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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(yè)]
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 , U& r& T+ M2 N/ U: {( w& D

  m5 B6 X: w' k4 W# x% l7 e$ V/ e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(lái)說(shuō)：左圖我們會(huì)盡量把尺寸做到20.45至20.5之間
5 c& J8 R1 ^, d8 N; E                              右圖我們會(huì)盡量把尺寸做到20.4至20.45之間4 q( P& o! w" q3 {( u
                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(lái)的？
作者: 深?yuàn)W的幸福    時(shí)間: 2014-5-23 22:56
長(zhǎng)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 Tolerances0 q# Y* X# l+ Q, I3 H- f
In Fig. 9-2, there were several dimensions that were toleranced using unilateral tolerances
. a, b% G: x# a2 d4 v) `(such as .375 +.000/-.031,  3.019 +.012/-.000 and .438 +.000/-.015) or unequal bilateral tolerances (such- Q9 p, S/ r8 R
as +1.500 +.010/-.004 ). If we look at the length of the shaft, we see that there are several different ways we0 T  \# S3 A3 F! h; E8 d+ P
could have applied the tolerances. Fig. 9-4 shows several ways we can dimension and tolerance the length* A9 p9 Q- I) a' J- W% V8 q* R
of the shaft to achieve the same upper and lower tolerance limits (3.031/3.019). From a design perspective,
6 |+ {, z- t- Y* Y% L$ f/ yall of these methods perform the same function. They give a boundary within which the dimension is
% J4 P+ }" F# v7 y/ j. t6 H# eacceptable.$ T, T: b5 Z- V/ b+ H
[attach]320368[/attach]; T/ ?5 Q+ [6 ?& F9 M# ~/ d
The designer might think that changing the nominal dimension has an effect on the assembly. For' k7 W- P% Z- S4 g# D" ^3 [
example, a designer may dimension the part length as 3.019 +.012/-.000. In doing so, the designer may
* x7 }4 e  `1 U+ Rfalsely think that this will help minimize the gap for Requirement 1. A drawing, however, doesn’t give6 u, u( |# t# ~" ]7 `# v
preference to any dimension within the tolerance range.4 [5 |2 T5 q7 G+ U) g
Fig. 9-5 shows what happens to the manufacturing yield if the manufacturer “aims” for the dimension$ v' p1 \9 n" E% I8 L8 W
stated on the drawing and the process follows the normal distribution. In this example, if the manufacturer0 p/ @3 {, f% S- ~% E
aimed for 3.019, half of the parts would be outside of the tolerance zone. Since manufacturing shops want
% P8 d" w2 u9 a% D3 f; Zto maximize the yield of each dimension, they will aim for the nominal that yields the largest number of
( @* ^, I" c" R4 ?  z2 K9 Ogood parts. This helps them minimize their costs. In this example, the manufacturer would aim for 3.025.
3 |% ?, E9 Z( w. W5 ^This allows them the highest probability of making good parts. If they aimed for 3.019 or 3.031, half of the( [" O: E6 w2 d5 l2 L$ c" n
manufactured parts would be outside the tolerance limits.' F. ?2 Q8 r% ]  Z# D9 w4 w1 S
As in the previous example, many manufacturing processes are normally distributed. Therefore, if we
3 }. t5 B" q9 d5 F0 Uput any unilateral, or unequal bilateral tolerances on dimensions, the manufacturer would convert them to
2 P9 l6 R6 Z  x8 X+ ia mean dimension with an equal bilateral tolerance. The steps for converting to an equal bilateral tolerance
: [+ y, z* M' ~5 z3 n; [follow.) V# O1 m- Z' l. R
[attach]320369[/attach]& K2 f4 D0 ]) W& l- \! k

