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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(shí)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(shí)間: 2014-5-23 20:19
本帖最后由 HC小丁 于 2014-5-23 20:22 編輯 3 ~' S  K3 U* Z3 p# A$ n

0 i) W! q' l2 l7 i/ P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(shí)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(gè)側(cè)面；后一種標(biāo)法一般用于一個(gè)刀具完成的加工成型，如鉆孔，砂輪磨槽。
作者: hb406863722    時(shí)間: 2014-5-23 21:00
對(duì)于我們加工的來說：左圖我們會(huì)盡量把尺寸做到20.45至20.5之間
0 F3 b7 y0 D4 ?; V                              右圖我們會(huì)盡量把尺寸做到20.4至20.45之間
6 C2 x( y1 h) f* j* o7 T% e                便于裝配
作者: SYZQ1991    時(shí)間: 2014-5-23 22:20
是不是根據(jù)入體原則來的？
作者: 深?yuàn)W的幸福    時(shí)間: 2014-5-23 22:56
長見識(shí)了，我原先以為是個(gè)人的習(xí)慣問題，
作者: aaxin74    時(shí)間: 2014-5-24 10:31
一般是另一個(gè)部件的基本尺寸一樣的
作者: 茉莉素馨    時(shí)間: 2014-5-26 23:12
9.2.3 Converting Dimensions to Equal Bilateral Tolerances2 y- V4 D9 M' ^6 n7 B, K1 {
In Fig. 9-2, there were several dimensions that were toleranced using unilateral tolerances
# Q. P( W( M3 C. I' N9 N(such as .375 +.000/-.031,  3.019 +.012/-.000 and .438 +.000/-.015) or unequal bilateral tolerances (such
9 A$ X! f, }2 G: [4 bas +1.500 +.010/-.004 ). If we look at the length of the shaft, we see that there are several different ways we" D) {9 n) f# ]5 w. E, E# Q
could have applied the tolerances. Fig. 9-4 shows several ways we can dimension and tolerance the length
5 J4 g& m1 ?8 @: U, r; Uof the shaft to achieve the same upper and lower tolerance limits (3.031/3.019). From a design perspective,& i" B' K: o! V( F; J" z
all of these methods perform the same function. They give a boundary within which the dimension is
( O9 c) D% ?6 @" `acceptable.
% R4 N6 H4 w& `[attach]320368[/attach]
  a2 D! P  Z9 E: B8 s- b3 XThe designer might think that changing the nominal dimension has an effect on the assembly. For
$ G4 J% p3 f# T7 K1 y0 h  eexample, a designer may dimension the part length as 3.019 +.012/-.000. In doing so, the designer may7 a: n" D8 L9 s  k
falsely think that this will help minimize the gap for Requirement 1. A drawing, however, doesn’t give
; m& x2 |+ P0 @7 P( T6 npreference to any dimension within the tolerance range.
9 b. d; B- l5 r% L- rFig. 9-5 shows what happens to the manufacturing yield if the manufacturer “aims” for the dimension
6 h4 Z" D% c5 M9 O' Jstated on the drawing and the process follows the normal distribution. In this example, if the manufacturer% {7 M" c* Q% B) Y: i1 |" e7 s
aimed for 3.019, half of the parts would be outside of the tolerance zone. Since manufacturing shops want
" t4 ?% A6 G5 `1 _( K) j0 mto maximize the yield of each dimension, they will aim for the nominal that yields the largest number of
7 a" U2 k! C; e9 T- kgood parts. This helps them minimize their costs. In this example, the manufacturer would aim for 3.025.
7 t5 Q- H. a* w( Z; p4 n0 BThis allows them the highest probability of making good parts. If they aimed for 3.019 or 3.031, half of the' x% ?4 b& Y0 |; ~. r  X4 n* A
manufactured parts would be outside the tolerance limits.
$ R, k6 Z4 F- A, Y+ m, [As in the previous example, many manufacturing processes are normally distributed. Therefore, if we: {4 j7 M1 C; O& m
put any unilateral, or unequal bilateral tolerances on dimensions, the manufacturer would convert them to3 |. h. l$ Z# d  M% R5 o
a mean dimension with an equal bilateral tolerance. The steps for converting to an equal bilateral tolerance
1 N' S$ E6 M8 Cfollow.
. |. T1 R: n  s/ m0 q[attach]320369[/attach]
& o3 H+ R- i$ t, l% i
! }, r6 z" `  k. ]7 m! Z1. Convert the dimension with tolerances to an upper limit and a lower limit. (For example, 3.028 +.003/2 D2 O1 t+ {; D; n8 K6 n" v
-.009 has an upper limit of 3.031 and a lower limit of 3.019.)  G! Z( ?! P" P& Y$ \' z
2. Subtract the lower limit from the upper limit to get the total tolerance band. (3.031-3.019=.012)' l- Q7 S" I# E' E
3. Divide the tolerance band by two to get an equal bilateral tolerance. (.012/2=.006)
0 X- N* `. @$ D  O& v4. Add the equal bilateral tolerance to the lower limit to get the mean dimension. (3.019 +.006=3.025).
1 K: r1 ~0 \6 S2 jAlternately, you could subtract the equal bilateral tolerance from the upper limit. (3.031-.006=3.025)
- k6 H: h. ^+ K3 l- O4 U8 U. F5 i# F9 ]4 k4 Z
As a rule, designers should use equal bilateral tolerances. Sometimes, using equal bilateral tolerances
, v1 {3 _( V0 `! }) H6 W8 |" fmay force manufacturing to use nonstandard tools.  In these cases, we should not use equal bilateral
% ]+ D+ h: P$ I$ f# Itolerances.  For example, we would not want to convert a drilled hole diameter from Æ.125 +.005/-.001 to
, x; g# c) n! {! ?2 PÆ.127 ±.003. In this case, we want the manufacturer to use a standard Æ.125 drill. If the manufacturer sees
. R6 F2 r  W$ G) j1 \Æ.127 on a drawing, he may think he needs to build a special tool. In the case of drilled holes, we would
; g3 d' h8 U8 W' g( _also want to use an unequal bilateral tolerance because the mean of the drilling process is usually larger% j- n/ \7 K/ p
than the standard drill size. These dimensions should have a larger plus tolerance than minus tolerance.
9 X! _. j: G( |+ C8 w  jAs we will see later, when we convert dimensions to equal bilateral tolerances, we don’t need to keep
+ z( }0 l  @  Utrack of which tolerances are “positive” and which tolerances are “negative” because the positive toler-8 i. c1 ?( U6 M7 w+ @% c6 B0 X
ances are equal to the negative tolerances. This makes the analysis easier. Table 9-1 converts the neces-
# N' \' e- s8 r2 hsary dimensions and tolerances to mean dimensions with equal bilateral tolerances.2 b' X  P1 w3 L5 s5 d# @
[attach]320370[/attach]
1 }6 d" j9 g0 g) v- r# o/ C7 {- h
"Dimensioning and Tolerancing Handbook, by Paul J. Drake, Jr."5 ^+ |9 ~( }; u; K2 F
作者: 亂試佳人    時(shí)間: 2014-5-27 08:32
我來看看高手們?cè)趺凑f，我對(duì)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(hào)    時(shí)間: 2014-5-27 16:02
左圖，尺寸盡量避開20.4  e) b. U0 m0 H
右圖，盡量把尺寸避開20.5
作者: 夫俗孒    時(shí)間: 2014-5-28 10:59
影響裝配
作者: 很奇怪的藥    時(shí)間: 2014-5-29 18:58
明顯第一個(gè)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(gè)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(shí)間: 2014-5-29 19:43
若是我的話一般第一個(gè)是標(biāo)注孔尺寸才這樣標(biāo)，第二個(gè)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(shí)間: 2014-5-29 19:52
茉莉素馨 發(fā)表于 2014-5-26 23:12 2 a5 D9 `8 c8 |9 R; V
9.2.3 Converting Dimensions to Equal Bilateral Tolerances6 k9 x4 V) D: G, l  Q: r9 s6 O
In Fig. 9-2, there were several dimension ...

