A blind threaded hole is made in the following order: first, a hole of diameter d1 under the thread, then the lead-in chamfer is made S x45º (Fig. 8, A) and finally the internal thread is cut d(Fig. 8, b). The bottom of the thread hole has a conical shape, and the angle at the apex of the cone φ depends on drill sharpening A. When designing, φ = 120º (nominal drill sharpening angle) is assumed. It is quite obvious that the depth of the thread must be greater than the length of the threaded end being screwed in fastener. There is also some distance between the end of the thread and the bottom of the hole. A, called "undercut".
From Fig. 9, the approach to assigning the dimensions of blind threaded holes becomes clear: thread depth h is defined as the difference in tie length L threaded part and total thickness H attracted parts (there may be one, or there may be several), plus a small supply of threads k, usually taken equal to 2-3 steps R threads
h = L - H + k,
Where k = (2…3) R.
Rice. 8. Sequence of making blind threaded holes
Rice. 9. Screw fastening assembly
Pull length L fastener is indicated in its symbol. For example: “Bolt M6 x 20.46 GOST 7798-70” - its tightening length L= 20 mm. Total thickness of attracted parts H calculated from the drawing general view(the thickness of the washer placed under the head of the fastener should also be added to this amount). Thread pitch R also indicated in the symbol of the fastener. For example: “Screw M12 x 1.25 x 40.58 GOST 11738-72” - its thread has a fine pitch R= 1.25 mm. If the step is not specified, then by default it is major (large). Lead-in chamfer leg S usually taken equal to the thread pitch R. Depth N threaded holes larger than value h by the size of the undercut A:
N = h + a.
Some difference in calculating the dimensions of a threaded hole for a stud is that the screwed-in threaded end of the stud does not depend on its tightening length and the thickness of the parts being pulled. For the GOST 22032-76 studs presented in the assignment, the screwed-in “stud” end is equal to the diameter of the thread d, That's why
h = d + k.
The resulting dimensions should be rounded to the nearest larger integer.
Final image of a blind tapped hole with required sizes shown in Fig. 10. The diameter of the threaded hole and the sharpening angle of the drill are not indicated in the drawing.
Rice. 10. Image of a blind threaded hole in the drawing
The reference tables show the values of all calculated values (diameters of threaded holes, undercuts, washer thicknesses, etc.).
Necessary note: the use of a short undercut must be justified. For example, if the part at the location of the threaded hole in it is not thick enough, and through hole under the thread may compromise the tightness of the hydraulic or pneumatic system, then the designer has to “squeeze”, incl. shortening the undercut.
The dimensions of the countersinks are indicated as shown in Fig. 63, 64.
If the holes in the part are located on the axes of its symmetry, then angular dimensions should not be entered. Other holes should be coordinated by angular size. In this case, for holes located along the circle at equal distances, the diameter of the center circle is specified and an inscription about the number of holes is specified (Fig. 65, 66).
On the drawings of cast parts that require machining, the dimensions are indicated so that only one dimension is placed between the untreated surface - the casting base and the processed surface - the main dimensional base (Fig. 67). In Fig. 67 and 68, for comparison, provide examples of dimensioning in the drawing of a cast part and a similar part manufactured by machining.
The dimensions of holes in the drawings may be applied in a simplified manner (according to GOST 2.318-81) (Table 2.4) in the following cases:
▪ the diameter of the holes in the image is 2 mm or less;
▪ there is no image of the holes in the section (section) along the axis;
▪ making holes according to general rules makes the drawing difficult to read.
Table 7
Simplified dimensioning Various types holes.
Hole type
d1 x l1 –l4 x
d1 x l1
d1 x l1 –l4 x
d1 /d2 x l3
Continuation of the table. 7
Hole type
Example of simplified hole sizing
d1 /d2 x φ
Z x p x l2 – l1
Z x p x l2 – l1 – l4 x
The dimensions of the holes should be indicated on the shelf of a leader line drawn from the axis of the hole (Fig. 69).
2.3.2. Image, designation and sizing of some parts elements
Most common the following elements: chamfers, fillets, grooves (grooves), grooves, etc.
Chamfers - conical or flat narrow cuts (blunting) of sharp edges of parts - are used to facilitate the assembly process, protect hands from cuts from sharp edges (technical requirements
safety), giving products more beautiful view(requirements of technical aesthetics) and in other cases.
The dimensions of chamfers and the rules for indicating them on drawings are standardized. According to GOST 2.307-68*, the dimensions of the chamfers at an angle of 45° are applied as shown in Fig. 70.
Rice. 70 The dimensions of chamfers at other angles (usually 15, 30 and 60o) are indicated according to
general rules: put down linear and angular dimensions (Fig. 71, a) or two linear dimensions (Fig. 71, b).
The size of the chamfer height c is selected according to GOST 10948-64 (Table 8). Table 8
Normal dimensions of chamfers (GOST 10948-64)
Chamfer height |
|||||||||||||||||||
Note: For fixed landings, chamfers should be taken: at the end of the shaft 30°, in the hole of the sleeve 45°.
Fillet – rounding of external and internal corners on machine parts - widely used to facilitate the manufacture of parts by casting, stamping, forging, and to increase the strength properties of shafts, axles and other parts in places of transition from one diameter to another. In Fig. 74 the letter A marks the location of stress concentration that can cause a crack or break in the part. The use of fillets eliminates this danger.
Rice. 74 The dimensions of the fillets are taken from the same series of numbers as for size c
Rounding radii, the dimensions of which on the drawing scale are 1 mm or less, are not depicted and their dimensions are indicated as shown in Fig. 74.
To obtain a full profile thread along the entire length of the rod or hole, a groove is made at the end of the thread to allow the tool to exit. Grooves come in two designs. In the drawing of the detail, the groove is depicted in a simplified manner, and the drawing is supplemented with an extension element on an enlarged scale (Fig. 49, 51). The shape and dimensions of the grooves, the dimensions of the run-out and undercut are established by GOST 10549-80, depending on the thread pitch p.
In Fig. 75 shows an example of a groove for outdoor metric thread , and in Fig. 76 – for internal metric thread.
Rice. 76 The dimensions of the groove are selected from the tables of GOST 10549-80 (see appendix 5), their
Below are the dimensions of the grooves for external metric threads:
Edges grinding wheel always slightly rounded, so in the place where the part is undesirable to have an indentation from the edges, a groove is made for the grinding wheel to exit.
Such a groove in the detail drawing is depicted in a simplified manner, and the drawing is supplemented with an extension element (Fig. 77, 78).
The dimensions of the grooves depending on the diameter of the surface are established by GOST 8820-69 (Appendix 4).
The dimensions of the grooves for the exit of the grinding wheel can be calculated by
formulas (all dimensions in mm): |
|||
a) at d = 10÷50 mm |
d1 = d –0.5, |
d2 = d + 0.5, |
|
R1 = 0.5; |
|||
b) at d = 50 100 mm |
d1 = d – 1, |
d2 = d + 1, |
|
R1 = 0.5. |
|||
2.3.3. Roughness of part surfaces
Depending on the method of manufacturing the part (Fig. 79), its surfaces may have different roughness (Tables 9, 10).
Rice. 79 Surface roughness is a collection of micro-irregularities
processed surface, examined over a section of standardized length (L). This length is called the base length, it is selected depending on the nature of the surface being measured. The greater the height of the micro-irregularities, the greater the base length.
To determine surface roughness, GOST 2789-73 provides six parameters.
Altitude: Ra – arithmetic mean deviation of the profile; Rz – height of profile irregularities at ten points; Rmax – the highest profile height.
Steppers: S – middle step local profile protrusions; Sm – average pitch of irregularities; Ttp is the relative reference length, where p is the value of the profile section level.
Most common in technical documentation are the parameters Ra (arithmetic mean deviation of the profile) and Rz (height of profile irregularities at ten points).
Knowing the shape of the surface profile, determined by the profilograph at its base length L, it is possible to construct a roughness diagram (Fig. 80),
The dimensions of several identical elements of the product (holes, chamfers, grooves, spokes, etc.) are applied once, indicating the number of these elements on the leader line shelf (Figure 1a). If some elements are located around the circumference of the product, instead of numerical dimensions defining mutual arrangement of these elements, only their number is indicated (Figure 1b). The dimensions of two symmetrically located elements of the product (with the exception of holes) are grouped in one place and applied once, without indicating their number (Figure 2). The number of identical holes is always indicated in full, and their dimensions are indicated only once. If identical elements are located evenly on the product, it is recommended to set the size between two adjacent elements, and then the size (spacing) between the outer elements as the product of the number of spaces between the elements and the size of the gap (Figure 3). When applying a large number of dimensions from a common base (from the “0” mark), a common dimension line is drawn, and dimension numbers are placed at the ends of the extension lines (Figure 4a). Dimensions of diameters of a cylindrical product complex shape applied as shown in Figure 4b.
The coordinate method of applying the dimensions of product elements is allowed if there are a large number of them and an uneven arrangement on the surface: dimensional numbers are indicated in the table, indicating the holes in Arabic numerals (Figure 5a) or capital letters (Figure 5b).
Identical elements located in different parts products are considered as one element if there is no gap between them (Figure 6a) or if these elements are connected by solid thin lines (Figure 6b), otherwise the full number of elements is indicated (Figure 6c).
If identical elements of the product are located on different surfaces and shown in different images, the number of these elements is recorded separately for each surface (Figure 7). The dimensions of identical elements of a product lying on the same surface can be repeated in the case when they are significantly removed from each other and are not related to each other in size (Figure 8). If there are many holes in the product drawing that are similar in size, from which groups can be formed, then the holes in each group are designated conventional sign
(in the image where the dimensions defining their position are indicated), and the number of holes and their sizes for each group are indicated in the table (Figure 9).
Simplified hole sizing
| examples of simplified application of hole sizes in drawings | hole type | Image of a hole and structure of simplified recording of dimensions |
|---|---|---|
| simplified sizing |  |
 |
| smooth through |  |
 |
| smooth through with chamfer |  |
 |
| smooth dull |  |
 |
| smooth solid with chamfer |  |
 |
| smooth through with cylindrical countersink |  |
 |
| smooth through with conical countersink |  |
 |
| smooth through with conical countersink and boring |  |
 |
| threaded through and threaded blind with chamfer |  |
 |
| threaded blind with countersink |  |
 |
threaded through with countersink
Accepted designations of hole elements used in the recording structure: d 1 - diameter of the main hole; d 2 - countersink diameter; l 1 - length of the cylindrical part of the main hole; l 2 - thread length in a blind hole; l 3 - countersink depth; l 4 - chamfer depth; z - thread designation according to the standard; φ - central angle of the countersink; α - chamfer angle.
A blind threaded hole is made in the following order: first, a hole of diameter d1 under the thread, then the lead-in chamfer is made S x45º (Fig. 8, A) and finally the internal thread is cut d(Fig. 8, b). The bottom of the hole for the thread has a conical shape, and the angle at the apex of the cone φ depends on the sharpening of the drill. When designing, φ = 120º (nominal drill sharpening angle) is assumed. It is quite obvious that the depth of the thread must be greater than the length of the screwed-in threaded end of the fastener. There is also some distance between the end of the thread and the bottom of the hole. A, called "undercut".
From Fig. 9, the approach to assigning the dimensions of blind threaded holes becomes clear: thread depth h is defined as the difference in tie length L threaded part and total thickness H attracted parts (maybe
there may be one, or maybe several), plus a small supply of threads k, usually taken equal to 2-3 steps R threads
h = L – H + k,
Where k = (2…3) R.
Rice. 8. Sequence of making blind threaded holes
Rice. 9. Screw fastening assembly
Pull length L fastener is indicated in its symbol. For example: “Bolt M6x20.46 GOST 7798-70” – its tightening length L= 20 mm. Total thickness of attracted parts H is calculated from the general drawing (the thickness of the washer placed under the head of the fastener should be added to this amount). Thread pitch R also indicated in the symbol of the fastener. For example: “Screw M12x1.25x40.58 GOST 11738-72” - its thread has a fine pitch R= 1.25 mm. If the step is not specified, then by default it is major (large). Lead-in chamfer leg S usually taken equal to the thread pitch R. Depth N threaded holes larger than value h by the size of the undercut A:
N = h + a.
Some difference in calculating the dimensions of a threaded hole for a stud is that the screwed-in threaded end of the stud does not depend on its tightening length and the thickness of the parts being pulled. For the GOST 22032-76 studs presented in the assignment, the screwed-in “stud” end is equal to the diameter of the thread d, That's why
h = d + k.
The resulting dimensions should be rounded to the nearest larger integer.
The final image of a blind threaded hole with the required dimensions is shown in Fig. 10. The diameter of the threaded hole and the sharpening angle of the drill are not indicated in the drawing.
Rice. 10. Image of a blind threaded hole in the drawing
The reference tables show the values of all calculated values (diameters of threaded holes, undercuts, washer thicknesses, etc.).
