Eccentric clamps, in contrast to screw ones, they are fast-acting. It is enough to rotate the handle of such a clamp less than 180° to secure the workpiece.

The operation diagram of the eccentric clamp is shown in Figure 9.

Figure 9 – Scheme of eccentric clamp operation

When you turn the handle, the radius of rotation of the eccentric increases, the gap between it and the part (or lever) decreases to zero; The workpiece is clamped by further “compacting” the system: eccentric - part - fixture.

To determine the main dimensions of the eccentric, you should know the magnitude of the workpiece clamping force Q, the optimal angle of rotation of the handle for clamping the workpiece, and the tolerance for the thickness of the workpiece being secured.

If the angle of rotation of the lever is unlimited (360°), then the magnitude of the cam eccentricity can be determined by the equation

where S 1 is the installation gap under the eccentric, mm;

S 2 - eccentric power reserve, taking into account its wear, mm;

Tolerance for workpiece thickness, mm;

Q – workpiece clamping force, N ;

L - clamping device rigidity, N /mm(characterizes the amount of spin of the system under the influence of clamping forces).

If the angle of rotation of the lever is limited (less than 180°), then the amount of eccentricity can be determined by the equation

The radius of the outer surface of the eccentric is determined from the condition of self-braking: the angle of rise of the eccentric, made up by the clamped surface and the normal to the radius of its rotation, must always be less than the friction angle, i.e.

(f=0.15 for steel),

Where D And R- the diameter and radius of the eccentric, respectively.

The clamping force of the workpiece can be determined by the formula

Where R - force on the eccentric handle, N (usually accepted ~ 150 N );

l - handle length, mm;

– friction angles between the eccentric and the part, between the trunnion and the eccentric support;

R 0 - eccentric rotation radius, mm.

To approximate the clamping force, you can use the empirical formula Q12 R(at t=(4- 5) R and P=150 N) .

It is more difficult than shown above to calculate eccentrics with an involute curve, in which the angle of elevation is always constant, as well as with a curve outlined by an Archimedes spiral, in which the angle of elevation decreases as the handle is turned.

Some of the eccentric clamps used in fixtures are shown in Figure 10.

Very often, it is irrational to clamp workpieces directly with an eccentric, since the magnitude of the eccentricity (the amount of pressure) is only a few millimeters. It is much more expedient to combine eccentric clamps with lever or some other clamps, or design them folding.

Literature

6bas..

Control questions

What should you know to determine the basic dimensions of the eccentric?

Why is it very often irrational to clamp workpieces directly with an eccentric?

a,c - for pressed flat workpieces; b - for fastening flat workpieces using a swinging beam; G - for tightening shells using a flexible clamp

Figure 10 – Examples of eccentric clamps of different designs

Lecture 6 Lever Clamps

Lever Clamps They are quite widely used in assembly and welding devices, most often for fastening sheet blanks located horizontally. Such clamps are fast-acting, create high clamping forces, the magnitude of which, if necessary, can be adjusted within a fairly wide range using spring shock absorbers. The designs of these clamps can be easily standardized, thereby ensuring versatility of their use.

The disadvantage of lever systems is the possibility of accidental, and if poorly designed, spontaneous opening of the grips. Therefore, such clamps should be used only when accidental loosening of the workpiece will not lead to an accident or danger for workers. The possibility of accidental opening of the lever clamp can be reduced by using massive handles, the gravity of which in the working position has the same direction as the force of the worker applied to the handle when securing the part. The reliability of lever systems is further increased by various locking devices: latches, locks, etc. The operation diagram of the lever system is shown in Figure 1. The clamp consists of a stand 1, on which, using a finger, 2 handle-bracket is attached 3. To the last one through the connecting strips 4, sitting on 5 axles, a lever is hinged 6, sitting on axis 7 and having an adjustable stop 8 (set stop overhang 8 fixed with a lock nut 0 ). The stroke of the handle-brace is limited by the stop 10. When tilting the handle 3 to the right around the fixed hinge 2 link 4 raises the working lever 6, allowing installation of the assembled part. When the handle moves back, the workpiece is clamped.

