Homemade clamps with an eccentric clamp. Installing a furniture eccentric with your own hands

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An eccentric fastener (rastexes, minifixes, eccentric clamp - whoever calls it that) is one of the most common types of furniture fasteners.

Minifixes are good because the parts fastened with their help can be disassembled and reassembled many times, without loss of rigidity, which would not happen, where with each assembly/disassembly the fastening will lose its rigidity.

There is only one drawback to minifix furniture - it is painstaking work to install it. If you do not have expensive filler equipment, to install it yourself you need to very carefully mark and accurately drill three different holes in three different planes, which usually takes a lot of effort and time.

This work does not tolerate mistakes in marking. After all, you won’t be able to adjust the connection in the end.

Also, its cost cannot be called completely cheap. The price of a minifix is usually 3-4 times more expensive than a confirmation.

Therefore, it should be used in the most necessary cases.

Eccentric clamp used in places where parts are attached (T- or L-shaped), the connection of which must be hidden from prying eyes. For example, they fasten:

Table tops for computer and other tables made of chipboard
Dresser tops
Bottom and roofs and other parts where it is not possible to drill holes on the front of the part.

The installed minifix rod of the eccentric clamp is completely hidden in the chipboard body, and only the eccentric remains visible, which is installed with inside products.

Types of eccentric couplers

Depending on the manufacturer, there are several modifications of the minifix, which includes:

Rod (rastex)
Eccentric (minifix)
Plastic or metal bushing (depending on manufacturer)
Minifix stub (optional)

There are also corner (hinged) and double-sided couplers. But to use them you need to be a complete pervert, and also think carefully about where they can be used. Nowadays, they have practically ceased to be used due to their uselessness.

The eccentric clamp remains popular today, the rod of which it's already underway with chipboard thread, without plastic sleeve. That is, it consists of only two parts: the rod and the eccentric.

But, just in case, in this article we will analyze the installation of two types of this fastener - both with and without a bushing.

Installation instructions for eccentric coupler (without bushing)

Required tool:

Screwdriver
Forstner cutter 15 mm
Drill 7 mm (for rod body)
Drill 5 mm or confirmat (for screwing in the rod)
Ruler, awl, pencil

The standard thickness of the tie rod body is 6 mm, and the length is 44 mm. The eccentric diameter is 15 mm and its depth is 12.5 mm. Photo of eccentric and rod:

As mentioned above, to install a minifix, three holes of different diameters need to be made in the parts to be joined.

So let's start assembling.

For high-quality, so that the eccentric captures the rod head, it should protrude 6 mm:

To screw the rod into the chipboard, a hole is made with a 5 mm drill (or a confirmed one); if it is a sidewall, its center should be located at a distance of 8 mm from the edge, 10-11 mm deep (the rod should be screwed in tightly and to the very end, this can be seen from the mark on the picture).

In another part, markings are made for two holes.

The first is at a center distance of 34 mm from the edge, under the hole with a Forstner cutter with a diameter of 15 mm. Its depth must be equal to the thickness of the eccentric (about 12 mm) so that the eccentric fits flush into the part.

The second hole is made at the end of the part, strictly in the center, with a 7 mm drill (1 mm larger than the rod body).

Installing a tie with a plastic sleeve

The principle of assembling a minifix with a bushing is exactly the same as when installing a metal minifix, with the only difference being You need another hole for the rod.

Video: installing a furniture eccentric coupler

It’s hard to imagine a carpentry workshop without a circular saw, since the most basic and common operation is precisely longitudinal sawing blanks 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 complicated 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 its attachment to 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 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 begin, you need to decide on the necessary set of tools and materials that will be needed during the work process.

The following tools will be used for work:

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

During the work you will also need the following materials:

Plywood.
Solid pine.
Steel tube with internal diameter 6-10 mm.
Steel rod with an outer diameter of 6-10 mm.
Two washers with an increased area and an internal diameter of 6-10 mm.
Self-tapping screws.
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;

Longitudinal part

The base of the longitudinal part;

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 made of (or, as an option, you can whip up a false table), which is not too bad to be deformed or damaged. 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 - upper and lower - 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

The entire longitudinal part consists of:

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 attach our entire structure to the 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.

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 in this case An oak plank works 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 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.

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° elevation angle again equal to zero 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, will represent a straight line in Cartesian coordinates. 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.

The eccentric clamp is clamping element improved designs. 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 wrench, 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 and.

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

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 jaws: round and cylindrical work 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 cams are distinguished by the following designs: round eccentric (GOST 9061-68), eccentric (GOST 12189-66), double eccentric (GOST 12190-66), eccentric forked (GOST 12191-66), eccentric double-bearing (GOST 12468-67) .

Practical use of eccentric mechanisms in various clamping devices 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. Main design parameters 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 clearance 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
Designation	Outer eccentric cam, mm	Eccentricity,	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.

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.

Significant forces with a small contact area of the working surface of the eccentric can 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 turn 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 is clear that when the part and the eccentric touch the points a and B, angle a is 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.

Easy to manufacture, with a high gain, a fairly compact eccentric clamp, which is a type of cam mechanisms, has another, undoubtedly, main advantage...

... – instantaneous performance. If in order to “turn on and off” a screw clamp it is often necessary to make at least a couple of turns in one direction and then in the other, then when using an eccentric clamp it is enough to turn the handle only a quarter turn. Of course, they are superior to eccentric ones in terms of clamping force and working stroke, but with a constant thickness of the fastened parts in mass production, the use of eccentrics is extremely convenient and effective. The widespread use of eccentric clamps, for example, in stocks for assembling and welding small-sized metal structures and elements of non-standard equipment, significantly increases labor productivity.

The working surface of the cam is most often made in the form of a cylinder with a circle or Archimedes spiral at the base. Later in the article we will talk about the more common and more technologically advanced round eccentric clamp.

The dimensions of eccentric round cams for machine tools are standardized in GOST 9061-68*. The eccentricity of the round cams in this document is set to 1/20 of the outer diameter to ensure self-braking conditions over the entire operating range of rotation angles at a friction coefficient of 0.1 or more.

The figure below shows the geometric diagram of the clamping mechanism. The fixed part is pressed against the supporting surface as a result of turning the eccentric handle counterclockwise around an axis rigidly fixed relative to the support.

The position of the mechanism shown is characterized by maximum possible angle α , while the straight line passing through the axis of rotation and the center of the eccentric circle is perpendicular to the straight line drawn through the point of contact of the part with the cam and the center point of the outer circle.

If you turn the cam 90˚ clockwise relative to the position shown in the diagram, then a gap is formed between the part and the working surface of the eccentric equal in magnitude to the eccentricity e. This clearance is necessary for free installation and removal of the part.

Program in MS Excel:

In the example shown in the screenshot, based on the given dimensions of the eccentric and the force applied to the handle, it is determined installation size from the axis of rotation of the cam to the supporting surface, taking into account the thickness of the part, the self-braking condition is checked, the clamping force and the force transfer coefficient are calculated.

The value of the friction coefficient “part - eccentric” corresponds to the case “steel on steel without lubrication”. The value of the friction coefficient “axle - eccentric” is selected for the “steel on steel with lubrication” option. Reducing friction in both places increases the power efficiency of the mechanism, but reducing friction in the area of contact between the part and the cam leads to the disappearance of self-braking.

Algorithm:

9. φ 1 =arctg (f 1 )

10. φ 2 =arctg (f 2 )

11. α =arctg (2*e /D )

12. R =D/ (2*cos (α ))

13. A =s +R *cos (α )

14. e ≤ R*f 1+ (d/2)* f 2

If the condition is met, self-braking is ensured.

15. F = P * L * cos(α )/(R * tg(α +φ 1 )+(d /2)* tg(φ 2 ))

1 6 . k = F/P

Conclusion.

The position of the eccentric clamp chosen for calculations and shown in the diagram is the most “unfavorable” from the point of view of self-braking and gain in strength. But this choice is not accidental. If in such a working position the calculated power and geometric parameters satisfy the designer, then in any other positions the eccentric clamp will have an even greater force transmission coefficient and better conditions self-braking.

When designing, moving away from the considered position towards reducing the size A if other dimensions are kept unchanged, it will reduce the gap for installing the part.

Increase in size A can create a situation where the eccentric wears out during operation and significant fluctuations in thickness s, when it is simply impossible to clamp the part.

The article has deliberately not mentioned anything so far about the materials from which the cams can be made. GOST 9061-68 recommends using wear-resistant surface-cemented steel 20X to increase durability. But in practice, an eccentric clamp is made from a wide variety of materials, depending on the purpose, operating conditions and available technological capabilities. The above calculation in Excel allows you to determine the parameters of clamps for cams made of any materials, just remember to change the values of the friction coefficients in the initial data.

If the article turned out to be useful to you, and the calculation is necessary, you can support the development of the blog by transferring a small amount to any (depending on the currency) of the specified wallets WebMoney: R377458087550, E254476446136, Z246356405801.

Respecting the author's workI beg download file with calculation programafter subscription to article announcements in the window located at the end of the article or in the window at the top of the page!

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.

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.

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

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