Setharian:
-you are right that a TMsaModel.Create shoudl be the right way, but (1) .
[edit]Also this still gives:
[Pascal Warning] OpenGL15_MainForm.pas(197): W1020 Constructing instance of 'T3dsModel' containing abstract method 'TModel.Render'
so even if i do not use render i need to implement it?[/edit]
-I did not mark the procedures override or reimplement because the application does not work anymore then.
-The try finaly are on the TODO list.

(1):
But in the current implementation i can do

T3dsModel(mesh1).LoadFromFile('models\tulip.3ds');
TMsaModel(mesh1).SaveToFile('tulip.txt');

What i am trying to accomplish is something like an interface, but without the com part (in the end everything should also be compileable with fpc).
I would like to keep that possible. Thinking about it again i might have to use a TBaseModel and inherit TModel from that and also inherig T3dsModel from that. I don't know if that works.