Date:         Mon, 11 Apr 1994 20:24:10 -0500
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Green Eric L <elg9316@usl.edu>
Subject:      Grinders and sanders


To cut out rusted metal, a number of tools are usable. Tins snips are
the cheapest. You can also use your jigsaw that you use for cutting
wood, except fitted with a metal-cutting blade, but those things are
notoriously difficult to handle. They're best for cutting weird shapes
in metal, just as with wood.  A jigsaw can be got for about $15 to $20
at a pawnshop (which is where I got mine -- just plug it in first to
make sure it jigs!). A wood-cutting circular saw can be used for
making rough cuts in LARGE panels... just fit it with a metal-cutting
wheel instead of a rip blade. One neat little tool is a high-speed rotary
tool from Dremel or etc... this little wunder rips along at 20,000 RPM and
is great for precision work. That's what I used to grind the little washer
to pull the clutch bushing in my car that's in the blind hole... try it,
nope, still not right, grind a LITTLE bit, try it again, still not right.
A very worthwhile investment (around $35-$40), useful for all sorts of neat
things like, e.g., slotting a rounded-off bolt so you can get a screwdriver
on it at least, or for that matter re-dressing the tip of your screwdriver
(can do a VERY precise job of it). 

Still on cutting, if you have an air compressor, an air hammer fitted
with a chisel/sheetmetal cutter bit is how many body shops "rip" old
panels off. A rotary cut-off tool is similar to the Dremmel tool I
mention above, except MUCH larger, and thus more useful for
large-scale cutting and grinding. A rotary grinder looks sort of like
a right-angle cut-off tool, and is most useful for grinding down a
weld bead on the exterior of a car...  it removes too much metal too
quickly to be used for final finish work.  Use a rotary sander or a
sanding disk on your drill for the last little bit of finish work. A
rotary grinder spins much faster than typical drills, but you can do
the same job with a grinding bit on your drill. It's just slower.
Unless you want to open a body shop, you probably want to stick with
the drill. 

A selection of metal files, both round and flat, will assist in final
"dressing" of a cut. If you're trying to weld in a new section of
panel you'll probably be butt-welding it in, meaning you need to match
the edges of new metal and old. A bit of strategic file-work will
assist doing that. But you'll probably use fiberglass for most small
holes in the "skin"... it's not the "right" way (which is to put new
metal), but done in moderation so that panel strength isn't affected
by lack of metal, it'll do okay. Whatever you do, do *NOT* put Bondo
in holes. Bondo attracts moisture and will cause rust, plus as it
swells and shrinks due to moisture it will gradually work its way out
of the hole until it plops out onto the pavement. Fiberglass doesn't
have that problem (it's waterproof).  You'll patch the hole with
fiberglass and resin, sand down the fiberglass pretty much flush with
the "skin", then use Bondo only as a final smoothing layer. Buried
between fiberglass and paint it can't do its rust-causing trick.

Now to the rust problem: There's several possibilities here. First,
you can get out ye old sanding block and sand sand sand. Then there's
the drill-mounted steel brush. This'll have to be followed up by ye
old sanding block if it's an external surface, because steel brushes
tend to scratch the sheetmetal, but is great for "rough" removal of
flaking encrusted rust. A drill-mounted sanding disk works okay, but
I've never had much luck with them... the blasted disk never seems to
want to stay in one piece or in one place.  3-M sells a VERY good rust
and paint remover which works quite well... it looks like an
abrasive-encrusted fiber wheel that mounts on your drill bit.
Unfortunately, it IS a bit expensive, and works best on flat surfaces.
Edged surfaces tear off the expensive encrustations. Note that once
this removes all the rust, little pits will be left where the rust was
rooted out. You'll need to smooth the surface with Bondo and then sand
the Bondo smooth before you can get a good paint job. Else your paint
job will have pits in it too. A "glazing putty" will fill in the last
little imperfections in the Bondo job. If this is the backside of a
panel, of course you're not worried about that, but for the visible
side it's a real concern.

