I'm building (slowly, due to lots of travel interruptions) a small gantry.
The legs are made from 4" square steel tube. The central stem of each leg is
open to allow a 3-1/2" square tube to extend or retract. All the other members
are essentially welded closed. I wanted to paint the inside of the vertical
open tubes, about 30" long. I was wondering how to do that and someone on this
NG helpfully suggested I try a 3" roller. Today I did just that - taped the
roller to a yardstick and had at it.
It worked just great! What a clever idea .. for anyone who fabricates with
square tube, this is a trick worth remembering.
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
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.
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
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.
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
Yea, I'm selective when I'm helpful.
... when he is an prooven idiot like Ignorant er Ignor-rat er Ignoramus or
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,
Just from your POV. You won't get answers from me that help you solve your
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.
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
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
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.