How to draw part features such as threads, holes, counterbores, gears and welds. 11 terms. For each term: meaning, how to show it on a drawing, examples, common mistakes, and differences between JIS and ASME.
Printed from Kezuriba (kezuriba.net/en/drafting/elements/)
Thread representationneji no zushirepresentation of screw threads
Threads are drawn as simplified representations, not as a helix. The major diameter of an external thread and the minor diameter (crest) of an internal thread are drawn with thick continuous lines, and the root diameter with thin continuous lines.[1][2]
Threads are drawn in simplified form. For an external thread, the major diameter (crest) is a thick continuous line and the root diameter a thin continuous line. For an internal thread, the minor diameter (crest) is a thick continuous line and the root diameter a thin continuous line, with hatching up to the thick line.
How to write it on the drawing
Exterior viewDraw an external thread with the major diameter as a thick continuous line and the root diameter as a thin continuous line; draw an internal thread with the minor diameter as a thick continuous line and the root diameter as a thin continuous line.[1][2]
View from the endIn the end view, draw the root diameter as a thin continuous line arc of about 3/4 of the circumference, normally leaving the upper-right quarter open.[1]
Thread lengthShow the end of the full thread with a thick continuous line.[2]
Sectional viewExtend hatching to the thick continuous line that represents the crest.[1]
Hidden threadsDraw both crest and root with thin dashed lines.[1]
ExampleM8 external thread: draw the major diameter 8 as a thick continuous line and the root diameter as a thin continuous line; in the end view, draw only 3/4 of the root circle as a thin continuous line.(An example built from the rules in the sources)[1][2]
Common mistakes
Drawing the full root circle in the end viewWhy: the crest circle and root circle cannot be told apart, and external and internal threads get misread.Fix: draw the root side as a 3/4 arc. Do not mix in older representation methods.[1][2]
Standards: JIS B 0002-1 (general rules) and JIS B 0002-3 (simplified representation).[3][1]
Thread designationneji no arawashikatadesignation of screw threads
A thread is designated by combining the thread designation (type and diameter, plus pitch if needed), tolerance class and direction of winding. Where there is only one pitch, as for metric coarse threads, the pitch is omitted, and left-hand threads get LH.[1][4]
Thread designation: point to the thread with a leader and write the designation (type and diameter). Omit the pitch for coarse threads; for fine threads write the pitch like "×1.25". Add LH for left-hand threads.
How to write it on the drawing
Indicate with a leaderWrite the thread designation on a leader pointing at the threaded portion.[4]
Tolerance class only when neededThe tolerance class can be omitted when not needed.[1]
Nothing is normally added for right-hand threadsRight-hand threads are generally not marked, but add RH if needed.[1]
ExampleM10 (pitch omitted because it is coarse), M10×1.25 (pitch given because it is fine). Add LH for a left-hand thread.(An example built from the rules in the sources)[1][4]
Common mistakes
Forgetting the pitch of a fine threadWhy: omitting the pitch means coarse thread, so a part meant to be fine gets machined as coarse.Fix: always write the pitch for fine threads.[1][4]
JIS and ASMEUnified (inch) threads are designated by major diameter, threads per inch, series (UNC, UNF) and class.[4]
Standard: JIS B 0123:1999 (Designation of screw threads).[5][1]
The part at the end of the threaded portion where the thread form is not fully formed. Draw it as a slanted thin continuous line when it matters for function or to show machining dimensions; it may be omitted.[1][2]
Incomplete thread: the part at the end of the threaded portion where the thread is not fully formed. Draw it with a thin continuous line slanted to the axis when needed, and omit it if it does not matter for function.
How to write it on the drawing
Slanted thin continuous lineDraw a slanted thin continuous line from the end of the threaded portion. It can be omitted if not needed for function.[1][2]
Gear teeth are not drawn one by one; the gear is shown by a drawing with lines for the tip circle and reference circle (pitch circle), together with a data table giving module, pressure angle, number of teeth and so on.[6][7]
Do not draw gear teeth one by one: draw the tip circle as a thick continuous line, the reference circle as a thin chain line, and the root circle as a thin continuous line (may be omitted). In section, draw the root as a thick continuous line and do not hatch the teeth.
