GOST 6951-71 nut taps with bent shank. design and dimensions (as amended n 1, 2, as amended)

Photo of taps for threading

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Mtsh M 3 GOST Sh1-11 (Modified edition, Amendment, No. 2).

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An example of a symbol for a tap with a nominal thread diameter (/ = 3/8 ″, length 1 = 165 mm, degree of accuracy O, right:

Met Zh1U D GOS1051-11

Same, left:

Mtik SHJ D GOS! 05I1 (Modified edition, Amendment, No. 1),

3. Center holes - form A according to GOST 14034-74.

Taps with a diameter of up to 8 mm are allowed to be made with external centers.

4 By agreement with the consumer, it is allowed to manufacture taps with stepless shanks.

5. Tolerances on the thread of the taps:

metric thread according to GOST 16925-71

inch "according to GOST 7250-60.

6. At the request of the consumer, it is allowed to manufacture taps with other front and back angles.

7. The number of teeth and the dimensions of the profile of the chip grooves are indicated in Appendix 1 to GOST 3266-81.

8. (Deleted, Amendment No. 2).

9. Recommendations on the applicability of taps on automatic machines are indicated in the appendix.

10. Technical requirements - according to GOST 3449-71.

ANNEX to GOST 6951-71 Reference

RECOMMENDATIONS FOR APPLICATION OF TAPERS IN NUT-CUTTING MACHINES

(Modified edition, Amendment No. 1)

Editor V. N. Shalaeva Technical editor E. V. Mityai Proofreader M. M * Gerasimenko

Rented at nab. 07.05 84 Go to print. 09/27/84 0.75 p l. 0.75 uel cr -ott 0.58 uch * ed l.

Circulation 8000 Price 3 kopecks

Order "Badge of Honor" Standards Publishing House, 123840, Moscow, GSP,

Novopresnensky per., 3

Vilnius Printing House of Standards Publishing House, 12/14 Mindaugo str. Zac 2693

Varieties and labeling

Industrial enterprises produce many varieties of nut taps, which have their own design features and operational capabilities. According to the design features, the following types of tools are distinguished.

Chip and groove. The tap has a shortened length, in other words it is called a flute. Its design features facilitate threading in objects made of tough low carbon steel, aluminum alloy, or high strength alloy steel.

By the type of thread produced, nut taps are divided into these types.

• Metric. This tool is used to cut a metric type of thread. As a result of the work, elements with the shape of a triangle are obtained. The marking of such parts has the letter "M". To select a tap for a specific diameter, experts advise using a specific table.
• The inch tool is characterized by the tapered shape of the working part. For this tap, the unit of measure for diameter is inch.
• Pipe.This type of tool can be in the form of a cylinder and a cone. This kind of device is usually used to form pipe threads.

The production of elongated and other nut taps that operate on manual or machine control is regulated by GOST 3266-81. Products with a bent shank must be manufactured strictly in accordance with the specially issued GOST 6951-71. The type and size of the thread begins the marking of the fixtures, for example, M6, M8, M4, M5, M3, M2. After these designations, you can see the accuracy class according to ISO2 or DIN. Also, the mark of the material may be present in the marking of the tap.

If the tool has the HSS designation, it means that it is made of hardened steel. On the tail section of the nut tap, you can see information about the thread run, the angle of inclination of the grooves, the pitch of the spiral grooves, the rotation of the grooves, the group of application, internal cooling.

Preparing for internal threading

In order for the thread to cut without problems, the hole must be carefully prepared.

The drill must be suitable for the material of the part, correctly and well sharpened. The sharpening angle should be no more than 140 °. This avoids overheating and unintentional heat treatment of the material of the part, leading to a deterioration in the quality of the thread.

The drill must be carefully secured, it is necessary to exclude the beating of both the drill in the chuck and the chuck itself.

When drilling blind holes, you need to carefully control the depth and be sure to give a depth allowance relative to a given cutting depth - even the best tap will not cut the thread to the end.

You will need the following tools and accessories:

• Low speed drilling machine. The use of hand drills is not recommended.
• Drill selected from the table.
• Larger diameter drill (about twice) for countersinking.
• A set of taps with a knob.
• Vise for fixing the part.
• Kern and hammer.
• Mineral oil for lubrication of the tap and hole during operation.
• Wiping material.

