Painting your PrintNC is a good thing, for two reasons :
Rust is a result of the steel oxidation with oxygen, when put in presence of water. Normal air humidity will bring enough water to allow steel to rust. That's why protecting your steel tubes is important.
You can powder coat the steel frame pieces, but it may cost more money. Many use spray paint from a can. Part of the experience is to paint it really cool colors.
There's advantages and disadvantages to do the painting before or after the assembly.
However, painting before the assembly should be avoided as much as possible, because drilling / tapping operations will generate metal shards that will scratch and destroy all the paint applied.
Before painting. You will need to prepare your steel tubes.
There's several ways to remove rust / mill scale
You can use a classic orbital sander with a 120 grit then a 180 grit in order to prepare correctly your steel tubes.
You can also buy a
Scotch-Brite Clean and Strip XT Pro Disc - Rust and Paint Stripping Disc - 4.5” diam. x 5/8-11 Quick Change Thread - Extra Coarse Silicon Carbide for an angle grinder to remove the mill scale.
Another method to clean your steel is to “pickle” them. This method is purely optional.
Please note that this method involves manipulation of dangerous materials. Please be mindful when manipulating them! Also, plan for where the liquid will drain into. It may leave a yellow stain on concrete.
|If you cut a lemon into 3 pieces and use the lemon as a sponge, rub it on the steel. Wait about an hour. Be sure to remove the acidic residue before painting. Also, once you clean the steel with water, it will begin to rust very quickly. So, be prepared to prime the metal. (Thanks to user “salvo” for the tip.)|
An alternative to pickling with muriatic acid is to use white vinegar. This method will eat away all the rust and mill scale leaving a clean smooth surface to prime/paint on. See photo with and without mill scale (dark mill scale tube in the middle).
Make a waterproof container similar to the method used for muriatic acid. I instead used some building construction vapour barrier because I had some on hand and instead of building a box, I stacked up some 2x4 wood to make a makeshift bathtub. See photo.
Put some paper towel over top of the steel to keep the tops wet and let soak for 2-3 days.
Use a hose to remove the majority of gunk left on the steel from the vinegar bath. Hosing off all the vinegar is important to neutralize the acid, don't forget the inside of the tube. After hosing off, use a wire wheel on an angle grinder or drill to easily remove the remainder. Be prepared to paint the steel as they no longer have the protective coating of mill scale and will start to rust quicker. Keep them dry away from moisture till painted. If you do find you need to store them before cleaning for a short period if time, look out for any rust, flash rusting etc. If you do find any hit it again with the wire wheel before painting. Any rust at this point should be minimal and come off quickly.
Acetone can be used to clean your steel tubes and also de-grease them thoroughly. Use rags and wipe all the faces until all surfaces are clean.
If you paint on tapped holes, you may have trouble to screw bolts in them afterwards. In order to avoid any issues, apply some painter's scotch on all tapped holes.
Now that your steel tube have been prepared, they are ready to be painted.
Before starting the actual painting job, run some lumber through each steel tubes to allow easy painting of all faces. Be sure to put cardboard or something under/near the paint area for any overspray.
Apply one coat of primer. (some spray paints act as a primer and paint)
Apply one to two coats of paint for a nice finish.
If you have drips or over sprays, wait until the paint is dry. Then with a scotch brite pad or fine steel wool, rub in the same direction. Then lightly spray paint that area a few times.