How to write it on the drawing
Tip circle: thick continuous lineDraw it as the gear outline with a thick continuous line.[7]
Reference circle: thin chain lineIn both the end view and the axial section, show the position of the reference circle (pitch circle) with a thin chain line.[7]
Add a data tablePlace a data table beside the drawing to summarize the tooth specifications.[6][7]
Do not draw the tooth repetitionThe tooth form can be left undrawn (US teaching materials also show examples that substitute phantom lines for the repeating teeth).[8]
Common mistakes
Drawing the tooth profile and dimensioning itWhy: the tooth form is determined by the values in the data table (module, number of teeth, profile shift coefficient, etc.), and the drawn shape is not a reference.Fix: specify tooth specifications in the data table.[6][7]
Standard: JIS B 0003:2012 (8 types: spur, helical, double helical, crossed helical, straight bevel, spiral bevel, hypoid and worm gears; there is no corresponding international standard). Terms are in JIS B 0102.[6][9]
Gear data tablehaguruma no yomokuhyogear data table
A table that collects, item by item, gear specifications that are hard to show in the drawing. It gives the gear tooth profile, reference rack tooth profile, module and pressure angle, number of teeth, profile shift coefficient, reference pitch circle diameter, finishing method, tooth thickness (span measurement and number of teeth spanned), accuracy, mating gear drawing number, and so on.[7][6]
Data table: specifications that are hard to show in the drawing (module, pressure angle, number of teeth, reference circle diameter, profile shift coefficient, finishing method, accuracy, etc.) are collected in a table beside the drawing.
How to write it on the drawing
Place a table beside the drawingPlace a table to the right of the part drawing or similar, and write the items and values.[7][6]
ExampleShimane University spur gear drawing example: module 4, pressure angle 20°, 20 teeth, profile shift coefficient 0, reference pitch circle diameter 80, base circle diameter 75.18, finishing method hobbing, span measurement 30.6418 (3 teeth spanned), accuracy JIS grade N8, mating gear drawing number.[7]
Standard: JIS B 0003:2012, clause 4.1 "Data table and drawing entries for part drawings".[6]
Spring representation and data tablebane no zushi to yomokuhyospring drawing / spring specification table
Springs are often designed and made to a given force at a given length, or a given length under a given force, so in addition to shape and dimensions, a data table of the design and manufacturing specifications that are hard to show in the drawing is added.[10]1 source (for reference)
How to write it on the drawing
Use the drawing and the data table togetherDraw the spring shape in accordance with JIS B 0001 and add a data table.[10]
Simplified drawingSimplified drawings follow ISO 2162-1 (figures attached to JIS B 0004).[10]
Standard: JIS B 0004:2007 (compression, tension and torsion coil springs, leaf springs, torsion bars, volute springs, spiral springs, disc springs, etc.). Terms are in JIS B 0103.[10][11]
A system of symbols that shows the location, type, size and method of a weld on a drawing. It consists of an arrow pointing to the joint, a horizontal reference line, and a tail for supplementary information; the basic symbol placed on the reference line gives the type of weld.[12][13][14]
Welding symbol: the arrow tip points to the joint to be welded, and the basic symbol giving the weld type is placed on the horizontal reference line. Below the line means the arrow side; above means the other side. Supplementary information goes in the tail.
How to write it on the drawing
Point to the joint with the arrowPlace the arrow tip on the joint to be welded.[13][14]
Draw the reference line horizontallyAlways draw the reference line horizontally and read it from left to right.[13]
Arrow side and other sideWhich side of the reference line the basic symbol is placed on distinguishes a weld on the arrow side from a weld on the other side. In US teaching materials, below the line is the arrow side and above is the other side.[13][14]
Write supplementary information in the tailInformation that cannot be expressed by symbols, such as the welding process and specifications, goes in the tail.[13][14]
Common mistakes
Placing the symbol on the wrong side of the reference lineWhy: the opposite face gets welded, and the groove or fillet ends up on the wrong side.Fix: check in the standard which side of the reference line is the arrow side before placing the symbol.[14][13]
JIS and ASMEISO 2553:2013 gives both System A, based on the former ISO method, and System B, based on Pacific Rim standards. JIS Z 3021 is based on System B; where System A is needed, follow ISO 2553. US teaching materials (AWS-based) also use the arrow, reference line and tail structure.[12][14][13]
Standard: JIS Z 3021:2016 (prepared based on System B of ISO 2553:2013).[12][15]
Fillet weld symbolsuminiku yosetsu no kigofillet weld symbol
The basic symbol for a fillet weld, in which the corner of two members meeting at a right angle is built up with a triangular cross-section. The symbol is a right triangle.[14]1 source (for reference)
The fillet weld symbol is a right triangle (vertical side on the left). Write the leg length to the left of the symbol and the weld length to the right. Below the reference line means an arrow-side weld.
