ST Sync Mode Problem 1

[beachcomber]

Hello everyone,
I am trying to get to grips with sync mode so I created a simple casting (see attached).
What I want to do is change the dimension from the centre of the depression to the end of the rib.
How do I do this?
This is a real item from I job I worked on in the past that was modelled in a different system 12 years ago.
I would also like to be able to change the diameter of the depression, but since adding a round the dimension has become detached.

bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.

Where would we be without sat-nav?

 

[burhop]

Hi BC,

I've seen this before where you get rounds on top of rounds or where rounds won't work in the new geometry.

I went back and deleted a few rounds where there were tiny surfaces (Round 5,6) and complex rounds at the outer at the flat base. Heres the video:

http://screencast.com/t/NTg4YTk2Yj

I'm not a modeling expert (I'm, the FEA guy remember) so there may be a better way. I have heard them say its best to move things like rounds, shelling, etc. to the end of the process.

Mark

 

[beachcomber]

Thanks burhop,
unfortunately that's not what i wanted, although I probably wasn't clear in my first posting.
The position of the depression is correct with regard to the back plate and what I wanted was to set the end of the rib to be it's correct dimension of 90mm.
I put the rounds on because that would be the finished state when the drawing was done. Without the rounds you can change the dimension, but if you decrease it the top edge of the rib moves away from the top edge of the back plate, ie the angle of the sloping face of the rib is maintained.

bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.

Where would we be without sat-nav?

 

[beachcomber]

Just tried deleting the rounds but unable to delete 4,8,11., but I can then change the dim and it behaves as required.
This is not the same behaviour as when there are no rounds.
having put some of the rounds back on it still modifies, but now I can't delete any of the rounds.
If it's such a chore to change 1 dimension on such a simple model I really can't see any use for sync mode other than modifying imported parts.

bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.

Where would we be without sat-nav?

 

[burhop]

Ah, I see. What you might also do is put an angle dimension on the rib (or just rotate the rib face with the handle). Since you want an exact linear dimension, you would likely need to drive the angle from an equation based on the rib length.

 

[donyoung]

hmm, I don't think that the ribs (as modeled) can be changed
in any way except for moveing them to the right or left

dy

 

[dcstaples]

OK. So here is the scoop. Generally, when you edit a dimension you want to move the target face. And most often, when doing so, you want to retrim the adjacent faces. In some cases, you want to move the target face and tip the adjacent faces -- there is a switch on quickbar for this. In your particular case, though, you want neither of these -- you want to edit the linear dim and directly tip the target face. This is not a highly common construct, though it certainly happens from time to time.

So, you get out your ST toolkit. I've posted a quick video of one way below. A few things to note about this method:

1. When drawing the initial line, I am hitting the N key on the keyboard to define which edge I want the internal reference plane to align with. Look carefully and you will see initially one of the canted edges is green, so I hit N to get one of the ortho edges.
2. Once I move the steering wheel onto the edge of round to indicate this is the center of rotation, I hit the SHIFT key when choosing the gold ball at the end of the arrow. This means I want to stay in plane. Basically I am just putting the arrow straight down the plane.
3. Then, when you rotate, it uses that initial arrow position and you snap to the end of the line you drew and its now rotated such that 90 is satsified.

http://screencast.com/t/YjdjMTBk

Admittedly there are a few steps here, but this not your most common construct, so we did not add it to the UI explicitly. We continue to add stuff based on user demand, but this had not be a high request so far.

Dan Staples

 

[dcstaples]

After looking at this, I think there is a better geometric solution to where the rib joins the part from a mfg/design standpoint. If the rib were tangent to the round, you wouldn't have the messy situation where you have a 90 degree round right next to much shallower connect angle.

I made some changes to make the rib tangent to the round and it just looks a whole lot neater at the joint. A nice side effect, is you can now edit the dim to 90 mm and the rib will tip as you desired, since it is maintaining tangency on the other end.

See the video here of the result. It starts with me selecting the face and highlighting the round to show you the area of the change, but that is not relevant to the edit. you just edit the dim:

http://screencast.com/t/MGEyN2I2YTM

 

[beachcomber]

Thanks Dan,
That helps a lot.
As I said I'm trying to teach myself in quiet moments at work so I think a lot of my problems stem from inexperience with sync.
However, I think having to put additional construction lines in just to modify a feature sort of defeats the object.
I agree that the second method for the rib is geometrically better, but I don't think that's how it would be made.
This is a low volume cast item that would probably have a hand-made pattern and the rib would be a simple triangle fitted to the base and back plate. The rounds would be added after, as in the model.

My other question was how to change the cylinder diameter.


bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.

Where would we be without sat-nav?

 

[donyoung]

BC,

> My other question was how to change the cylinder diameter.

I've found this solution:
- first get rid of the draft. It is possible to change the dimension
without that but doing so will change the draft's angle.
- select 'Draft'
- select the "bowl's" bottom face
- from the pull-down - select Face
select the side wall
enter 0 and press Enter to accept
- now put in a new dimension select either the upper or lower
circular edge of the sidewall
- change the dimension but keep in mind that it will change
after re-applying the draft
- now reapply the draft 5° (same procedure as before)

The LiveRules set are the default ones. This will obviously result
in thinning the wall thickness of that 'bowl'

dy

 

[beachcomber]

Thanks Don, I'll try that but I still think it's defeating the object of a parametric design tool if you have to delete features to make changes to geometry that has already been defined.
Maybe I'm missing the point of sync mode.

bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.

Where would we be without sat-nav?

 

[donyoung]

BC,

I agree, one has a hard time to get the secrets of non-history
modelling. I'll try to explain it a bit:

- you create a cutout with a certain diameter an depth
- a draft is applied to the sidewall
- a radius at the bottom is applied
- a radius at the top edge is applied

In trad mode neither feature does modify the one it is applied
to. The cutout is still there unmodified: use GoTO and you can
verify this.
Now you change the diameter of that 'bowl'. Actually you change
the *unmodified* cutout and all those features that come later
in history will adjust accordingly (hopefully).

Now in sync (or non-history mode; ST1)
- you create a cutout with a certain diameter an depth
- a draft is applied to the sidewall. Now your cutout is
actually a cone as if it where modeled that way
- a radius at the bottom is applied and it will remove the lower edge.
Any dimension referring to this edge will turn brown
- a radius at the top edge is applied, again same as before.

Now think of the final result as if it where initially modeled by using
a revolved cutout using a sketch with the two rounds and the draft.
You may change one of the rounds by setting a new value (a round is
a procedural feature). The draft is not a procedural feature and thus
can only be changed by nullifying it (new Draft with angle 0). In ST2
it will become a procedural feature.
When now the diameter of the upper edge of the draft changes (set off
LiveRule 'Concentric') it obviously gets wider at the top and thus the
draft angle will increase and the included angle of the rounds will
change too. In St2 it will behave as expected: the hole thing gets
wider and the draft's angle will persist (that I think stems from the
fact that the draft is now a procedural feature).

Take note: when in Sync a feature modifies another one and by that a
face will be completely removed that feature can't be deleted later on.
Take a square bar .5 x .5. Now apply a chamfer of .5 to one of the long
edges. The resulting model is now a triangular bar. When you try to delete
the chamfer SE will complain because it does not know what was there
before (it can't heal the 'wounds'). When the chamfer is applied with
.4 then the deletion will succeed. The chamfer will leave part of the
two faces and thus SE knows how to close the 'gap'.

dy

 

[PatCouture]

Thanks Don for the explanation I didn't see it that way but it makes a lot of sense.

Patrick