Figure 11 – Lever clamp action diagram

Screw 8 is used to change the installation gap (to be able to adjust the pressing force when the thickness of the workpieces being fixed or wear of the clamp changes).

The calculation of the magnitude of the clamping force, depending on the design of the lever system, is carried out according to the rule of shoulders (you can also use the graphic-analytical method - constructing force polygons).

For levers of the 1st kind (Figure 12, a) and 2nd kind (Figure 12, b) The clamping force Q can be calculated using the following equations:

For levers of the 1st kind;

For levers of the 2nd kind,

Where R- force applied to the end of the handle, N;

a - leading lever arm;

b - driven lever arm;

f - coefficient of friction in the hinge;

r- radius of the hinge pin.

a-1st kind; b- 2nd kind

Figure 12 – Lever diagram

For more complex mechanisms, the clamping force also depends on the angle of “inclination” of the levers (Figure 13). The greatest clamping force is provided at tilt angles close to zero.

Lever clamps, as a rule, are used in combination with others, forming more complex lever-screw, lever-spring and other amplifiers, which make it possible to transform either the magnitude of the pressing force, or the magnitude of the clamping stroke, or the direction of the transmitted force. Such amplifiers can be very diverse in design.

Good day to fans homemade devices. When there are no vices at hand or they are simply not available, then simple solution You will be able to assemble something similar yourself, since special skills and hard-to-find materials are not required to assemble the clamp. In this article I will tell you how to make a wooden clamp.

In order to assemble your clamp, you need to find a strong type of wood so that it can withstand heavy loads. In this case, an oak plank will work well.

To begin the manufacturing phase necessary:
*Bolt, the size of which is best taken around 12-14mm.
*Nut for bolt.
*Whetstones made of oak wood.
*Part of the profile is made of wood with a cross-section of 15mm.
*Carpenter glue or parquet glue.
*Epoxy.
*Varnish, can be replaced with stain.
*Metal rod 3 mm.
*Small diameter drill.
*Chisel or chisel.
*Hacksaw for wood.
*Hammer.
*Electric drill.
*Medium grit sandpaper.
*Vise and clamp.

First step. Depending on your requests, the size of the clamp can be made different; in this case, the author cuts out blocks measuring 3.5 x 3 x 3.5 cm - one piece and 1.8 x 3 x 7.5 cm - two pieces.

After this, we clamp a 75mm long block in a vice and drill a hole using a drill, stepping back 1-2cm from the edge.

Next, match the hole you just made with the hole in the nut and trace the outline with a pencil. After marking, armed with a chisel and hammer, cut out a hexagonal countersunk for the nut.

Second step. To secure the nut in the block, you need to coat the machined groove with epoxy resin inside and immerse the same nut there, drowning it a little in the block.

Typically completely dry epoxy resin is achieved after 24 hours, after which you can proceed to the next stage of assembly.
Third step. The bolt, which ideally fits our fixed nut in the beam, needs to be modified; to do this, take a drill and drill a hole close to its hexagonal head.

After this, we move on to the bars, they need to be combined together so that there are longer bars on the sides, and a shorter bar between them. Before the three beams are clamped together, you need to drill holes at the fastening point with a thin drill so that the workpiece does not split, because this arrangement is not suitable for us.

Using a screwdriver, we tighten the screws into the prepared drilling places, having previously coated the joints with glue.

We secure the almost finished clamping mechanism with a clamp and wait for the glue to dry. For convenient use The clamp requires a lever with which you can clamp your workpieces; this will be a metal rod and a round piece of wood with a cross-section of 15 mm sawn into two parts, in both of them you need to drill a hole for the rod and put it all on glue.

The final stage. To complete the assembly you will need varnish or stain, we sand our homemade clamp, and then coat it with varnish in several layers.

The eccentric clamp is an improved design clamping element. Eccentric clamps (ECC) are used for direct clamping of workpieces and in complex clamping systems.

Manual screw clamps are simple in design, but have a significant drawback - to secure the part, the worker must perform a large number of rotational movements with a key, which requires additional time and effort and, as a result, reduces labor productivity.

The above considerations force, where possible, to replace manual screw clamps with quick-release clamps.

