I'm trying to subdivide a ripped game model for 3D printing. I end up with wrinkles and small bumps when I use the subdivision surface modifier. I converted triangles to quads via the face drop-down menu before subdividing, however, some triangles still remain. How do I work around this to remove the wrinkles? (Assuming the wrinkles are caused by the remaining triangles)
You can convert your geometry to a perfect quad topology with the following steps for each star wing/corner. This will also serve as a good exercise.
Go tab into Edit Mode and then press A to select all and go to menu Face > Tris to Quads.
Press AA to unselect everything. Hover over a sphere and press L to select it. Do this with every sphere and the 2 eyes and then press H to hide them. This will make your editing much easier. If you want to unhide them, press AltH.
Notice that there are these 2 edges shown below that did not cooperate in the Quads conversion. Press 2 to go into Edge Select mode and just select them manually on each star corner and press X > Dissolve Edges.
Press 3 to go into Face Select mode and select these faces and delete them with X > Faces
Press 1 to back into Vertex Select mode and select these vertices then go to menu Edge >
Bridge Edge Loops which will create these horizontal faces.
Hover over this new face area and press CtrlR to add
Loop Cuts and scroll your mouse wheel 2 ticks forward to add 3 loop cuts then press click LMB or Enter to confirm and then press Esc to put them in without offset. Then fill in the missing faces at the bottom by selecting the vertices as shown and pressing F to fill a face.
In the animation below do the following to fill the face at the star corner: (1) Select those 3 vertices and press M > Merge At Center; (2) Select all vertices around missing face and press F to fill a face; (3) Select those 2 vertices and press J to split the face so that they become quads; and (4) select those 2 vertices and press X > Dissolve Edges so they also become quads.