Necessary note: the use of a short undercut must be justified. For example, if the part at the location of the threaded hole in it is not thick enough, and a through hole for the thread can break the tightness of the hydraulic or pneumatic system, then the designer has to “squeeze”, incl. shortening the undercut.
PARTS SUBJECT TO JOINT MECHANICAL TREATMENT
During the manufacture of machines, some surfaces of parts are not processed individually, but together with the surfaces of mating parts. The drawings of such products have special features. Without pretending to full review possible options, let us consider two types of such details found in tasks on the topic.
Pin connections
If in an assembly unit two parts are joined along a common plane and there is a need to accurately fix their relative position, then connecting the parts with pins is used. Pins allow you not only to fix parts, but also to easily restore their previous position after disassembly for repair purposes. For example, in the assembly of two body parts 1 And 2 (see Fig. 11) it is necessary to ensure the alignment of the borings Ø48 and Ø40 for the bearing units. The flanges are pressed using bolts 3 , and the once-adjusted alignment of the borings is ensured by two pins 6 . A pin is a precise cylindrical or conical rod; The hole for the pin is also very precise, with a surface roughness of no worse than Ra 0.8. Obviously, the easiest way to completely match a pin hole, the halves of which are located in different parts, is to first align the two parts in the required position, fasten them with bolts and make a hole for the pin with one pass of the tool in both flanges at once. This is called co-processing. But such a technique must be specified in the design documentation so that the technologist takes it into account when forming technological process assembly manufacturing. Specifying joint machining of pin holes is carried out in design documentation in the following way.
The ASSEMBLY drawing specifies the dimensions of the holes for the pin, the dimensions of their location, and the roughness of the hole processing. The named sizes are marked with “*”, and in technical requirements The following entry is made in the drawing: “All dimensions are for reference, except those marked *.” This means that the dimensions along which holes are made on the assembled assembly are executive and they are subject to control. And in the drawings of the DETAILS, holes for the pin are not shown (and therefore are not made).
Bores with connector
In some machines, bored holes for bearings are located simultaneously in two parts with their parting plane located along the axis of the bearing (most often found in gearbox designs - the “housing-cover” connection). Bores for bearings are precise surfaces with a roughness no worse than Ra 2.5, they are made by joint processing, and in the drawings this is specified as follows (see Fig. 12 and 13).
In the drawings of EACH of the two parts numeric values The dimensions of surfaces processed together are indicated in square brackets. In the technical requirements of the drawing, the following entry is made: “Processing according to dimensions in square brackets should be carried out together with the detail. No...." The number refers to the designation of the drawing of the counter part.
Rice. 11. Specifying a hole for the pin in the drawing
Rice. 12. Boring with connector. Assembly drawing
Rice. 13. Specifying boring with a connector on the drawings of parts
CONCLUSION
After reading the process of creating a part drawing described above, a doubt may arise: do professional designers really work out every small detail so carefully? I dare to assure you – that’s exactly it! It’s just that when making drawings of simple and standard parts, all this is done in the designer’s head instantly, but in complex products- just like that, step by step.
BIBLIOGRAPHICAL LIST
1. GOST 2.102-68 ESKD. Types and completeness of design documents. M.: IPK Publishing House of Standards, 2004.
2. GOST 2.103-68 ESKD. Development stages. M.: IPK Publishing House of Standards, 2004.
3. GOST 2.109-73 ESKD. Basic requirements for drawings. M.: IPK Publishing House of Standards, 2004.
4. GOST 2.113-75 ESKD. Group and basic design documents. M.: IPK Publishing House of Standards, 2004.
5. GOST 2.118-73 ESKD. Technical Proposal. M.: IPK Publishing House of Standards, 2004.
6. GOST 2.119-73 ESKD. Preliminary design. M.: IPK Publishing House of Standards, 2004.
7. GOST 2.120-73 ESKD. Technical project. M.: IPK Publishing House of Standards, 2004.
8. GOST 2.305-68 ESKD. Images – views, sections, sections. M.: IPK Publishing House of Standards, 2004.
9. Levitsky V. S. Mechanical engineering drawing: textbook. for universities / V. S. Levitsky. M.: Higher. school, 1994.
10. Mechanical engineering drawing / G. P. Vyatkin [etc.]. M.: Mechanical Engineering, 1985.
11. Reference guide to drawing / V. I. Bogdanov. [and etc.]. M.:
Mechanical Engineering, 1989.
