Draft question

[michaelpaul]

I was just wondering if there is a better/easier way to create a draft when the base of the feature is on a curved surface but you want the dimensions of the base to remain as modeled and have the draft remove material from the top of the feature.

Here is an example.

View attachment 4412

I realize I could add draft and use the top surface of the feature as my neutral plane but.......then the base expands which is not what I want.

View attachment 4413

The next simplest solution is to create a datum plane at the lowest point of the base protrusion and use that as my neutral plane. in this case, I simply created a datum plane through the edge that is lowest. If the low point were a point, then the plane would just have to go through that point.

View attachment 4414


This works, but if the design intent of my model ever changes and the lowest point of the protrusion on the base changes then my datum plane will not be in the correct location so the design does not reflect the intent.

the only other thing I knew to try was to use each curve at the base of the protrusion as my draft hinge.

This would work but A) it requires me to create four separate draft features, one for each face of my protrusion and B) it curves the face which is not what I want. granted, if I were only drafting my model .5 degrees the curvature probably is negligible but still it's not exactly what I'm looking for.

View attachment 4415


View attachment 4416


Solidworks had an option to create a parting line draft in which it would draft everything relative to a specified draft direction and a chain (the base of my protrusion). The chain would be similar to the Pro E draft hinge except that A) I could select the entire chain at once and create one draft feature and B) it would not add curvature to the faces as it drafted them (I haven't use SW for 2 years so my recollection of this may be fuzzy but I believe this to be the case).

At any rate, is there a better way to create the drafted surfaces that I desire or are the options I've already tried the only ones available?

Thanks

Michael

 

[Tobyk]

In the draft dashboard go to references.
Click on Detail next to the draft hinges.
Click on rule-based.
Select and edge. (this becomes the "anchor")
Then go to the options tab and click on the appended area and then select the rest of the edges for your hinges.
OK and select your pull direction.


Now that was easy and obvious wasn't it?

Tobyk

 

[dgs]

The question is where do you want the dimensions of the square to remain the same? If it is truly along the curved bottom edge, then you cannot maintain the square section. This isn't a Pro|E limitation, it's a geometry limitation.


That being the case, Pro|E's neutral curve draft is the way to do this. There are several ways to select all the edges, Tobyk has given you one of them (and yes, Pro|E's curve selection methodology leaves a lot to be desired). investigate the options in the curve 'Details' dialog box.


If, however, maintaining the the flat sides of the square is important, you need a neutral plane draft. Then you need to decide where on the square you want it to be the same - at the top of the peaks on the undulating surface or the bottom of the valleys or where? Then, create your plane relative to the undulating surface. Then when the height changes, so will the plane and your draft will be correct.


My recent experience with SW's draft features (SW 2006) is that the Pro|E's draft features are much more powerful. I couldn't see how to do a neutral curve draft nor can you do a split split draft (you split first and draft independently.)

 

[michaelpaul]

The question is where do you want the dimensions of the square to remain the same? If it is truly along the curved bottom edge, then you cannot maintain the square section. This isn't a Pro|E limitation, it's a geometry limitation.

That is true. I didn't think entirely about what I wrote. What I want is to not add material to the base in the manner that selecting the top surface would. I realize that because of the nature of the curve, the true base dimensions of the feature will change slightly, but this is more easily controllable by using the curves at the base as the hinge.

My recent experience with SW's draft features (SW 2006) is that the
Pro|E's draft features are much more powerful. I couldn't see how to
do a neutral curve draft nor can you do a split split draft (you split
first and draft independently.)

That is true but it's a difference in philosophy in how the surface is treated in SW. In ProE, you cannot split a surface like you do in SW. in SW, you can split a surface and then it becomes two different surfaces. So, you do have to create two draft features (one on each side of the split). So far, there's nothing with ProE's draft function that I've found more powerful, just less intuitive. Of course with Pro E, you have whole lot more draft features because you cannot draft while extruding your feature anyway.

One thing you can do in SW that I don't think you can do in Pro is draft a surface that is already drafted. maybe you can do it in Pro but I've tried it before and it wouldn't let me (which really only means that I may not have blindly stumbled on the option if it does exist). I found this useful on occasion in SW when you had a surface that was drafted and then shelled, but then you wanted to add a different draft to a portion of that surface after the shell.

six of one, half a dozen of the other. both packages get you there, they just take a different path.

Michael

Edited by: michaelpaul

 

[michaelpaul]

In the draft dashboard go to references.
Click on Detail next to the draft hinges.
Click on rule-based.
Select and edge. (this becomes the "anchor")
Then go to the options tab and click on the appended area and then select the rest of the edges for your hinges.
OK and select your pull direction.


Now that was easy and obvious wasn't it?

Tobyk

Ummmmmm, wow. I NEVER would have stumbled across that! I mean, WTF is rule based mean and how am I to know that it does what I want it to?

Thanks for the lesson. It should be useful in the future.

Michael

Michael

 

[Tobyk]

I just tried it again.

You can do it without ruled based as well.
Still have to click on details but then click in the references area and then holding ctrl down as you select the other hinge edges.


So it doesn't have to be as convoluted as I originally said.

Still it would be nice to not have to click on details just to add the extra hinge edges.

Tobyk

 

[dgs]

Phooey, I just lost my whole post.

'Rule based' simply means using a rule to define the set of edges. That rule could be a chain of tangent edges, a chain of adjacent edges or a loop of edges around a surface.


As you discovered, once in the Details box you can use control to build your own set as well, as long as they make a chain.


You can also use shift outside the details dialog to pick a chain of edges, although this is a bit harder. Pro|E uses the logic of Excel here. In excel using shift-pick gets you a 2 cells and all the cells in between - a chain of cells. Using control-pick you can build a set of non-adjacent cells. Since an edge set in Pro|E must be a chain of some kind, Pro|E won't let you use the familiar control-pick method and forces you to use shift-pick. I find the distinction helpful in Excel, but a little odd applied to 3D geometry. Nonetheless, once you understand it it helps in making use of it.

That I want is to not add material to the base in the manner that selecting the top surface would. I realize that because of the nature of the curve, the true base dimensions of the feature will change slightly, but this is more easily controllable by using the curves at the base as the hinge.

I'm not sure you completely understand the nature of the draft hinge in Pro|E. It's where the surface 'pivots' to create draft. The geometry will not change, by definition, at the hinge. If the square needs to stay square and the sides planar, you must use a hinge plane based draft (technically a curve based on a planar section will do the same thing too). If you require removal of material, then define your draft hinge plane as being at the lowest point on that undulating curve.

One thing you can do in SW that I don't think you can do in Pro is draft a surface that is already drafted. maybe you can do it in Pro but I've tried it before and it wouldn't let me (which really only means that I may not have blindly stumbled on the option if it does exist). I found this useful on occasion in SW when you had a surface that was drafted and then shelled, but then you wanted to add a different draft to a portion of that surface after the shell.

Pro|E doesn't care, mostly, how the surface was created, only that it's 'draftable'. Draft on draft is possible, I've done it many times. There are occasions where the means of creating the first draft are such that Pro|E assumes the surface isn't draftable, when in reality it is, but that's usually pretty easily over come.


One thing to remember is that creating a 3 degree draft feature on top of a 2 degree draft feature (both using the same reference plane) does not result in 5 degrees of draft. Draft is not the distance the surface is pivoted, it is measured from reference plane. A 3 degree draft on top ofa 2 degree draft (again, both using the same reference plane) results in 3 degrees of draft.

 

[dgs]

Oh, man on SW vs. Pro|E - I can do some pretty sophisticated split drafts in a single feature in Pro|E. I haven't figured out how to do them in SW, but to be fair I haven't tried that hard either. It just may take more features and some more digging on my part to figure it out.

 

[michaelpaul]

I'm not sure you completely understand the nature of the draft hinge in Pro|E.

I understand the hinge, my explanation of it was just not 100% accurate.

Draft on draft is possible, I've done it many times.

I'll have to try it again because I know that the couple of times (it's certainly not something you do often) I tried it, it didn't work. I just didn't spend a lot of time trying to figure it out either.

Michael