Fixing Too-Small Screw-holes on 3D-Printed Box

Way back a couple years ago, I thought I'd ask my professor if I could design a 3D-printed enclosure using software we had just learned to use (Pro-Engineer, which from what I've heard isn't the best software to use for CAD-projects).  The response was yes!  So I set out measuring my passive-infrared (PIR) kit I'd gotten earlier and thought on how to make the design to hold a speaker and the PCB well.  The kit just takes 5V in and activates a speaker during detection (a "ding-dong" noise).  Took a lot of measurements, and a mistake I made was that I didn't look for proper screw sizes BEFORE designing the screw holes; I assumed I'd be able to find a screw that would work easy.

I won't be sharing the files for the box, but the box is simplistic enough (by design) to be able to copy easily if you want, it doesn't matter to me.  I was pushing for symmetry about the "Y-axis", as in you could fold it over and it would be the same.  I really liked being able to see the precision of working with CAD software and re-creating that with a 3D-printer.  It's better to see in person, but you can see some of the tiny edges that were needed for the screen on front and holding the speaker in the back.  The speaker would sit behind the PCB and be held in by that strip of plastic you see in the middle of the circle.  The PCB would be screwed in and held up by those 4 circles.

 Didn't come out perfectly though, measurements were slightly off ever though I painstakingly measured again and again.  Screw holes didn't line up and were too small.  So some advice for the readers, make sure the parts you need exist (or are easily found) BEFORE you design something needing those parts.  Sounds like common sense, but you may make the same silly mistake in the haste of trying to get things done.

Tools needed:
--Dremel tool
--Mounted pillar drill
--Wire cutters (for bits of hanging plastic)
--Proper diameter and length screws (whatever needs for your project)
--Fine-toothed hack saw

1) Started off thinking this was a job for the dremel tool, in the process learning that a dremel (at least the one I have) isn't very good for plastic.  For starters, it melts plastic and gets stuck on the drill bit and hardens to very difficult-to-remove plastic on the drill bit.  It's best to use a more powerful drill, like a mounted pillar drill; it just works better/quicker.

Be cautious and wear safety glasses when working with a pillar drill as the plastic still melts to the drill bit and then flings off at high speeds.

I also needed to make the bottom part a little bigger for the power wires at the bottom.  Found the best way to do that was using a hack saw, making a bunch of cuts close together, then coming in with the pillar drill to cut out the pieces.

2) After drilling out all the outside holes and testing the screws I had on hand (size 6, 1.5 inches long), I had some other screws that fit easily for holding the PCB in place.  I only needed to put in one here as the PCB already fit snug and if there are any problems (highly unlikely unless someone hits it hard) I can always drill out the PCB a little to make up for my faulty measurements on the screw holes.

3) After securing the PCB, make sure the screws fit snug on the outside and you can tighten and loosen them repeatedly with no problem.  The solid plastic print (you have an option to do a "solid print" or a "hollow print") for 3D-printing held up moreso than I thought it would.  The drilling likely melted some of it around the screw holes, making it slightly stronger for screws.

That's essentially it, just some manual work, it'd be better to see if I could film what I'm doing as I don't have pictures using the drill (probably a bit of a safety hazard to try filming yourself and using a drill :p) but that may come at a later time.  Also, I was having some issues for the first time with my camera and I couldn't get the best pictures.

Regardless, here's the put-together final product: