1. Datum Placement in Creo

Video Transcript

So, I want to take a minute to talk about the importance of datum flag placement in Creo. 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. 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. 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 I want to talk about why that is, and I’ve had some people tell me, it doesn’t matter.

The truth is yes, it completely changes what we think the datum is. 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. And the datum C, it’s actually the center plane that bisects that slot feature on the cap. 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.

Now there is no offset. That actually means the datum, A is the center plane, that bisects the thickness of that cap, instead of the just the mating surface. 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. And so we really want that inner surface to be our datum, not not the center of the surface, if that makes sense.

And 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. So, the placement of your datum plane is really important. 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. And I’ve actually been guilty of this. 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.

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. And it’s very explicit in the standard. And it’s quoted here at the bottom, the datum feature symbol shall not be applied to centerline center planes or axes. It needs to be something that’s actually measurable, by the by the metrology department. So it can’t be something that’s derived or calculated has to be based right off that that actual diameter of that boss. 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. Otherwise, the flag has to be offset from the size dimension. So hopefully you guys find this useful and you can avoid some mistakes I’ve made in the past.

And remember, do not place the datum flag on the actual center line or on the actual center plane marks on your drawings. It may look prettier, but it it’s not allowed in the standard. And it you lose credibility when you do stuff like that. People know that you don’t really know the standard that well.

So hopefully you guys find this helpful and you’re able to avoid some of the pitfalls I’ve made. We’ll talk to you later.

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2. Full Rounds in Creo

Video Transcript

– On this little tuning fork idea here, I want to try to show you what it means to create a whole round in Creo. I’ll show you how I used to do it, and this is not how you do it. 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. And say, “Yep, from a front view, “that looks like a full round.” And that was probably okay. I mean, what’s that size there? It’s a fraction of a hundredth of a millimeter. So that’s okay.

The problem came when someone after me went to take my model. 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. And now all of a sudden I’ve got this sharp point right there. And it no longer goes as deep as I want it to. So, then they have to go through and try and figure out why my rounds aren’t working. So if you intend to have a full round there, let me go ahead and delete that. If you want to have a full round there, you still use the same round feature. Grab your two opposing surfaces. I’m going to hold Ctrl, select my second surface. And then if I look at this dialog box here, it’s looking for a third surface as a driving surface. So I’m going to select that third surface, I’m releasing Ctrl, and it automatically puts that full round in there. And now, if someone goes and they’re going to change this from 60 to, let’s say, 90. The way I had it before, you’d find a flat in between there and maintain those two rounds I put in.

Now it knows I’m intending to put a full round. So it goes ahead and just follows that geometry. So, hopefully you find that useful. Another thing, if you want to do multiple full rounds, so let’s do that on some of these top edges here. Let’s grab this surface, this surface. Select this as my driving surface. You can see it’s thrown a full round around this tower here. And it’s created one set. If I want to do a second one, I can’t really hold Ctrl and select my next surface sets. But if I release Ctrl and select this as one of my two opposing surfaces, now I’m going to hold Ctrl, grab the opposing surface, release Ctrl, select the next one.

You can see where it’s created two sets. And you could go through and you could keep doing that. Let’s say I want to put a third data set in here, make this my driving surface. It is possible to do multiple full rounds in the same feature. Whether or not you want to or not, it’s usually better to break those out as separate rounds, unless they’re all related somehow. That way people aren’t searching through different round features to try and find the one they’re looking for. So, and again, with this, if I say, “Okay,” if I change something on this original extrusion here, Let’s edit this.

Let’s say, instead of making that 250, let’s make it 245. Or let’s make it smaller, so 230. You can see this is still a full round. This is still a full round. And these are both still full rounds, so, it just makes for a nice, more robust model. Especially if that’s what you’re intending, is if those’ll always remain full rounds. Maybe it’s a design requirement or a tooling requirement. It’s just, it’s very nice for the next person that grabs your model, if it’s using the full round feature that Creo has built in.

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