Scraper and scraper tool. The essence of the scraping process and scrapers

231. What is scraping?

Scraping - - / that is the process of obtaining the required accuracy under the working conditions of the shapes, sizes and relative position of the surfaces to ensure a snug fit or tight connection.

When scraping, thin chips are cut from uneven surfaces that have already been previously processed by cutting with a file or other cutting tool.

232. What tools are used for scrapping?

Scraping is done by tools called

Scrapers. For the manufacture of scrapers, tool carbon steels UІ0, UYUA, U12, U12A, alloy steel X05, as well as carbide alloys are used.

Ggini inserted into steel holders. Used or failed trihedral or flat files after appropriate grinding can also serve as scrapers.

233. Name the types of scrapers.

There are manual and mechanical scrapers, and they can be flat single-sided and double-sided, solid and with inserted plates, trihedral solid and trihedral single-sided, semicircular one-sided

They are both bilateral, spoon-shaped and universal (Fig. 36).

234. What tools, except scrapers, are used in scraping?

When scraping, cast-iron plates are used to check the surfaces of flat parts for paint, flat and trihedral rulers to check the flatness of a surface, a prism, a rectangular parallelepiped plate, control rollers, probes and other tools for controlling the quality of scraping and grinding. In addition to the tools mentioned, brushes and cleaning materials should be used.

235. What parts does a universal scraper consist of?

The universal scraper consists of a replaceable plate (the working part of the scraper), a body, a stick, a screw and a handle.

236. In what cases is scraping used?

Scraping is applied when you need to remove

Traces of processing with a file or other tool, as well as when you want to get a high degree of accuracy and a small surface roughness of machine parts connected to each other. Scrapering is especially often used in the processing of degales of friction pairs.

237. What needs to be done before proceeding with scraping?

Before proceeding to shabrennya, it is necessary to check the degree of surface roughness and the place of unevenness to be scraped. To detect surface irregularities are plates, rulers, prisms, rollers, probes. When scraping onto paint, scab paint is used. In some cases, scraping is carried out to shine.

238. Name the tool and material used for scraping on the paint.

To scrape parts onto paint, use a plate or ruler, and also paint.

As a paint for scraping, a mixture of machine oil with Parisian blue or ultramarine is used, which has a light paste consistency. Sometimes a mixture of engine oil with soot is used,

239. Explain the process of shabrettz on the paint.

Paint is applied with a thin layer of slab or a ruler.

With a brush or frequent rags, after which the plate or ruler is superimposed on the surface of the part intended for scraping.

After several circular motions of the plate or reciprocating movements of the ruler over the part or part on the plate, the part is carefully removed from the plate.

Appeared colored spots on the part indicate irregularities protruding on the surface of the part. These irregularities are removed by scraping.

240. What spots appear on the surface of the product when it is lapped to the plate on the paint?

When lapping the part to the plate on the paint, larger or smaller colored spots appear on the surface of the part, between which there are light gaps.

Colored spots appear due to irregularities on this surface. 95

The highest irregularities on the surface have a lighter color than the paint due to some abrasion of the paint during grinding movements. The main bulges are characterized by a good paint coating and therefore they have a dense color.

Light and shiny spots on the surface of the part indicate recesses on the surface that are not coated with paint.

241. What is the order of spot removal?

The sequence for removing stains from the surface determines their color.

Scraping begins with the most protruding places indicated by the light color of the paint. Then there are spots with a dense color. Light spots do not scrape.

The degree of accuracy and surface roughness is determined by the number of spots of paint squared with a side of 25 mm (about 16 - good scraping, 25 - very accurate scraping).

242. What are the disadvantages and advantages of scraping?

The disadvantages of scraping are too slow

The processing process and considerable laboriousness, which requires a lot of precision, patience and time from the locksmith. The advantage of this type of processing is the ability to obtain high precision with simple tools (up to 2 microns). The advantages also include the possibility of obtaining precise and smooth curved surfaces, processing closed surfaces and surfaces all the way. Cast iron and steel surfaces of low hardness are well scrapped.

Hardened steel surfaces should be ground.

243. What safety rules should be followed when scraping?

First of all, around the workplace you need to observe cleanliness and order, otherwise the employee may slip and fall, and ultimately get injured. The tool must be used carefully and skillfully, in between work and after its completion, you need to put the tool in a drawer. The scraper should always be held so that the cutting part is facing away from the worker.

Scraper should be well sharpened. When scraping, be sure to remove sharp edges from the parts.

A scraper is a tool for finishing parts, removing a thin layer of material by scraping, up to 0.01 mm. It is used in metalwork for stripping metal before soldering or assembling critical structures, less often for polishing wooden products. Scraping is done after roughing with a file or a cutter. During the operation, the surface is checked by applying to a calibration plate covered with a thin layer of paint. Irregularities covered with paint scrape repeatedly.

There are two types of scrapers: for metal parts and construction. Scrapers for metal are made of tool-type steel by installing carbide steel plates in the groove on the body. Overall dimensions and sharpening angles vary depending on the material and the processing mechanism of the original product, as well as on the angle of the tool to the plane being machined.

Removes a thin layer of metal

Scraping surface shape

The working surface of the tool can be flat, with three faces or shaped for a specific task.

Flat scraper - a tool for interacting with straight surfaces and scraping sharp corners. Suitable for soft metals like aluminum, babbitt. By design, it can be one-sided or two-sided - the latter lasts longer. The length of the tool with the cutting part on one side is up to 250 mm, on both sides - up to 400 mm.

Width differs according to the scribing method:

• 5-10 mm - for high precision machining;
• 12-20 mm - for scraping of small accuracy;
• 20-30 mm - for rough rough scraping.

Reinforced mechanical flat "scraper"

Sharpening angle - 65-75⁰ for roughing, 90⁰ - for finishing; the width of the active cutting part is 1-3 mm.

A trihedral scraper is used for scraping the inner surfaces of cylindrical parts. Tool types:

• with a straight tip;
• curved.

Trihedral scraper working part with grooves

Length - 70-100 mm, optimal sharpening angle - 60⁰. Grooves are cut on the working part to facilitate sharpening.

Shaped scraper - a tool with a cutter machined to a given shape. Cope with inaccessible edges and corners of the part. Usually it is structurally collapsible - a handle and several plates of various shapes with a thickness of about 2 mm.

Shaped nail scraper

Scraper handle and working part

An integral scraper can grind surfaces only at a given angle. For processing other materials or complex irregularities, re-sharpening or changing equipment is required. Manufacturers offer tools with interchangeable insert inserts to avoid unnecessary operations. To scrape off the corner after a flat surface, you just need to change the nozzle.

Universal scraper is a prefabricated tool, which consists of five parts:

• metal case;
• handle made of wood or metal;
• metal holder;
• clamping screw;
• interchangeable tool steel plate.

Compound tool designs

The plate is placed in the clamping mechanism of the housing and is screwed in, which can be located externally on the housing or inside the handle. In the latter case, the screw is twisted by turning the knob clockwise, and loosen - against.

Rationalizers of the scientific and technical sphere, in particular S.G. Kononenko, developed an improved design, also collapsible. It consists of a handle, a body and a removable plate, but fastening is carried out without the help of a screw. At the end of the plate there is a shank resembling the bifurcated tail of a swallow. It is securely fixed in the groove and allows you to remove the plate in a couple of seconds without effort.

Tool Automation Degrees

Automation of equipment accelerates the construction and work with metal. Scraping is a long and laborious process. Today, the only tool that provides quick scaling is an electric scraper.

It is applied for:

• removing paint residues;
• removal of plaster layers;
• scraping off the frozen adhesive for tiles;
• remove traces of cement and screed.

Construction Unit Model

The construction electric scraper is not used for grinding metal - it is used exclusively in construction. This is a device with a housing in the form of a cylinder, inside of which an engine is installed. The nozzle moves on the principle of "back and forth", starting work at the moment when it is pressed firmly against the work surface, which ensures grinding accuracy.

