What kind of drill is needed to cut a thread m6

drill, needed, thread

Download the table “Drill diameter for metric thread”

Trapezoidal thread Tr
Tr 8×1.5 6.6 Tr 14×3 11.25
Tr 10×1.5 8.6 Tr 14×4 10.25
Tr 10×2 8.2 Tr 16×4 12.25
Tr 10×3 7.5 Tr 18×4 14.25
Tr 12×2 10.2 Tr 20×4 16.25
Tr 12×3 9.25 Tr 22×3 19.25
Tr 14×2 12.2 Tr 22×5 17.25

To tap an internal thread, you first need to drill a hole of a certain diameter. The table shows the most popular threads and drill diameters required for drilling thread holes.

How to find which drill bit without a table ?

Suppose you want to cut a thread M10x1.5.

  • Find out the nominal thread diameter: 10 mm.
  • Find out the nominal thread pitch: 1.5 mm
  • Subtract the second from the first value: 10-1.5 = 8.5 mm
  • Result. 8.5 mm !

Having mastered this method, you can easily and simply choose the right drill for tapping.

How to use the filter on the website to select a drill for a thread ?

In the Drills for metal section, a filter with the “For thread” parameter has been implemented, thanks to which you can find the required drill in just 2 mouse clicks:

  • Choosing a thread.
  • Click “Apply”.
  • We get the right drills.

For which materials the values ​​are indicated in the table ?

The specified hole diameters are suitable for cutting metric threads in:

  • gray cast iron
  • carbon steels of ordinary quality
  • quality structural steels
  • structural alloy steels
  • high-alloy steels
  • corrosion-resistant, heat-resistant and heat-resistant alloys
  • heat-resistant steels
  • aluminum casting alloys
  • copper

A complete list of threads and diameters can be found in GOST 19257-73. an official technical document with all the nuances and details.

Before starting work, we recommend taking a look at the practical advice in the article How to properly tap a thread. There you can also find the right coolant for different materials.

Drill diameters for metric (M) threads

And there is also a pipe (read about pipe dies). Well, in this article we will analyze all the nuances of cutting metric threads and, of course, we will learn how to calculate the diameter of a drill for a thread.

drill, needed, thread

So, as I said, we take the diameter and step as the basis for calculations. Just subtract the thread pitch from the diameter and the resulting figure will be the diameter of the required drill. Let’s calculate the diameter of the drill for the M8 thread (standard).

8 minus 1.25 (standard pitch) we get 6.75 mm. this is the drill you need to cut the M8 thread. And for example, thread 81. the drill will turn out to be 7 mm in diameter.

I hope everything is clear. I will also provide you with the necessary plate of standard threads (that is, you can find out which pitch is standard for a certain diameter) and the diameter of the drills for them.

Standard thread table and drill diameter for them.

thread diameter thread pitch drill for thread
M2 0.45 1.5 mm
M3 0.5 2.5 mm
М4 0.7 3.3 mm
M5 0.8 4.2 mm
M6 one 5 mm
M7 one 6 mm
М8 1.25 6.7-6.8
M9 1.25 7.7-7.8
M10 1.5 8.5
M11 1.5 9.5
M12 1.75 10.2-10.3
M14 2 12 mm
М16 2 14 mm
M18 2.5 15.5
M20 2.5 17.5
M22 2.5 19.5
M24 3 21
M27 3 24 mm
M30 3.5 26.5
M33 3.5 29.5
M36 four 32 mm

In addition to the standard thread, there are steps 0.75 (for small threads up to M10), 1 mm, 1.25 mm, 2 mm (for large taps and dies).

I hope this article helped you independently calculate the required drill diameter for the thread to be cut.

How to Use & Install Helicoil Thread Inserts | Fasteners 101

drill, needed, thread

By the way, do not cut the threads “dry”, but add machine or household oil. This will reduce the load on the die and make cutting much easier.

Useful table. thread diameter and pitch

Many of you have come across internal threading with a tap and many have a question. what diameter should be a drill for threading, for example, M8 or M10. Indeed, when threading, the initial task is to drill a hole of a suitable diameter so that the tap does not cut the metal too tightly and at the same time does not dangle. Therefore, I will tell you how you can calculate the correct drill diameter for any metric thread yourself.

In fact, everything is simple, as you know, there are only 2 thread parameters: diameter and pitch. You can also notice (for those who do not know) that the thread is standard (with a standard pitch) and any other. For example, the standard thread for 10mm is 1.5mm, which is M101.5. But you see quite often threads 101.25 and 101. The letter M on the thread means that the thread is metric.