How to write it on the drawing
Place the right triangle on the reference lineIn US teaching materials, a right triangle with the vertical side on the left and the hypotenuse toward the right is placed above or below the reference line.[14]
DimensionsHow to write fillet weld dimensions follows clause 5.5 of JIS Z 3021.[12]
Standard: JIS Z 3021:2016, 4.4 (basic symbols) and 5.5 (fillet welds).[12]
Groove welds and groove dimensionskaisaki yosetsu to kaisaki sunpogroove weld / groove dimensions
Welding in which a groove is machined at the end of the members and filled with weld metal. The groove shape is shown by a basic symbol, and root opening, groove angle, root radius, root face and groove depth are specified by dimensions.[12][14]
Groove weld: a groove is machined at the end of the members and filled with weld metal. The groove shape is shown by a basic symbol (V-groove, etc.), and groove angle, root opening, root face and groove depth are specified by dimensions.
How to write it on the drawing
Add dimensions to the basic symbolWrite dimensions such as root opening and groove angle alongside the basic symbol (details in clause 6 of JIS Z 3021).[12][14]
Standard: JIS Z 3021:2016 clause 6 "Groove dimensions" (6.2 root opening, 6.3 groove angle, 6.4 root radius and root face, 6.5 groove depth).[12]
Weld-all-around and field weld symbolszenshu yosetsu / genba yosetsu no kigoweld all around / field weld
Supplementary symbols placed where the arrow and reference line meet. A circle means welding all around the joint; a flag means welding in the field rather than in the shop.[14]1 source (for reference)
At the junction of the arrow and reference line, a circle means weld all around and a flag means field weld (welded at the installation site, not in the shop).
How to write it on the drawing
At the junction of the arrow and reference lineDraw the weld-all-around circle centered on the junction, and draw the field weld flag rising from it.[14]
Common mistakes
Confusing it with the all-around symbol of geometric tolerancingWhy: the shapes look alike, but the circle in a welding symbol means weld all around, while the circle in geometric tolerancing means applying a tolerance such as profile all around.Fix: tell them apart by which symbol system they appear in.[14][16]
Standard: JIS Z 3021:2016, 4.5 "Supplementary symbols".[12]
Representing keywayski-mizo no arawashikatakeyway / keyseat
A keyway cut in a shaft or hole is shown by the width of the groove and a dimension that defines its depth. In the Shimane University gear part drawing, the keyway in the bore is specified by "width 10 JS9" and "38.3 +0.2/0 from the inner surface opposite the bore to the groove bottom".[7][4]
Keyway: specify the groove width with a tolerance class (such as JS9) and the depth with a measurable dimension (from the inner surface opposite the bore to the groove bottom) (example from the Shimane University gear part drawing).
How to write it on the drawing
Width by tolerance classGive the groove width a tolerance class suited to the fit with the key (JS9 in the example).[7]
Depth by a measurable dimensionSpecify it with a dimension that can be measured: for the bore side, from the opposite inner surface to the groove bottom; for the shaft side, a depth referenced to the shaft diameter, for example.[7][4]
Standard: JIS B 0001:2019, clause 11.8 "Representation of keyways".[17]
Explanations without a mark are those on which two or more sources from different publishers agree. Because the text of the standards is paid, they were checked against technical materials from measuring-instrument and parts manufacturers, teaching materials from universities and public testing institutes, and public pages of the standards, and the explanations are written in Kezuriba's own words. The diagrams of the entry fields were drawn by Kezuriba.