Problem - Flipped objects in different visibility states move out of position

[JBerns]

PROBLEM: Objects move out of position when flipped. Distance increases with each flip.

STATUS:

I am developing a steel grate stair tread. It has a Top, Side, and eventually a Front view.

The block uses a combination of parameters, actions, lookups, and geometric/dimensional constraints.

You can choose 5 - 10 bar configurations.

It will be able to flip side-to-side to change on which side is the tread nosing.

The spacing between the hole and slot is controlled by a linear parameter and a lookup table.

Development was going well until I ran into a problem using a Flip operation on objects in the Side and Top visibility states. 

The block appears to behave well for all bar configurations and flip states in the Side visibility state. The problem begins in the Top vis state.

I have attached the drawing.

RECREATE ISSUE:

1. Select the block named, BC_Stair_Tread_2 (right-side of drawing).

2. Using the Top visibility state (left lookup), Select 5-bars (bottom lookup).
3. Note the centerlines through the holes and slots are correct as shown in next image.
4. 
5. Select Flip. The slot centerlines are out of position.
6. 
7. Select Flip again. The centerlines are farther out of position. (Array objects also get confused sometimes in this vis state).
8. 

With each flip, the centerlines move farther out of position. I have checked to ensure that Chain and Cycling are disabled.

Can anyone explain why the centerlines behave as they do and offer a solution?

Thank you for your time and attention. I look forward to your replies.

Kind regards,

Jerry

[Libbya]

What are you trying to achieve with the constraints in the block?  What purpose do they serve?

[JBerns]

Force of habit from working with Inventor - creating a fully constrained sketch.

I see that AutoCAD is not so demanding. Too many geo/dim constraints cause problems as you mentioned in the other post.

I removed those "unnecessary" constraints and the Flip action worked satisfactorily.

In your opinion, Andrew, is this block becoming too complex? Should I make separate blocks for the three views of the stair tread?

Regards,

Jerry

[Libbya · Accepted solution]

I think that having the three views is probably fine although I am curious about how you would use the block.  It makes sense to have the three views and have the selections within the block alter all three views, but I imagine you would want at least the potential for the views to be visible at the same time.  As is, if you want more than one view visible at the same time, you will need to add a second block and you won't have the connection between the views where changes in one affect the other.

I understand that inventor is heavy on the use of constraints.  However, within dynamic blocks everything is intrinsically constrained - it is within a block.  In other words, provided you build the dynamic block correctly, endpoints of lines will remain coincident, vertical lines will remain vertical, horizontal lines will remain horizontal, lines of a specific length will remain a specific length, etc, etc... unless you specifically add parameters/actions that cause them not to.  If a specific dynamic change is not desired, then 99% of the time, adding constraints to try to force the desired outcome will cause more problems.  Similarly, 99% of the time the solution is, IMO, more easily accomplished using the dynamic parameters/actions.  There are a handful of situations where constraints are extremely useful and can accomplish things that would otherwise be impossible and as such it is good to have them in your back pocket.  They should, IMO, just be reserved for a last resort when a specific block is not possible without them. 

[JBerns]

@Libbya,

The usage of the stair tread block will likely require it to be placed twice in a drawing. For example, in a top and front view or in a front and side view. Yes, the user will have to match the dimensions accordingly. I would consider this similar to a door or window block that must be placed in plan and elevation views. I would not expect changing the block in one view to change it in the other view.

Eliminating geo/dim constraints in my dynamic blocks will likely eliminate a lot of the problems I have encountered.

Thanks for the much appreciated feedback and guidance.

Where again did you find documentation on using parentheses and brackets (braces) in Lookup Table - Input Properties?

Regards,

Jerry

[JBerns]

@Libbya,

Please disregard the Input Properties documentation request.

I tried some different search terms today and discovered this link:

https://knowledge.autodesk.com/support/autocad/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/AutoC... 

Very powerful new capabilities to add to dynamic block knowledge.

Kind regards,

Jerry