If a conical tapered feature is a datum feature, do the angle and diameter(s) need to be defined with basic dimension, as opposed to a plus / minus angle angles and diameters? My thought is that it does because the datum feature simulator would collapse / expand as appropriate at the basic angle...
Not knowing more about the assembly than presented in this forum, I would choose the cross holes as primary and the width as secondary. The cross holes locate the handle on a pin in the assembly and would restrict degrees of freedom on two planes. The holes IMO are driving the design...
Section 4.5.2 tells us that the datum feature simulators are in-line, it is not discussing the datum features. The datum features need to have the appropriate control to locate the to each other. The CF in the one example does that, the other example is incomplete.
Drstrole
GDTP - Senior Level
The best way to learn, IMO, is the school of hard knocks. You can sit down and learn the standard, but still not understand how to select datum features, and properly tie features back to them with the correct tolerance. Working with and getting schooled by machinists and inspectors can help...
I am looking for input on how to specify flatness per unit length for longer pieces of shaft, 300+ mm in length. Pre 2009 we used straightness of a median plane and specified it per 30mm. Using the 2009 standard, we would use flatness and thus my question. Do I specify the length per inch...
1 – I agree it makes sense that they should be inline, but there still needs to be a control (profile) to control the extent of inaccuracy. So while it make sense treating them as one feature, it doesn’t for the relationship between each surface. Also, as you indicated 2.7.5 says it is for...
I agree it can not have SØ or Ø coming only from one plane. I assumed a secondary and or tertiary datum feature and continued on. Appologies for getting of topic or being misleading.
fsincox - yes the tolerance zone can be SØ if that is applicable - figure 7-35 of the 2009 standard.
Drstrole...
First, does a spherical tolerance zone address the design requirements?
I agree with Evan that it would be a spherical tolerance zone, but would like to add that if the design allows it could perhaps be bi-directional. Figure 7-28 of the 2009 standard shows an example for a hole, but this may...
fsincox - I agree, if that’s how it works put it on the drawing that way. When we try to second guess or make things easier, I have found that usually the opposite occurs.
Drstrole
GDTP - Senior Level
I agree with pmarc's suggestion. Possibly the hole is actually the tertiary datum feature and the right and left edge be profiled back A/B/C, with the hole being teriary, if that is how the part works.
Drstrole
GDTP - Senior Level
The way I understand your posting, you have several of the same parts mounting to different mounting patterns of the same geometry. Figure 7-37 of the 2009 standard provides an example, if this is what you are refering to. If not I applogize for my misunderstanding.
Drstrole
GDTP - Senior Level
Jim,
I went back an reread the tip and looked at the illustration. I appologize it does recommend not to do that, it eludes that it could be done, but then shows an example using one hole as secondary and then another as teriary datum features. I appologize for the misrepresentation from my...
I apologize for using 4.5.7 that was an error. I agree 4.5.8 indicates that MMC is recommended, I won’t argue whether or not it is intended to mean must be or can be.
However, as an extended principle using a two-hole pattern as the secondary datum feature referenced at MMC there is quite a bit...