For good follow-up, you may wish to treat the surface with a rust
remover chemical. Except for the 3-M wheel, all of the above leaves
little craters of rust unscathed, invisible to the naked eye but ready
to strike again. Even sanding, if you don't get it absolutely shiney
smooth, can leave rust behind.  For the backside of a panel
especially, a rust remover treatment that leaves a protective coating
works great. Steel brush off the flaking rust, cut out the rustiest
metal, and then apply a rust neutralizer to the remaining
slightly-rusty metal. Duro sells a couple named "Extend" (goes on like
a paint) and "Naval Jelly" (has to be washed off after application).
Do note that Extend has to be sanded to roughen the surface before it
will accept paint... but in the meantime it'll continue to protect the
metal from corrosion. But it IS expensive. A couple of outfits that
advertise in Hemming's Motor News advertise a mixture of phosphoric
acid and zinc phosphate which also works well. It has to be washed off
too, but leaves a bit of a zinc coating which seems to discourage rust
until you get some paint over it.  One of those places is Bill Hirsche
Automotive, 1-800-828-2061.

If you have extensive rust problems, by far the least frustrating way
to get it off is to sandblast it off. This requires a sandblaster, an
abrasive "sand", and a LARGE compressor. The largest 110v compressor
that Sears sells is barely adequate to run the smallest tip available
on common siphon-feed abrasive-blasters. This is okay if you're just
wanting to sandblast a small area, but if you have extensive rust you
probably want a bigger tip. To run a medium tip (the best tip for
most work), you'll need a compressor capable of 12-16 CFM at 90PSI
(CFM=Cubic Feet Per Minute of air). It's likely that you would want to
rent such a compressor, rather than buy it, because it's so rare
otherwise that you'll need a huge compressor (the biggest 110v
compressor that Sears has will run just about any other air tool). Do
note that this size compressor requires 220V and will NOT usually plug
into the clothes dryer plug... you'll need to make up an adaptor. Or
rent a gas-powered compressor, which is extremely noisy and somewhat
irritating (have to fill it up with gasoline every few minutes, it
seems!), but at least doesn't require an electrician. Once you have an
abrasive blaster, whether it be from Sears, TiP, or someone else, then
you need to select the proper abrasive. For the exterior of a car, the
usual abrasive recommended is ground walnut shells. This will not pit
the underlying sheetmetal and will leave a smooth semi-shiny finish.
It IS slow, though, since walnut shells don't cut so well. Faster and
safer than using a rotary grinder to grind the old rust and paint off,
though... you can't accidentally grind right through the metal, since
walnut shells don't cut metal very well.  For the underside of the car
you can go for the quick and effective. Make sure you don't blast any
wiring or rubber parts, but a nice fast-cutting abrasive (see what's
available locally, check your Yellow Pages under "Sand" or
"Sandblasting Supplies") will work fine and leave a nice "toothy"
finish that a good undercarriage paint will stick to like glue. The
Hirsche place above sells such an undercarriage paint (they call it a
"super paint"), but undoubtedly you can get a similar durable
undercarriage paint locally. 

Note that whenever you're grinding, sand-blasting, or otherwise
raising a dust storm, it's advisable to wear a respirator. Paint dust
or any similar non-biodegradable dust can cause lung disease in even
moderate doses. If you're just hacking at it with a drill you may be
able to get away with just a little disposable dust mask, but if
you're going to go full-bore at it pay the $40 for a "real"
sandblasting respirator, the one that looks like a gas mask except the
filter cartridges don't contain charcoal. Especially if you're going
to do sandblasting with a "rough" abrasive, most of which have some
free silica in them. Silicosis is a form of CPOD which is extremely
rapid in its onset and rapidly disables the sufferer. Death usually
happens within five years, from complications of CPOD (pneumonia,
chronic bronchitis, congestive heart failure, etc.).

One final word: I am by no means an expert. I'm still learning. So don't
take my word as gospel about anything (except the silicosis business and
the need for a respirator). Check with "real" experts before you do anything
that can cause structural weakness in your car or cause problems when
it comes to re-painting the whole car (do keep paint over your metal, even
if you have to temporarily use a spray can of Rust-Oleum to do so!).

--
Eric Lee Green    elg@usl.edu     (318) 984-1820
        P.O. Box 92191  Lafayette, LA 70509