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IS 1369-3 (1995): Fasteners - Thread Run-Outs andUndercuts, Part 3: Dimensions for Screw Thread Run-Outs andUndercuts for Internal Threads (Blind Tapped Holes) [PGD31: Bolts, Nuts and Fasteners Accessories]

IS 1369 ( Part 3 ) : 1995

Indian Standard

FASTENERS-THREADRUN-OUTSAND UNDERCUTS

PART3 DIME’NSIONS FOR SCREW THREAD RWN-OUTS AND UNDERCUTS

FOR INTERNAL THREADS ( BLIND TAPPED HOLES )

Third Revision )

UDC 621-882.083.006-78

@ BIS 1995

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, ‘9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

June 1995 Price Group 2

Bolts, Nuts and Fasteners Accessories Sectional Committee, LM I4

FOREWORD

This Indian Standard ( Part 3 ) (Third Revision ) was adopted by the Bureau of Indian Standards, after the draft finalized by the Bolts, Nuts and Fasteners Accessories Sectional Committee ( LM 14 ) had been approved by the Light Mechanical Engineering Division Council ( LMDC ).

When a threading operation is not performed throughout the iength of the component, then clue to the necessary throat angle or taper lead on the screwing tool, the last few threads cannot be Perfectly formed. The length of these washout threads makes the thread run-out -on the Component.

An undercut of reasonable width allows threads to be cut on a component up to end without the end face of the screwing tool fouling the component. Design requirements are usually for a reasonable degree of control on the diameter at the root or crest of the undercut to avoid weakeni!lg the section at this point, and for sufficient radius at the end of the undercut to avoid stress concentration. The production requirement is for an adequate width of undercut to allow the use of dies ar,d taps with a reasonable throat angle or taper lead.

It is well known that too narrow undercuts or the ~demand for perfect or full threads UP to the shoulder or to the bottom of blind holes add subsequently to manufacturing cost by necessitating the use of special taps and dies. This may require a second screwing operation, or resort to process, such as thread milling or grinding. It is suggested that where recommendations for any of the standard forms of undercut appear at first sight to be inapplicable, an endeavour shall be made to accommodate them by alterations in design, for example, by using through tapped holes. A counterbore or undercut on the first few threads of an internal thread may readily be drilled when tapping a hole and is much simpler to produce than equivalent undercut on the mating external thread.

This standard IS 1369 ‘Dimensions for screw thread run-outs and undercuts’ originally published in 1961 and subsequently revised in 1975 and 1982. This revision has been taken up to publish this standard in three parts. This standard ( Part 3 ) covers the dimensions for screw thread run-outs

- and undercuts for internal threads ( blind tapped holes ). The dimensions for screw thread run- outs and undercuts for external thread have been covered separately in IS 1369 ( Part I ) : 1993 and IS 1369 ( Part 2 ) : I993 respectively.

In the preparation of this standard considerable assistance has been derived from DIN 76 ( Part 1 ) : 1983 ‘Thread run-outs and thread undercuts ~for IS0 metric threads in accordance with DIN 13’.

IS 1369 ( Part 3 ) : 1995

Indian Standard

FASTENERS-THREADRUN-OUTSAND UNDERCUTS

PART 3 DIMENSIONS FOR SCREW THREAD RUN-OUTS AND UNDERCUTS FOR INTERNAL THREADS ( BLIND TAPPED HOLES )

( Third Revision ) 1 SCOPE

This standard covers the dimensions for run-outs and undercuts for internal IS0 metric screw threads in accordance with IS 4218.

1.1 Recommendations for length of full threads in blind tapped holes are also made in this standard.

2 RUN-OUTS

2.1 Run-out, whenever it occurs, shall include the washout threads and clearance, where a clearance is required.

2.2 Run-out for Internal Threads

The width of run-out ‘c’ shall be measured from the point at which the thread root ceases to be fully formed. The dimensions for run-out for

internal threads shall be as given in Table 1. The dimension ‘e’ indicates the additional length needed for tapping and swarf clearance.

3 UNDERCUTS

3.1 Undercuts for Internal Threads

The form of undercut is illustrated in Table 1. Two values of width of undercut g, and g? are provided. The values of width g, which is the clear width and gn which is measured from the starting of the transition angle are given in Table 1. The diameter of the undercut ds shall be as given in Table 1.

4 GUIDE FOR APPLICATION

4.1 Guidelines for application outs and undercuts values are notes in Table 1.

of -thread run- given in foot

IS 1359 ( Part 3 ) : 1995

Table 1 Dimensions for Thread Run-outs and Undercuts for Internal Threads ( Blind Tapped Holes )

( CIauses 2.2 and 3.1 )

All dimensions in millimetres.

i

THREAD RUN-OUT THREAD UNDERCUT

1) Special designs, that is 90” or 60” countersink, shall be indicated on the drawing. A 60’ countersink is recommended for studs with thread run-out and for centre holes and a parallel countersink is recommended for studs screwed in light alloys.

nr d, Mia = Id, da Max standards.

