And they went to change that from a 90 degree slot to let’s say, a 60, I’m sorry, 90 millimeter slot to a 60 millimeter slot. The problem came when someone after me went to take my model. I mean, what’s that size there? It’s a fraction of a hundredth of a millimeter.
And say, “Yep, from a front view, “that looks like a full round.” And that was probably okay. But I would hold Ctrl, grab my two surfaces, and then try and bring them out as close as I can get them to one another. I’ll show you how I used to do it, and this is not how you do it. – On this little tuning fork idea here, I want to try to show you what it means to create a whole round in Creo. So hopefully you guys find this helpful and you’re able to avoid some of the pitfalls I’ve made. People know that you don’t really know the standard that well. And it you lose credibility when you do stuff like that. It may look prettier, but it it’s not allowed in the standard. So hopefully you guys find this useful and you can avoid some mistakes I’ve made in the past.Īnd remember, do not place the datum flag on the actual center line or on the actual center plane marks on your drawings.
Otherwise, the flag has to be offset from the size dimension. So remember when the datum flag aligns with the dimension, then the datum is understood as the center line or center plane of that dimension. So it can’t be something that’s derived or calculated has to be based right off that that actual diameter of that boss. It needs to be something that’s actually measurable, by the by the metrology department. And it’s quoted here at the bottom, the datum feature symbol shall not be applied to centerline center planes or axes.
So I’ve thrown the datum flag on the right hand side here you can see where the date of flight is actually on the axis of the screw boss or of the round boss on this cap. I’d get a drawing that’s a little bit too cluttered and I don’t want to try and jam a datum flag in there too. As a side note, there’s also a place that’s called on the standard where you definitely do not want to place your datum. So, the placement of your datum plane is really important. And so we really want that inner surface to be our datum, not not the center of the surface, if that makes sense.Īnd that’s actually important because how you define your datums, and how the datums are understood by the people making the part is all part of getting rid of that ambiguity. And the reason why that’s important because elsewhere in the GD and T stand, they show you a nice little application for this cover this cap, and how it mates up against the body. That actually means the datum, A is the center plane, that bisects the thickness of that cap, instead of the just the mating surface.
So what if datum A was aligned with the dimension arrows instead of being offset? If we did that, like shown in the drawing on the left hand side here, datum A, you can see the flag is in line with the 12.7 dimension. And the datum C, it’s actually the center plane that bisects that slot feature on the cap. So in the case of datum A, the way we have it on our drawing right now, we’re only looking at that, that flat surface, whereas datum B because we have it in line with the dimension, it’s actually pointing to the axis of that boss. The truth is yes, it completely changes what we think the datum is. And I want to talk about why that is, and I’ve had some people tell me, it doesn’t matter. And in A, you’ll notice that there’s an offset between the datum flag and the linear dimension, the 12.7 dimension, whereas on B and C, the datum flag is actually aligned with the linear dimension. And if we look at the three main datums here, A, B, and C, you notice I highlighted A in green, and then B and C are highlighted in blue. This is just a quick sample drawing that I whipped together based on on one of the examples from the ASME Y 14.5 standard. So, I want to take a minute to talk about the importance of datum flag placement in Creo.