# Parametric (variable) round rectangle

**URL:** <https://discourse.shapr3d.com/t/parametric-variable-round-rectangle/40709>\
**Category:** Modeling Questions\
**Created:** [April 24, 2026, 5:38pm UTC](https://discourse.shapr3d.com/t/parametric-variable-round-rectangle/40709 "2026-04-24T17:38:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![xmd](https://avatars.discourse-cdn.com/v4/letter/x/4491bb/32.png) [@xmd](https://discourse.shapr3d.com/u/xmd)\
**Post date:** [April 24, 2026, 5:38pm UTC](https://discourse.shapr3d.com/t/parametric-variable-round-rectangle/40709/1 "2026-04-24T17:38:35Z")

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I made a rounded rectangle (RoundRect) by :

- create a Rectangle
- create a Circle
- drag the circle so it touches the Rectangle corner
- use the Trim tool to delete segments of the Rectangle and Circle
- set the circle Radius to a variable

it works nicely at my initial 5mm circle radius:

 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/3/4/343d514c88d3b434810ca0c93fe9488f9c8a24dc.png)

However, if I change the radius, say to 10mm, the two points of the arc stay fixed, so the end result is not what I want:

 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/2/8/286639dea8b45336de07533d0ac58b1d52b1ae6d.png)

The problem appears to be that I locked the wrong points – if the radius changes, the edges of the Rectangle must logically change lengths too.

Is there a way to set this up so the radius can be changed while keeping the proper geometry?

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<div class="post-metadata">

**Author:** ![Xdrakosha](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/xdrakosha/32/24881_2.png) [@Xdrakosha](https://discourse.shapr3d.com/u/Xdrakosha)\
**Post date:** [April 24, 2026, 5:54pm UTC](https://discourse.shapr3d.com/t/parametric-variable-round-rectangle/40709/2 "2026-04-24T17:54:30Z")

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Use tangent constraint. In general - learn how to use constraints this is the most important thing in the CAD.

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<div class="post-metadata">

**Author:** ![xmd](https://avatars.discourse-cdn.com/v4/letter/x/4491bb/32.png) [@xmd](https://discourse.shapr3d.com/u/xmd)\
**Post date:** [April 24, 2026, 6:22pm UTC](https://discourse.shapr3d.com/t/parametric-variable-round-rectangle/40709/3 "2026-04-24T18:22:03Z")

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Thank you, that was it. The solution:

- select one line segment and the arc that touches it.
- Change the Constraint to Tangent. Repeat for all 8 of them.
- Also, unlock all of the locked points, especially including the Arc Center, which needs to be free to move

Now it works, here is 10mm radius:

 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/0/5/059acaf201f2daf07112885d9462c7eebdd9be66.png)