Eccentric clamps are easy to manufacture for this reason, they are widely used in machine tools. The use of eccentric clamps can significantly reduce the time for clamping the workpiece, but the clamping force is inferior to threaded clamps.
Eccentric clamps are available in combination with clamps and without them.
Consider an eccentric clamp with a clamp.
Eccentric clamps cannot work with large tolerance deviations (±δ) of the workpiece. With large tolerance deviations, the clamp requires constant adjustment with screw 1.
| Calculation of the eccentric |
The material used for the manufacture of the eccentric are U7A, U8A With
heat treatment up to HR from 50....55 units, steel 20X with carburizing to a depth of 0.8... 1.2 With hardening HR c 55...60 units.
Consider the scheme of the eccentric. Line KN divides the eccentric into two? symmetrical halves consisting, as it were, of 2 x wedges screwed onto the "initial circle".
The axis of rotation of the eccentric is displaced relative to its geometric axis by the amount of eccentricity "e".
For clamping, the section Nm of the lower wedge is usually used.
Considering the mechanism as a combined one consisting of a lever L and a wedge with friction on two surfaces on the axis and the point "m" (clamping point), we obtain a force dependence for calculating the clamping force.
where Q is the clamping force
P - force on the handle
L - handle arm
r - distance from the axis of rotation of the eccentric to the point of contact With
blank
α - slope angle of the curve
α 1 - angle of friction between the eccentric and the workpiece
α 2 - angle of friction on the axis of the eccentric
To prevent the eccentric from moving away during operation, it is necessary to observe the condition of self-braking of the eccentric
where α -
sliding friction angle at the workpiece contact point ø -
coefficient of friction
For approximate calculations Q - 12P Let's consider the scheme of a double-sided clamp with an eccentric
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Wedge clamps
Wedge clamping devices are widely used in machine tools. Their main element is one, two and three-beveled wedges. The use of such elements is due to the simplicity and compactness of 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. Usually self-braking wedges are used. The self-braking condition of a single-sided wedge is expressed by the dependence
α > 2ρ
Where α - wedge angle
ρ - the angle of friction on the surfaces Г and Н of the contact of the wedge with the mating parts.
Self-braking is provided at an angle α = 12°, however, in order to prevent vibrations and load fluctuations during the use of the clamp from weakening the fastening of the workpiece, wedges with an angle of α are often used.<12°.
Due to the fact that a decrease in the angle leads to an increase in
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 it is more difficult to release the loaded wedge than to put it into working condition.
This can be achieved by connecting the actuator stem to the wedge. When the rod 1 moves to the left, it passes the path "1" to idle, and then hitting the pin 2, pressed into the wedge 3, pushes the latter. During the reverse stroke of the rod, it also pushes the wedge into the working position with a blow to the pin. This should be taken into account in cases where the wedge mechanism is driven by a pneumatic or hydraulic actuator. Then, to ensure the reliability of the mechanism, it is necessary to create different pressures of liquid or compressed air from different sides of the 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 fluid 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 introduction of the wedge into its original position. In these cases, the locking of the wedge is mandatory.
With large production programs, quick-acting clamps are widely used. One of the types of such manual clamps are eccentric, in which clamping forces are created by turning the eccentrics.
Significant efforts with a small area of contact with 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 be with a different profile of the working surface: 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, biv). 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 rollers with one or two bearings.
Eccentric clamps are always manual, therefore the main condition for their correct operation is to maintain the angular position of the eccentric after it has been rotated for clamping - “eccentric self-braking”. 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 characteristic of the eccentric. At a certain ratio, the condition of self-braking of the eccentric is fulfilled.
Usually, the diameter B of a round eccentric is set from design considerations, and the eccentricity e is calculated based on self-braking conditions.
The line of symmetry of the eccentric divides it into two parts. One can imagine two wedges, one of which, when the eccentric is turned, fixes the part. The position of the eccentric when it contacts the surface of the smallest part.
Usually, the position of the section of the profile of the eccentric, which is involved in the work, is chosen as follows. so that with the horizontal position of the lines 0\02, the eccentric would touch the point c2 of the clamped fly of medium size. 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 the arc С1С3. In this case, the part of the eccentric, limited on the figure by a dashed line, can be removed (in this case, the handle must be rearranged 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. It can be seen from the scan that when the part and the eccentric touch points a and B, the angle a is equal to zero. Its value is greatest when the eccentric is touched by point c2. At small angles of the wedges, jamming is possible, at large angles - spontaneous weakening. Therefore, clamping when touching the detail of the eccentric points a and b is undesirable. For a calm and reliable fastening of the part, it is necessary that the eccentric comes into contact in the section C \ C3 with the part, when the angle a is not equal to zero and cannot fluctuate over a wide range.
Good day to lovers of homemade devices. When there is no vice at hand or they simply are not available, then the easiest solution is to assemble something similar yourself, since special skills and hard-to-reach materials are not required to assemble the clamp. In this article, I will show you how to make a wooden clip.
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 is well suited.
In order to proceed to the manufacturing stage necessary:
* Bolt, the size of which is better to take in the region of 12-14mm.
* A nut for a bolt.
* Bars made of oak wood.
* Part of the profile made of wood with a section of 15mm.
* Joiner's glue or parquet.
* Epoxy.
* Lacquer, 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 sticks measuring 3.5 x 3 x 3.5 cm - one piece and 1.8 x 3 x 7.5 cm - two pieces.
After that, we clamp a bar 75 mm long in a vice and drill a hole with a drill, stepping back from the edge 1-2 cm.
Next, match the hole you just made with the hole in the nut and circle the outline with a pencil. After marking, armed with a chisel and a hammer, cut out a hex pot for the nut.
Second step. To fix the nut in the bar, it is necessary to coat the machined groove with epoxy resin inside and immerse the same nut there, drowning it a little in the bar.
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, for this we take a drill and drill a hole close to its hexagonal head.
After that, we move on to the bars, they must be combined together so that the bars are longer on the sides, and the bar is shorter between them. Before the three beams are clamped together, it is necessary to drill holes in the place of fastening with a thin drill so that the workpiece does not split, because this arrangement does not suit us.
Using a screwdriver, we twist the screws into the finished drilling places, having previously smeared the joints between each other with glue.
We fix 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, it will just serve as a metal rod and a round-profile piece of wood with a 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 need varnish or stain, we grind our homemade clamp, and then varnish it in several layers.
On this, the manufacture of the clamp with your own hands is ready and it will go into working condition when the varnish dries completely, after which you can work with this device with complete confidence.
It is difficult to imagine a carpentry workshop without a circular saw, since the most basic and common operation is the 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 emphasis.
So, the parallel stop is the movable part of the machine, which is the 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 curve may jam.
In addition, the rip fence of a circular saw must be of a fairly rigid construction, as the worker is exerting force by pressing the workpiece against the fence, and if the fence is allowed to move, this will lead to non-parallelism with the consequences indicated above.
There are various designs of parallel stops, depending on the methods of its attachment to the circular table. Here is a table with the characteristics of these options.
| Rip fence design | Advantages and disadvantages |
| Two-point attachment (front and back) | Advantages:· Pretty rigid construction · Allows you to place the stop in any place of the circular table (to the left or right of the saw blade); Does not require the massiveness of the guide itself Flaw:· For fastening, the master needs to clamp one end in front of the machine, and also go around the machine around and fix the opposite end of the stop. This is very inconvenient when selecting the required position of the stop and is a significant drawback with frequent readjustment. |
| Single point attachment (front) | Advantages:· Less rigid construction than when fixing the fence in two points · Allows you to place the fence in any place of 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 in order to provide the necessary rigidity of the structure. |
| Fastening in the groove of the circular table | Advantages:· Fast changeover. Flaw: Complexity of the design, Loosening of the circular table structure, Fixed position from the line of the saw blade, Quite a complex design for self-manufacturing, especially from wood (made only from metal). |
In this article, we will analyze the option of creating a design of a parallel stop for a circular with one attachment point.
Preparation for work
Before starting work, it is necessary to determine the necessary set of tools and materials that will be needed in the process.
The following tools will be used for work:
- Circular saw or can be used.
- Screwdriver.
- Bulgarian (Angle grinder).
- Hand tools: hammer, pencil, square.
In the process, you will also need the following materials:
- Plywood.
- Massive pine.
- Steel tube with an inner diameter of 6-10 mm.
- Steel rod with an outer diameter of 6-10 mm.
- Two washers with an increased area and an inner diameter of 6-10 mm.
- Self-tapping screws.
- Joiner's glue.
The design of the stop of the circular machine
The whole 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 a complex structure that includes a set of parts.
The pressing force is large enough to ensure structural strength 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
- , 2 pcs.);
- The base of the longitudinal part;
- clamp
- Cam handle
Making a circular
Preparation of blanks
A couple of things to note:
- planar longitudinal elements are made from, and not from solid pine, like other parts.
At 22 mm, we drill a hole in the end for the handle.
It is better to do this with drilling, but you can just fill it with a nail.
In the circular saw used for work, a home-made movable carriage is used from (or as an option, you can make a false table “in haste”), which is not very a pity to deform or spoil. We drive a nail into this carriage in the marked place and bite off the hat.