  W$ l; Y* P7 t. |, D1. Convert the dimension with tolerances to an upper limit and a lower limit. (For example, 3.028 +.003/2 i: n8 e) t* X) H: A$ x5 a
-.009 has an upper limit of 3.031 and a lower limit of 3.019.)$ i: r  s4 Q, _9 h5 T
2. Subtract the lower limit from the upper limit to get the total tolerance band. (3.031-3.019=.012)
0 |8 d' ^9 s  H2 C3 s3. Divide the tolerance band by two to get an equal bilateral tolerance. (.012/2=.006)
) c" N" k3 ]5 z+ c1 w4 E: G4. Add the equal bilateral tolerance to the lower limit to get the mean dimension. (3.019 +.006=3.025).1 q6 X* T% ]4 _6 C& F5 k& |
Alternately, you could subtract the equal bilateral tolerance from the upper limit. (3.031-.006=3.025)1 l/ X% L0 e# Q2 P! a: d, @
+ I; K, F# u1 H& ~
As a rule, designers should use equal bilateral tolerances. Sometimes, using equal bilateral tolerances; q8 q+ D& r# _: b+ ~
may force manufacturing to use nonstandard tools.  In these cases, we should not use equal bilateral- b) F1 U0 f1 Y; k$ Z4 q
tolerances.  For example, we would not want to convert a drilled hole diameter from Æ.125 +.005/-.001 to+ K2 q  y$ b5 t+ P; G
Æ.127 ±.003. In this case, we want the manufacturer to use a standard Æ.125 drill. If the manufacturer sees' r0 V5 a4 o3 e" u1 Z
Æ.127 on a drawing, he may think he needs to build a special tool. In the case of drilled holes, we would2 I7 E7 F/ m6 m9 e: D7 x
also want to use an unequal bilateral tolerance because the mean of the drilling process is usually larger
1 a+ ^( V( G0 Z: R! H' \than the standard drill size. These dimensions should have a larger plus tolerance than minus tolerance.
/ D4 U; x4 @# d- t6 T+ j& W! ~/ r! `As we will see later, when we convert dimensions to equal bilateral tolerances, we don’t need to keep6 g" V5 |; E6 }4 e$ p- R3 h* l
track of which tolerances are “positive” and which tolerances are “negative” because the positive toler-
8 V# p* B0 f( Y( ?$ A  m, lances are equal to the negative tolerances. This makes the analysis easier. Table 9-1 converts the neces-! T  D2 ]- U% }
sary dimensions and tolerances to mean dimensions with equal bilateral tolerances.' J+ j  g, S$ h
[attach]320370[/attach]
5 U+ d/ A5 R. \4 |- _! s* {
9 O9 b* h; j! i5 {"Dimensioning and Tolerancing Handbook, by Paul J. Drake, Jr."; _$ `4 s- @5 Z2 s$ M6 \# n
作者: 亂試佳人    時(shí)間: 2014-5-27 08:32
我來(lái)看看高手們?cè)趺凑f(shuō)，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
. `3 N3 Z" y  ]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(guò)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(guò)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 4 [, s; k/ p8 `0 B2 R
9.2.3 Converting Dimensions to Equal Bilateral Tolerances
2 Z) T* ]! i& b7 w6 k4 U, fIn Fig. 9-2, there were several dimension ...
' I1 `: S$ V# w+ j" X9 ?0 ]
  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(guò)機(jī)加的來(lái)說(shuō)，可能理解會(huì)不一樣6 R& D( H; A9 O9 O* D$ b
作者: 機(jī)械inspiration    時(shí)間: 2014-5-29 20:09
2#的言簡(jiǎn)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(lái)Just    時(shí)間: 2014-5-29 21:00
tedwu 發(fā)表于 2014-5-23 20:57
; L" v# ~. L# v% e: {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 ...
' d  _; |; d2 G$ }
大俠說(shuō)的第一種標(biāo)法是什么意思呢？不是很理解耶？？2 \7 X6 l8 b4 ~! j# n5 h7 d
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 ' {2 U8 d7 M5 j. p4 N
左圖，尺寸盡量避開20.4+ c* ~& w' V9 {# M- Q3 d; h& v( ]
右圖，盡量把尺寸避開20.5
4 r  B4 b0 W( q4 s" `, L
交流交流。。
: L  R. [' x) C& o( E% r% U
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 ; n  s+ F! X9 }5 k* g
9.2.3 Converting Dimensions to Equal Bilateral Tolerances5 i  u9 l" _  n! P2 s- `8 h
In Fig. 9-2, there were several dimension ...

& O5 b" |9 X! w+ @0 C& F加工的時(shí)候都控制在中差附近過(guò)程能力才高啊，cpk才好嘛。



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