= l*OSd. For nuts, the countersink diameters da are specified in the individual product

3J Permissible deviation forthe calculated dimension t - f 0.5~.

4) Recommended length of full thread of blind hole shall be:

Id - for steel, l.Sd - for cast iron, and 2d - for aluminium alloys.

IS 1369 (-Part 3 ) : 1995

Pitch of Nominal Thread

Thread Run-out Thread

P f Including Blind Hole Extension )

Thread Undercut

Diameter __ ( Coarse Thread )

e & b/i; AL

r

d ( Guideline Values ) w

~.____..

C D c D normal 1J short *I long 3) HI3 normal”) short 3) nolmal 4) short 5)

_ ---- -___ ---

~0.2 - 1.3 0.8 2 d 0.1 + 0.8 0.5 1.2 0.9 0.1 0.25 1.1.2 ) 1.5

-- --_ j 1 24 d+Ol

-- - 1 0.6 ~_-_ 1 1.4 0.12 __- -

0.3 1‘4 1.8 _____ 1.2 2.9 d+ 0~1 --- __-. - ___ T 0.75 1.6 1.25 __~_ 0.16

____- p-_-- ~___

0.35 1.6, 1.7, 1.8 2.1 1.3 3.3 d 0.2 + 1.4 0.9 1.9 1.4 0.16 -___ 0.4 2, 2.3 ( 2.3

-~__ 1.5 3.7 / d + 0.2 --~--p-_.__ 1.6 1 2.2 1.6 0.2 -~-

0 45 2.2, 2.5, 2.6 2.6 --- ___

1.6 4.1 d + 0.2 _ --.-- ~

1.8 1.1 2.4 1.7- -a:2--

I_- --------

0.5 3 2.8 1.8 4.5 d + 0.3 2 1.25 2.7 2 0.2 0.6 3.5 1 3.4 - 2.1 5.4 d + tJ.3

__---- 2.4 1.5 r---- 2.4 0.4 __- -

0.7 4 3.8 ____

24 6.1 d -t 0.3 -. -~.-- -- __ ..-__ __ ---

2.8 1.75 3.8 2.75 0.4

--- -~ --- ~-___-~_

0.75 4.5 4 2.5 6.4 d + 0.3 3 1.9 4 2.9 o-4 -- -- _-

.~_ ______- 0.8 5 4.2 2.7 6.8 c/+0.3 3.2 2 3 0.4 --&z----------

- --?I,7 1 5.1 3.2 8.2 d + 0.5 ~~-------37----- 4 2.5 5.2 0.6 --- ___ ~ -- ----

1.25 8 6.2 3.9 10 d + 0.5 5 3.2 6.7 4.9 0.6 __- 1.5 10 7.3 ---__

/ --- -- 4.6 11.6 d + O-5

-~ 6 3.8 7.8 0.8 -7-- - -- _ - .___ ._ ~-~ __--

1.75 12 8.3 5.2 13.3 d+0.5 7 4.3 9.1 6.4 1

---~_ ---

2 14, 16 9.3 5.8 14.8 rl + 0.5 8 5 10.3 7.3 1 --_ -__ 2.5 18, 20, 22 11.2 __-.-- ___ 7 17.9 d-to.5 10 6.3 13 -F3- -1~2-’

___ --%i-27- - __ -____ ___ _ __ -- -_1_ __

3 13.1 --F2-- 21 d-/-0,5 12 7.5 15.2 10.7 1.6

--- __-~ ___---_

3.5 30, 33 15.2 9.5 24.3 d -I- 0.5 14 9 17.7 12.7 1.6 -- --362F lh8

~___ __-- __ -~ --- _-- -.-_ 4 ___~~ -~- 1015 26.9 d+0.5 16 10 20 14 2 ._ ___ --- -- __ __-

11.9 29.4 d+0.5 _- ___

4.5 42,45 18.4 18 11 23 16 3 _

____ ~.

5 48, 52 ’ 20.8

-m

-“- 33.3 d+0*5

-1

20 12.5 26 18.5 2.5 -- -

_~___ -p- ~ 5.5 56, 60 ;y4 35.8 d + 0.5 22 14 28 20 3.2 ~__~__

6 64, 68 38.4 n + 0.5 -------S------------ 24 15 21 3.2

-- _----

The dimensions specfiied are appro- 6.3 to 4 P 4 to 2.5P IOt 06.3P - 4P 2.5P - - 0.5 P ximately equal to

1) Thread run-out e-normal shall apply when no indications to the contrary appear in the individual standards or 0x1 the drawings.

2) Thread run-out e-short shall apply only when a short extension is required for technical reasons. 01 Thread run-out e-long shall apply only when a long extension is required for technical reasons.

‘) Thread undercut-normal shall apply when no indications to the contrary appear in the individual standards or on the drawings.

5) Thread undercut-short shall apply only when a short thread undercut is required for technical reasons.

3

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This Indian Standard has been developed from DOG : No. LM 14 ( 03 14 ).

Amendments hued Since Publication

Amend No. Date of Issue Text Affected

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