Problems with Solidify Modifier and Model Shape I'm currently making a 3D model of a tray to 3D Print. Unfortunately, when I try to give it a thickness of 4mm using the solidify modifier, it will mess up the shape/diameter/other of the object. 

Does anybody have any ideas on how to make it apply correctly? I've played around with the modifier a bit, and got it to apply the correct thickness without changing the diameter of the tray. But it still does not apply to the model correctly. 

This is a screenshot of the tray without the modifier



This is the tray from underneath



This is the desired thickness of 4mm. As you can see it looks fine - that's because I still haven't applied the Modifier. I think the Subdivision surface modifier is messing it up. 



When the modifier is applied...



It makes a very weird vertice pattern, not too sure where to start moving them. 



File Link:
I checked the file, the subdivision surface modifier is first then the solidify modifier. Also there were some extra (double) vertices that messed up the modifiers.

Solution:


Deactivate all modifiers
Go in edit Mode and select all with A
Press Alt+M "by Distance" (should remove 12 vertices)
Move solidify modifier to top with the small arrow
Select the object and go in object mode to RMB and select smooth shade
Go in the "Object Data Properties Panel" the green upside down triangle
Unfold the "Normals" section and activate "Auto smooth" default value of 30 is fine
Smile


The surface now looking better, the thickness can be slightly reduced as the subD modifier works over it, so you can adjust it a bit by increasing the offset in the solidify modifier.

Also the offset of the solidify modifier is working based on the normals of the objects faces, which should normally face outwards.
Using a positive offset you make your object thicker then it was, negative offset it gains thickness inwards.

Your main problem with the subD modifier is though that you would need to have a control-loop at the bottom to ensure the form/thickness.

Here the file with a control-loop at the bottom.