The most widespread are also.

Although it is fast-acting, it does not provide high clamping force on the part, so it is used only for relatively small cutting forces.

Advantages:

• simplicity and compactness of design;
• widespread use of standardized parts in the design;
• ease of setup;
• ability to self-braking;
• speed (drive response time is about 0.04 min).

Flaws:

• the concentrated nature of the forces, which does not allow the use of eccentric mechanisms for securing non-rigid workpieces;
• the clamping forces with round eccentric cams are unstable and significantly depend on the size of the workpieces;
• reduced reliability due to intensive wear of the eccentric cams.

Rice. 113. Eccentric clamp: a - the part is not clamped; b - position with clamped part

Eccentric Clamp Design

Round eccentric 1, which is a disk with a hole offset relative to its center, is shown in Fig. 113, a. The eccentric is freely mounted on axis 2 and can rotate around it. The distance e between the center C of disk 1 and the center O of the axis is called eccentricity.

A handle 3 is attached to the eccentric, by turning which the part is clamped at point A (Fig. 113, b). From this figure it can be seen that the eccentric works like a curved wedge (see shaded area). To prevent the eccentrics from moving away after clamping, they must be self-braking. The self-braking property of the eccentrics is ensured the right choice the ratio of the diameter D of the eccentric to its eccentricity e. The ratio D/e is called the characteristic of the eccentric.

With a friction coefficient f = 0.1 (friction angle 5°43"), the eccentric characteristic should be D/e ≥ 20, and with a friction coefficient f = 0.15 (friction angle 8°30") D/e ≥ 14.

Thus, all eccentric clamps, whose diameter D is 14 times greater than the eccentricity e, have the property of self-braking, i.e., they provide reliable clamping.

Figure 5.5 - Schemes for calculating eccentric cams: a – round, non-standard; b- made according to the Archimedes spiral.

Eccentric clamping mechanisms include eccentric cams, supports for them, trunnions, handles and other elements. There are three types of eccentric cams: round with a cylindrical working surface; curved, the working surfaces of which are outlined along an Archimedes spiral (less often - along an involute or logarithmic spiral); end

Round eccentrics

Due to ease of manufacture, round eccentrics are most widespread.

A round eccentric (in accordance with Figure 5.5a) is a disk or roller rotated around an axis displaced relative to the geometric axis of the eccentric by an amount A, called eccentricity.

Curvilinear eccentric cams (in accordance with Figure 5.5b) compared to round ones provide stable clamping force and a larger (up to 150°) rotation angle.

Cam materials

Eccentric cams are made of steel 20X, carburized to a depth of 0.8...1.2 mm and hardened to a hardness of HRCe 55-61.

Eccentric jaws are distinguished as follows: designs: round eccentric (GOST 9061-68), eccentric (GOST 12189-66), double eccentric (GOST 12190-66), forked eccentric (GOST 12191-66), double-support eccentric (GOST 12468-67).

The practical use of eccentric mechanisms in various clamping devices is shown in Figure 5.7

Figure 5.7 - Types of eccentric clamping mechanisms

Calculation of eccentric clamps

The initial data for determining the geometric parameters of the eccentrics are: tolerance δ of the size of the workpiece from its mounting base to the place where the clamping force is applied; angle a of rotation of the eccentric from the zero (initial) position; required force FZ of clamping the part. The main design parameters of eccentrics are: eccentricity A; diameter dc and width b of the eccentric pin (axis); outside diameter eccentric D; width of the working part of the eccentric B.

Calculations of eccentric clamping mechanisms are performed in the following sequence:

Calculation of clamps with a standard eccentric round cam (GOST 9061-68)

1. Determine the move hTo eccentric cam, mm:

If the rotation angle of the eccentric cam is not limited (a ≤ 130°), then

where δ is the tolerance of the workpiece size in the clamping direction, mm;

Dgar = 0.2…0.4 mm – guaranteed gap for convenient installation and removal of the workpiece;

J = 9800…19600 kN/m – rigidity of eccentric EZM;

D = 0.4...0.6 hk mm – power reserve, taking into account wear and manufacturing errors of the eccentric cam.

