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標(biāo)題: 公差,，這兩種標(biāo)注,，表示意義有什么區(qū)別的,？ [打印本頁]
作者: wucaida    時間: 2014-5-23 20:05
標(biāo)題: 公差,，這兩種標(biāo)注,，表示意義有什么區(qū)別的,？
這兩種標(biāo)注,，表示意義有什么區(qū)別的,？
作者: HC小丁    時間: 2014-5-23 20:19
本帖最后由 HC小丁 于 2014-5-23 20:22 編輯 ! n0 b* D" T" M) z  c/ b

5 ~- s- x$ l" Z+ C' |基本尺寸不一樣,，實(shí)際加工尺寸可能是一樣的,，但設(shè)計(jì)尺寸不同
作者: tedwu    時間: 2014-5-23 20:57
前一種標(biāo)法，尺寸兩側(cè)分別加工成型,，如銑或磨削兩個側(cè)面,；后一種標(biāo)法一般用于一個刀具完成的加工成型，如鉆孔,，砂輪磨槽,。
作者: hb406863722    時間: 2014-5-23 21:00
對于我們加工的來說：左圖我們會盡量把尺寸做到20.45至20.5之間
; y, u7 u/ \1 h9 B) b- \1 T+ `+ k7 K                              右圖我們會盡量把尺寸做到20.4至20.45之間
- x8 g9 e7 W  r7 n) x  U                便于裝配
作者: SYZQ1991    時間: 2014-5-23 22:20
是不是根據(jù)入體原則來的,？
作者: 深奧的幸福    時間: 2014-5-23 22:56
長見識了，我原先以為是個人的習(xí)慣問題,，
作者: aaxin74    時間: 2014-5-24 10:31
一般是另一個部件的基本尺寸一樣的
作者: 茉莉素馨    時間: 2014-5-26 23:12
9.2.3 Converting Dimensions to Equal Bilateral Tolerances% d; u1 E; A+ k* d3 _: M
In Fig. 9-2, there were several dimensions that were toleranced using unilateral tolerances
, X$ w- Q# P. o' ]6 S/ A- i1 M(such as .375 +.000/-.031,  3.019 +.012/-.000 and .438 +.000/-.015) or unequal bilateral tolerances (such
5 K0 [# R4 z  Q4 fas +1.500 +.010/-.004 ). If we look at the length of the shaft, we see that there are several different ways we$ D: Z9 V/ ^1 B
could have applied the tolerances. Fig. 9-4 shows several ways we can dimension and tolerance the length
! U8 |9 q6 q0 {0 K; |of the shaft to achieve the same upper and lower tolerance limits (3.031/3.019). From a design perspective,5 O/ u/ [' G. h$ A' C, t
all of these methods perform the same function. They give a boundary within which the dimension is
. c' z$ r& P5 X, W! xacceptable.
" N. f2 |) P2 d! S4 K( L. ]6 H[attach]320368[/attach]- C; z9 C, l5 q4 D6 A$ A
The designer might think that changing the nominal dimension has an effect on the assembly. For
6 h" y+ J5 c, w5 ]example, a designer may dimension the part length as 3.019 +.012/-.000. In doing so, the designer may9 P1 n1 r, a8 I9 i  w9 X  Y
falsely think that this will help minimize the gap for Requirement 1. A drawing, however, doesn’t give
. S2 E% X, z8 y( s& b# lpreference to any dimension within the tolerance range.
8 j7 p5 j  D/ n& l4 }Fig. 9-5 shows what happens to the manufacturing yield if the manufacturer “aims” for the dimension5 q9 N. y! g4 c- w3 J
stated on the drawing and the process follows the normal distribution. In this example, if the manufacturer. `7 l$ K3 j, L( R' R6 x: h
aimed for 3.019, half of the parts would be outside of the tolerance zone. Since manufacturing shops want
4 J3 q  z+ m5 A8 u: I4 o; X+ gto maximize the yield of each dimension, they will aim for the nominal that yields the largest number of
8 i4 }1 ~4 {* r8 F2 T, Vgood parts. This helps them minimize their costs. In this example, the manufacturer would aim for 3.025.