The procedure for working with power tools:

• Firmly fasten the workpiece in a vise.
• Connect the device to the network and set the speed of movement of the nozzle depending on the material of the workpiece.
• Press the working part firmly against the workpiece surface.
• Without changing the pressure, gradually advance the tool forward.

There are three types of nozzles:

• narrow
• wide;
• putty knife;
• wood chisel.

Scraper result

Wide are used in the processing of large surfaces, narrow - for cleaning hard-to-reach places, spatulas - for delicate surfaces. Spatulas and chisels vary in width, just like ordinary nozzles.

How to learn to scrape correctly

Patterning in home construction does not imply preliminary preparation of surfaces, but scraping metal in an industrial environment requires skill.

To work with a tool with your own hands, you need to know what scraping is - this is the order of operations performed sequentially.

1. Lubricate the control plate with a black paint - a mixture of soot and engine oil.
2. Attach the part that needs scrapping to the plate and smoothly swipe it back and forth.
3. Look at the spots on the surface. White indicates the absence of paint and indicates the deepest places, black indicates the presence of paint and indicates the average depth, gray indicates the presence of protrusions requiring scrapping.
4. Prepare a sharpened tool and start scraping off bumps. Hold the scraper at an angle of 30-40⁰, make a forward movement with pressure, and come back calmly. Start with long strokes - from 20 mm, and slowly reduce the amplitude - to 5 mm. Move the tool in different directions - strokes should be crossed at an angle of 45 °.
5. At the end of scrubbing, wipe the part and repeat painting. Check the cleanliness of the grinding using the check box.

Scraping Mechanics

A control frame of 25x25 mm allows you to determine how deep the scraper is. To do this, attach the frame to the part and count the number of spots inside it:

• 5-6 - roughly;
• 7-10 - clean;
• 11-14 - exactly;
• from 22 - jewelry.

How to choose a scraper depending on the surface:

• straight - for grinding edges;
• shaped - for bent parts;
• narrow - for hard alloys and materials;
• wide - for scraping soft materials;
• radius - for flat surfaces.

Scraper point sharpening angle:

• standard - 60-70⁰;
• for bronze and cast iron - about 100⁰;
• for soft alloys - 40⁰.

Nuances and techniques of scraping

The mechanism of scraping depends on the type of surface. The order of processing parts with flat surfaces:

1. Roll the part along the calibration plate, identify irregularities.
2. Pretreat with a tool with a long cutting edge. Start from the edge of the part. Break all the round spots of paint in half, and the oval spots into several parts.
3. Roll the part over the test plate again.
4. Finish with a short edge scraper - up to 15 mm.

Preparing for Scraping

Scraping metal is to remove bumps from the surfaces of metal parts.

There are two methods of scraping:

• away from you when the tool is installed at an angle of 25 °, and the pressure is carried out when moving forward;
• upon yourself when the working movement is moving the tool back.

The second method is more productive - when working on your own, there are notches and roughnesses on the surface that take time to eliminate.

Scaling Mechanisms:

• draft - with a change of direction, the stroke length of the tool is 2-3 cm;
• semi-finished - with a narrow tool, stroke length - 0.5-1 cm;
• finishing - with a scraper from 5 to 12 mm wide, stroke length - 0.3-0.5 mm
• cross - with short strokes with GOI paste.

GOI paste - a substance that improves the efficiency of scraping.

Grinding bar for refueling

Tricks of work:

• Use a disc tool to process large surfaces. To make it yourself, fasten the sharpened cutting disc in the holder. When one face becomes dull, turn the disc over and continue manipulating.
• Choose a one-piece scraper made of solid tool steel, type SHX15. The folding handle can be made of carbon steel.
• A mechanized scraper speeds up the grinding procedure by 15-20 times.

How to make a do-it-yourself scraper

It’s not difficult to buy a worthy scraper, but having materials at the farm you can make a tool that is ideal for your own needs.

