This is a quick instructable to make the most useful accessory to 3D printing, the Glue.

Things needed:
Nail Polish bottles - online, I got mine from an Australian beauty Salon Supplies
Acetone - Local Hardware store
Scrap plastic Material - Byproduct of 3d printing

Optional - Syringe and 4ml fish tank air line hose

Steps:

1. Fill Nail polish bottle with Acetone to about 2/3rds full

2. Add scrap Plastic bits in a single colour until you cant fit any more

3. Put the lid on and leave overnight for the plastic to melt

4. Add more and repeat until its as thick as you require.

Step 1: Uses

Gluing: Paint some of the acetone or acetone mix onto both sides of the parts to be joined. Press together and hold for about 10 seconds. Full strength is achieved in about an hour depending on how big the part is. Thicker is better for bridging gaps and small joint surfaces, a thinner mix is better for joining two large surfaces as it will use more of the existing plastic surface when bonding. Basically it melts the two surfaces together chemically and they bond in a very strong join, similar to welding but you know, plastic.

Smoothing: Using either plain Acetone or coloured to match paint a thin layer over the part to be smoothed. Its a great way to make contrast between different parts. It does not to as good a job as other methods of smoothing though, but can do targeted parts of a model whereas acetone vapor smoothing does the whole model at once. Thinner mix is better for smoothing (less plastic), it will give a better surface finish.

Colouring: This works best with dark colours on light of course, but as the added material from the brush bottle will spread a little, it gives quite nice mottled colours. Simply paint or dab at bits of it and let it dry a little, then repeat until you are happy with the strength of the colour.

Strengthening: If there is a little thin part that is printed and ends up rather weak, you can paint a layer of the coloured mix on and it will harden the thin part up. See the example on the Colonial One ship. The fins were way too thin and really flexible, a coat of black acetone mix has made them strong enough for the whole model to stand on upright. The thicker the mix, the better for this use.

Hope this little tip helps, and if you like it please vote for it in the 3D Printing competition!