2D Constraints and Expressions

David Waight

Has anybody got any examples or advice they could share concerning 2D constraints and expressions.

I am trialling V13 with a view to changing over to Bricscad, but I am struggling with getting the hang of constraints.

I understand what constraints are as I already use parametrics in another CAD package but it is a points based system as opposed to the way Bricscad has implemented them, so I can't get much further than the tutorial videos without getting totally confused.

I would really like to move over to Bricscad but this is a deal breaker for me as I use parametrics everyday.

If someone has any drawings that they could share with me or could perhaps look at what I am trying to achieve and perhaps point me in the right direction, I will gladly send drawings of what I am trying to achieve.

Thanks in advance,

David Waight

Roy Klein Gebbinck

Two questions:
What field are you working in?
'Parametrics' can mean many things, can you post a small sample, or give a short description, of what you are typically trying to achieve?

Louis_Verdonck

Dear David

To learn more about parametric constraints in Bircscad V13 and the use of expressions in dimensional constraints, read the topic 'Parametric Constraints' under User Guide / Drawing Accurately in the Bricscad Help. Please make sure you have most recent V13 update: 13.1.7, which you can download from the Bricsys website.

David Waight

@ Roy,

Thanks for the reply, I am working in the Packaging trade and I have attached a pdf explaining the type of thing I am trying to achieve.

There are more parameters etc. to this Carton but it should give you an idea of what I am trying to achieve.

I know there are a couple of German addons for packaging but they aren't exactly what I need are outside of my budget.

@ Louis,

Thanks for the information, I will download the latest version and look at the User Guide.

Many Thanks,

David Waight

Carton.PDF

Roy Klein Gebbinck

David, I have created a small sample to help you get started.
I have described each step in a text-file Sample.txt included in the zip.
Each step has been saved in a separate drawing.

Be sure to read the Help first:
User Guide > Drawing Accurately > Parametric Constraints.

2DConstraints_Sample.zip

Sample.png

David Waight

Roy,

Thank you very much for this effort it is way more than I expected!

This makes me realise I am on the right, but have got a bit of a way to go.

I experimented some more last night and made a bit more progress, hopefully I will crack this before the trial runs out!

One thought did occur to me, do you think it would be possible to link the dimensions/expressions to a table so you could adjust the drawing by altering reference text?

Once again, thank you for the response it is greatly appreciated.

David Waight

Roy Klein Gebbinck

David, I don't think that using input from a table is possible.
But you can create a 'Pseudo Table' in combination with dimension constraints that use a 'Text Only' dimstyle.
See: 2DConstraints_Sample_2.zip

There are two articles on the Blog that may interest you:
http://blog.bricsys.com/2012/03/why-you-should-use-constraints-in.html
http://blog.bricsys.com/2012/05/how-to-make-your-drawing-beautiful-with.html

Finally two problems that I have been unable to solve:
Sub-assemblies:
Is there a way to create and reuse sub-assemblies? For example for the 4 identical dust flaps in Carton.pdf.
'Reversal' of design intent:
For example an angular constraint of 45 degrees between two lines results in an actual angle of 135 degrees after some manipulation. Or a 90 degrees arc with tangential constraints results in a 270 degrees arc. In both cases the result is geometrically correct but not intended.

2DConstraints_Sample_2.zip

Scott McKenzie

 A great tutorial, thanks for posting!

I have noticed that, after creating a constraining dimension, using _DCHORIZONTAL, when prompted for the dimension text, you cannot enter an expression at that prompt; to enter the expression, I am having to open up the properties panel and then edit the expression field for the dimension.  Just wondering if this is what others are experiencing, or maybe I am doing something wrong?

Roy Klein Gebbinck

Scott, you are right: you cannot directly enter an expression when creating a dimensional constraint. It is however possible to enter a new numerical value.

Roy Klein Gebbinck

BTW:

Apart from these operations:
myNumber+myNumber
myNumber-2
myNumber*myNumber
myNumber/2

You can also use these more 'complex' operations in your expressions (there may be more, I couldn't find a list in the Help):
sqrt(myValidNumber)
cos(myAngle)
sin(myAngle)
tan(myAngle)
acos(myValidNumber)
asin(myValidNumber)
atan(myNumber)
abs(myNumber)
round(myNumber)
floor(myNumber)
ceil(myNumber)
log(myValidNumber)

So something like this is a valid expression (if myNumber is a valid name of a dimensional constraint):
round(sqrt(abs(myNumber))+myNumber)

Joe Dunfee

I have been looking at the issue of Dynamic Blocks vs. 2D Constraints.  I see that BricsCAD v13 does not support the defining of Dynamic Blocks. And while the 2D constraints have some of the features I would need, what I did not notice was the ability to create a dynamic array (for things like holes along an edge, etc). I did find the word "array" in the manual, on the page about function expressions.  But, I think that was in regards to an array of numbers, not of objects. Please correct me if I am wrong.

I see that there are some low-cost 2-d parametric add-ins, which are similar to the features now built into to version 13. But they also seem to also be missing the dynamic array function.

The cheapest way to add the dynamic array function is to buy the add-in called CADTroon for $1,500?  Since AutoCAD LT version 13 is under $900, perhaps, for this particular need, BricsCAD may have lost its price advantage.

Is there any other Parametric add-in that gives the user the ability to create dynamic arrays, but costs much less than CADTroon?

Joe Dunfee

David Waight

Joe,

It seems that what you require could already be built into the LGS constraint solver but not implemented in Bricscad.

If you look at page 10 of the PDF link below, you will see on the 3rd and 4th bullet points down, Linear & Circular patterns.

www.bricsys.com/lgs/docs/en_INTL/V7/LGS2D_overview.pdf‎

We can only hope that in V14 they will be activated along with easier access to the user created expressions.

Regards,

David Waight