6 S2 H' k* O2 l7 E+ ]This allows them the highest probability of making good parts. If they aimed for 3.019 or 3.031, half of the
; f: G2 J- C9 f& A1 R4 ~manufactured parts would be outside the tolerance limits.+ r9 n# M. X0 I7 R' h) Y' o5 ]
As in the previous example, many manufacturing processes are normally distributed. Therefore, if we- K! a. F  H0 R, U  v' p) O
put any unilateral, or unequal bilateral tolerances on dimensions, the manufacturer would convert them to
" }* i! \  i$ Ua mean dimension with an equal bilateral tolerance. The steps for converting to an equal bilateral tolerance
) P- y2 x( X" Q7 cfollow.( @& s+ A2 S9 b, k" f- G" k
[attach]320369[/attach]
! y7 }: i& z( x; c. X/ H- p
9 W- p6 I& U3 S' z1. Convert the dimension with tolerances to an upper limit and a lower limit. (For example, 3.028 +.003/% Z0 _4 O$ f! {+ d; L2 B
-.009 has an upper limit of 3.031 and a lower limit of 3.019.)
; \9 p( D) X3 b* O# ]2. Subtract the lower limit from the upper limit to get the total tolerance band. (3.031-3.019=.012): o6 X  c0 |% |% N! w3 o
3. Divide the tolerance band by two to get an equal bilateral tolerance. (.012/2=.006)
9 i) \  E. b8 n- c! b" E( }4. Add the equal bilateral tolerance to the lower limit to get the mean dimension. (3.019 +.006=3.025).
9 i  V0 n9 o5 g& p; c! xAlternately, you could subtract the equal bilateral tolerance from the upper limit. (3.031-.006=3.025)( F6 V  b- v$ G8 g3 T  ]

+ j8 w: c1 P* s2 z# `) X" h+ RAs a rule, designers should use equal bilateral tolerances. Sometimes, using equal bilateral tolerances
$ T& O9 Y# B6 s) q% [+ t1 @may force manufacturing to use nonstandard tools.  In these cases, we should not use equal bilateral
7 r; x# }1 y0 k# d# H5 itolerances.  For example, we would not want to convert a drilled hole diameter from Æ.125 +.005/-.001 to
3 s; g5 B7 u" f9 v0 u( b2 c; }Æ.127 ±.003. In this case, we want the manufacturer to use a standard Æ.125 drill. If the manufacturer sees) s8 P3 O2 S0 B1 Y! Y5 v: b  v
Æ.127 on a drawing, he may think he needs to build a special tool. In the case of drilled holes, we would& @) D' w5 \& e* F3 |3 R
also want to use an unequal bilateral tolerance because the mean of the drilling process is usually larger$ i% ?: @8 c. T5 w) f2 e! |. t) C
than the standard drill size. These dimensions should have a larger plus tolerance than minus tolerance.
" L6 A2 |/ v2 Q; g/ a( S" UAs we will see later, when we convert dimensions to equal bilateral tolerances, we don’t need to keep0 ~, R( C7 O& ]! n
track of which tolerances are “positive” and which tolerances are “negative” because the positive toler-! O! G2 X0 _6 ?7 A' a" d
ances are equal to the negative tolerances. This makes the analysis easier. Table 9-1 converts the neces-/ n9 J* Q3 ~+ b1 t) @8 W
sary dimensions and tolerances to mean dimensions with equal bilateral tolerances.
: w3 I  A9 V4 c( w9 M; z[attach]320370[/attach]
! J0 K1 n$ }5 k6 g
3 Q5 F1 [2 u8 r! E"Dimensioning and Tolerancing Handbook, by Paul J. Drake, Jr."
- l, S( D. ^- ]& n( G8 H' S+ J
作者: 亂試佳人    時間: 2014-5-27 08:32
我來看看高手們怎么說,，我對這些太不熟悉了，這幾天看書貌似看懂了,，其實(shí)還是不懂
作者: 檳城6號    時間: 2014-5-27 16:02
左圖,，尺寸盡量避開20.4. L; j4 s% D. f8 V$ r. p
右圖，盡量把尺寸避開20.5
作者: 夫俗孒    時間: 2014-5-28 10:59
影響裝配
作者: 很奇怪的藥    時間: 2014-5-29 18:58
明顯第一個是過盈配合,，比如你是孔軸之間的配合,，當(dāng)然要確保他們之間固定死，(液氮冷卻后塞進(jìn)去)20是計(jì)算的標(biāo)準(zhǔn)值,，+0.5和+0.4是為了過盈配合而要求的,，第二個應(yīng)該是間隙配合，要求兩配合之間留有間隙,。應(yīng)該和加工沒什么關(guān)系
作者: hongshichao0    時間: 2014-5-29 19:43
若是我的話一般第一個是標(biāo)注孔尺寸才這樣標(biāo),，第二個是標(biāo)注軸尺寸才有的，具體還有什么其他含義聽聽其他大俠的高見
作者: hongshichao0    時間: 2014-5-29 19:52
茉莉素馨 發(fā)表于 2014-5-26 23:12 , D4 J0 A5 @0 `  w' d
9.2.3 Converting Dimensions to Equal Bilateral Tolerances
" K( r, \; S; @In Fig. 9-2, there were several dimension ...
/ }/ y- W: U- B6 r/ [8 _
  英文看不懂,，但是圖能看個大概含義,，應(yīng)該還是有區(qū)別的，對于干過機(jī)加的來說,，可能理解會不一樣! }5 t; C$ w2 o+ Y( |
作者: 機(jī)械inspiration    時間: 2014-5-29 20:09
2#的言簡意賅了
作者: 機(jī)械inspiration    時間: 2014-5-29 20:10
8#扯的太深了,，不知道他是否真理解,，反正我是看不懂,！
作者: 李其超    時間: 2014-5-29 20:32
走正差和負(fù)差
作者: 未來Just    時間: 2014-5-29 21:00
tedwu 發(fā)表于 2014-5-23 20:57
6 T. u( r" l) u: v! ~" a" p前一種標(biāo)法，尺寸兩側(cè)分別加工成型,，如銑或磨削兩個側(cè)面,；后一種標(biāo)法一般用于一個刀具完成的加工成型，如鉆 ...
9 l5 s) A) J! M0 i4 N  J! j
大俠說的第一種標(biāo)法是什么意思呢,？不是很理解耶,？？$ f1 i  S$ a: a' Y  c. \
作者: 檳城6號    時間: 2014-5-29 21:23
檳城6號 發(fā)表于 2014-5-27 16:02 1 d; i8 P) {+ I! G  O" `
左圖,，尺寸盡量避開20.4! M, x- c% a% u0 q" G
右圖,，盡量把尺寸避開20.5
  R% ~3 i# t( h
交流交流。,。) |7 J% `3 f$ W# t
作者: 河之東    時間: 2014-6-1 17:42
加工的最終尺寸是一樣的,，但第二個尺寸采用的是基軸制。這兩種標(biāo)法表示與之對應(yīng)的裝配件公稱尺寸不一樣,，前一個的配合件設(shè)計(jì)的公稱尺寸是20,，后一個是20.5.
作者: lbflzcl    時間: 2014-6-1 18:44
看不懂,，請大俠詳解
作者: 衣錦夜行    時間: 2014-6-2 14:01
實(shí)際是一樣的，但加工精度就不同了
作者: namenon    時間: 2014-6-10 10:38
學(xué)習(xí)了
作者: stoplonely    時間: 2014-6-10 13:55
好文,。收藏學(xué)習(xí),。
作者: seekfor    時間: 2014-6-13 00:13
茉莉素馨 發(fā)表于 2014-5-26 23:12 9 R; |% G# `% s
9.2.3 Converting Dimensions to Equal Bilateral Tolerances! b$ ]* @: ^" |
In Fig. 9-2, there were several dimension ...
+ }. \# X$ d1 p7 B: [
加工的時候都控制在中差附近過程能力才高啊，cpk才好嘛,。



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