painting inside of square steel tube

You could also just cap the ends after pouring paint in and shake/swish it around. Saves cleaning a roller. :)

There is some sort of airless spray gun nozzle extension for just such an application. Structural painters put it on a pole and stick it through tubes. Randy

I wish I knew that when I put my trailer together!
i

Yeah, but you have to have a whole spray painting setup, and I don't!
Randy Zimmerman wrote:

I wouldn't have given *you* that tip!
Nick

FWIW, there have been many reliable methods used to apply anti-corrosive coatings to the interior sections of metal parts, for many years/decades, that we might not consider relating to our small steel projects.
New automotive panels were typically stamped, welded with additional reinforcements, dipped in etchant, dried, then dipped in or flooded with primer or other coatings, baked, then assembled into a body shell, before being painted with the attractive finish coatings. Naturally, the types of primers and specific ratios and grades of thinners/reducers would be important for a big operation like car manufacturing.
Replacement hoods, doors and various other assemblies generally always had signs; visible runs (usually just on the underside/insides), indicating that they had very likely had been dipped in primer. Drainage ports would need to be designed into the parts to avoid wasting coating compounds, and creating other problems. Most of these processes have probably been replaced with other methods that don't produce all the airborne vapors of drip-drying and baking.
Dipping wouldn't seem practical for most smaller project items, but tubular shapes (or hollow parts) can be temporarily capped at one end, then rotated/turned to produce practically the same results (flooding the interior), without requiring huge volumes of compounds and/or dipping tanks. This would apply to etching acids and primers or paints. As far as just etching, using polyvinyl film products in the way that numerous folks use it to remove rust, could prove to be useful, while providing a form-fitting basin.
The roller method produced good results for these frame members, and seems to have been the ideal process for this project.
WB ......... metalworking projects

Maybe a bug sprayer would work.
Fred

Put the tube on two saw horses. Put a clean bucket under one end. Raise the far end up a bit on something so paint will run down the tube and into the bucket. Pour paint into the raised up end. When all the paint has run out into the bucket, empty the bucket into the paint can. Rotate the tube 90 degrees and pour paint again.
This also will work to clean the tube with solvent before painting.
A bit messy, but you shouldn't have to buy any new tools!
Best regards, Paul Redmond, OR

Play nice, Nick.
Harold

That sounds like it would work even with small tube, Paul. Very clever indeed. I might thin the paint a little, as your method may put on a very thick coat.
Also it would have some issues if the tube had holes drilled in it, but you could always paint first and drill the holes second.
Grant

Of course not. No one expects you to be helpful. Why help anyone learn new methods, when you prefer to just sit back and be an asshole?

That is one reason why I have Nick killfiled. Hard to expect anything useful from him!
i

Sounds like a contrast media (barium) enema. :(
--Andy Asberry-- ------Texas-----

FWIW, there's a Hyundai commercial featuring their new factory in Alabama that shows the entire body of a car being dipped in some sort of liquid. It doesn't show it long enough or with enough detail to see what the dipping sauce is.
Shawn

Yea, I'm selective when I'm helpful.
... when he is an prooven idiot like Ignorant er Ignor-rat er Ignoramus or Gunner.
Again, I'm selective to whom I give tips. Grant is one of them. Others made it into my don't-answer-them-list. Like Gwinn. Too much OT, comprende?
Nick

Just from your POV. You won't get answers from me that help you solve your childish problems. And just as a reminder, you killfiled me when I have prooven that you didn't weld your trailer's frame in the area of biggest stress.
Idiot -> no useful answer.
Nick

Well, you forgot to metion that they are electrostatically charged. And you won't get that paint as a normal mortal.
Nick

Or as they say, you could just put a cork in it.

Well, I didn't actually forget to mention electrostatic methods, but just ignored that process, as I was commenting on the older methods.
The dipping and flooding methods can be improvised on a smaller scale, and are very effective at getting into all hidden areas. I haven't seen the results of any of the new processes, since I haven't had any new cars apart for examination. I can understand that the electrostatic method can essentially "spray around corners", but I kinda doubt that it's as completely effective at corrosion control as the old dipping/flooding methods were (penetrating seams, for example).
In a shop years ago, we had a customer that wanted guards painted that were fabricated from sheetmetal and expanded steel sheet (for some sort of indoor recreational equipment, IIRC). We call this heavy screen expanded steel/metal here in the U.S... it's a sheetmetal product that's slit and then stretched to form a heavy gauge screen.
Spray painting a product like that is very wasteful of paint, energy and time (prior to true HVLP equipment), and is not very effective at total uniform coverage. Dipping in thinned paint was far more cost effective and provided excellent coverage (and no *hey, ya missed a spot*).
So I was commenting on the effectiveness of methods that would be relatively easy for HSMs to improvise. Nearly everyone has spilled some paint on something, and found how well it covers, conforms to shapes and migrates into hidden areas on it's own. A little control of thinning and drying makes a very good protective coating. Something like the dipped, protective plastic-like material used on new endmills and cutting tools.
WB ......... metalworking projects