Looking to install a cheap slab door in this door frame, which measures 32"7/8 at it's widest point:
I was going to get a hollow 32" slab door, but I'm worried that there will be a noticeable gap. There doesn't seem to be any options for 33" doors that I could trim down, and if I'm going cheap and hollow, I'm pretty sure I can't trim a 34" door down that far. Is 32" going to look/fit OK? If not, what are some options?
You'll get a much better end result if you install a pre-hung door.
Remove all the existing casings and jamb. If you remove the casings carefully, you can reuse them. After removing the casings and jamb, you will probably find the opening can take a 32" door including the jamb that comes with the door. Install that pre-hung door, and then re-cut the original casings to fit. After installing the casings, finish the new door and jamb to match the original casings.
Unless you're an expert carpenter/woodworker, in the end this should turn out much better than trying to fit a door slab to an opening that wasn't intended for a door. The existing jamb was likely not installed with the precision required for a door, i.e. the jambs are probably not as plumb and parallel as they ought to be.
Add a 3/4 inch piece of wood to one side, which will reduce the width to 32 1/8. A 32 inch door would fit nicely.
You are correct about the 34" door. To trim one down, it would need to finish out at about 32 5/8" to fill the jamb properly, actually 32 11/16" at the widest but anyway... you will not have enough material to fasten hinges or the latch for the knob.
If you set a 32" door in the opening, it would look really bad, at least in my opinion, with a huge gap on the latch side, and the latch would not want to work with out something extra added to it.
Adding to the jamb is an option, ten you may have issues with the finish matching the existing, the trim having a difference around the jamb, one side now being way different than the other.
My fix, if you have the capacity, is to add 3/4" to the door. If you can get it ripped to 1 3/8 wide and glue it to the edge, holding it in place with screws, until the glue dries, then you can remove the screws if you choose. Use filer to flush up the joint and sand flush. This is an over simplification, the added piece will not want to follow the door exactly, so it will take some finesse to make it look good. Filler sanding and paint will do the rest.