12. Kauzov A. M. Execution of drawings of parts: reference materials
/ A. M. Kauzov. Ekaterinburg: USTU-UPI, 2009.
APPLICATIONS
Annex 1
Assignment on topic 3106 and an example of its execution
Task No. 26
Example of task No. 26
Appendix 2
Common mistakes students when performing detailing
The carving is made cutting tool with removal of a layer of material, knurling - by extruding screw protrusions, casting, pressing, stamping depending on the material (metal, plastic, glass) and other conditions.
Due to the design of the thread-cutting tool (for example, a tap, Fig. 8.14; dies, Fig. 8.15) or when retracting the cutter, when moving from a section of the surface with a full-profile thread (sections l) to a smooth one, a section is formed where the thread seems to move to no (sections l1), a thread run-out is formed (Fig. 8.16). If the thread is made to a certain surface that does not allow the tool to be brought all the way to it, then an under-thread is formed (Fig. 8.16.6, c). The run-out plus the undercut forms an undercut of the thread. If it is necessary to make a full profile thread, without a run, then to remove the thread-forming tool, a groove is made, the diameter of which is for external thread should be slightly smaller than the internal diameter of the thread (Fig. 8.16, d), and for internal thread- slightly larger than the outer diameter of the thread (Fig. 8.17). At the beginning of the thread, as a rule, a conical chamfer is made, which protects the outer turns from damage and serves as a guide when connecting parts to the thread (see Fig. 8.16). The chamfer is performed before cutting the thread. The dimensions of chamfers, runs, undercuts and grooves are standardized, see GOST 10549-80* and 27148-86 (ST SEV 214-86). Fastening products. Thread exit. Runaways, undercuts and grooves. Dimensions.
Constructing an accurate image of thread turns requires a lot of time, so it is used in rare cases. According to GOST 2.311 - 68* (ST SEV 284-76), in the drawings the thread is depicted conventionally, regardless of the thread profile: on the rod - with solid main lines along the outer diameter of the thread and solid thin lines - along the inner diameter, along the entire length of the thread, including the chamfer ( Fig. 8.18, a). In the images obtained by projection onto a plane perpendicular to the axis of the rod, an arc is drawn along the internal diameter of the thread as a continuous thin line, equal to 3/4 of the circle and open anywhere. In the images of the thread in the hole, solid main and solid thin lines seem to change places (Fig. 8.18.6).
A solid thin line is applied at a distance of at least 0.8 mm from the main line (Fig. 8.18), but not more than the thread pitch. Hatching in sections is brought to the line of the outer diameter of the thread on the rod (Fig. 8.18, d) and to the line of the internal diameter in the hole (Figure 8.18.6). Chamfers on a threaded rod and in a threaded hole that do not have a special constructive purpose, in projection onto a plane perpendicular to the axis of the rod or hole, are not depicted (Fig. 8.18). The thread boundary on the rod and in the hole is drawn at the end of the full thread profile (before the start of the run) with the main line (or dashed if the thread is shown as invisible, Fig. 8.19), bringing it to the lines of the outer diameter of the thread. If necessary, the thread run is depicted with thin lines , carried out at approximately an angle of 30° to the axis (Fig. 8.18, a, b).
A thread shown as invisible is depicted with dashed lines of the same thickness along the outer and inner diameters (Fig. 8.19). The length of the thread is the length of the section of the part on which the thread is formed, including the run-out and chamfer. Typically, drawings indicate only the length l of the thread with full profile(Fig. 8.20, a). If there is a groove, external (see Fig. 8.16, d) or internal (see Fig. 8.17), then its width is also included in the length of the thread. If it is necessary to indicate the run-out or the length of the thread with a run-out, the dimensions are applied as shown in Fig. 8.20, b, c. The undercut of the thread, made all the way, is depicted as shown in Fig. 8.21, a, b. Options “c” and “d” are acceptable.
On drawings in which threads are not made (on assembly drawings), the end of a blind hole can be drawn as shown in Fig. 8.22 On cuts threaded connection in the image on a plane parallel to its axis, only that part of the thread that is not covered by the thread of the rod is shown in the hole (Fig. 8.23).
There are threads: general purpose and special ones intended for use on certain types of products; fasteners, intended, as a rule, for a fixed detachable connection components products, and running gear - to transmit movement. Right-hand threads are predominantly used; LH is added to the designation of left-hand threads. In the designation of multi-start threads, the stroke is indicated, and in brackets - the pitch and its value
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