# Compensation for dimensional changes after turning a GS into a solid part

#### Mans

##### Member
I know it is possible to change a Generative shape (superficial shape) into a solid shape in the part design section but what about the initial dimensions that have been specified in the GS section? Surely, they all will change after the GS is turned into a solid shape. The applied thicknesses onto the GS will change all its initial dimensions. How I can change a GS into a solid part with the same earlier dimensions in the GS. For example, when I designed a piston with 70 mm diameter in GS and changed it into a solid part with 4 mm thickness, the diameter would change into 74 mm (also other its dimensions), so how I can achieve a solid piston with the same previous 70 mm diameter?

#### MrCATIA

##### Super Moderator
Dimensions DO NOT change when solid shapes are made from surface shapes; the geometrical size remains exactly the same.

If you made a Ø70 cylinder with a surface representing the inside diameter, the solid cylinder will maintain the Ø70 on the inside. The 4mm thickness on the solid will give you a Ø78 on the outside.

how I can achieve a solid piston with the same previous 70 mm diameter?
If the Ø70 is the outside dimension, then click on the arrow to change the offset direction to point to the center when using the ThickSurface command.

Last edited:

#### Mans

##### Member
What about a more complicated shape with different directions of components? For example

when I change this GS piston (with the specified dimensions) into a solid part, not only its main diameter is changed but also the size of its rod hole becomes tighter and the thickness affect its diameter. If I even modify the thickness of the piston (using a -4mm offset) what I can do for modifying the size of the hole and take it back into the original size, also about other more complex shapes

#### MrCATIA

##### Super Moderator
Mans,

Unlike Version 4 and previous versions, CATIA V5 was developed for solids modeling techniques (Part Design workbench) can be used as the primary tools. Surface modeling is intended to only be used as secondary tools. The piston example above is fairly simple and can easily be modeled 100% with solids only. The solid-only model will also result in a smaller file size, easier to understand tree diagram, an easy to modify model, and data that can easily be used for downstream activities (drafting, analysis, NC, 3D printing, etc.)

What about a more complicated shape with different directions of components?
If you had a complete and closed surface model (either modeled yourself, or maybe from a STEP conversion), you could use the Close Surface tool to convert this into a solid with complete accuracy.

There are other tools, Split and Sew, that can be used to integrate surface shapes into the solid model.

when I change this GS piston (with the specified dimensions) into a solid part, not only its main diameter is changed but also the size of its rod hole becomes tighter and the thickness affect its diameter.
The hole should not be added till after the surface is thickened to make the solid. Then the hole can be added with the Hole Wizard (to add the openings on both sides, and the faces of the inside of the hole) again with the Part Design tools. Chamfer, Fillets, Grooves can be added very easily also as solid features - not surfaces.

I suggest you focus your training on the Part Design workbench and learn surface modeling later.

Last edited:

#### Mans

##### Member
I previously worked with 3D AutoCad for about 7 years but from last year I came to CATIA (though I left it for a while).

I mostly worked with part design but recently GSD absorbed my interest, while I don't know in which field of industry it is used?

Please enlighten me, what the usage of GSD in the practical works of engineers is and which kind of parts are designed with that?

Thank you

#### Mans

##### Member
Dear master

The close surface worked and just now, I could to covert a simple GS into a solid part with the same accurate dimensions

Thank you a bunch

#### MrCATIA

##### Super Moderator
recently GSD absorbed my interest, while I don't know in which field of industry it is used? What the usage of GSD in the practical works of engineers is and which kind of parts are designed with that?

Thank you
Surface modeling (GSD Workbench) is typically used for complex shapes. A computer mouse and a bicycle seat are two examples. It is often used in the automotive industry to define the shape of the car body, and the shape of other car parts such as the car seat and the dashboard. Many plastic parts (such as a plastic bottle) require surface geometry to define their shape. Airbus and Boeing are big users of CATIA because of it's surface modeling capabilities which are used to define the aerodynamic shape of their aircraft.

I hope this helps

Last edited:

#### MrCATIA

##### Super Moderator
Dear master

The close surface worked and just now, I could to covert a simple GS into a solid part with the same accurate dimensions

Thank you a bunch
Great! Glad to hear it worked for you.

#### Mans

##### Member
So, GSD is not an appropriate workbench for designing a complex mechanical device like a car engine and so on? It mostly is used for the objects that have often thin thickness and notable surfaces?

#### MrCATIA

##### Super Moderator
So, GSD is not an appropriate workbench for designing a complex mechanical device like a car engine and so on?
Most (all?) car engine components can probably be modeled quicker and easier with CATIA V5 solids then with surfaces. Based on my experience using both, I would guess that surfacing modeling of these components would take at least 4 times as long as solids. Much longer for the engine block.

Did you model the piston both ways? What was your experience?

…. mostly is used for the objects that have often thin thickness and notable surfaces?
I would not say surface modeling is for thin-walled parts only. But most of my previous examples are thin-walled (probably for fabrication and weight reasons).

Last edited:

#### Mans

##### Member
Designing the piston in part design workbench is very easier than using GS, and as you told, this takes long less than designing it with absolute surfaces, initially. Nonetheless, GSD is very interesting and joyful because of its numerous techniques of shaping, though it is harder than part design. GSD allows us to design dreamy curvature things which sometime is not possible to do that in PD. But in the practical engineering works it depends on the requirements that which one is used.

As I have worked with solid parts in Auto Cad a lot, GSD is an interesting new workbench for me, while it has many additional facilities to design complex curvature objects.

However, PD and GSD each one has its particular technical usage and in some situations they are beside each other to create and industrial thing. So I can't opine which one is better; both are excellent in the circle of their particular tasks, nevertheless I mostly love GSD .