If the rotation angle of the eccentric cam is limited (a ≤ 60°), then

2. Using tables 5.5 and 5.6, select a standard eccentric cam. In this case, the following conditions must be met: Fz ≤ Fh max and hTo≤ h(dimensions, material, heat treatment and others technical specifications according to GOST 9061-68. There is no need to test the standard eccentric cam for strength.

Table 5.5 - Standard round eccentric cam (GOST 9061-68)

Designation	Outer eccentric cam, mm	Eccentricity,	Cam stroke h, mm, not less
			Angle of rotation limited to a≤60°	Angle of rotation limited to a≤130°
Note: For eccentric cams 7013-0171...1013-0178, the values ​​of F3 max and Mmax are calculated based on the strength parameter, and for the rest - taking into account ergonomic requirements with a maximum handle length of L = 320 mm.

3. Determine the length of the eccentric mechanism handle, mm

Values M max and P z max are selected according to table 5.5.

Table 5.6 - Round eccentric cams (GOST 9061-68). Dimensions, mm

Drawing - drawing of an eccentric cam

DIY eccentric clamp

The video will show you how to make a homemade eccentric clamp designed for fixing a workpiece. Eccentric clamp, made with your own hands.

/ 13.06.2019

DIY eccentric clamp made of metal. Eccentric clamp

Eccentric clamps are easy to manufacture and for this reason they are widely used in machine tools. The use of eccentric clamps can significantly reduce the time for clamping a workpiece, but the clamping force is inferior to threaded clamps.

Eccentric clamps are made in combination with and without clamps.

Consider an eccentric clamp with a clamp.

Eccentric clamps cannot work with significant tolerance deviations (±δ) of the workpiece. For large tolerance deviations, the clamp requires constant adjustment with screw 1.

Eccentric calculation

The materials used for the manufacture of the eccentric are U7A, U8A With heat treatment to HR from 50....55 units, steel 20X with carburization to a depth of 0.8... 1.2 With hardening HR from 55...60 units.

Let's look at the eccentric diagram. The KN line divides the eccentric into two? symmetrical halves consisting, as it were, of 2 x wedges screwed onto the “initial circle”.

The eccentric rotation axis is shifted relative to its geometric axis by the amount of eccentricity “e”.

Section Nm of the lower wedge is usually used for clamping.

Considering the mechanism as a combined one consisting of a lever L and a wedge with friction on two surfaces on the axis and point “m” (clamping point), we obtain a force relationship for calculating the clamping force.

where Q is the clamping force

P - force on the handle

L - handle shoulder

r - distance from the eccentric rotation axis to the point of contact With

workpiece

α - angle of rise of the curve

α 1 - friction angle between the eccentric and the workpiece

α 2 - friction angle on the eccentric axis

To avoid the eccentric moving away during operation, it is necessary to observe the condition of self-braking of the eccentric

where α - sliding friction angle at the point of contact with the workpiece ø - friction coefficient

For approximate calculations of Q - 12P, consider the diagram of a double-sided clamp with an eccentric

Wedge clamps

Wedge clamping devices are widely used in machine tools. Their main element is one, two and three bevel wedges. The use of such elements is due to the simplicity and compactness of the designs, speed of action and reliability in operation, the possibility of using them as a clamping element acting directly on the workpiece being fixed, and as an intermediate link, for example, an amplifier link in other clamping devices. Typically self-braking wedges are used. The condition for self-braking of a single-bevel wedge is expressed by the dependence

α > 2ρ

Where α - wedge angle

ρ - the angle of friction on the surfaces G and H of contact between the wedge and the mating parts.

Self-braking is ensured at angle α = 12°, however, to prevent vibrations and load fluctuations during the use of the clamp from weakening the workpiece, wedges with an angle α are often used.

Due to the fact that decreasing the angle leads to increased

self-braking properties of the wedge, it is necessary when designing the drive to the wedge mechanism to provide devices that facilitate the removal of the wedge from the working state, since releasing a loaded wedge is more difficult than bringing it into the working state.

This can be achieved by connecting the actuator rod to a wedge. When rod 1 moves to the left, it passes path “1” to idle, and then, hitting pin 2, pressed into wedge 3, pushes the latter out. When the rod moves back, it also pushes the wedge into the pin with a blow working position. This should be taken into account in cases where the wedge mechanism is driven by a pneumatic or hydraulic drive. Then, to ensure reliable operation of the mechanism, different pressures of liquid or compressed air should be created with different sides drive piston. This difference when using pneumatic actuators can be achieved by using a pressure reducing valve in one of the tubes supplying air or liquid to the cylinder. In cases where self-braking is not required, it is advisable to use rollers on the contact surfaces of the wedge with the mating parts of the device, thereby facilitating the insertion of the wedge into its original position. In these cases, it is necessary to lock the wedge.

For large production programs, quick-release clamps are widely used. One type of such manual clamps is eccentric, in which clamping forces are created by turning the eccentrics.

Considerable effort in small area touching the working surface of the eccentric may cause damage to the surface of the part. Therefore, usually the eccentric acts on the part through the lining, pushers, levers or rods.

Clamping eccentrics can have different working surface profiles: in the form of a circle (round eccentrics) and with a spiral profile (in the form of a logarithmic or Archimedean spiral).

A round eccentric is a cylinder (roller or cam), the axis of which is located eccentrically with respect to the axis of rotation (Fig. 176, a, b). Such eccentrics are the easiest to manufacture. A handle is used to rotate the eccentric. Eccentric clamps are often made in the form of crank shafts with one or two supports.

Eccentric clamps are always manual, so the main condition proper operation their purpose is to maintain the angular position of the eccentric after turning it to clamp it - “self-braking of the eccentric”. This property of the eccentric is determined by the ratio of the diameter O of the cylindrical working surface to the eccentricity e. This ratio is called the eccentric characteristic. At a certain ratio, the condition for self-braking of the eccentric is satisfied.

Typically, the diameter B of a round eccentric is set for design reasons, and the eccentricity e is calculated based on the self-braking conditions.

The line of symmetry of the eccentric divides it into two parts. You can imagine two wedges, one of which secures the part when turning the eccentric. The position of the eccentric when it comes into contact with the surface of a minimum size part.

Typically, the position of the section of the eccentric profile that is involved in the work is chosen as follows. so that when the lines 0\02 are in a horizontal position, the eccentric would touch the clamped medium-sized fly with point c2. When clamping parts with maximum and minimum dimensions, the parts will touch, respectively, points cI and c3 of the eccentric, symmetrically located relative to point c2. Then the active profile of the eccentric will be arc C1C3. In this case, the part of the eccentric, limited by the dashed line in the figure, can be removed (in this case, the handle must be moved to another place).

The angle a between the clamped surface and the normal to the radius of rotation is called the angle of elevation. It is different for different angular positions of the eccentric. From the scan it can be seen that when the part and the eccentric touch the points a and B, angle a equal to zero. Its value is greatest when the eccentric touches point c2. At small wedge angles, jamming is possible, at large angles, spontaneous loosening is possible. Therefore, clamping when eccentric points a and b touch the part is undesirable. For calm and reliable fastening of the part, it is necessary that the eccentric comes into contact with the part in section C\C3, when the angle a is not equal to zero and cannot fluctuate within wide limits.

It’s hard to imagine a carpentry workshop without a circular saw, since the most basic and common operation is longitudinal sawing of workpieces. How to make a homemade circular saw will be discussed in this article.

Introduction

The machine consists of three main structural elements:

• base;
• sawing table;
• parallel stop.

The base and the sawing table itself are not very complex structural elements. Their design is obvious and not so complicated. Therefore, in this article we will consider the most complex element - the parallel stop.

So, the rip fence is a moving part of the machine, which is a guide for the workpiece and it is along it that the workpiece moves. Accordingly, the quality of the cut depends on the parallel stop because if the stop is not parallel, then either the workpiece or the saw blade may become jammed.

In addition, the parallel stop of a circular saw must be of a rather rigid structure, since the master makes efforts to press the workpiece against the stop, and if the stop is displaced, this will lead to non-parallelism with the consequences indicated above.