The rules for cutting pipe threads generally coincide with the above, only for cutting large diameters, special equipment is used for more accurate centering

Design features

The first tools for cutting internal threads were distinguished by a primitive design and consisted of a tetrahedral rod, at the working end of which, sharpened under a gentle cone, cutting teeth were sawn out. When using such a tap, the thread was cut by screwing it into the inside of the nut or into a previously prepared hole in the workpiece. Naturally, such a tool had many disadvantages, the most significant of which should be attributed to the absence of the back surface on the cutting part, as well as the negative value of the rake angle. Over time, the design of taps has become more sophisticated, and today they allow you to create accurate, high-quality internal threads.

Any tap for threading on the inner surfaces of the workpiece, regardless of its geometric parameters and purpose, has the following elements:

• side grooves (there can be from 2 to 6);
• conical intake part;
• a calibrating part that has a cylindrical shape.

Tap design

The grooves located on the lateral surface of the tool, along its entire length, simultaneously perform two functions: ensuring the removal of chips from the processing zone and facilitating the supply of a cooling lubricant (coolant) to such a zone. The shape that the tap groove has in cross-section is determined by its two surfaces, one of which is the front face of the cutting tooth of the tool, and the second is its back. By the type of profile, chip grooves are of the following types:

• single-radius (with grooves of this shape, mainly taps of the calibration type are produced);
• with straight front and back surfaces (tools with grooves of this shape are used to cut threads inside the nuts);
• with straight leading and radial flanks (most taps are produced with this type of flute).

Tap Chip Profiles

The grooves can be located in different ways: there are rectilinear, as well as spiral, right or left. With straight grooves, general purpose universal taps are produced. With helical left-hand flutes, taps are produced which are used to cut threads on the pass. The chips generated by such a tool move in front of it along the hole being machined, thereby eliminating the risk of damage to the already cut thread. When using taps with the right-hand direction of the flute, the chips are led out of the machining zone to the tool shank. For this reason, right-hand taps are ideal for tapping blind holes.

The intake part of the tap, as mentioned above, has a conical shape, which makes it easier for the tool to enter the hole to be machined. The specific value of the angle of inclination of the intake part, which can be in the range of 3–20 °, is chosen depending on what type of processing the tool will be used for - roughing, intermediate or finishing.

Tap designs in accordance with GOST

The cylindrical sizing part is performed with a reverse understatement of up to 0.1 mm, which is necessary in order to reduce the frictional forces arising in the process of threading. To reduce the friction force between the working part of the tap and the surface to be machined, the backing of the rear surface of the cutting teeth, performed from their top by 1/3 of their width, also allows the relief of the back surface of the cutting teeth. Thus, an underestimation of the rear surface of the cutting teeth is created, the value of which for tools with a diameter of 12–30 mm is about 0.1 mm.

Geometry of the cutting and calibrating part of the tap

Types by appointment

Modern industry produces various types of taps, which differ from each other in design and functionality. So, according to their purpose, taps can be one of the following types.

Locksmiths

These tools are most often hand-held and are used in combination with a special wrench, with which the tap is imparted to rotation. As a rule, they are produced and used in sets consisting of two or three tools, each of which removes only a part of the allowance from the treated surface. The dimensions of the taps included in such a set (in particular, their working diameters) differ. The first of the tools, the shank of which is marked with a single dash, is used for roughing, the second (with two dashes on the shank) for intermediate, and the third (respectively, with three dashes) for finishing the cut thread.

Complete hand taps

Machine or machine-hand

These are tools with which the thread can be cut both manually and on machines of various types (turning, drilling, modular, etc.). Such taps differ from locksmiths only in a slightly shortened intake part and a higher resistance to mechanical stress.

Machine-hand taps triple

Nut

With the help of such tools, as their name implies, they perform threading in nuts. Nuts, in which a thread has already been cut with such a tap, do not twist from the tool, but move to its elongated tail. The shanks of the nut taps, with the help of which the thread is cut on drilling machines, have a straight shape. Nuts with already threaded threads, moved to such a shank, are simply shaken off from it after removing the tool from the chuck of the machine.To cut nuts on threading machines, taps are used, the shanks of which have a curved shape. When threading in this way, the nuts, under the pressure of each other, are pushed along the curved shank of the tool, reach its end part and fall into the prepared container.

