Purpose, types, nature, techniques and sequence of execution

The fitting operations of the metalwork include: fitting, fitting, lapping and finishing.

For fits  one part to another is first of all necessary for one of the parts to be completely finished - it is the fit for it. In fitting the sliding parts, the most significant obstacle is sharp edges and corners of the rifled surfaces. They are customized until the mating parts will not enter one into the other freely, without a gap. If the connection to the lumen is not visible, they lead on the paint. Traces of friction of one surface over another can also be visible on the surfaces being fitted. These traces, having the appearance of shiny spots, show that these places interfere with the movement of one part over the other. Brilliant places (or traces of paint) file the file until the part is completely finished. When any fitting work can not leave sharp edges and burrs on the details; they need to be smoothed with a file, as you can get hurt about them. The quality of the treatment of the ends and edges can be judged by tracing them with your finger.

The concept of “smoothing the edges” should not be confused with the concept of “chamfering”. When chamfering on the edge of the parts do a small flat ribbon, inclined at an angle of 45 ° to the side edges of the part.

By fitting called mutual fitting of parts mating without a gap. Both closed and semi-closed circuits are fitted. The fit is characterized by high machining accuracy. In the fitting parts, the hole is called the armhole, and the part entering the armhole is the liner. Templates, counterpatterns, die tools (punches and dies), etc., are fitted to the template. The template and counter pattern are working parts, so that when the template sides and the counter pattern are in contact, there is no gap between these sides for any of the possible mutual options. rearrangement of template and counter-template.

Lapping  - surface treatment products priterom, which is a tool from soft materials with grinding powder. With the help of a lap, the thinnest metal layer (up to 0.02 mm) is removed from the workpiece. The thickness of the metal layer, removed with a lap in one pass, does not exceed 0.002 mm. Lapping is done after working with a file or a scraper to finish the surface of the workpiece and give it the greatest accuracy. Lapping is a very accurate finishing finishing operation and is used to provide tight, tight detachable and movable joints (the connection of parts of taps, valves, well-holding fluid and gases). The accuracy of grinding parts is made from 0.001 to 0.002 mm, or until the mating surfaces are completely coincident. The allowance for this operation is 0.01-0.02 mm. Grinding is done on the stove. Electrocorundum, emery (aluminum oxide), silicon carbide, crocus (iron oxide), chromium oxide, Viennese lime, tripoli, crushed glass, diamond dust, GOI pastes and other materials are used as abrasives. Of the lubricants most commonly used lube oil, kerosene, gasoline, toluene, alcohol.

In order to grind the parts, an abrasive powder mixed with oil is applied to the lapping plate with a thin, even layer. The part is laid with a rubbed surface on the slab and in a circular motion to move it across the entire slab to obtain a matte or glossy (shiny) surface.

In the process of grinding mechanical removal of metal particles combined with chemical reactions. When working with abrasive substances, the surface being treated is oxidized under the action of abrasive and oxygen. Motion priter, this film of oxidized metal is removed from the surface, but the surface immediately oxidized again. In this way, the metal is removed until the surface acquires the required accuracy and cleanliness of processing.

Fine-tuning  perform on pre-polished surfaces, with left allowance for debugging from 0.01 to 0.02 mm. Lapping is a type of lapping and serves to obtain not only the desired shapes and surface roughness, but also the specified dimensions of parts with high accuracy. Finished surfaces are more durable, which is a determining factor for measuring and calibration instruments and very precise parts.

Work tools and fixtures

An important condition for high-quality machining of customized surfaces and holes is the right choice of files. Files are chosen according to the section profile depending on the shape of the surfaces and holes to be machined: for recesses and holes having a square section - square files, for rectangular - flat and square files, for triangular - triangular, rhomboid and semicircular, for hexagon holes - trihedral and square . Files should have a width of the working part of no more than 0.6-0.7 the size of the side of the recess or hole, the length of the file is determined by the size of the treated surface (along the length) plus 200 mm. When machining curvilinear surfaces of holes in the form of radial, oval or complex curvilinear contours, round or semi-circular files are used, in which the radius of curvature must be less than the radius of curvature of the contour to be machined. The fitting is done with files with small and very small notches - № 2, 3, 4 and 5, as well as abrasive powders and pastes.

