aysuio 发表于 2015-10-6 22:50 static/image/common/back.gif
大侠可能对直线度平面度的适用范围有点混淆，
直线度是二维的，平面度是三维的。直线度的公差带是没有方 ...
直线度是可以在某些平面上指定的。既然在平面上可以指定，就是可以应用在平面上的。ASME Y14.5 中的图 Fig. 5-6 Specifying Straightness of a Flat Surface 恰巧指的就是本题案例相同的情况。而您13楼给出的图示，也是在指定的平面上的。
本帖最后由 aysuio 于 2015-10-7 05:08 编辑
ValleyViews 发表于 2015-10-7 02:44 static/image/common/back.gif
直线度是可以在某些平面上指定的。既然在平面上可以指定，就是可以应用在平面上的。ASME Y14.5 中的图 Fi ...
:）
大侠，别用您啦，小子真担待不起，我是小弟：D
大侠这么认真，小子自然很愿意来跟大侠说一下。
In Y14.5
Application:
1. Straightness tolerance specifies a tolerance zone within which the EACH (This word is not in the standard, but the following explanations indicate the "EACH" information) considered element in the surface or derived median line must lie.
2. Straightness tolerance is applied in the view where the elements to be controlled are represented by a straight line.
These 2 sentences give us 3 information:
1. straightness tolerance controls each line elements of a surface when it is applied to the surface, or the derived median line when it is applied to the feature of size.
2. Straightness tolerance is ONLY applied in ONE VIEW where it refers to.
3. Straightness tolerances is applied to a nominal straight line. If the line is a curve, please use profile tolerance.
For this problem, straightness tolerance is applied to the surface, and in 2 VIEWS.
So it means 2 straightness tolerance control the straightness of each line elements of the surface in 2 VIEWS.
Line element is a 2D element, like it just has dimensions in X and Y, and NEVER think about you can measure line elements in Z axis. What you do is just to measure the line one by one according to the actual local sizes of the component (Means the straightness tolerance zone totally depends on the actual local sizes of your produced part)
When you talk about the flatness tolerance. This is a 3D element. I.E. it has dimesions in X,Y,Z. So when you check the tolerance, you check the whole surface at the SAME TIME where the flatness tolerance refers to.
This is why the straightness tolerance in that figure which I posted before can be 0, but the flatness tolerance can reach 0.6
If you still have any problem about this, please read the standard again from the first sentence of form tolerance section, then I think you will understand about this problem clearly and thoroughly.
If you are willing to talk with me about the problem, feel free to contact me :) I'm here with you.
Hi, Valleyviews,
You were saying the fig in Y14.5-2009. And yes, it is talking about this problem. I was confused by this section before, but this question just helped me to get over it! I hope that this question also let you clear some confusing theories up. Have a good day!
请解释下为什么不是0.05。
机械设计手册给直线度的定义是：在给定方向上公差带是距离为公差值t的两平行平面之间的区域（第三章5-271）。
该面既要0.05又要0.2，那理所当然的可以认为平面度最大值为0.05。
类似于茴字有四种写法，实际应用中并没有多大的意义。
补充内容 (2015-10-8 10:07):
最近智商余额不足，给定方向上这几个字被我无视了。
大侠，我自以为解释得很清楚了。。。再让我解释，说不过去啦吧- -！
0.2,平面度可以限定直线度,反过来直线度也可以影响平面。4.7,只需考虑孔的尺寸和位置公差,c如果有平面度需要考虑,但是0位置度变的无意义。
bukeking 发表于 2015-10-7 20:26 static/image/common/back.gif
0.2,平面度可以限定直线度,反过来直线度也可以影响平面。4.7,只需考虑孔的尺寸和位置公差,c如果有平面度需要 ...
你好，如果直线度不能控制平面的话，这张图的意义何在，两向可以控制，一向足以影响，我认为没有问题。此处大部分人都可能直接标平面度，设计者应该是在完全符合性能要求的前提下，考虑到批量件或是工件长宽相差太多，结合机床的精度，让加工者选择合适的走刀方向进给量速度等参数，以最经济方式做出。
看了第一题，觉得也是0.6，第二题就不懂了
本帖最后由 ValleyViews 于 2015-10-8 02:24 编辑
aysuio 发表于 2015-10-7 04:58 static/image/common/back.gif
:）
大侠，别用您啦，小子真担待不起，我是小弟：D
大侠这么认真，小子自然很愿意来跟大侠说一下。
四海之内皆兄弟也。
Talking about your explanation, I think that every sentence is understandable except this one: “Line elements is a 2D element, like it just has dimensions in X and Y, and NEVER think about you can measure line elements in Z axis.” My understanding is that even though you measure line elements in specified view direction ( either front view or side view ), it doesn't mean the measured line element is a 2D element. Furthermore, actually it is still a 3D element. When you measure it with an indicator, what will you get? You must get some values in Z axis.
本帖最后由 aysuio 于 2015-10-8 03:20 编辑
bukeking 发表于 2015-10-8 00:19 static/image/common/back.gif
你好，如果直线度不能控制平面的话，这张图的意义何在，两向可以控制，一向足以影响，我认为没有问题。此 ...
第一，这张图的意义在于让你更清楚地理解，何为平面度，何为直线度。基本概念都理解不到位，为何把题往实践上套?
第二，你估计连直线度平面度怎么测都不大清楚吧？我相信我之前写的解释很全了，你有仔细看么？直线度是有 “方向”的，是分“视角的”。
第三，你说的很好，设计人员要根据现有的加工情况，实际要求，对图纸进行标注。但这只是一点。你标注的公差，你觉得是这个意思，人家觉得是那个意思，然而事实是，公差只会表达一个意思，不会有歧义。是否看过一个大侠的文章：切莫让感觉蒙蔽双眼。设计公差需要的是严密的逻辑而不是感觉。你没细读过标准，没有仔细比较过直线度和平面度之间的差别， 所以你的概念是混淆的。所我的建议是，请细读标准，可以先读美标，写的严密，逻辑，而且较为简单。
读标准这个事儿我说过好多次啦。大侠们自己斟酌吧。
PS：
第一题是我从老外论坛上弄下来的，每个能够说出答案的人，都说的有理有据，不像咱们，说的理由甚至不沾边。
虽然小弟本身水平也不咋地，但是深知基础的重要，也知道只有说话有根据，才能说服别人，就像998大侠说的，用计算说服别人，用有根有据扎扎实实的理由说服。与君共勉。