The machine is only part of the system. The other part is the media itself. There are a ton of different medias out there. Sand is not one of them. Please do not use silica sand to blast, it will mess you up.
Not only are there a ton of different types of medias but within those types there are different sizes. This makes things very complicated when trying to decide what media will suit you best. I have been dealing with a company in Tacoma, WA called Tacoma Company and have found them to be very helpful. They will also sell very small quantities of media that will allow you to experiment without having a bunch of media left over that does not suit your applications. There is also a company here in the SF Bay area called Temple and Associates that is very good.
The 3 types of medias I use consistently are glass, plastic, and garnet.
I generally use these medias as follows:
Garnet:
This media is a garnet red/magenta color. It varies from a coarse to very fine powder. Garnet is a true abrasive which will etch glass, plastic, chrome, etc. I use this media to remove rust, staining, and to clean parts to "white metal". This is a fast working media on rust, etc.
Glass bead/Glass shards:
Glass is mostly used to polish. It is a slow working media that I use on metal part too delicate for garnet. I also use this to polish pieces that have gone through the garnet process and are "white metal". The glass bead at low pressure will give a as cast appearance to aluminum and steel that has been taken to white metal. Glass shards are what you see most of the time. They are usually referred to as glass beads. They are a bit more jagged that the beads. Glass beads are very uniform and consistant in size for a more uniform finish.
Plastic media:
This is my favorite media. When used at the right pressure, this media will clean parts without damaging the original finish. It can be used on chrome, plastic, cadmium plating and other fragile surfaces. Plastic is very good at removing paint and debris. Plastic is not technicaly an abrasive since it removes debris by impact.
There are 2 types of plastic media that I am aware of.
The first is Urea which is the standard media you will see. It is multicolored and likely made from ground up recycled materials. It works great and I use this one most of the time.
The second is synthetic plastic media. It is a uniform color and I believe it is purpose produced. This is supposed to be a more delicate material and is a bit more expensive.
As stated above, all the medias come in multiple sizes. I recommend experimenting with different medias and sizes, air pressures, and distance from the gun to the item to find what works best for you.
Jason