Nobody needs to convince me that GDT is a superior method of defining a part. I've been convinced of that for a long time. But...
I disagree with the notion that a plus/minus dimension is always ambiguous. Often, yes... but not always.
I think section 2.7.1 of Y14.5-2009 nicely lays out...
This is actually how we had them inspecting parts early on. Unfortunately, that was only giving us a pass/fail, and we prefer to have more concrete information on the true shape of the part for qualification purposes. I suppose I could have basic dims to the relevant edges, and have them...
Yes, I know that.. but how do THEY know that if I don't supply them with those instructions? That's the whole point of this thread...
To be clear, I've already resolved my issue.
This thread is becoming more of a "Why wouldn't you just use GD&T for everything?" discussion. While no longer...
Design intent and good engineering evaluation does. While I 100% agree that GDT is a better method of designating design intent, it's not always necessary to ensure a properly functioning part.
Again... design intent. Some edges need to be more tightly-toleranced than others due to required...
Thanks, pylfrm. That thread is directly relevant to what I'm looking to do.
What some people have a hard time understanding is that not every vendor is educated in ASME Y14.5, or exactly how to interpret profile tolerances. What every vendor DOES understand, is how to pull a direct dimension...
I just browsed through ASME Y14.8-2009 and found several examples (figure 2-1 is the first) with the following note:
1- DIMENSIONS ARE RELATED TO DATUM A (PRIMARY) DATUM B (SECONDARY) AND DATUM C (TERTIARY)
This is related to machining operations on a cast part, but seems to be sufficient for...
Dave,
Thanks for the reply. As I mentioned, yes I believe a profile with basic dims would fill the need, and I understand FCFs. Sometimes it's just not worth the fight to force GDT upon a vendor that does not have expertise in it, if linear dimensioning can be used sufficiently in its place...
I have designed a part containing both GD&T and ordinate dimensions. I have the edges of the part (an irregular shape, but mostly orthogonal) all defined by ordinate dimensions from a common origin, which is the primary locating hole in the part. Since a hole provides no rotational reference...
We require our vendors to measure to one additional decimal place of accuracy when qualifying parts, and it certainly is not rounded. For a plastic molded part with tolerance of ±0.005", we may need to reject parts that measure ±0.0053".
In some applications, half a thou can cause unintended...
I was going to suggest precisely what cowski mentioned. Molding the lenses first, then overmolding them with the frame would work quite well. Of course, this option will often increase capital and piece price, so if you're looking for low cost, stripping it off the mold as MikeHalloran...
I've skimmed through Y14.8-2009, and I found it to be just as you said. Good for additional rules that only apply to plastic parts, but not good for application of existing rules of Y14.5-2009 to plastic parts.
All of the methods I can think of using for completely describing drafted/rounded...
As ajack said, it seems as though it's an attempt to say they really want 0° draft, but they'll accept small amounts of draft as needed to produce the part. They should probably specify a maximum allowable draft and work with the fabricator to determine how small they can make it.
Dave,
The issue with taking it as fabrication error is that it allows for additional variation at the point we truly care about. For example, on a drafted rectangular slot, the smallest portion of the draft may be a critical dimension that must be molded to within ±.002". If they make the...
I'm looking for resources that will help with the application of GD&T on injection molded plastic parts. How does the application of GD&T callouts differ when draft is applied? Our software tools for application of GD&T and for analysis of GD&T do not seem to be built to easily define drafted...
