Radiussed corners on a 2d parametric drawing.

Andrew McIntyre

I am having difficulty resizing a drawing that contains multiple corners radiussed to 3mm. Each time I attempt to resize, the radiussed corners become detached or distort hideously so that it is generally quicker and simpler to re-do the complete drawing using non-parametric procedures. Is there a quick and easy way to deal with this?!

Nick Van Laar

Try applying all geometric constraints first, then apply dimensional constraints.  Can you share a sample of what you are trying to do?

Roy Klein Gebbinck

@ Andrew:
The fact that corners become detached means you have forgotten coincident constraints between the endpoints of arcs and lines. To keep a fixed radius for all corners you need to add dimensional constraints. Add one radius constraint 'rad1=3' and use 'rad2=rad1', 'rad3=rad1' etc. for all other corners.
This should fix a lot of your problems but using 2D constraints is usually not 'quick and easy'.

One typical problem that you may run into is what I call 'reversal of design intention'.
Imagine a constrained rectangle with rounded corners. After some manipulations the left and right edge can be distance L apart with the upper and lower edge having a length of L+rad+rad instead of L-rad-rad. This problem can be solved by adding dimensional constraints.

Andrew McIntyre

Thanks for this.

Actually Roy, constraining the arcs and addiing coincident constraints to the lines didn't work for me so I went a step further and tried containing the constrained arcs within constrained boxes - an exercise that was both tedious and unsuccessful !

Concurrently I downloaded a free copy of 'Solvespace' which did what I wanted at the first attempt. Solvespace retains the corner points of the lines that contain the arcs but converts them to non-printing lines, so I tried this technique in Bricscad, but again without success.

With regard to a sample Nick - I am now simply experimenting with arbitrary rectangles with rounded corners - and yes - I have tried adding the geometric constraints first, but without success.

So to sum up - if anyone can come up with a tutorial for a rectangle with adjustable height and width but with corners constrained to a fixed radius I would be more than grateful ! I know parametrics can be difficult, but they surely needn't be THIS difficult - as Solvespace has shown.

Louis_Verdonck

 Please notice that in order to keep arcs attached to lines correctly, apart from a coincident constraint, a tangent constraint is needed too.

Nick Van Laar

Attached is a rectangle with filleted corners, fully constrained.  Is this what your are looking to do?

parametric demo.dwg

Nick Van Laar

@Nick Van Laar:

Attached is a rectangle with filleted corners, fully constrained.  Is this what your are looking to do?

BTW- The "Coincident" constraint is unnecessary in this instance as long as the rectangle is drawn and the corners are radiused (?) using the fillet command.  All end points are automatically coincident.  

Nick Van Laar

Here is a second demo that is fully parametric.  Just change d2 and the other dimensions update (in relation to d2) as well according to their formulas.

parametric demo2.dwg

Andrew McIntyre

Nick - that's wonderful! Many thanks for your time, patience & expertise.

The answer of course was in the tangent snaps which I foolishly overlooked.

I can now resume what had become a frustrating project . . .

Joe Dunfee

 Since it is so tedious to do just a simple rectangle with all its constraints, I strongly suggest building a library of basic shapes that you are likely to use.  If you want a rectangle with radii, then you simply insert it from your block library.  Include constraints like making each radii equal, and then add a dimensional constraint to one of them, and you will have an easy way to change it.

-Joe

Roy Klein Gebbinck

Here is my 'rounded rectangle' attempt.

@ Nick:
Your samples are not fully parametric rectangles. In both samples the top and bottom edge are not exactly parallel and stretching the right half of the rectangles up or down shows that the shape is not constrained as intended.

@ Joe:
Your idea to insert 2D constrained drawings as blocks (and then explode them) does not work in all cases. Formulas (such as 'd1=W-R-R' in my drawing) are lost.

Rounded_Rectangle.dwg

Andrew McIntyre

Well - thanks to all of you for this enlightening exchange.

I think I'll be going with your solution Roy since it seems to be the easiest to replicate.

Can anyone recommend a good 'Peter & Jane' type book for parametric newbies?!

Nick Van Laar

@Roy Klein Gebbinck:

Here is my 'rounded rectangle' attempt.

@ Nick:
Your samples are not fully parametric rectangles. In both samples the top and bottom edge are not exactly parallel and stretching the right half of the rectangles up or down shows that the shape is not constrained as intended.

Nice catch. I found that after I posted. I forgot to add 2 perpendicular constraint sets. 

Side question:

Is Bricscad missing a mid-point constraint?

parametric demo2(fixed).dwg

Dmitry Ushakov

@Andrew McIntyre:

So to sum up - if anyone can come up with a tutorial for a rectangle with adjustable height and width but with corners constrained to a fixed radius I would be more than grateful ! I know parametrics can be difficult, but they surely needn't be THIS difficult - as Solvespace has shown. 

Hello Andrew,

We have a dedicated tutorial at Bricsys TV: http://bricsys.tv/m/?transform-a-smartphone-into-a-tablet

Best regards,

Dmitry

Roy Klein Gebbinck

@ Nick: For a midpoint constraint you can use the coincident constraint combined with a midpoint osnap.