Tapping with a Nut Tap

Requirements for the design and dimensions of both hand and machine taps for cutting metric threads are stipulated by GOST 3266-81, which is called: “Machine and hand taps. Design and dimensions ".

GOST 3266-81 Machine and hand taps. Design and dimensions

How to unscrew a broken tap

If you nevertheless violated the recommendations and broke the tap, do not despair. Despite the fact that it is almost impossible to drill a broken tap - its strength is higher than that of a conventional drill, there are ways to save the situation.

Extractor. For taps, a special extractor is used with hardened curved thin pins, which are inserted into the grooves at one end, and are clamped at the other in a special cylindrical mandrel

By gently turning the mandrel with a wrench, you can unscrew the damaged tool.
Spot welding. An L-shaped rod is welded to the fragment, for which the structure is unscrewed with pliers.
Acid etching

An acid is selected that acts more strongly on the material of the tap than on the material of the part. The method is dangerous and not recommended for use in home workshops.
Electrospark method. A minus is applied to the part, and the positive electrode of contact welding gently touches the fragment. In the course of an electric spark discharge, it loses the smallest particles of metal in the form of incandescent splashes. After several discharges, as a rule, the jamming disappears, and the fragment can be unscrewed.

But the best way is not to break the tap at all.

Design features

First, the internal thread was cut with simple devices in the form of a tetrahedral rod sharpened under a cone. At the conical end, cutting teeth were sawn out, which, when the rod was screwed into the hole, were scratched in it with a thread. With further improvements, the tap has a positive rake angle, chip ejection grooves and better edge-to-thread matching.

Tap device

In a modern tap, the following required structural elements are present:

• The head (or intake) part in the form of a gentle cone, which serves to start the formation of the thread profile.
• A certain number (2-6) of lateral grooves providing chip evacuation and lubricant (coolant) supply.
• Calibrating part, in the form of an elongated cylinder, completing the precise shaping of the profile.
• Shank used to fix the tap in the chuck or gate clamping device.

A distinction is made between the following types of chip grooves:

• Single radius - the cross section is an arc of a circle, used on calibration tools.
• Straight - U-shaped cross-section, used for threading nut threads.
• Mixed - straight anterior and arcuate posterior. This is how most of the general-purpose tool is made.

Varieties of tap grooves

In addition, the grooves are divided into:

• Straightforward. Used in a universal tool.
• Left spiral. Left-handed is used for threading on the passage. The chips are pushed into the space in front of the tap, thus protecting the already formed profile from damage.
• Right spiral. Right-handed taps are provided for cutting blind holes, with such grooves the chips are pushed out and do not clog the hole.

The conical shape of the head part facilitates the centering of the tap in the hole and the entry into the threading of the first threads. The taper angle varies between 3 ° and 20 °, the specific value is determined based on the purpose of the tool - roughing, intermediate or finishing.

The cylindrical part is actually a reverse taper with a very small taper angle. The understatement reaches 0.1 mm, which allows to reduce friction during cutting.

Main tap sizes:

• thread pitch;
• profile height;
• full profile height;
• outer thread diameter;
• intake length;
• intake cone angle;
• the amount of relief.

In addition, the tools are divided into left-hand and right-hand taps.

APPENDIX 4 (reference). POSSIBLE DEFECTS WHEN EXPRESSING THE THREAD WITH STRIPLESS TAPERS AND METHODS FOR THEIR ELIMINATION

APPENDIX 4 Reference

If something went wrong or what to do with a broken tap

The tap, like any other tool, does not last forever and is subject to natural wear and tear. To prevent this from happening ahead of time, the above recommendations should be followed. The most common reasons leading to a breakdown:

• Skew.
• Hole too small.
• Excessive effort on the crank.
• Failure to comply with the reverse half-turn rule after each full turn of the crank.

Broken tap

There is no need to rush, try to run the thread as quickly as possible, or try to skip the tap from the set. All this will result in a large loss of time when removing a broken tool and when re-threading.

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An example of a symbol for a tap with a nominal thread diameter (M2 mm, pitch P = 1.5 mm, length 1 = 250 mm, accuracy class 3, right-hand: