How to cut threads | Do it yourself
When repairing furniture and various household items, in the course of work, there is often a need to connect structural parts with the support of threaded connections. Cutting high-quality threads at home is a labor-intensive task that requires skills, but this problem can be solved.
You will need
- For work you will need: a vice, a file, taps, dies, wrenches, machine oil and desire.
Instructions
1. A thread is essentially a helical groove cut on the outer or inner cylindrical surface. It is mainly used to connect different parts to each other. In mechanical engineering it can be used to transform translational motion into rotational motion and vice versa.
There are two types of threads, such as metric, with a profile angle of 60o and pipe with an angle of 55o. In metric thread, the diameter and pitch of the thread are measured in millimeters. When designating metric threads, alphabetic and numerical markings are used, say M8x1.5. The number eight corresponds to the thread diameter, and 1.5 indicates the thread pitch, the distance between the turns.
In inch threads, measurements are taken in inches and number of threads per inch. One inch is equal to 2.54 cm. For example, an inch thread is written as 1 1/4″.
2. In order to cut an external thread, you need to take a die of the required size and prepare a workpiece, and in particular, select a workpiece of a certain diameter. The diameter of the workpiece for thread cutting is determined according to the tables.
In practice, to cut, say, a thread with a diameter of M6, you need a rod with a cross-section of 5.92 mm, that is, about one tenth of a millimeter smaller; for an M8 thread, the workpiece must have a diameter of 7.9 mm.
Here, as an example, is an extract from the table of rod diameters for metric threads: Thread diameter/rod diameter (mm) – 5/4.92; 6/5.92; 8/7.9; 10/9.9; 12/11.88; 16/15.88; 20/19.86; 24/23.86After selecting the workpiece, it is clamped in a vice, a file is used to chamfer the end to ensure positive engagement of the die, and the thread is cut using rotational-pressing movements, not forgetting to lubricate the part with machine oil.
3. The internal thread is cut with a tap. Pre-drilled holes must be smaller than the diameter of the thread you need. An extract from the table of drill diameters for drilling holes is given below.
Thread diameter/hole diameter (mm) – 2/1.6; 3/2.5; 4/3.3; 5/4.2; 6/5.0; 8/6.7; 10/8.4; 12/10.2; 16/13.9; 20/17.4; 24/20.9 To cut threads inside a part, you need to have two taps, roughing and finishing.
We also clamp the part into a cleat and, using rotational movements and slight pressure, cut the thread with a rough tap, periodically lubricating the tap with machine oil, after which we make a finishing pass. The thread is ready for use.
Tip 2: How to cut internal threads
Many years ago, when the era of fasteners was just beginning, the production of nuts was a task only possible for a highly qualified craftsman. Today, internal thread cutting is a routine operation. However, to perform it well, you need to have certain skills and abilities.
You will need
- Electric drill, set of drills and taps, thread gauge, caliper, table of metric thread sizes.
how to cut a thread with a tap
Threaded connections are used everywhere; there is not a single mechanism that does not have such a connection. Starting from an airplane and ending with a mobile phone - everywhere there are connections with bolts, nuts and screws, and where there are bolts there are threads. Sometimes there is a need to cut the thread yourself. If buying bolts and screws with different threads is not a problem, cutting threads inside a part is by no means an easy task.
What is a carving made of, a tool for cutting threads.
The tool for cutting internal threads is called a tap. Taps are made from special high-speed steel PM5. Taps are hardened in a special way; do not purchase Chinese taps or taps from unverified manufacturers - the steel may be soft.
Such a tool can and will cut threads in plastic, wood or PCB, it may be possible to cut threads in copper and aluminum, but it will break the first time you try to cut threads in metal.
What diameter to drill a hole for the thread.
To cut threads simply and effortlessly, you need to drill the hole correctly. If you take a drill that is too small, cutting threads will be problematic, the tool may jam, or even break, especially when cutting threads in hard steels and cast irons.
If you drill a hole that is too large, the tap will not cut a sufficient depth of turns, as a result the screw will not hold well in the part, and the connection will not be strong.
How to properly cut a thread with a tap.
To cut high-quality threads, two or even three taps are often used. The first tap is used to cut a rough thread, the second tap is used to make a finishing thread, and the third tap is usually used to “calibrate” the thread (used for more precise threads).
To properly cut threads in a part, you need to take tap No. 1. The tap is pre-lubricated with machine oil. Holding the tool perpendicular to the surface, gradually twist it inward. After twisting the tap one turn, make a half turn back, this is done so that metal shavings do not clog the tap.
After the thread is cut, clean the part from chips and debris, and if necessary, drive the thread with a No. 2 tap.
General rules for counting threads.
To calculate the diameter of a threaded hole, you can use the following formula:
Tap hole = Thread diameter – thread pitch.
Explanation: a thread has two parameters, the first is the thread pitch, the second is the thread diameter. If you have a tap with the designation M8x1, then this means that the tap has a metric thread (this is indicated by the letter M), 8 is the nominal diameter, 1 is the thread pitch.
Example: You need to cut an M8 thread with a pitch of 1.25. According to the formula, we make the calculation: Hole for the tap = 8 – 1.25 = 6.75. We drill a hole with a 6.7 drill bit if the tap is new, or 6.8 if the tap is old.
M4 threaded hole
Let's say you need to cut a thread for M4 in increments of 1 and 1.25. Let's do the calculation:
Thread hole diameter M4 = 4 – 1 = 3
Hole diameter for M4 thread in increments of 1.25 = 4 – 1.25 = 2.75
To cut a thread for M4, you need to drill a hole with a diameter of 3mm for threads with a pitch of 1, and 2.75mm for threads with a pitch of 1.25.
M5 threaded hole
It is often necessary to cut a thread for M5 in steps of 1. The calculation is as follows:
The diameter of the hole for the M5 thread = 5 – 1 = 4.
To cut a thread for M5 in steps of 1, you need a drill with a diameter of 4 mm.
Which hole to drill for M6 thread
The M6 thread is probably the most common in the world, so we’ll do a calculation to find out the diameter of the hole for the M6 thread. According to the formula:
M6 threaded hole pitch 1 = 6 – 1 = 5
M6 threaded hole pitch 1.25 = 6 – 1.25 = 4.75
Thus, you will need a drill with a diameter of 5 mm for a thread M6x1, and a diameter of 4.75 for a thread M6x1.25
Which hole to drill for M8 thread
The M8 thread is also quite common, so let’s do the calculation:
Thread hole diameter M8 = 8 – 1 = 7
Thread hole diameter M8x1.25 = 8 – 1.25 = 6.75
The diameter of the drill for M8 thread is 7 and 6.75 mm, respectively, for a thread pitch of 1 and 1.25.
Which hole to drill for M10 thread
Sometimes it is necessary to cut M10x1.5 and M10x1.25 threads. Let's make a calculation for these values.
Hole diameter for M10 thread pitch 1.5 = 10 – 1.5 = 8.5
Hole diameter for M10 thread pitch 1.25 = 10 – 1.25 = 8.75
Thus, according to the formula, we obtain the following values: for step 1.5 we take an 8.5mm drill, for step 1.25 we take a drill with a diameter of 8.75mm.
Which hole to drill for M12 thread
In order for the connection to be reliable and durable, a calculation will be made for the M12 thread.
Hole diameter for M12 thread pitch 1.5 = 12 – 1.5 = 10.5
Hole diameter for M12 thread pitch 1.75 = 12 – 1.75 = 10.25
We drill a hole with a 10.5 drill for a pitch of 1.5, and a 10.25 drill for a pitch of 1.75.
M16 thread hole diameter
And finally, let’s do the calculation for M16 thread with step 2.
Threaded hole M16 = 16 – 2 = 14
You need to drill with a drill with a diameter of 14.
Drill diameter for thread table.
To more accurately determine the holes for threading, you can use the table below. The table is valid for steels, aluminum, copper and their alloys. The main thread pitch is highlighted in bold in the table.
| Thread | Thread pitch | Nominal hole diameter (maximum) |
| M2 | 0,25 | 1,75–1,77 (1,81) |
| 0,4 | 1,60–1,62 (1,68) | |
| M2.5 | 0,35 | 2,15–2,17 (2,22) |
| 0,45 | 2,05–2,07 (2,13) | |
| M3 | 0,35 | 2,65–2,67 (2,72) |
| 0,5 | 2,50–2,52 (2,58) | |
| M4 | 0,5 | 3,50–3,52 (3,64) |
| 0,7 | 3,30–3,33 (3,46) | |
| M5 | 0,5 | 4,50–4,52 (4,64) |
| 0,8 | 4,2–4,23 (4,42) | |
| M6 | 0,5 | 5,50–5,52 (5,64) |
| 0,75 | 5,20–5,23 (5,42) | |
| 1,0 | 4,95–5,00 (5,21) | |
| M7 | 0,5 | 6,50–6,52 (6,64) |
| 0,75 | 6,20–6,23 (6,42) | |
| 1,0 | 5,95–6,00 (6,26) | |
| M8 | 0,5 | 7,50–7,52 (7,64) |
| 0,75 | 7,20–7,23 (7,42) | |
| 1 | 6,95–7,00 (7,21) | |
| 1,25 | 6,70–6,75 (6,96) | |
| M9 | 0,5 | 8,50–8,52 (8,64) |
| 0,75 | 8,20–8,23 (8,42) | |
| 1 | 7,95–8,00 (8,21) | |
| 1,25 | 7,70–7,75 (7,96) | |
| M10 | 0,5 | 9,50–9,52 (9,64) |
| 0,75 | 9,20–9,23 (9,42) | |
| 1 | 8,95–9,00 (9,21) | |
| 1,25 | 8,70–8,75 (8,96) | |
| 1,5 | 8,43–8,50 (8,73) | |
| M11 | 0,5 | 10,50-10–52 (10,64) |
| 0,75 | 10,20–10,23 (10,42) | |
| 1 | 9,95–10,00 (10,21) | |
| 1,5 | 9,43–9,50 (9,73) | |
| M12 | 0,5 | 11,50–11,52 (11,64) |
| 0,75 | 11,20–11,23 (11,42) | |
| 1 | 10,95–11,00 (11,21) | |
| 1,25 | 10,70–10,75 (10,96) | |
| 1,5 | 10,43–10,50 (10,73) | |
| 1,75 | 10,20–10,25 (10,56) | |
| M14 | 0,5 | 13,50–13,52 (13,64) |
| 0,75 | 13,20–13,23 (13,42) | |
| 1 | 12,95–13,00 (13,21) | |
| 1,25 | 12,70–12,75 (12,96) | |
| 1,5 | 12,43–12,50 (12,73) | |
| 2 | 11,90–11,95 (12,30) | |
| M16 | 0,5 | 15,50–15,52 (15,64) |
| 0,75 | 15,20–15,23 (15,42) | |
| 1 | 14,95–15,00 (15,26) | |
| 1,5 | 14,43–14,50 (14,73) | |
| 2 | 13,90–13,95 (14,30) | |
| M18 | 0,5 | 17,50–17,52 (17,64) |
| 0,75 | 17,20–17,23 (17,42) | |
| 1 | 16,95–17,00 (17,21) | |
| 1,5 | 16,43–16,50 (16,73) | |
| 2 | 15,90–15,95 (16,30) | |
| 2,5 | 15,35–15,40 (15,88) | |
| M20 | 0,5 | 19,50–19,52 (19,64) |
| 0,75 | 19,20–19,23 (19,42) | |
| 1 | 18,95–19,00 (19,21) | |
| 1,5 | 18,43–18,50 (18,73) | |
| 2 | 17,90–17,95 (18,3) | |
| 2,5 | 17,35–17,40 (17,88) |
Select a drill from the set as close as possible to the calculated hole diameter. For hard materials, steel and cast iron, a slight increase in the drill is allowed; for soft materials, wood, textolite, plastic, a decrease in the diameter of the drill is allowed. To make everything completely clear, watch the video on how to cut a thread with a tap by hand.
When drilling with a hand drill, remember that the hole is slightly larger due to the tool beating (the hole is broken), accordingly, choose a drill with a margin to the smaller side.
When cutting threads, do not forget to add machine oil or lubricant VD-40 or another similar one.
Take your time. It is better to cut the threads slowly and carefully.
Good luck with your thread cutting.
Source: http://prosto-pro-remont.ru/raznoe/45-narezka-rezby
Diameter of threaded drill (table)
SVERLA.info » Articles » Threaded drill diameter
The main thread pitch is highlighted in color
| Metric thread, M | |||
| Tap | Drill | Tap | Drill |
| M1.4x0.3 | 1.1 | M14x1.25 | 12.8 |
| M1.6x0.35 | 1.25 | M14x1 | 13 |
| M2x0.4 | 1.6 | M16x2 | 14 |
| M2.5x0.45 | 2.05 | M16x1.5 | 14.5 |
| M3x0.5 | 2.5 | M16x1.25 | 14.8 |
| M3.5x0.6 | 2.9 | M16x1 | 15 |
| M4x0.7 | 3.3 | M18x2.5 | 15.5 |
| M4x0.5 | 3.5 | M18x2 | 16 |
| M5x0.8 | 4.2 | M18x1.5 | 16.5 |
| M5x0.5 | 4.5 | M18x1 | 17 |
| M6x1 | 5 | M20x2.5 | 17.5 |
| M6x0.5 | 5.5 | M20x2 | 18 |
| M7x1 | 6 | M20x1.5 | 18.5 |
| M7x0.5 | 6.5 | M22x2.5 | 19.5 |
| M8x1.25 | 6.8 | M22x2 | 20 |
| M8x1 | 7 | M22x1.5 | 20.5 |
| M8x0.75 | 7.2 | M24x3 | 21 |
| M8x0.5 | 7.5 | M24x2 | 22 |
| M9x1.25 | 7.8 | M24x1.5 | 22.5 |
| M9x1 | 8 | M27x3 | 24 |
| M10x1.5 | 8.5 | M27x2 | 25 |
| M10x1.25 | 8.8 | M27x1.5 | 25.5 |
| M10x1 | 9 | M30x3.5 | 26.5 |
| M11x1.5 | 9.5 | M30x3 | 27 |
| M11x1.25 | 9.8 | M30x2 | 28 |
| M11x1 | 10 | M30x1.5 | 28.5 |
| M12x1.75 | 10.2 | M33x3.5 | 29.5 |
| M12x1.5 | 10.5 | M33x3 | 30 |
| M12x1.25 | 10.8 | M33x2 | 31 |
| M12x1 | 11 | M33x1.5 | 31.5 |
| M14x2 | 12 | M36x4 | 32 |
| M14x1.5 | 12.5 | M42x4.5 | 37.5 |
| Pipe thread, G | |||
| Tap | Drill | Tap | Drill |
| G 1/8 | 8.8 | G 1 1/4 | 39.5 |
| G 1/4 | 11.8 | G 1 3/8 | 42 |
| G 3/8 | 15.25 | G 1 1/2 | 45.5 |
| G 1/2 | 19 | G 2 | 57.5 |
| G 5/8 | 21 | G 2 1/4 | 63.5 |
| G 3/4 | 24.5 | G 2 1/2 | 72.5 |
| G 7/8 | 28.25 | G 2 3/4 | 78.5 |
| G 1 | 30.75 | G 3 | 85.5 |
| G 1 1/8 | 35.5 |
| Inch UNC thread | |||
| 1/4x20 | 5.1 | 7/8x9 | 19.5 |
| 5/16x18 | 6.5 | 1x8 | 22.25 |
| 3/8x16 | 8 | 1 1/8x7 | 25 |
| 7/16x14 | 9.4 | 1 1/4x7 | 28.25 |
| 1/2x13 | 10.8 | 1 3/8x6 | 30.75 |
| 9/16x12 | 12.2 | 1 1/2x6 | 34 |
| 5/8x11 | 13.6 | 1 3/4x5 | 39.5 |
| 3/4x10 | 16.5 | 2x4 | 45 |
| Inch fine thread UNF | |||
| 1/4x28 | 5.5 | 3/4x16 | 17.5 |
| 5/16x24 | 6.9 | 7/8x14 | 20.5 |
| 3/8x24 | 8.5 | 1x12 | 23.25 |
| 7/16x20 | 9.9 | 1 1/8x12 | 26.5 |
| 1/2x20 | 11.5 | 1 1/4x12 | 29.75 |
| 9/16x18 | 12.9 | 1 3/8x12 | 33 |
| 5/8x18 | 14.5 | 1 1/2x12 | 36 |
| Trapezoidal thread Tr | |||
| Tr 8x1.5 | 6.6 | Tr 14x3 | 11.25 |
| Tr 10x1.5 | 8.6 | Tr 14x4 | 10.25 |
| Tr 10x2 | 8.2 | Tr 16x4 | 12.25 |
| Tr 10x3 | 7.5 | Tr 18x4 | 14.25 |
| Tr 12x2 | 10.2 | Tr 20x4 | 16.25 |
| Tr 12x3 | 9.25 | Tr 22x3 | 19.25 |
| Tr 14x2 | 12.2 | Tr 22x5 | 17.25 |
To cut internal threads with a tap, you first need to drill a hole of a certain diameter. The table shows the most popular threads and drill diameters required for drilling holes for threads.
How to find which drill bit for thread without a table?
Suppose you need to cut an M10x1.5 thread.
- Let's find out the nominal thread diameter: 10 mm.
- Find out the nominal thread pitch: 1.5 mm
- Subtract the second value from the first: 10-1.5 = 8.5 mm
- The result is 8.5 mm!
Having mastered this method, you can easily and simply select the right drill bit for cutting threads.
How to use the filter on the website to select a drill bit for threading?
For metal drills, a filter with the “For thread” parameter has been implemented, thanks to which you can find the desired drill in literally 2 mouse clicks:
- Choosing a thread.
- Click “Apply”.
- We get suitable drills.
For which materials are the values indicated in the table?
The indicated hole diameters provide cutting of metric threads in:
- gray cast iron
- carbon steels of ordinary quality
- quality structural steels
- alloyed structural 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 you get started, we recommend that you read the practical tips in the article How to properly cut a thread with a tap. And there you can find suitable coolant for different materials.
Source: https://sverla.info/articles/diametr-sverla-pod-rezbu/