Also, high-quality machining of parts contributes to the correct selection of fasteners, such as manual vices, allowing you to quickly fasten the workpiece. Their design allows clamping the part in a vice with a tapered device, which spreads and reduces the jaws when rotating the round handle with the knurled surface. Oblique jaws are used for clamping parts when filing inclined surfaces and chamfering. The slanting jaws are inserted between the jaws of a conventional parallel locking vice.

Lekalny vice is applied to performance of operations at which high precision of basing and reliability of fixing of a detail is required (when marking, drilling, expansion, flat and profile grinding). These clutches differ from machine clutches by high precision manufacturing and the possibility of their installation on three mutually perpendicular planes. The fixed sponge is one with the body. The design of the movable jaw allows it to move along the precisely ground surface of the body. The direction of the lips set two keys. The movable sponge is held on the plane of the housing with screws that pass through the remote stop and the bar.

The remote stop with the screws tightened allows the parts to move along a sliding fit relative to the body guides. The sponge is moved with the help of a screw rotating in a nut fixed on the body and locked with a pin in the movable sponge. The side surfaces of the curved vice are strictly perpendicular to the ground base and parallel to each other, and the clamping surfaces of the jaws are perpendicular to the base and the upper surface of the vice housing. All the main parts of the vice are made of steel U7A, subjected to heat treatment to hardness HRC 55-58 and grinding with tolerances according to the second accuracy class. Clamps are widely used when performing fitting operations performed by a mechanic. For example, a clamp with a differential clamping screw has the following design. The differential clamping screw clamps the package of plane-parallel parts and regulates both the parallelism of the jaws and the clamping force, which is especially important during surface work.

The clamp has two clamping strips connected by two screws. Differential screw, i.e. with two cuts of different diameter and different pitch. The screw has a spring-loaded tip, self-aligning in the recess of the bar. Such a device makes it possible at the beginning to clamp the parts with a screw, and only then with a screw, which, with small dimensions, the clamp allows to obtain a reliable fastening with considerable clamping force.

To facilitate the work and provide higher accuracy in processing the edges of parts, locksmiths use special tools to ensure optimal installation of the workpiece, secure its fastening in the required position and create exact directions to the processing tool (file, file, abrasive bar, and lap). There are various designs of devices: from the simplest filing square to complex frame devices with roller guides, goniometers, sinus rulers. Parallels are used for machining rectilinear surfaces of patterns and patterns. The parallel with prismatic guides inserts consists of two hardened and well ground at right angles with grooved slats, in which are placed two guides of the liner, tightly seated in the slots. Moving the slats relative to each other and clamping the workpiece is done with two screws.

For metalwork processing of internal right angles for templates, gauges and curved tools used sliding squares. For manual processing of patterns, patterns and various calibers before and after quenching, they are used universal parallel. This device replaces several parallels used to process individual elements of a template profile. It consists of a body, on the side surfaces of which there are a large number of holes with an M6 thread. The holes are arranged in vertical and horizontal rows at a distance of 10 mm from each other. A slat with a longitudinal groove, which serves as a guide plane along which the working tool moves, is attached to one of the end surfaces of the housing on pins and screws. On the front side of the case there is a vertical groove with a through slot along its entire length, in which a slider is placed, moving along the groove. In the desired position, the slider is fixed with a screw located on the back of the case. In the upper part of the slider there is a through hole, two sides of which form a prism. A screw is screwed from the end of the slider, with which a pin that serves as an axle is pressed to the prism. On this axis, the process hole is put on the processed template when reproducing the arc sections of its profile. The diameter of the protruding part of the pin is 2 mm. The setting for a given radius is performed by moving the slider along the groove with the control of the distance from the axis of the pin to the working plane of the device. The installation is carried out according to the block of terminal measures and with the help of a curve ruler.

Preparing for sawing begins with the marking and naming of the marking scratches, and then, using the marking risks, drill holes and cut through the armholes formed by drilling. The best is obtained marking on a metal surface, polished with emery paper.

One hole is drilled for sawing when the armhole is small; Two or more holes are drilled in large armholes in order to get the smallest allowance for sawing. Large jumpers are difficult to remove from the drilled armhole, however, holes should not be placed too close to avoid squeezing, which can lead to breakage of the drill.

  Sawing in the workpiece square hole.  First, mark the square, and in it - the hole (Figure 15.2.1, a), then drill the hole with a drill, the diameter of which is 0.5 mm smaller than the side of the square.

Four corners are cut in the drilled hole with a square file, not reaching 0.5 ... 0.7 mm to the marking marks, after which the hole is cut to marking marks in the following sequence; First, sides 1 and 3 are sawed through, then 2 and 4 and the hole is fitted on the tap so that it enters the hole only to a depth of 2 ... 3 mm.

Figure 15.2.1 Sawing a square hole: a - marking, b - method of work. (NI Makienko. General plumbing course M .: Higher School. 1989.)

Further processing of the sides (Figure 15.2.1, b) is carried out until the square head is light, but doesn’t fit tightly into the hole.

  Sawing in the workpiece triangular holes.  The contour of the triangle is marked, and there is a hole in it and drilled with a drill, without touching the markings of the triangle (Fig. 335, a, b). Then, three corners are sawed in a round hole and sides 1, 2 and 3 are successively sawn, not reaching 0.5 mm before the marking risks, after which the sides of the triangle are fitted (Fig. 335, c).

Figure 15.2.2 Sawing a three-sided hole: a - marking, b - drilled hole, c - the order of sawing, d - checking with an insert (NI Makienko. General plumbing course Moscow: Higher School. 1989.)

When working with a three-sided file, they tend to avoid undercuts of the sides and file them in a strictly straight line. The accuracy of processing is checked by an insert.

When fitting, make sure that the liner enters the hole being cut freely, without tilting and tightly. The gap between the sides of the triangle and liner when checking the probe should be no more than 0.05 mm.

Fitting a file is one of the most difficult to work as a locksmith, since the processing has to be carried out in hard to reach places. It is advisable to carry out this operation bornapilniki, grinding borgolovkami, using filing and stripping machines.

When fitting the liner to the finished hole, the work is reduced to the usual filing. When fitting over a large number of surfaces, the two mating base sides are first treated, then the other two are brought in until the desired conjugation is obtained. Details must enter one into the other without pitching, freely. If the product is not visible on the lumen, they lead on the paint.

Sometimes on the surfaces being fitted and without paint, traces of friction of one surface over another can be distinguished. Traces that look like shiny spots ("fireflies") show that this place interferes with the movement of one part over the other. These places (protrusions) are removed, achieving or lack of gloss, or uniform gloss over the entire surface.

When any fitting work can not leave sharp edges and burrs on the details, they need to smooth out a personal file. How well the edge is smoothed can be determined by tracing it with your finger.

Matching is the exact mutual fitting of parts that connect without gaps in any re-styling. The fitting is characterized by high machining accuracy, which is necessary for the backlash-free coupling of parts (a light gap of more than 0.002mm is visible).

Both closed and semi-closed circuits are fitted. Of the two parts to be fitted, it is accepted to call the opening of the pier, and the detail entering the armhole is called the liner.

Arms are open (Figure 15.2.3) and closed (Figure 15.2.2). It is done by fitting files with small and very small notches - № 2, 3, 4 and 5, as well as abrasive powders and pastes.

Figure 15.2.3 Fitting: a - armhole, b - liner, c - sawing, d - checking by liner (Makienko, NI. General plumbing course Moscow: Higher School., 1989.)

In the manufacture and fitting of templates with semicircular outer and inner contours, a part with an inner contour is first made - a hole (Figure 15.2.3, a). The liner is fitted to (fit) the machined armhole (Figure 15.2.3, b).

When processing the armholes, at first, wide planes are precisely sawn off as base surfaces, then in rough outline - edges (narrow faces) 1, 2, 3 and 4, then a semicircle is marked with compasses, cut out with a hacksaw (shown in dashed figure), and an exact filing of a semicircular recess is made ( Figure 15.2.3, c) and check the accuracy of the processing with the insert, as well as symmetry with respect to the axis (using calipers).

When processing the liner, they first saw wide surfaces, and then the ribs 1, 2 and 3. Next, cut corners and cut with a hacksaw. After that, an exact filing and fitting of the fins 5 and 6 are performed. Then, an exact filing and fitting of the liner to the armhole are performed. The fit accuracy is considered sufficient if the liner enters the armhole without skewing, pitching and gaps (Figure 15.2.3, d).

In the manufacture and fitting of oblique inserts in the holes of the "dovetail" type (Figure 15.2.4, a, b), the insert is first processed (processing and testing it is easier).

Processing are in the following order.

At first, wide planes are precisely sawn off as base surfaces, and then all four narrow edges (edges) 1, 2, 3 and 4. Next, mark the sharp corners (Figure 15.2.4, a), cut them with a hacksaw and precisely cut them. First, edges 5 and 6 are sawn (figure 15.2.4, a) in a plane parallel to edge 1, then edges 7 and 8 (figure 15.2.4, a) along a ruler and at an angle of 60 ° to edge 4. The acute angle (60 ° ) measured angular pattern.

Figure 15.2.4.Packing oblique inserts: a - layout of external corners, b - sawing the outer surface, c - layout of internal corners, d - sawing internal corners, d - liner check (Makienko NI. General plumbing course M. : Higher school., 1989.)

The gap is processed in the following order. At first, wide planes are precisely sawn, and then all four edges.

Next, the grooves are marked, cut with a hacksaw (in Figure 15.2.4, shown in strokes) and filing edges 5, 6 and 7. First, the groove width is made less than required by 0.05 ... 0.1 mm while maintaining strict symmetry of the side edges the groove relative to the axis of the armhole (the depth of the groove is immediately accurate in size). Then, when fitting the liner and the armhole, the groove width gets the exact size according to the protrusion of the liner. The accuracy of fitting is considered sufficient if the liner enters the armhole tightly by hand without lumen, rolling and warps (Figure 15.2.4, d).

Manual sawing, fitting and fitting are very labor-intensive operations. In modern conditions, these operations are performed using metal-cutting equipment for general and special purposes, in which the role of locksmith is reduced to machine control and dimensional control.

Curvilinear and shaped parts are processed on grinding machines with special profiled abrasive wheels. Electrospark, chemical and other processing methods that exclude additional finishing manually are also widely used.

However, when performing assembly and repair work, as well as during final processing of parts obtained by stamping, it is necessary to perform these works manually.

The use of special tools and devices to improve the performance of sawing and fitting. Such tools and devices include manual files with interchangeable blades, wire files covered with diamond chips, filing prisms, filing marks, etc.

TO  category:

Metal cutting

The essence of sawing and fitting

In the practice of metalworking, the processes of sawing and fitting are quite common, especially when carrying out repair and assembly work, as well as in the tool shops of engineering plants.

The essence of the sawing process is that square holes, rectangular, oval, and other shapes are obtained by machining round holes with files of different profiles.

In some cases, blanks of machine parts and products with holes of the desired shape are obtained by the method of stamping, but their final processing is also carried out by files by sawing according to the dimensions indicated on the drawings. In order not to damage the walls of the hole being cut by the side edges of the file, its section must be smaller than the size of the hole. Cutting holes in parts with narrow, flat and rectilinear surfaces is done with basting, frames and parallels.

Fitting - the final exact fit of one part to another without any gaps, rocking and distortions. In this case, one of the parts before fitting and fitting must be processed within the specified accuracy.