Exist various designs parallel stops depending on the methods of attaching it to the circular table. Here is a table with the characteristics of these options.

Rip fence design	Advantages and disadvantages
Two-point mounting (front and rear)	Advantages:· Quite rigid design, · Allows you to place the stop anywhere on the circular table (to the left or right of the saw blade); Does not require the massiveness of the guide itself Flaw:· To fasten it, the master needs to clamp one end in front of the machine, and also go around the machine and secure the opposite end of the stop. This is very inconvenient when selecting the required position of the stop and with frequent readjustment it is a significant drawback.
Single point mounting (front)	Advantages:· Less rigid design than when attaching the stop at two points, · Allows you to place the stop anywhere on the circular table (to the left or right of the saw blade); · To change the position of the stop, it is enough to fix it on one side of the machine, where the master is located during the sawing process. Flaw:· The design of the stop must be massive to ensure the necessary rigidity of the structure.
Fastening in the groove of a circular table	Advantages:· Fast changeover. Flaw:· Complexity of the design, · Weakening of the circular table structure, · Fixed position from the line of the saw blade, · Quite a complex design for self-made, especially made of wood (made only of metal).

In this article we will examine the option of creating a parallel stop design for a circular saw with one attachment point.

Preparing for work

Before you start work, you need to decide necessary set tools and materials that will be needed during the work process.

The following tools will be used for work:

1. Circular saw or can be used.
2. Screwdriver.
3. Grinder (Angle grinder).
4. Hand tools: hammer, pencil, square.

During the work you will also need the following materials:

1. Plywood.
2. Solid pine.
3. Steel tube with an internal diameter of 6-10 mm.
4. Steel rod with an outer diameter of 6-10 mm.
5. Two washers with an increased area and an internal diameter of 6-10 mm.
6. Self-tapping screws.
7. Wood glue.

Design of a circular saw stop

The entire structure consists of two main parts - longitudinal and transverse (meaning relative to the plane of the saw blade). Each of these parts is rigidly connected to the other and is complex design, which includes a set of parts.

The pressing force is large enough to ensure the strength of the structure and securely fix the entire rip fence.

From a different angle.

The general composition of all parts is as follows:

• The base of the transverse part;

1. Longitudinal part

, 2 pcs.);
• The base of the longitudinal part;

1. Clamp

• Eccentric handle

Making a circular saw

Preparation of blanks

A couple of points to note:

• flat longitudinal elements are made from, and not from solid pine, like other parts.

We drill a 22 mm hole in the end for the handle.

It is better to do this by drilling, but you can simply hammer it with a nail.

The circular saw used for work uses a homemade movable carriage from (or alternatively, you can make it “on a quick fix» false table), which you don’t really mind deforming or ruining. We hammer a nail into this carriage in the marked place and bite off the head.

As a result, we get a smooth cylindrical workpiece that needs to be processed with a belt or eccentric sander.

We make a handle - it is a cylinder with a diameter of 22 mm and a length of 120-200 mm. Then we glue it into the eccentric.

Transverse part of the guide

Let's start making the transverse part of the guide. It consists, as mentioned above, of the following details:

• The base of the transverse part;
• Upper transverse clamping bar (with an oblique end);
• Lower transverse clamping bar (with an oblique end);
• End (fixing) strip of the transverse part.

Upper transverse clamping bar

Both clamping bars– the upper and lower ones have one end that is not straight 90º, but inclined (“oblique”) with an angle of 26.5º (to be precise, 63.5º). We have already observed these angles when cutting the workpieces.

The upper transverse clamping bar serves to move along the base and further fix the guide by pressing against the lower transverse clamping bar. It is assembled from two blanks.

Both clamping bars are ready. It is necessary to check the smoothness of the ride and remove all defects that interfere with smooth sliding; in addition, you need to check the tightness of the inclined edges; There should be no gaps or cracks.

With a tight fit, the strength of the connection (fixation of the guide) will be maximum.

Assembling the entire transverse part

Longitudinal part of the guide

All longitudinal part comprises:

, 2 pcs.);
• The base of the longitudinal part.

This element is made from the fact that the surface is laminated and smoother - this reduces friction (improves sliding), and is also denser and stronger - more durable.

