Make holes in PLA print I have  a print I need to make holes in.
I have read some other threads where the answers was in short, "don't, print the holes", and "make sure to make the hole from the top or bottom".
The problem is I need the hole in the side of a print with about 1 mm walls.  

The holes I need is to run a USB cable in and a few to hold 3 mm LEDs.
One of the holes needs to be 10 mm.  

What is my best option?
I read that there is a risk it cracks, so I was thinking maybe I can use a soldering iron for the smaller holes?
That will melt the plastic and create nice smooth walls, right? Less risk of cracks?
The piece will not be loaded in any way, it's just holdin it's own weight.  

I never anticipated that it would be an issue to drill holes in prints. If I had known it I might have tried more to change the print before ordering it.
(I don't have a printer to make a new one with.)

Note: The part has already been printed. This is a question about post-printing processing, not modelling for a new print.
You're going to have to drill those holes. The plastic will melt if you drill too quickly. If at all possible, use a slow speed drill, a hand drill, or wrap a cloth around a drill bit and twist it with your hand. If you go too fast, the part will melt. If you press to hard the part will break.

Once the hole has been drilled you will need to reinforce it with a metal/plastic tube of the required diameter. Press the tube into the hole. I don't know what your wall thickness is, but try to ensure the tube is the same length.

If at all possible you should get flanged tubes like these from mc master car:



The parts with the 1/2 inch inner diameter and 5/8 outer diameter should fit your 10 mm requirement. The rest is up to you. Go to mcmaster.com/inserts scroll down to "Other Inserts" then "Tube and tube fittings".