Simplest at home

The simplest metalwork scraper can be made with your own hands if you have only one carbide plate for the working part.

Ready product

Necessary tools and materials:

• tetrahedral bar 15x15;
• quick-change plate T5K10;
• bolt with washer;
• sandpaper;
• bulgarian;
• vise.

Sawn slot and groove

The sequence of steps for the manufacture of:

1. Saw off a piece from the bar with a grinder 25-30 cm long. This is the future case.
2. Clamp the case in a vice and perform a cutting wheel of the grinder cuts lengthwise to a depth of 2-3 cm.
3. Measure the cutting insert and cut a groove in the bar under it with a depth of about 0.5-1 cm.
4. Drill a hole for the clamp bolt across.
5. Sand all cuts and place the plate in the groove.
6. Tighten the bolt with a screwdriver or hexagon.

Insert the plate into the housing

Complex tool on machine tools

In the presence of machines and electrical equipment, you can make a do-it-yourself scraper of complex design.

Scraper with attached handle

Tools and materials:

• scraper plate
• milling machine;
• lathe;
• steel bar 2x1.5 cm;
• steel rod with a diameter of 0.5 cm.

Turned parts: base, cover and threaded rod

1. Turn the base from the metal bar under the plate and cover.
2. At the base of the tool, drill a transverse hole to secure the cover to the screw.
3. Cut the threads at the tip of the steel bar, and drill a longitudinal hole of the same diameter in the cover and base of the scraper. Cut the internal thread.
4. Fasten the rod to the base.
5. Carve a handle from a tree - you can use a leg from an ordinary chair.
6. Drill a hole in the handle and install the scraper rod inward.
7. You can further strengthen the handle with a metal ring, having previously turned it out of soft metal.

Tool assembly

Ring at the beginning of the handle

File temporary fixture

A file scraper is worth making only when there is no other material at hand. The file for a high-quality scraper should be wide enough - about 8-10 mm and made of solid material. The optimal length of the tool coincides with the length of the palm or significantly more. The handle is comfortable, fits well in the hand, without injuring the palm of the hand when working.

Manufacturing sequence:

1. Sharpen the working edge of the file under the scraper plate. To remove a large allowance, grind a straight line, for a fine cut - a rounded line.
2. Using a bar or electric emery, sharpen the tool so that a 1 cm notch forms on one side, the end face becomes flat, and fillets form on the sides.

Narrow file - base for scraper

The next step is to fill the tool with diamond paste on an abrasive block, for example, F120:

1. Fasten the bar to the work surface.
2. Install the scraper with the end face on the bar and draw it towards you several times until small irregularities are drained.

Scraper refueling scheme

If the tool slides during operation, refuel it.

To scrape the surface of dirt or bumps or to grind a metal layer to a uniform smooth texture, use a scraper - what is it now you know. Choose the tool according to the type of surface to be treated and the requirements for the final roughness of the material.

Scraping and lapping

TO  category:

Grader repair

Scraping and lapping

Scraper. It is a plumbing operation to remove very thin layers of metal (0.005 ... 0.07 mm thick) for the final finishing of adjacent surfaces in order to ensure their tight fit. Scraping is carried out manually, using a manual mechanized tool and on machines. In all cases, the main cutting tool is a scraper, which can be flat, flat curved, trihedral, shaped and have one-sided and two-sided cutting faces.

Flat scrapers are used for processing flat surfaces, curved - for finishing grooves and grooves and processing soft metals (babbit, aluminum, etc.). Triangular scraper process curved concave surfaces, shaped - inaccessible places. For the treatment of cast iron are scrapers equipped with plates of hard alloys (VK6 and others).

Before scrapping, the metal surface is painted with a mixture of engine oil with azure, minium or blue. To do this, the paint is first applied to the plate with a swab, and already from the plate, the paint is transferred to the part during its circular movements along the painted surface of the plate. Strongly colored places are first subjected to scrambling, i.e.

most prominent and then faintly colored. They scabbard (Fig. 3.13) "from themselves" and "to themselves." The scraper is held at an angle of 25 ... 80 ° to the work surface. They are scrapping, changing the direction of movement of the scraper by an angle of 40 ... 60 °. The whole process includes roughing, semi-finishing and finishing scraping. After each treatment, the quality of scraping on the paint is checked (by the number of spots on an area of \u200b\u200b25X25 mm). If these spots become 20 ... 25, scrapering is completed.

On curved surfaces, paint is applied using a painted mating shaft. Scraping is conducted along an arc with a trihedral scraper. Since manual Shabreniye is laborious, it is mechanized with the help of pneumatic and electromechanical scrapers.

Fig. 3.13. Scraping techniques:
  a - “from myself”; b - “on yourself”

Lapping. Serves to achieve high surface quality of parts working in contact with each other, and to ensure the density and tightness of the interface. When grinding, the accuracy of surface treatment reaches 0.0001 mm, so it is the thinnest surface treatment operation. Lapping is carried out using hard and soft abrasive materials.

Solid abrasive materials include natural minerals such as natural corundum, emery, quartz, flint, and diamond, and artificial materials such as normal, white, and chromium electrocorundum, as well as monocorund, silicon carbides, boron, synthetic diamond, and albor . Moreover, the grinding of steel is carried out by electrocorundums and monocorundum; silicon carbides are used to grind cast irons.

GOI pastes of three grades (coarse, medium and thin), diamond pastes (large, medium, small, thin) belong to soft abrasive materials. Annealed steel, cast iron, copper and aluminum alloys are rubbed with soft abrasive materials. Especially successful pastes are final finishing lapping work (to a mirror shine surface).

Along with abrasive materials, when grinding, kerosene, gasoline, mineral oils, and soda water are used as cutting fluids.

Lapping is carried out with a special lapping tool, which can be flat, cylindrical, etc., depending on the shape of the surface being treated. Lapping is made of cast iron, bronze, copper, glass, oak, maple, etc.

The preliminary grinding in is carried out, as a rule, with copper grindings with grooves, the final grinding with smooth cast-iron grindings.

For GOI pastes, molded glass lapping is well suited.

Lapping begins with the process of applying abrasive materials to lapping, called carting. Flat lapping is carried out with a hardened steel roller or bar. To do this, the abrasives are preliminarily poured either on the lapping or on the plate, on which the roller is then rolled. Sometimes lapping is covered with pre-grease, to which abrasive grains adhere. A round lapping is drawn between two plates.

The flat surfaces of the parts are rubbed on the flat lapping plates with the circular movements of the part (Fig. 3.14, a). Good results are obtained by simultaneously grinding in the thin parts assembled in a bag (Fig. 3.14, b). Lapping of conical surfaces is carried out by rotating in both directions of the part with a knob or rotor. So cork faucets and valves are ground (Fig. 3.14, c).

Manual lapping is a laborious and lengthy process. Lapping is more productive using special lapping machines, as well as ordinary drilling and planing machines, suitably adapted for this.

Fig. 3.14. Methods for grinding parts:
  a - flat parts; b - packages of similar parts; in - conical surfaces; 1 - a gate; 2 - lapping plate

The quality of lapping is checked by means of straightedges, patterns, for lumen and paint (according to the number of spots).

TO  Category: - Repair of motor graders

  - This is the final locksmith operation, which consists in scraping very thin layers of material from the surface of the workpiece using a cutting tool - a scraper. Scraping is used in cases where it is necessary to process surfaces with very low roughness. As a rule, mating surfaces undergo mating surfaces moving relative to each other (rubbing surfaces). With its help, a snug fit of the mating surfaces, reliable retention of lubricant between the rubbing surfaces and the exact dimensions of the parts are achieved.

Both flat and curved surfaces (for example, machine guides), surfaces of sliding bearings, parts of devices, and also surfaces of various tools and devices (for example, calibration plates, squares, rulers) are processed by scraper. In one pass, the scraper can remove a very thin metal layer with a thickness of not more than 0.7 mm from the surface of the workpiece. With medium effort applied to the tool, the thickness of the removed chips is 0.01 ... 0.03 mm.

Scraping is a very time-consuming operation  and requires extremely highly qualified locksmiths. In the practice of locksmithing, scrapping takes about 20%, therefore, mechanization of labor and the replacement of manual scrapping with machine tools are of great importance.

Tools and devices for scraping. Scrapers

The scraper is the cutting tool. Scrapers vary in design  - one-piece and composite, the shape of the cutting edge - flat, trihedral and shaped, as well as the number of cutting faces - one-sided and two-sided.

Scrapers are made fromcarbon tool steels of grades U10 ... U13. Composite scrapers can be equipped with high speed steel or carbide inserts.

To scrape flat surfaces, one- or two-sided scrapers with a straight or curved cutting edge are used (Fig. 4.3, a, b, c). The geometric parameters of the scrapers depend on the type of processing, the material of the workpiece and the angle of installation of the tool with respect to the surface being machined. The end surface of the scraper is sharpened at an angle of sharpening 90 ... 100 ° relative to the axis of the tool. When roughing, the angle of sharpening is 75 ... 90 °, when finishing - 90 °, and when finishing - 90 ... 100 °. The point angle for cast iron and bronze is chosen equal to 90 ... 100 °, for steel - 75 ... 90 °, and for soft metals - 35 ... 40 °.

The choice of the length of the cutting edge and the radius of its rounding depends on the hardness of the processed material and the given roughness of the machined surface. The harder the material being processed and the higher the requirements for the cleanliness of the processed surface, the narrower the cutting edge of the scraper should be and the smaller the radius of curvature.

For rough scraping, scrapers with a cutting edge width of 20 ... 30 mm are used, for finishing - 15 ... 20 mm and for finishing - 5 ... 12 mm.

For scrapping concave surfaces, for example plain bearing shells, trihedral scraper designed  (Fig. 4.3, d), which have three cutting edges and can be straight and curved; their point angle is 60 °. These scrapers have longitudinal grooves (grooves) on their faces, which makes sharpening and refueling more convenient.

In addition to solid ones, compound scrapers are used  (Fig. 4.3, e), allowing to quickly replace the cutting inserts, and therefore convenient for performing various scraping work. Such a scraper consists of a holder body 2, a handle 4 and a clamping screw 3. A replaceable cutting insert 1 made of carbon, high-speed steel or hard alloy is fixed in the holder 2 by rotating the screw 3 using the handle 5.

In a simpler design of the scraper (Fig. 4.3, f), the cutting inserts 6 are fixed in the handle 7 with a nut.

When scrapping loose leaf bearings, to reduce the number of regrindings during operation, scraper rings are used (Fig. 4.4), which can be made from a worn tapered roller bearing ring.

Since scraping is the final operation of metalwork, the quality of its implementation must be monitored throughout the process. For these purposes, verification tools are intended.

Testing tools (Fig. 4.5) include: test plates for monitoring wide flat surfaces; flat test rulers (Fig. 4.5, a, b) used to control the scraping of long and relatively narrow flat surfaces; trihedral angle rulers (Fig. 4.5, c) used to control scraping of surfaces located at an internal angle, corner plates - to control the quality of scraping of surfaces at right angles; as well as test rollers - to control the scraping of cylindrical surfaces and recesses. The quality control of scraping with all of these tools is based on identifying irregularities on the surface treated with scraping. Irregularities on the surface to be treated become visible after applying it to the painted test tool or vice versa, after applying the painted tool to the treated surface and moving them relative to each other.

It is very important that the test tools are kept in proper condition, therefore, after work, the test tool should be cleaned, lubricated and only then put into a case or covered with a lid.

Scraping process.  It consists in the gradual removal of painted protrusions. When scrapping, the scraper is taken in the right hand by the handle, and the left hand is pressed on it (Fig. 164).

Fig. 164. Scraping techniques: a - from myself, b - to myself, c - to myself according to the method of A. A. Baryshnikov

The scraper in relation to the processed surface is set at an angle of 25-30 °, at. In this case, the cutting angle is obtuse (30 + 90 \u003d 120 °). Metal is removed by scraping. The working move when scrapping is moving forward, away from you (when working with a flat scraper with a downward bent end, moving backward towards yourself). When moving backwards, the scraper must be lifted.

The method of scraping from itself has a number of disadvantages, for example:

a) during the working stroke, the scraper strongly cuts into the body of the part to be scrapped, as a result of which the chip has an uneven cross-section. The surface is uneven and torn;

b) at the end of each movement from the scraper there are burrs, which have to be additionally scraped.

Locksmith A. A. Baryshnikov uses a scraper of a new design, which differs from the usual ones in longer (up to 500 mm), which allows the possibility of scrapping on yourself.

When scrapping according to this method, the scraper is installed to the work surface not at an angle of 30 °, as is done when scrapping using the method from oneself, but at an angle of 75-80 °. The second end of the scraper with a wooden handle rests on the shoulder of the worker.

The scraper should be taken by the rod with the left and right hands in the girth.

The advantages of this method are as follows:

a) the increased length of the scraper allows you to use, in addition to the hands, also the shoulder of the worker. In addition, a long scraper is springy, so the cutting part of it cuts into the metal and exits the metal smoothly. The surface in this case is more even, without flaws;

b) as experience has shown, the self-scraping method is much more productive than the self-scraping method.

In those cases when it is required to obtain a smoother surface, it is recommended that scrapping be carried out in three stages (draft, semi-finishing and finishing).

Rough (preliminary) scraping  consists in rough surface treatment: traces and risks of the previous treatment are removed. Work is performed by a scraper with a width of 20-30 mm, a stroke length of 10-15 mm. The direction of the scraper must be changed all the time, and so that the next stroke goes at an angle of 90 ° to the previous one. In one stroke of the scraper, chips 0.02-0.05 mm thick are removed. Scraping is performed until visible risks disappear. The quality of the scraping is checked for paint, which is applied to the test plate. After superimposing and moving the plate, protruding places are visible, which again will scrape.

Semi-finished (spot) scraping  consists in removing only gray, that is, the most prominent places that are identified after checking for paint. Scraping is done with a flat narrow scraper 12-15 mm wide; scraper stroke length from 5 to 10 mm; 0.01–0.02 mm chips are removed in one stroke of the scraper.

Finishing (finishing) scraping  produced when necessary to obtain very accurate products. With light pressure on the scraper, thin chips are removed (less than 0.01 mm). Scrapers with a width of 5 to 12 mm are used, the stroke length of the scraper is 3-5 mm (small strokes).

Cross scraping  performed to improve the appearance of the surface (applying "frost"). It is carried out in short strokes.

When scrapping, paste GOI (State Optical Institute) is used. When using GOI paste, the quality of work improves and labor productivity increases.

GOI pastes are divided into rough pastes with a cutting ability of 45; 40; 35; thirty; 25 and 18 microns; medium with a cutting ability of 17; fifteen; 10 and 8 microns; thin with a cutting ability of 7; 6; 4 and 1 microns.

When scabbing, coarse paste is used, much less than average. After the first transition of scraping, the paste diluted with kerosene is applied to the test plate, the latter is applied to the surface of the product and grinding is started. Lapping is carried out until the paste from green does not turn into black mass. After wiping the cleanly scuffed surface, paste again and repeat the grinding process 3-4 times.

Having wiped a cleanly scuffed surface, break wide brilliant spots with a scraper and grind again with paste. Lapping is continued until the desired scraping accuracy is obtained.

The quality of scraping is determined by the number of spots (dots) when applying a check frame with a square hole of 25X25 mm.

Depending on the purpose of the parts, scrapping is considered complete with a different number of spots per square area with a side of 25 mm.

For example, on the details of metal-cutting machines (beds, tables, carriages, calipers, etc.) there should be 8-16 spots, test plates and rulers-20-25 spots, tools and measuring instruments - 25-30 spots, etc. .