At the stage of forming the blanks, we have already sawed them to size, all that remains is to refine the edges. This is done using edge tape.

The edging technology is simple (you can even glue it with an iron!) and understandable.

The base of the longitudinal part

We also additionally fix it with self-tapping screws. Do not forget to maintain a 90º angle between the longitudinal and vertical elements.

Assembly of transverse and longitudinal parts.

Right here VERY!!! It is important to maintain an angle of 90º, since the parallelism of the guide with the plane of the saw blade will depend on it.

Installation of the eccentric

Installing the guide

It's time to secure our entire structure to circular saw. To do this, you need to attach the cross stop bar to the circular table. Fastening, as elsewhere, is carried out using glue and self-tapping screws.

... and consider the work completed - a circular saw ready with your own hands.

Video

Video on which this material was made.

The devices use two types of eccentric mechanisms:

1. Circular eccentrics.

2. Curvilinear eccentrics.

The type of eccentric is determined by the shape of the curve in the working area.

Working surface circular eccentrics– a circle of constant diameter with a displaced axis of rotation. The distance between the center of the circle and the axis of rotation of the eccentric is called eccentricity ( e).

Let's consider the diagram of a circular eccentric (Fig. 5.19). Line passing through the center of a circle ABOUT 1 and center of rotation ABOUT 2 circular eccentrics, divide it into two symmetrical sections. Each of them is a wedge located on a circle described from the center of rotation of the eccentric. The eccentric lifting angle α (the angle between the clamped surface and the normal to the radius of rotation) forms the radius of the eccentric circle R and radius of rotation r, drawn from their centers to the point of contact with the part.

The elevation angle of the eccentric working surface is determined by the relationship

Eccentricity; - angle of rotation of the eccentric.

Figure 5.19 – Design diagram of the eccentric

where is the gap for free insertion of the workpiece under the eccentric ( S 1= 0.2…0.4 mm); T – workpiece size tolerance in the clamping direction; - eccentric power reserve, protecting it from passing through the dead center (= 0.4...0.6 mm); y– deformation in the contact zone;

where Q is the force at the point of contact of the eccentric; - rigidity of the clamping device,

The disadvantages of circular eccentrics include changing the angle of elevation α when turning the eccentric (and therefore the clamping force). Figure 5.20 shows the development profile of the working surface of the eccentric when it is rotated through an angle ρ . IN initial stage at ρ = 0° elevation angle α = 0°. With further rotation of the eccentric, the angle α increases, reaching a maximum (α Max) at ρ = 90°. Further rotation leads to a decrease in angle α , and at ρ = 180° the angle of elevation is zero again α =0°

Rice. 5.20 – Reaming the eccentric.

The equations of forces in a circular eccentric can be written with sufficient accuracy for practical calculations, by analogy with calculating the forces of a flat single-bevel wedge with an angle at the point of contact. Then the force on the length of the handle can be determined by the formula

Where l– distance from the eccentric rotation axis to the force application point W; r– distance from the axis of rotation to the point of contact ( Q); - friction angle between the eccentric and the workpiece; - friction angle on the eccentric rotation axis.

Self-braking of circular eccentrics is ensured in relation to its outer diameter D to eccentricity. This ratio is called the eccentric characteristic.

Round eccentrics are made of 20X steel, cemented to a depth of 0.8...1.2 mm and then hardened to a hardness of HRC 55...60. The dimensions of the round eccentric must be used taking into account GOST 9061-68 and GOST 12189-66. Standard circular eccentrics have dimensions D = 32-80 mm and e = 1.7 - 3.5 mm. The disadvantages of circular eccentrics include a small linear stroke, inconstancy of the lifting angle, and, consequently, of the clamping force when securing workpieces with large fluctuations in size in the clamping direction.

Figure 5.21 shows a normalized eccentric clamp for clamping parts. The workpiece 3 is mounted on fixed supports 2 and is pressed against them by a bar 4. When clamping the workpiece, a force is applied to the eccentric handle 6 W, and it rotates about its axis, resting on the heel 7. The force arising on the eccentric axis R transmitted through bar 4 to the part.