Templates, counterpatterns, dies and punches of stamps, etc. are put in order. The template and counter pattern are working very precisely, so that when the preset sides of the template and counter pattern are not connected, there is no gap between them when any of the possible reciprocal permutations.

They make fitting in both closed (closed) and semi-closed (open) contours. These contour cavities (holes) are called the armhole m.

The correctness of their contours is checked by special gauge-templates, called workings.

Sawing and file fitting are very time-consuming manual processes; wherever possible, they are trying to mechanize.

The fit is the final exact fit of one part to another without gaps, pitching and warps. Both closed and semi-closed circuits are fitted. The correctness of the fitting of parts is checked with special gauge-templates, which are called workings (Fig. 115, c).

When sawing and fitting semicircular details  first make the part with an internal contour. This detail is called the armhole (Fig. 115, d), since it is easily processed and measured with round rollers and washers. To the treated armhole fit the liner.

The armholes are processed in the following order: first, a wide plane is precisely sawn off as a base, then in rough outline — edges 1; 2; 3 and 4, after which they mark the semicircle with a compass, cut them with a hacksaw (as shown by the dotted line in the figure), precisely trim the rib 1 and the semicircular notch and check for a washer-pattern, as well as for symmetry with respect to the axis using a caliper.

Fig. 115   Sawing and fitting parts:

in - check production, d - fitting the liner and armhole, d - fitting oblique-angle liners

When processing the liner, wide planes are first sawed, and then all four edges. Next, mark and cut with a hacksaw corners, as shown by the dotted line in the figure. After that, exact filing of ribs 5 and 6 is performed in parallel and in the same plane. Then accurate filing and fitting of the liner to the armhole is performed. The accuracy of fitting is considered sufficient if the liner enters the armhole without distortions, pitching and gaps.

When sawing and fitting oblique inserts and armholesshown in fig. 115, d, processing begins with a liner, since it is easier to process and check. The insert is processed in the following order: at first it is roughly sawn, then exactly sawed a wide plane as a base and all four narrow edges. Next is the marking of sharp corners, cutting them with a hacksaw and accurate filing. And first, edges 5 and 6 are sawed in a plane parallel to edge 1, then edges 7 and 8 along the ruler, square and at an angle of 60 ° to edge 5. They must be symmetrical with respect to the axis of the liner, since the latter must be turned towards the armhole. An acute angle of 60 ° is measured by special angular patterns.

The pier is processed in the following order: first, a wide plane is precisely sawn, and then all four edges are set. Next, the grooves are marked, grooved with a hacksaw (shown in dotted lines) and filing ribs 5, 6 and 7. First, the groove width is made less than required by 0.05-0.1 mm while maintaining the strict symmetry of the side edges of the groove with respect to the armhole axis; the depth of the groove is immediately accurate in size. Then, when fitting the liner and the armhole, the groove width gets the exact size according to the shape of the protrusion of the liner. The accuracy of fitting is considered sufficient if the liner enters the armhole tightly by hand, without gaps, pitching and warps.

Increase productivity.  When sawing and fitting, it is possible to increase productivity by using special tools and fixtures. These tools and devices include: manual files with interchangeable plates, filing prisms, filing marks, etc.

Manual file with replaceable plates  consists of a body made of alloy metal, in which replaceable inserts of high-quality carbon steel are fixed. Plates have notches. Under each tooth there is a hole through which the removed chips are pressed, which prevents the teeth from clogging with chips.

This file is used for processing different metals (steel, aluminum, copper), as well as materials (wood, leather, rubber, etc.). After wear, the plates are changed. Experience has shown that prefab files are much more productive than normal ones.

Fill prism (Fig. 116, a) consists of two plates 1 with guides 2-3. A clamping plate 4, a rectangular angle 5 and a ruler 6 are fixed on the side surface of the plate with the threaded hole 7. The workpiece is installed between the guides 2-3 so that the metal layer to be removed protrudes above the planes of the guides, then the part is rigidly attached with the clamping plate 4. After installing the workpiece, the prism is fixed in a metal vice (Fig. 116, b). Square 5 and ruler 6 are used to verify the installation of the workpiece.

Fig. 116. Fill prisms:

a - general view: 1 - plates, 2, 3 - guides, 4 - clamping plate, 5 - square, 6 - ruler, 7 - threaded hole; b - filing techniques, details in a prism

Sliding frame  is a type of filler prism and has the same purpose. It consists of two metal rectangular bars with grooves along the edges, which include two guide rails connecting these bars.

The rectangular block is tightly connected with screws to one end of the guide rails. Such a device allows installation in the sliding frame of the machined parts of different sizes (within the length of the guide rails).

The frame is installed in a metalwork vice, after which the workpiece is clamped in it, which is then sawn.

  Sawing holes

TO  category:

Glare, lapping, etc.

Sawing holes

Sawing is the processing of holes in order to give them a certain (specified) shape. In the products and their details there are holes round, oval, triangular, square, rectangular and other shapes. All such holes can be machined manually and mechanically.

Round and oval holes are cut with round, semi-circular and oval files, triangular holes with three-edged, hacksaw and diamond-shaped files, square holes with square files, and rectangular holes with square and flat files.

In order that the side edges of the file not to damage the side walls of the hole being cut, its section must be smaller than the size of the hole.

For cutting holes in parts with narrow, flat and straight surfaces, basting, frames and parallels are used.

Consider a few examples of sawing holes.

Production from a strip steel plate with a hole in the middle.

This work should be done as follows:
1) measure and mark the length of the plate on the strip and cut off the blank from the strip;
  2) straighten the plate on the plate;
  3) saw the sides 2 and 4 on the square applied to the sides 1 and 5;
  4) remove burrs from the edges of the plate;
  5) mark and center the center of the hole, mark and mark the contour of the hole for cutting;
  6) 2 mm from the line of the applied contour, apply the contour of the hole for sawing;
  7) straighten the plate;
  8) cut the cut hole at risk;
  9) deburr the edges of the hole ..

Fig. 1. Steel plate (detail)

Sawing in the workpiece template triangular holes on the markup (Fig. 2). Precision machining 0.05 mm probe.

The work must be performed in the following sequence:
  1) mark up the contour of the hole being cut and drill it;
  2) cut three corners of the trihedron in the round hole of the workpiece;
  3) consistently cut the sides of the hole, not reaching 0.5 mm to the risks;
  4) cut the sides / and 2 to the risks and adjust them to the square and using the control insert;
  5) cut up the risks to side 3 and fit it to the sides 1 and 2 on the square with the inspection of the liner;
  6) adjust the sides 1, 2 and 3 of the trihedron so that the liner enters the hole freely; the gap between the side of the template and the liner when checking the probe should be no more than 0.05 mm; after adjustment, remove burrs from sharp edges of a triangular hole. Sawing a square hole in the workpiece on the markup.

Fig. 2. A template with a hole triangular

Fig. 3. Collar with square hole

The hole is processed as follows:
  1) drill a hole in the workpiece -
  2) put risks on the boundaries of a given square hole;
  3) cut four corners in a hole with a square file, not reaching 0.5 mm before scratching;
  4) saw (align) in the hole side of the square, not reaching 0.5 mm to the risks;
  5) cut all sides of the square to the risks;
  6) fit the sides of the hole on the square head of the tap or sweep, while first cut sides (the head of the tap should enter the hole only with the ends and only to a depth of 1-2 mm), then sides 2 and 4 are cut and then finally treated one after the other all sides, finishing the fit, when the square head will easily enter the square hole without pitching;
  7) deburring sharp edges of a square hole.

Fig. 4. Sawing a window in a cast iron bar

Cutting out a window in a cast iron bar.

This work should be done as follows:
1) mark the window according to the size of the drawing and remove the jumper between the round holes of the workpiece with a crossbar;
  2) cut down the formed protrusions to scratch;
  3) cut a hole in the size of the caliper caliper flat personal file with semicircular ribs;
  4) remove burrs from the edges of the cut window.