As a result, we get an even cylindrical workpiece, which must be processed with a belt or eccentric grinder.
We make the handle - this is a cylinder with a diameter of 22 mm and a length of 120-200 mm. Then we glue it into the eccentric.
Cross section of the guide
We proceed to the manufacture of 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 oblique end);
- Lower transverse clamping bar (with oblique end);
- End (fixing) bar of the transverse part.
Upper cross clamp
Both clamping bars - upper and lower have one end not straight 90º, but inclined ("oblique") with an angle of 26.5º (to be precise, 63.5º). We have already observed these angles when sawing blanks.
The upper transverse clamping bar is used to move along the base and further fix the guide by pressing it 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 move and remove all defects that prevent smooth sliding, in addition, it is necessary to check the tightness of the inclined edges; gaps and cracks should not be.
With a snug fit, the strength of the connection (fixing the guide) will be maximum.
Assembly of the transverse whole part
Longitudinal part of the guide
The entire longitudinal part consists of:
- , 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), as well as denser and stronger - more durable.
At the stage of forming the blanks, we have already sawed them to size, it remains only to ennoble the edges. This is done with edging tape.
The edging technology is simple (you can even glue it with an iron!) And understandable.
The base of the longitudinal part
And also additionally fix with self-tapping screws. Do not forget to observe the 90º angle between the longitudinal and vertical elements.
Assembly of the transverse and longitudinal parts.
Right here VERY!!! it is important to observe the angle of 90º, since the parallelism of the guide with the plane of the saw blade will depend on it.
Installation of the eccentric
Guide rail installation
It's time to fix our entire structure on a circular machine. To do this, you need to attach the bar of the transverse stop to the circular table. Fastening, as elsewhere, is carried out with glue and self-tapping screws.
... and we consider the work finished - the do-it-yourself circular saw is ready.
Video
The video on which this material was made.
Eccentric clamps, in contrast to screw clamps, are fast acting. It is enough to turn the handle of such a clamp less than 180 ° to secure the workpiece.
The scheme of action of the eccentric clamp is shown in Figure 7. When the handle is turned, the radius of rotation of the eccentric increases, the gap between it and the part (or lever) decreases to zero; the clamping of the workpiece is carried out due to the further "compaction" of the system: eccentric - part - fixture.
Figure 7 - Scheme of the action of the eccentric clamp
To determine the main dimensions of the eccentric, one should know the magnitude of the clamping force of the workpiece Q, the optimal angle of rotation of the handle for clamping the workpiece ρ, the tolerance for the thickness of the workpiece to be fixed δ.
If the angle of rotation of the lever is unlimited (360°), then the value of the eccentricity of the Cam can be determined by the equation
where S 1 is the installation gap under the eccentric, mm;
S 2 - stroke margin of the eccentric, taking into account its wear, mm;
workpiece thickness tolerance, mm;
Q – workpiece clamping force, N ;
L - clamping device rigidity, N /mm(characterizes the amount of pressing of the system under the influence of clamping forces).
If the angle of rotation of the lever is limited (less than 180°), then the eccentricity value 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 elevation of the eccentric, composed by the clamped surface and the normal to the radius of its rotation, must always be less than the angle of friction, i.e.
(f=0.15 for steel),
Where D And R- respectively the diameter and radius of the eccentric.
The workpiece clamping force can be determined by the formula
Where R - force on the eccentric handle, N (usually taken ~ 150 N );
l - handle length, mm;
– angles of friction between the eccentric and the workpiece, between the trunnion and the eccentric support;
R 0 - radius of rotation of the eccentric, mm.
For an approximate calculation of the clamping force, you can use the empirical formula Q12 R(at t=(4- 5) R and P=150 N) .
a, b - for preloaded flat workpieces; b- for fixing flat workpieces with the help of a rocking beam; G- for tightening the shells with a flexible clamp
Figure 8 - Examples of different designs of eccentric clamps
TaskNo. 3 “Calculation of eccentric clamping parameters”
According to the input data of the tutor, select and calculate the parameters of the eccentric clamp (Figure 7), if the product must be pressed with force Q, clamping device rigidity L, the angle of rotation of the lever is unlimited, the installation gap under the eccentric S 1, the eccentric stroke reserve, taking into account its wear S 2, the tolerance for the thickness of the workpiece, the welder is right-handed .
Calculate the diameter of the eccentric.
Determine the length of the eccentric handle l.
Draw a sketch of the clamp. Select the material from which the clamp should be made.
Table 4 - Task options
|
Q, kN |
L, N/mm |
S 1 , mm |
S 2 , mm |