Figure 5.21 – Normalized eccentric clamp

Depending on the size of the bar ( l 1 And l 2) we obtain the clamping force Q. The bar 4 is pressed against the head 5 of the screw by 1 spring. The eccentric 6 with the bar 4 moves to the right after the part is released.

Curved jaws, unlike circular eccentrics, are characterized by a constant lift angle, which ensures the same self-braking properties at any angle of rotation of the cam.

The working surface of such cams is made in the form of a logarithmic or Archimedean spiral.

With a working profile in the form of a logarithmic spiral, the radius vector of the cam ( R) is determined by the dependence

p = Ce a G

Where WITH- constant; e - base of natural logarithms; A - proportionality factor; G- polar angle.

If a profile made along an Archimedean spiral is used, then

p=aG .

If the first equation is presented in logarithmic form, then it, like the second equation, is in Cartesian coordinates will represent a straight line. Therefore, the construction of cams with working surfaces in the form of a logarithmic or Archimedean spiral can be performed with sufficient accuracy simply if the values R, taken from the graph in Cartesian coordinates, set aside from the center of the circle in polar coordinates. In this case, the diameter of the circle is selected depending on the required stroke value of the eccentric ( h) (Fig. 5.22).

Figure 5.22 – Profile of a curved cam

These eccentrics are made of steels 35 and 45. The outer working surfaces are heat treated to a hardness of HRC 55...60. The main dimensions of curved eccentrics have been normalized.

Good day to lovers of homemade devices. When you don’t have a vice at hand or simply don’t have one, the easiest solution would be to assemble something similar yourself, since you don’t need any special skills or hard-to-find materials to assemble the clamp. In this article I will tell you how to make a wooden clamp.

In order to assemble your clamp, you need to find a strong type of wood so that it can withstand heavy loads. In this case, an oak plank will work well.

To begin the manufacturing phase necessary:
*Bolt, the size of which is best taken around 12-14mm.
*Nut for bolt.
*Whetstones made of oak wood.
*Part of the profile is made of wood with a cross-section of 15mm.
*Carpenter glue or parquet glue.
*Epoxy.
*Varnish, can be replaced with stain.
*Metal rod 3 mm.
*Small diameter drill.
*Chisel or chisel.
*Hacksaw for wood.
*Hammer.
*Electric drill.
*Medium grit sandpaper.
*Vise and clamp.

First step. Depending on your requests, the size of the clamp can be made different; in this case, the author cuts out blocks measuring 3.5 x 3 x 3.5 cm - one piece and 1.8 x 3 x 7.5 cm - two pieces.

After this, we clamp a 75mm long block in a vice and drill a hole using a drill, stepping back 1-2cm from the edge.

Next, match the hole you just made with the hole in the nut and trace the outline with a pencil. After marking, armed with a chisel and hammer, cut out a hexagonal countersunk for the nut.

Second step. To secure the nut in the block, you need to coat the machined groove with epoxy resin inside and immerse the same nut there, drowning it a little in the block.

As a rule, complete drying of the epoxy resin is achieved after 24 hours, after which you can proceed to the next stage of assembly.
Third step. The bolt, which ideally fits our fixed nut in the beam, needs to be modified; to do this, take a drill and drill a hole close to its hexagonal head.

After this, we move on to the bars, they need to be combined together so that there are longer bars on the sides, and a shorter bar between them. Before the three beams are clamped together, you need to drill holes at the fastening point with a thin drill so that the workpiece does not split, because this arrangement is not suitable for us.

Using a screwdriver, we tighten the screws into the prepared drilling places, having previously coated the joints with glue.

We secure the almost finished clamping mechanism with a clamp and wait for the glue to dry. For convenient use of the clamp, you need a lever with which you can clamp your workpieces; they will serve as a metal rod and a round piece of wood with a cross-section of 15 mm sawn into two parts; in both you need to drill a hole for the rod and put it all on glue.

The final stage. To complete the assembly you will need varnish or stain, we sand our homemade clamp, and then coat it with several layers of varnish.

At this point, making your own clamp is ready and it will go into working condition when the varnish is completely dry, after which you can work with this device with complete confidence.