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Hole diameter (drill) for thread

For threaded connections, metric threads are most often used. In addition to metric threads, there are still quite a few different types of threads, we will not dwell on them.

The internal thread is cut with taps. Tap is a metal-cutting tool for cutting internal threads in pre-drilled holes. There are hand and machine taps. When cutting deep threads, a set of two or three taps is usually used: the first tap pre-cuts a rough thread, the second cuts a full thread, and in the case of a third sword, the thread is calibrated.

Correct selection of thread hole diameters is of great importance. If the hole diameter is larger than it should, then the internal thread will not have a full profile. the connection will be fragile. If the diameter is less than the required one, it is difficult to enter the tap into it, this leads to the breakdown of the first turns of the thread or, in the worst case, to jamming and breakage of the tap.

The first column of the following table shows metric threads from M2 to M48. The second column shows the coarse pitch applied for each metric thread. Whenever possible, you should adhere to these pitch values ​​when threading. The third column shows the diameters of the hole (drill) for metric threads with a large pitch. In some exceptional cases, it is necessary to use a smaller pitch.The diameters of holes for a fine pitch are presented in the following columns of the table.

Thread diameter Step (standard) Hole diameter (drill) Step Hole Step Hole
M2 0,4 1.6 0.25 1.75
M3 0.5 2.5 0.35 2.65
М4 0.7 3.3 0.5 3.5
M5 0.8 4.2 0.5 4.5
M6 1.0 5.0 0.75 5.2 0.5 5.5
M7 1.0 6.0 0.75 6.2 0.5 6.5
М8 1.25 6,7 1.0 7.0 0.75 7.2
M9 1.25 7,7 1.0 8.0 0.75 8.2
M10 1.5 8.5 1.25 8.7 1.0 9.0
M11 1.5 9.5 1.0 10.0 0.75 10.2
M12 1.75 10.2 1.5 10.5 1.25 10.7
M14 2.0 12.0 1.5 12.5 1.25 12.6
М16 2.0 14.0 1.5 14.5 1.0 15.0
M18 2.5 15.4 2.0 16.0 1.5 16.5
M20 2.5 17.4 2.0 18.0 1.5 18.5
M22 2.5 19.4 2.0 20.0 1.5 20.5
M24 3.0 20.9 2.0 22.0 1.5 22.5
M27 3.0 23.9 2.0 25.0 1.5 25.5
M30 3.5 26.4 3.0 26.9 2.0 28.0
M33 3.5 29.4 3.0 29.9 2.0 31.0
M36 4.0 31.9 3.0 32.9 2.0 34.0
M39 4.0 34.9 3.0 35.9 2.0 37.0
M42 4.5 37.4 4.0 37.9 3.0 38.9
M45 4.5 40.4 4.0 40.9 3.0 41.9
M48 5.0 42.8 4.0 43.9 3.0 44.9

GOST 19257-73: Holes for cutting metric threads.

To cut the thread M6 which hole to drill

When making threaded holes for metric bolts, screws, studs, first a hole is drilled in the material, and then a thread is cut in it using a tap. But before you start drilling, you need to choose the optimal drill diameter for the planned internal thread, using a special correspondence table. The values ​​given in it apply to cast iron, steels, aluminum alloys and copper.

If the hole size is larger than the specified one, then there is a risk of getting an insufficiently deep threaded groove and, as a result, a weakened connection. If the hole size is too small, it will be difficult to work with the tap, since there is a lot of cutting resistance, heating of the tool, adhesion of chips to the cutting edges, jamming and even breakage of the tap.

How to cut a thread on a manual lathe (Intermediate method ideal for home workshop & hobby engineer)

The table is very easy to use. To do this, it is important to know the main parameters of metric threads. these are its pitch (P) and nominal diameter (d), which are measured in fractions of a meter. The step is understood as the distance between two vertices of adjacent turns. The outer diameter of the thread is taken as the nominal diameter, which is equal to the distance between the extreme points of the outer protrusions of the helical mowing line.

Varieties and parameters of thread

The parameters by which the thread is divided into different types are:

  • diameter units (metric, inch, etc.);
  • the number of thread runs (one-, two- or three-way);
  • the shape in which the profile elements are made (triangular, rectangular, round, trapezoidal);
  • direction of lifting the turns (right or left);
  • location on the product (external or internal);
  • surface shape (cylindrical or conical);
  • purpose (fastening, fastening and sealing, running).

Depending on the above parameters, the following types of thread are distinguished:

  • cylindrical, which is designated by the letters MJ;
  • metric and conical, denoted respectively M and MK;
  • pipe, for which the letters G and R are used;
  • with a round profile, named in the Honor of Edison and marked with the letter E;
  • trapezoidal, denoted by Tr;
  • round, used for the installation of plumbing fixtures. Kr;
  • resistant and resistant reinforced, marked as S and S45, respectively;
  • inch thread, which can also be cylindrical and conical. BSW, UTS, NPT;
  • used for connecting pipes installed in oil wells.
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Table of recommended diameters of holes for thread, mm

d thread Step d drill Step d drill Step d drill Step d drill Step d drill Step d drill
2 0.4 1.6 0.25 1.75
3 0.5 2.5 0.35 2.65
four 0.7 3.3 0.5 3.5
five 0.8 4.2 0.5 4.5
6 one five 0.75 5.2 0.5 5.5
7 one 6 0.75 6.2 0.5 6.5
eight 1.25 6.7 one 7 0.75 7.2 0.5 7.5
nine 1.25 7.7 one eight 0.75 7.2 0.5 8.5
10 1.5 8.5 1.25 8.7 one nine 0.75 9.2 0.5 9.5
eleven 1.5 9.5 one 10 0.75 10.2 0.5 10.5
12 1.75 10.2 1.5 10.5 1.25 10.7 one eleven 0.75 11.2 0.5 11.5
fourteen 2 12 1.5 12.5 1.25 12.6 one 13 0.75 13.2 0.5 13.5
sixteen 2 fourteen 1.5 14.5 one fifteen 0.75 15.2 0.5 15.5
eighteen 2.5 15.4 2 sixteen 1.5 16.5 one 17 0.75 17.2 0.5 17.5
twenty 2.5 17.4 2 eighteen 1.5 18.5 one nineteen 0.75 19.2 0.5 19.5
22 2.5 19.4 2 twenty 1.5 20.5 one 21 0.75 21.2 0.5 21.5
24 3 20.8 2 22 1.5 22.5 one 23 0.75 23.2
27 3 23.9 2 25 1.5 25.5 one 26 0.75 26.2
thirty 3.5 26.4 3 26.9 2 28 1.5 28.5 one 29 0.75 29.2
33 3.5 29.4 3 29.9 2 31 1.5 31.5 one 32 0.75 32.2
36 four 31.9 3 32.9 2 34 1.5 34.5 one 35
39 four 34.9 3 35.9 2 37 1.5 37.5 one 38
42 4.5 37.4 four 37.9 3 38.9 2 34 1.5 40.5 one 41
45 4.5 40.4 four 40.9 3 41.9 2 43 1.5 43.5 one 44
48 five 42.8 four 43.9 3 44.9 2 46 1.5 46.5 one 47

It can be seen from the table that the diameter of the drill is less than the outer diameter of the thread by approximately the step size, that is:

In practice, many home craftsmen constantly use this simple formula when there is no way to refer to the table.

For example, for М10х1.5: Dholes = 10. 1.5 = 8.5 mm

This method is quite acceptable when threading is performed manually in a locksmith’s workshop. If the planned threaded connection will not be subjected to serious loads during operation, then a slight increase in the size of the hole can be allowed. In the assembly industry, where a high dimensional accuracy of the threaded profile is required, any deviations are unacceptable. The diameters of the threaded hole with the tolerance field are set by GOST 19257-73.

Despite the fact that tapping is not a complex technological operation, there are some peculiarities of preparation for this procedure. So, it is necessary to accurately determine the dimensions of the preparatory hole for threading, as well as to choose the right tool, for which special tables of diameters of drills for thread are used. For each type of thread, the appropriate tool must be used and the diameter of the preparation hole must be calculated.

The thread diameter and bore must comply with standards, otherwise the grooves will come out too small and the threaded connection will be unreliable

Tap application

Before proceeding with threading, the diameter of the preparation hole must be determined and drilled. To facilitate this task, a corresponding GOST was developed, which contains tables that allow you to accurately determine the diameter of the hole for the thread. This information makes it easy to select the drill size.

To cut a metric type thread on the inner walls of a hole made by a drill, a tap is used. a screw-shaped tool with cutting grooves, made in the form of a rod, which can have a cylindrical or conical shape. On its lateral surface there are special grooves located along its axis and dividing the working part into separate segments, which are called combs. The sharp edges of the dies are precisely the working surfaces of the tap.

To make the threads of the internal thread clean and neat, and its geometric parameters correspond to the required values, it must be cut gradually, by gradually removing thin layers of metal from the surface to be treated. That is why, for this purpose, either taps are used, the working part of which is divided along the length into sections with different geometric parameters, or sets of such tools. Single taps, the working part of which has the same geometric parameters along its entire length, are needed in cases where it is necessary to restore the parameters of an existing thread.

The minimum set, with the help of which it is possible to perform sufficiently high-quality machining of the holes for the thread, is a set consisting of two taps. roughing and finishing. The first cuts off a thin layer of metal from the walls of the hole for cutting metric threads and forms a shallow groove on them, the second not only deepens the formed groove, but also cleans it.

Varieties of thread taps and their differences

Combined two-way taps or sets of two tools are used for tapping small holes (up to 3 mm). For larger metric holes, use a combination 3-pass tool or a set of 3 taps.

To manipulate the tap, a special device is used. a knob. The main parameter of such devices, which can have a different design, is the size of the bore, which must exactly match the size of the tool shank.

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Some types of tap wrenches

When using a set of three taps, differing in both their design and geometric parameters, the sequence of their use should be strictly observed. You can distinguish them from each other both by special risks applied to the shanks, and by design features.

  • The tap used for cutting metric threads in the first place has the smallest diameter among all the tools in the set and cutting teeth, the top of which is heavily cut.
  • The second tap has a shorter nose and longer flanges. Its working diameter is intermediate between the diameters of the rest of the tools from the set.
  • The third tap, with which the metric hole is processed last, is characterized by full ridges of the cutting teeth and a diameter that must exactly match the size of the formed thread.

Taps are mainly used for tapping metric threads. Significantly less often than metric taps are used for processing the inner walls of pipes. In accordance with their purpose, they are called pipe, and they can be distinguished by the letter G, which is present in their marking.

Internal threading technology

As mentioned above, before starting work, you need to drill a hole, the diameter of which must exactly fit the thread of a certain size. It should be borne in mind: if the diameters of the holes intended for cutting metric threads are chosen incorrectly, this can lead not only to poor-quality performance, but also to the breakage of the tap.

Considering the fact that the tap, while forming the threaded grooves, not only cuts the metal, but also pushes it, the diameter of the drill for making the thread must be slightly smaller than its nominal diameter. For example, a drill for threading M3 should have a diameter of 2.5 mm, for M4. 3.3 mm, for M5 you should choose a drill with a diameter of 4.2 mm, for a M6 thread. 5 mm, M8. 6.7 mm, M10. 8.5 mm, and for M12. 10.2.

All diameters of drills for GOST threads are given in special tables. In such tables, the diameters of the drills for making threads with both standard and reduced pitch are indicated, while it should be borne in mind that holes of different diameters are drilled for these purposes. In addition, if the thread is cut in products made of brittle metals (such as cast iron), the diameter of the drill for the thread obtained from the table must be reduced by one tenth of a millimeter.

You can familiarize yourself with the GOST provisions governing the cutting of metric threads by downloading the pdf document from the link below.

The diameters of drills for metric threads can be calculated independently. From the diameter of the thread that you want to cut, you must subtract the value of its pitch. The thread pitch itself, the size of which is used when performing such calculations, can be found from special correspondence tables. In order to determine what diameter the hole needs to be made with a drill in the event that a three-way tap will be used for threading, use the following formula:

To is the diameter of the hole to be made with a drill,

Dm. the diameter of the tap, which will be used to process the drilled element.

Tapping scheme

The gates, into which the threaded tap is inserted, can have a simple design or be equipped with a ratchet. Working with such devices with instruments fixed in them should be very careful. To obtain a high-quality and clean thread, the rotation of the tap clockwise, made half a turn, must be alternated with turning it one-fourth of a turn against the thread.

Threads will cut much more easily if lubricant is used during this procedure. The role of such a lubricant when cutting threads in steel products can be played by drying oil, and when processing aluminum alloys. alcohol, turpentine or kerosene. If such technical fluids are not on hand, then ordinary machine oil can be used to lubricate the tap and the threads to be cut (however, it has a lesser effect than the substances listed above).

To find out what hole diameter is required for an M6 female thread, you can use special tables. Or you can memorize a simple formula to find out which drill you need to take for a particular internal thread:

D. h = d

For the M6 ​​thread, the most common pitch is 1 mm, but there is also a fine M6 thread with a pitch of 0.75 mm and even 0.5 mm. The thread pitch can be seen on the tap. It usually says M6x0.5, where the second digit (after the “x”) is the thread pitch. For a standard pitch of 1.0 mm, it is usually written simply M6.

Centre Drilling & Tapping a M6 Thread

Let’s calculate the drill diameter for a standard internal thread M6 with a step of 1 mm using the formula: