We make a torque wrench with our own hands from simple parts

In vehicle maintenance instructions, you can often find tables indicating the torque for tightening fasteners.

It is especially important to observe the value on parts such as the intake manifold, cylinder heads, and suspension joints. Service station technicians use special devices: torque wrenches. This is an expensive item: if it is used occasionally, it is not worth purchasing. Therefore, many car enthusiasts who service cars themselves make a torque wrench with their own hands.

It’s not possible to make a tool completely free of charge: at a minimum, you need a factory key, as well as a device that fixes torque.

What is a torque wrench used for?

A certain tightening torque on the mating parts is necessary for uniform contact of the planes. In addition, if a gasket is installed along the contour, the uneven force of the bolted connections can destroy it.

A torque wrench allows you to tighten bolts with an accuracy of hundredths of a millimeter. In addition, it is often necessary to perform torque tightening of the bearing seat with high precision.

The manufacturer calculates torque values based on the type of material and design features of the unit. When building a car at a factory, all fasteners are tightened according to specifications: as a rule, this work is performed by assembly robots.

And when servicing, repairing, replacing parts, the required force is provided by a hand tool: a torque wrench.

Its main advantage is the ability to work in a wide range of settings. You simply set the operating limit with your own hands, or visually control the dynamometer needle.

That is, a universal torque wrench does not allow you to equally accurately tighten the nuts with a force of 2 N.m. and 100 N.m.

Tool manufacturers produce torque wrenches in several ranges:

the most popular “size”: 40 – 210 N.m. It allows you to perform most repair work on the vehicle chassis;
A precise torque wrench (from 2 N.m. to 50 N.m.) is intended for engine repair and maintenance. Setting up the carburetor, tightening the spark plugs, assembling the crankshaft and connecting rods. Work on replacing the intake or exhaust systems is also carried out with a small range torque wrench;
tightening limit from 200 N.m. and higher is intended for power elements of powerful structures. In relation to cars - perhaps only wheel nuts.

Homemade torque wrench without scale

This version of a homemade wrench does not have a scale, like a factory torque wrench, but the tightening torque on it can still be adjusted. This simple hand tool is used to apply equal force when tightening nuts and bolts. Thanks to the system, which is triggered at a certain load, it becomes clear that the desired limit has been reached. Read below to learn how to make a torque wrench with your own hands.

This tool is very simple to manufacture, yet it can be much more reliable than factory keys, and provides a large torque when tightening nuts or bolts, due to the length of the handle. To make a homemade torque wrench without a scale yourself, you will need very simple and affordable materials:

a piece of half-inch steel pipe;
two plates 5 mm thick with holes 12 mm in diameter;
a long bolt with a nut of suitable diameter;
one homemade thick-walled washer;
spring and metal ball from the bearing.

We weld “ears” made from a metal plate 5 mm thick to a half-inch steel tube. We place a thick-walled washer between the plates and fix it with a steel “finger”.

Inside the tube we install a pusher with a ball from the bearing (you must first make a small recess in it, equal to ½ the diameter of the ball). Following the pusher, we install a spring and press it with a bolt and nut, which is welded to the end of a half-inch tube. Another recess for the ball must be made in the thickest walled washer.

At the last stage of work, all that remains is to weld a lever to the washer - for example, from a small piece of pipe. Please note that the longer the lever, the less force you will have to apply when tightening the nuts or bolts. A socket wrench is welded to the lever.

The applied force is easily adjusted using a clamping bolt. The more you tighten the bolt, the more force you will need to apply when tightening. This practical homemade torque wrench without a scale can be made with your own hands from available and inexpensive materials.

Make yourself this simple and necessary tool!!!

So does a car owner need a torque wrench?

Some car owners and even some auto mechanics argue that a torque wrench, in general, for the average car enthusiast, is a useless and unnecessary thing. The wheels, they say, can be tightened without much precision, but everything else is the job of a specialist.

Meanwhile, these craftsmen themselves do not deny that they carry out repairs and replacements of many components on their cars themselves. Another thing is that over time, experience appears and a fairly accurate feeling of the sufficiency of the effort being applied, especially when it is a familiar and thoroughly familiar car. What should those who do not have such experience do? Broken bolts, broken studs, broken nuts or heads can all be the result of not having a torque wrench. Especially today, when foreign-made cars actively use various alloys and non-ferrous metals.

In addition, a torque wrench allows you to achieve such an important thing as uniform tightening of all bolts or nuts, which even on a wheel will not be at all superfluous, but there are situations where this is a prerequisite.

Homemade torque wrench: how to make it yourself

Reading time: 6 minutes

Every experienced car enthusiast or professional mechanic knows that many parts in a car require special torque when tightening. So, if a moment is transferred to the nut that is insufficient to fully tighten it, it may become loose when moving, and, on the contrary, by overtightening the fastener, you can cause the part to deform.

That is why a torque wrench is one of the most important components of every specialist’s tool kit. However, it is quite expensive, and some craftsmen make the instrument with their own hands.

Torque wrench

Required Tools and Process

In order to do it correctly, you will need:

set of socket heads;
extension;
ratchet/wrench;
torque wrench.

The replacement process itself should be performed according to the following scheme:

Disconnect the wires leading to the emergency oil level and coolant temperature sensors.
Drain the coolant.
Remove the thermostat.
Remove the air filter housing.
Disconnect the exhaust pipe inlet from the manifold.
Remove the casing, as well as the camshaft belt itself.
Disconnect the drive rods of both dampers from the carburetor.
Disconnect the wires going to the cylinder head.
Disconnect the hoses suitable for the cylinder head by loosening their clamps.
Remove the cylinder head.
Remove the worn gasket.
Clean the contact surface of the cylinder head from any remaining gasket material.

Installing the gasket and mounting the cylinder head in place is carried out in exactly the same sequence, but in reverse order. At the same time, it is worth paying close attention to such a factor as the tightening torque of the cylinder head of the VAZ 2114 8 valves - we will talk about it below.

Tips from professionals when making a key

The tool may not work the first time, and the measurement will be incorrect. However, any experienced master can give several detailed tips, following which every beginner will achieve the desired result.

If you do not have a lever or materials for it, you can use a regular wrench with an open-end grip on one side and a box grip on the opposite side. However, the ratio of length and torque should be calculated more carefully here, since the size of the arm will most likely be a fractional number.

For better fixation of the steelyard to the lever, you should be especially careful about the place where it is installed. The best option is a carefully drilled through hole, exactly at the point where the load is applied, and the device will never slip off the handle.

Working with a homemade torque wrench

Depending on the required tension, the master may have several steelyards with different weighing limits, each of which must have its own table depending on the load on the arm and torque.

Since all efforts when determining the degree of tightening are applied only to the scales, it is necessary to ensure a comfortable grip on the handle, since 20-30 kg with a poor grip will not allow you to comfortably work with the device.

General rules for using the tool

The tool itself is a rod with a handle at one end and an indicator mechanism at the other. At the working end of the handle, a socket head or a connecting socket for a horn attachment (wrench or union attachment) is installed.

The keys are equipped with indicator and adjustment mechanisms, both with and without overtightening protection.

Next, we will consider the types of torque wrenches that are most often used in work.

Click type

Often motorists purchase just such a key because of the high measurement accuracy, durability and the presence of a convenient scale with adjustment. It is impossible to tighten the thread with such a wrench, since a fuse is provided.

The main thing is to know how to properly work with a product of this type. The bottom line is that it is necessary to set the required value of the maximum force (tightening torque) in advance.

Next, the connection (bolt or nut) is tightened as usual until a clearly audible click appears. This sound signals that the required parameter has been reached. It is noteworthy that the device will then go into the “slip” mode and it will not be possible to tighten the connection.

Click type

It's no secret that all bolted connections must be tightened to a certain torque. In the literature it is often referred to as newton times a meter. N*m. For example, 10 N*m means that the bolt or nut is tightened with a torque of 10 newtons applied to a 1 meter long arm.

I don’t want to seem boastful, but the results are already there and I think they’re good for a start. Sorry for this slight digression from the topic. Today we’ll talk about the topic of torque wrench. What is it and what is it eaten with.

Which torque wrench to choose from these three types. Based on my operating experience, I will say that the best option for a garage mechanic is a click torque wrench. I will try to clearly justify this choice.

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The following types of torque wrenches are distinguished according to the indication method:

The torque wrench consists of the following elements:

How does a torque wrench work for a car?

There are two design solutions: torque limitation and visual process control. Let's look at each of them in detail.

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The so-called ratchet

Externally, it is not much different from a conventional lever with a ratchet for socket heads. Actually, this is what she is. A simple ratcheting mechanism with adjustable operating force turns an ordinary handle into a torque wrench. The secret is in the design of the ratchet. It allows the gear to rotate in any direction.

In the return direction, when you retract the handle for the next rotation of the head, the force is minimal. But in the working direction, where force is applied, the ratchet tooth jumps off the gear when the specified value is reached.

In the handle of the shank there is a rotating nozzle. It adjusts the tension of the ratchet spring.

How does the system work?

When the set torque value is reached, the ratchet gear begins to slip. The handle turns with a characteristic sound, but the nut does not tighten.

The ratcheting torque wrench is semi-automatic. It makes it possible to tighten the nuts without fear of overtightening them.

Measuring scale

The torque wrench does not have a torque limiting mechanism, but a dial or digital dynamometer is connected to the rotary mechanism. When force is applied to the handle, the needle deflects and the value of the applied force can be recorded.

The principle of operation is quite simple: the arrow maintains a constant position relative to the head of the key, and the handle bends like a spring torsion bar. As a result, the scale shifts relative to the tip of the arrow in proportion to the applied force.

The disadvantage of this model is that there is no automatic limiter. You simply control the force applied to the handle. This allows for a more accurate measurement (unlike a ratchet, which operates discretely), but there is a possibility of mechanical error when dosing force.

It is difficult to make a homemade torque wrench based on a ratchet; the technology requires metal-working machines and precision calibration. But a tool with a dynamometer is quite within the capabilities of a home craftsman.

Torque wrenches, their design and components

That is why such mechanisms indicate the maximum or recommended tightening force. These data are indicated directly in the passport data of the mechanisms or components. The parts should be tightened to the appropriate amount to ensure a reliable and effective connection.

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The reliability of mechanisms depends not only on the quality of the materials used, but also on the correct assembly of the components. In most cases, the use of specialized tools is required to ensure the reliability of threaded connections. These tools include a torque wrench, the purpose, types and selection of which should be familiarized with before you buy it.

Based on the display of relevant readings, the types of devices under consideration are divided into types. It is necessary to know what types of torque wrenches there are in order to choose the appropriate option for performing the corresponding manipulations. It should be noted that the instruments in question are quite expensive, so if it is necessary to use a device, its selection must be approached accordingly.

The dimensions of the key and fasteners must strictly correspond

Correctly, the torque of the connections should be indicated in the technical document

Judging by user reviews, there is no consensus on the quality and properties of the tool. This situation is understandable, since the level of qualifications and the specifics of the work performed can be very different, and therefore points of view differ significantly from each other.

Replacing the oil pressure sensor

To install a new sensor, you will need the following tools and consumables: two wrenches for “21”, an open-end wrench for “22” with an adapter, a rubber protective cap, an O-ring and block (usually included in the kit), a wire terminal for the sensor contact. Before replacement, you must remove the negative terminal from the battery. Operating procedure:

Remove the rubber protective cap from the top of the sensor and disconnect the wiring terminals. Unscrew the sensor from the fitting using a “21” wrench, carefully holding the tip of the fitting with a key of the same size. Remove the sensor. An O-ring and a metal washer are installed at the connection between the sensor and the fitting, which must be replaced if they are worn. The new sensor is installed in the reverse order.

Varieties

Tighten the nuts; is a torque wrench necessary?

Before choosing torque wrenches for cars, you should study the available product options. This will help you get to know the devices better, and roughly understand what you need and what characteristics or capabilities you should count on when purchasing it.

It is customary to distinguish 3 types of torque wrenches. But you can add one more device to this list, which is an adapter key.

Switches. When it comes to which torque wrench you should choose for repairing your own car in a garage, many are inclined to the simplest and most affordable option in the form of a pointer device. This key has a simple design and low cost. But the low price hides the corresponding quality. In terms of accuracy, they are much inferior to competitors, having an error of up to 10%. In this case, you should not count on a maximum tightening torque of more than 280 Nm. This key is not in demand among professional auto mechanics. But if you are doing work in the garage, and the procedure itself does not require increased accuracy, a pointer tool should be sufficient.
Clicky. They are the ultimate. When choosing a torque wrench for car maintenance, motorists often lean towards click tools. Structurally, it includes a clutch with a given torque, which begins to operate when the specified tightening parameters are exceeded. For such tools, the torque range can vary from 40 to 360 Nm, which already significantly exceeds the capabilities of a standard pointer device. This range greatly simplifies the selection of a specific tool with the required characteristics. Click devices can be divided into household and professional ones. For the former, the error indicators do not exceed 5%, while for the latter it is even at a level of up to 3%. But in cost they are superior to switch analogues.
Electronic. If there are increased demands on the car, it will be much more correct to choose an electronic torque wrench. This is the best tool for car maintenance, although it is rarely found in the garages of ordinary motorists. This is a professional-level device with the highest technical characteristics. The tightening scale here is electronic, and when the desired value is reached, a sound signal is heard, often supplemented by LED indicators. The range starts at 20 Nm. But the most significant feature of such a key is considered to be an error that does not go beyond 1%. The only, but significant reason to refuse to purchase an electronic device is the price. It is really high, which is why such devices are used mainly in car repair shops and service stations.
Adapter keys. This is a special electronic device that can hardly be considered a type of electronic torque wrench. The device is equipped with a mechanical drive, to which you can connect a ratchet, and install heads and other attachments on the adapter. Dynamometer adapters are equipped with various components. There are sets of several adapters that differ in range. The device has a digital display and additional buttons for settings. The operating principle is similar to electronic keys. There is a battery inside the box. At the same time, the price is significantly lower than that of electronic torque wrenches.

Arrow torque wrench

The driver himself must decide which torque wrench he should choose for further maintenance of his own passenger car.

If you literally carry out some work on the machine several times a year, when you need 1-2 uses of such a key, there is definitely no need to spend a lot of money on buying an electronic device. It’s much easier and cheaper to go to a car service center. But for such periodic work, click devices are perfect. They are much better than pointers, have a good percentage of error, and at the same time cost adequate money.

How to use a torque wrench

It should be taken into account that even key samples of the same type may have their own requirements and operating features, so you cannot use the tool without studying the technical description or instructions. The calibration interval must also be maintained to ensure accurate torque indication.

The maximum force is adjusted by combining the data on the scale of the handle and the key lever. The main scale provides coarse adjustment in steps of 5 Nm, and the additional scale provides fine adjustment within 5 Nm to obtain the exact required value.

Let's look at the features of using different types of keys:

I took MASTAK 012–40210C. The quality is not very good, I took it only because it covers the required range of forces. I recommend taking a closer look at normal brands - KING TONY, Jonnesway, Force. Blinov Artyom https://krasnodar.vseinstrumenti.ru/ruchnoy-instrument/klyuchi/dinamometricheskie/mastak/012–40210c/?respcount=1#tab-Responses

As I wrote above, I decided to use regular batteries; replacing them once every year or two is not difficult)

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Convert to Newton*meters: 4.98*0.21*10=10.45 Nm. I took the distance of 0.21 meters as the average between 0.2 and 0.22

To reduce the price tag you must use coupon MD4850

How to measure tightness

To correctly measure the tightening using a homemade device, you need to follow a few simple rules:

Assemble the device and bring it into working condition - attach the steelyard to the handle, set it to zero, if possible, set the weighing limit with an alarm, and at the end - put the necessary attachment on the working part of the device or initially select an open-end wrench of a suitable size.
Place the wrench on the nut or bolt. The device will show an accurate value only if the connection with the fastener occurs directly through the lever, and with the participation of one or more adapters and extensions, an error of up to 5-8% is possible when giving the result.
Carefully pull the steelyard so that its position is strictly perpendicular to the axis of the lever, and the load indicator is not distorted, decomposed into vectors.
If a normal force has been achieved, the device will confirm this with the measurement result, and the nut will not budge. If the tightening was not sufficient, the fastener will rotate around its axis until the required torque is achieved.

Important!
To prevent the bolt connection from breaking, you should not put an excessive load on the homemade dynamometer, and tighten only at the nominal values prescribed in the technical manual for servicing a particular part in the car. Otherwise, there is a risk of deformation of factory products.

Retightening a bolt on a car wheel

Tightening with hand scales

Alternatively, as a replacement for a factory or homemade torque wrench in the form of a ratchet, you can use a regular wrench or socket wrench. We attach to it a manual scale of the “canter” or “steelyard” type (or you can, for example, take one with a digital display), and tighten the bolt or nut. This is also quite a workable option at home if you don’t have anything at hand.

To tighten nuts or bolts with a certain force using hand scales, most often a steelyard of 20-30 kg and a piece of steel pipe 50 cm long (but possible less) with a suitable internal diameter of at least 25-30 mm will be enough to could be put on the key. In the event that large torques are required, you need to select the appropriate scales.

What you will need for work:

a wrench (open-end or socket) onto which a piece of steel pipe about 40–50 cm long is placed;
spring canter (hand scales) with a “limit” of approximately 20–30 kg. You can also use electronic scales to make a torque measuring device.

Tightening process

First, you need to install a spanner or open-end wrench on a bolt or nut, and attach the hook of a hand scale to the other end. Having calculated the required force in advance, we pull the scale ring, while maintaining 90 degrees, until the required value is reached.

Thus, even without having a torque wrench on hand in the garage or workshop, you can tighten the nut and bolt connection with the necessary force and precise torque.

Source

Maximum torque for bolt tightening

The car does not recognize the chip key

In order to properly tighten car bolts and nuts without damaging them, the technician must be aware of the maximum forces depending on the length, diameters of the elements, and the quality of the steel from which they are made. These data on the maximum torque are shown in the table.

Thread/pitch, mm	Strength class 4.6	Strength class 5.8	Strength class 8.8	Strength class 10.9	Strength class 12.9
5/0,8	2,1	3,5	5,5	7,8	9,3
6/1,0	3,6	5,9	9,4	13,4	16,3
8/1,25	8,5	14,4	23,0	31,7	38,4
10/1,5	16,3	27,8	45,1	62,4	75,8
12/1,75	28,8	49,0	77,8	109,4	130,6
14/2,0	46,1	76,8	122,9	173,8	208,3
16/2,0	71,0	118,1	189,1	265,9	319,7
18/2,5	98,9	165,1	264,0	370,6	444,5
20/2,5	138,2	230,4	369,6	519,4	623,0
22/2,5	186,2	311,0	497,3	698,9	839,0
24/3,0	239,0	399,4	638,4	897,6	1075,2
27/3,0	345,6	576,0	922,6	1296,0	1555,2
30/3,5	472,3	786,2	1257,6	1766,4	2121,6
33/3,5	636,5	1056,0	1699,2	2380,8	2860,8
36/4,0	820,8	1363,2	2188,8	3081,6	3696,0
39/4,0	1056,0	1756,8	…	3955,2	4742,4

As a rule, the instrument scale is graduated in Nm, but sometimes you can see force indicators in kilograms on it.

Torque wrench included with sockets

Main mistakes when making a key

Any high-precision tool cannot be manufactured completely without errors, since the master has neither accurate designs nor drawings at hand, and all this can lead to incorrect measurements and subsequent breakdown of car parts. However, many professionals have answers on this matter, offering car enthusiasts a number of recommendations in order to minimize errors and inaccuracies, in particular:

You should not use soft metal as a lever, which can easily bend when pressed, because the force applied to the steelyard, without maintaining orthogonality, will not give the desired result, and the purpose of the device will be completely lost.
You should not choose a cheap steelyard, because the accuracy of its measurements is very questionable, and the spring quickly stretches and fails. So, as of December 2022, the cost of scales should be in the region of 400-500.0 rubles. This is not much compared to the price of the torque wrench itself - about 3-4 thousand rubles, and it is better to change the low-quality component immediately.
When attaching the nozzle to the nut, you need to take into account that it must be perpendicular to the axis of operation of the lever, otherwise the measurement will not work.
Most steelyards have only an informational function and do not in any way limit the actions of the master, who can easily get distracted and tighten the bolt without paying attention to the scale reading.

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Thus, when using a homemade product, the master bears much more responsibility, because the device cannot have the same automatic force reduction functions as a purchased analogue.

Service station

A homemade device is best used to control bolt tension if in doubt. If it is necessary to control the tightening on any complex component part, the car owner should still contact a service station for diagnostics and repairs, and should not replace important components in his garage, because unauthorized intervention can cost much more than the money saved on the key.

Torque Wrench Selection

The goals you pursue form the basis of the requirements for such tools. The financial aspect is also important. The most expensive will be a key with electronic filling, but if your goal is not to achieve high accuracy, then you can take a closer look at click or torsion models. Don't forget to make sure how it fits in your hand. Comfort of use is very important, because it is necessary not only to keep the instrument intact, but also to avoid damaging its parts and to fit the fingers perfectly. The surface must be selected from non-slip materials so that the hand does not jump off the key at the most inopportune moment. Also, you should not feel any strain on your wrist with prolonged use. And now when all the details are taken into account, you can start purchasing.

Snap torque wrench

The modern design of such keys is designed to achieve the greatest efficiency of use. When the required parameter value is reached, a sound signal is emitted. This signal is different from the clicking sound that is heard when force is applied. The snap-on wrench minimizes confusion when working. Click-type wrenches have fewer moving components, which increases tool reliability and reduces wear. Snap-on keys retain calibration much longer than switch-type keys.

How the tool works

Semi-automatic torque wrenches resemble in shape and design a regular ratchet wrench, which is used for socket heads. The only significant difference from its “brothers” is the presence of a special ratcheting mechanism, which allows the built-in gear to rotate in two directions.

For example, to return the handle of a tool back after a full rotation, you need to apply relatively little force. But to tighten the nut you need to apply a little more force.

When the required value is reached, the ratchet gear simply begins to slip (a characteristic sound is heard), as a result of which the nut or bolt is no longer tightened. This eliminates the possibility that the thread will break.

Torque wrenches with a force measurement scale by default do not have the ability to limit torque when a specified value is reached. In this case, this moment must be controlled independently using a mechanical or electronic digital measuring scale.

A homemade almost torque wrench, depending on the design, can work according to the example of the first and second options described above.

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Why do we count Newtons and meters?

Before you start making a simple homemade torque wrench for tightening bolts and nuts, you will need to do some calculations. For example, to achieve a tightening torque of 10 N*m, you need to apply a force equal to one kilogram of force to a lever or arm 1 meter long.

But in a home workshop or garage, a meter lever is not the most practical and convenient option. Ideally, it is better to use a lever within 20–50 cm. And in order to correctly calculate how much force needs to be applied to the lever to achieve the required tightening torque, you need to count Newtons and meters.

However, it is not at all necessary to go into the jungle of mathematical equations. The required values can be easily calculated in proportion. That is, if we take as a basis that to obtain a torque of 10 N*m, you need to apply a force of 1 kg on a meter-long lever, then it is similarly easy to calculate how much force will need to be applied to a lever of shorter length.

The shorter the lever used, the greater the force required to tighten the bolt or nut - this is, so to speak, an axiom. For example, if instead of a meter lever you use a lever 50 cm long, then to obtain a torque of 10 N*m you need to apply a force equal to 2 kg.

If you use a lever with a length of, for example, 22 cm, then the force will be already 4.5 kg. In other words, you need to divide the torque (10 N*m) by the length of the lever (in this case - 0.22 m) and multiply by 0.1. Using this simple formula, you can easily calculate how much specific force is required to tighten the nut.

Buy or make?

In the process of performing auto repair work, almost every vehicle owner is faced with the fact that it is necessary to tighten a bolt or nut by applying a certain force, but there is no torque wrench at hand. Don’t run to the store to buy an expensive instrument, use it for 20–30 minutes and forget it for a year.

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Therefore, the best option is to make a homemade torque wrench for tightening nuts and bolts. Moreover, you can make a tool like a ratchet with a ratchet mechanism, as well as one made by analogy with a simpler design - using ordinary hand scales.

Torque Control Tools

The main tool for controlling tightening torque is a torque wrench. This is the name of a wrench that has a dynamometer (a device for measuring torque) built into it. The following types of devices exist:

Indicator - when tightening, displays the applied force digitally or using an arrow. The error is 6–8%.

The indicator torque wrench is inexpensive, but has the largest error
Digital is a subtype of indicator, but uses an LCD display to display the moment. Supports sound notification capabilities, uploading data to a computer, etc. The error is up to 1%.

Digital torque wrench - the most accurate
Limit - when the specified torque is reached, it stops tightening using a click mechanism. The error is up to 4%.

The limit (snap) torque wrench is easy to use

For non-professional use or a small car service, an indicator or limit key is suitable as the most affordable ones. Digital will be in demand in large car service centers.

How to choose the force to tighten the connection correctly

When working with a limit type key, in order to achieve the required torque, you should:

Before starting tightening, select the required tightening force, for example, 50 Nm. The force is set on the main scale of the device, but not 50, but 48 Nm.
On the auxiliary scale the force is set to 2 Nm, which in total will give us the required 50 Nm.
Using a socket of the required size, tighten the nut. When the force reaches 50 Nm, a click will be heard and tightening will stop.

Control of force when working with an indicator type key is carried out visually.

In addition to the torque wrench, you can find torque screwdrivers and screwdrivers on sale; they work on the same principle. When choosing a torque wrench, remember that the tightening torque you need should be 25% less than the maximum allowable for the wrench. Using the key “to the limit”, you will quickly disable it. And also be sure to read the instructions for its use.

Well, you can check the correct tightening of the connection with a protractor.

How to use a homemade torque wrench

Typically, a torque wrench is a fairly expensive tool. Its purchase is unlikely to be justified for private use. However, the simplest device is easy to make yourself. For this you will need:

ordinary spring scales with a hook and a round scale, allowing you to weigh up to 20 kg (the so-called steelyard);
a piece of rather thick pipe (2.5 cm) about half a meter long.

Having secured the hook of the scales to the end of the pipe, insert a wrench into the other end and pull the scales, tightening the nut. In this case, to create a torque of 10 Nm, a force of 2 kg will be required. Using this diagram, you can calculate in advance how much force in kilograms you will need to apply to tighten it.

How to make a torque wrench with your own hands so that it is convenient to use?

A meter key handle is not the most practical option. Let's use the rule for calculating force depending on the length of the lever. There is no point in studying formulas; quantities are calculated in proportions.

The shorter the lever, the more force must be applied (while maintaining the amount of torque):

lever 1 m, torque 10 N.m., force 1 kg;
lever 0.5 m, torque 10 N.m., force 2 kg;
lever 33 cm (already convenient to work), torque 10 N.m., force 3 kg.

For production you will need:

handle for working with square socket heads (for greater versatility - with an extension).
clamp for fixing the force measurement point.
measuring device: you can use ordinary scales such as a steelyard or a cantor. The optimal measurement range is from 100 grams to 50 kg.

Having measured the required length from the center of rotation, we fix the clamp on the lever.

The device is ready in 15 minutes. You can mark several points for installing the clamp, depending on the moment being measured.

Important! When tightening the fasteners, you need to pull the scales (dynamometer). We do not apply any force to the handle. A right angle is maintained between the lever and the direction of force (along the cantor spring).

It will be useful to have a ready-made table for calculating torque, depending on the steelyard readings.

If you don’t want to make a separate tool with your own hands, use a standard set of wrenches (open-end on one side, socket on the other). The principle of operation is exactly the same.

For each key (since they are of different lengths), we compile a calculation table in advance. You can use a ready-made smartphone application:

We enter the received data (lever length, cantor readings), and we see the finished result in newtons per meter.

Tighten the bolt with a homemade torque wrench - video

Conclusion: Having a steelyard worth 300 - 500 rubles. (it is found in almost every home), you can save on buying a factory torque wrench: the price is about 2000 - 3000 rubles.

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DIY torque wrench

A torque wrench is a tool for service station technicians, designed primarily to ensure uniform application of load on a particular fastener; it ensures uniform tightening of each bolt or nut.

The electronic or pointer scale on this product allows you to tighten parts with an accuracy of tenths and even hundredths of mm.

This is an expensive device, and if a person does not use the key daily, it is not worth purchasing. However, if you thoroughly know the principle of its operation, you can make it yourself at home.

Upon closer examination, the product is a regular lever with a ratchet at the end, which does not allow the master to overdo it with force and simply scrolls idle, in accordance with the preset parameters on the dynamometer.

A dynamometer is a simple spring mechanism that, when tensioned, causes the needle on the dial to deflect from zero to a user-specified limit value.

A gear wheel is hidden in the tool head itself, which is set in motion when the protrusion of the key hits it, but when the required torque in N * m is reached, this protrusion simply begins to jump off, and the mechanical effect on the gear stops. This measuring tool records the value as the product of the force exerted by the user’s hand on the shoulder relative to the point where the wrench is secured at the interface between the working attachment and the nut and the point of application of the load.

At the base of the lever there is a rotating limiter, with the help of which the master sets the exact value of the required maximum force before starting work.

DIY key parts

Thus, having some household appliances on hand, as well as a little ingenuity and knowledge of elementary physics, any man can make something like a key without leaving his home or garage, and the result will not differ much from the readings of a device purchased in a store.

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