth and round rod is coaxial, found skewed timely correction, otherwise cut out the threaded teeth deep side of the shallow side, or even appear messy teeth.

3.4 Natural Introduction and Chip Breaking

Cut into 4 circles, no longer apply axial force, let the plate tooth natural introduction, so as not to damage the plate tooth and has been processed thread, and should be often reversed to break the chip.

3.5 Use of Cutting Fluid

Sleeving should be added when the cutting fluid, generally can be added to the thick emulsion or oil.

3.6 Improving Thread Accuracy with Guide Sleeves

When the need to improve the accuracy of the thread, the plate tooth frame can be added guide sleeve!

Conclusion

Clamp work type to manual operation, the use of various tools to complete the processing of parts, assembly and repair work. The level of its skills lies in the standardization and rationality of the operation, which mainly depends on the correct understanding and grasp of the basic theory.