! _2 k( Z' r/ B  英文看不懂，但是圖能看個(gè)大概含義，應(yīng)該還是有區(qū)別的，對(duì)于干過機(jī)加的來說，可能理解會(huì)不一樣' d1 U& g) d/ U- \! z
作者: 機(jī)械inspiration    時(shí)間: 2014-5-29 20:09
2#的言簡意賅了
作者: 機(jī)械inspiration    時(shí)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(shí)間: 2014-5-29 20:32
走正差和負(fù)差
作者: 未來Just    時(shí)間: 2014-5-29 21:00
tedwu 發(fā)表于 2014-5-23 20:57 $ L% N9 |% K; I! ^+ y! a
前一種標(biāo)法，尺寸兩側(cè)分別加工成型，如銑或磨削兩個(gè)側(cè)面；后一種標(biāo)法一般用于一個(gè)刀具完成的加工成型，如鉆 ...
/ l7 f4 m% Q( X
大俠說的第一種標(biāo)法是什么意思呢？不是很理解耶？？, A5 C; y6 s/ p/ ~7 T0 J
作者: 檳城6號(hào)    時(shí)間: 2014-5-29 21:23
檳城6號(hào) 發(fā)表于 2014-5-27 16:02 ; I" y- B* c2 p, g4 c/ r7 Z* c" I
左圖，尺寸盡量避開20.4$ `/ G5 a; G0 K
右圖，盡量把尺寸避開20.5
3 Q0 k0 S$ b) p4 j' ^
交流交流。。
( N" A+ ]5 H) k- E5 a; c2 W# ?
作者: 河之東    時(shí)間: 2014-6-1 17:42
加工的最終尺寸是一樣的，但第二個(gè)尺寸采用的是基軸制。這兩種標(biāo)法表示與之對(duì)應(yīng)的裝配件公稱尺寸不一樣，前一個(gè)的配合件設(shè)計(jì)的公稱尺寸是20，后一個(gè)是20.5.
作者: lbflzcl    時(shí)間: 2014-6-1 18:44
看不懂，請(qǐng)大俠詳解
作者: 衣錦夜行    時(shí)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(shí)間: 2014-6-10 10:38
學(xué)習(xí)了
作者: stoplonely    時(shí)間: 2014-6-10 13:55
好文。收藏學(xué)習(xí)。
作者: seekfor    時(shí)間: 2014-6-13 00:13
茉莉素馨 發(fā)表于 2014-5-26 23:12 # c- k0 Z: [, r7 y( {! H, @. |: N' S
9.2.3 Converting Dimensions to Equal Bilateral Tolerances$ k7 N) G" H# |8 ~% ^6 y
In Fig. 9-2, there were several dimension ...

/ W, i$ v3 G7 y7 ?; m1 a6 Y加工的時(shí)候都控制在中差附近過程能力才高啊，cpk才好嘛。



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