Frame fabrication idea for rustable-materials space frame

I'm a fan of building space frames out of chromoly or stainless steel, but let's say you've built one out of some manner of garden-variety steel to save money.

Now you have to live in fear of the frame invisibly rusting from the inside out like the original Lotus Seven. Or do you?

Consider this: You drill a hole wherever one section will be welded to another, so that gases can pass through. When finished you put gas line fittings somewhere and bleed the frame through with nitrogen (helium or hydrogen would be easier to bleed, but they escape through solids and helium is costly). No rust on the inside now, right? And you only had to drill a few holes, add some gas fittings and pay for the gas itself. You could even pressurize the frame and check the pressure periodically to monitor for cracks.

on that same point.. you could put a slug of oil in each tube and seal.. movement when driving should keep it moving around enough to keep the insides coated

WWII aircraft (and Aggie FSAE cars) have linseed oil sprayed into the tubes for that exact reason.

GameboyRMH wrote: ... neat idea ...

Oxidation needs oxygen. Seal them and they shouldn't rust anyway but sucking/blowing some thin oil mist thru after the welding is done is a cool idea.

In olde Engerlund, the recommended method was to drill a hole in the top of a rocker panel or tube, add 'crankcase slops' then drive briskly to ensure a thorough coating.

If oxygen and water are sealed out it shouldn't rust (or at least not quickly). I have had reasonable success on coating difficult to reach panels bu getting access to the top, then using something like that Eastwood red preservative paint thinned to the max. Did that on an MGBGT using an undercoat sprayer, the thinned paint dripped out of all the tiny spaces of the rocker seams and when it dried EVERYTHING was sealed.

Ford (and other manufacturers) used to do something similar by dunking the whole car body in a primer bath. Daimler coming out of a dunk:

That's why you see holes in some odd places on cars, that way the primer can run out.

they still dunk the new car shells to prime them, right before they go into the booth to get powder coated by robots.. saw that on a tv show about the Camaro factory in Canada.or was it the Corvette factory in Kentucky? it's easy to mix these things up after a while.

They both do that. So does Ferrari in fact. Seems like a standard procedure in the industry.

Not to poke holes in your idea (but I totally wanted to use that cheesy pun) but one potential problem I see is welding everything up gas-tight. I'd think one might be pretty lucky to get it accomplished without a lot of grief.

I'm no welder, though.

On a different but kind of related note: Some of the Reilly and Scott TransAm cars I worked on originally had the breather to the dry sump tank (ran from the engine to the tank in the back) routed through the cage/frame. None of them still had that system in use. I thought it was cool...but I think it was too messy for long term (10+ years) use. Those cars got crashed and repaired a lot...people lost interest in maintaining a continuous and exclusive path for crankcase vapors through the left upper frame rail, cage top, downtube, etc. while performing major chassis repairs.

Clem

In reply to ClemSparks:

I read something (Best Damn Garage in Town?) where Darrell Waltrip's team once used part of the cage to hide a few extra gallons of fuel and another part was filled with steel shot so they could drop weight on the warm-up lap.

I remember an old formula ford that used the 2 of the chassis tubes as the coolant lines to and from the radiator. Don't remember which brand it was. Talk about rusting from the inside?!?!

Giant Purple Snorklewacker wrote: In reply to ClemSparks: another part was filled with steel shot so they could drop weight on the warm-up lap.

A new meaning to "Stay out of the marbles."

I think this is one of those ideas that is great in theory but doesn't work so well in the real world. Welding up a 4x4 bumper to be air tight for refilling tires is hard enough, but a whole space frame seems nigh on impossible.

'course, maybe I'm just not a great welder....

IIRC, back in the day CM aircraft frame used boiled linseed oil applied w/ a (syringe type tool) thru a small dia. hole drilled in each tube. The air frame was slowly rolled like in a rotisserie to coat all surfaces. Later coatings were like a primer/ sealer w/ same type application.

In reply to ultraclyde:

I think the guys who do it for a living have less trouble. I just spent a couple hours this week welding bungs onto my fuel rail and I managed to get it to hold 55psi with no leaks and I did it with a .030 mig wire so... I gotta think a pro holding a TIG torch isn't working too hard to do it.

GameboyRMH wrote: I'm a fan of building space frames out of chromoly or stainless steel, but let's say you've built one out of some manner of garden-variety steel to save money. Now you have to live in fear of the frame invisibly rusting from the inside out like the original Lotus Seven. Or do you?

Are you suggesting that chromoly tube doesn't rust?

I know it can rust, but it doesn't rust that badly. Of the chromoly tools I have, the only one that has any rust is a lug wrench that's always dirty, wet and scuffed up. Even then the rust doesn't seem to spread much, it just sort of shows up in spots.

About reliably making a gas tight weld, it takes a fair amount of skill and one secret: as the ends of the tube get closer to being welded closed, the hot air inside the tube will blow 'bubbles' in the weld. Drill a small hole, about maybe .100, somewhere in the tube you are welding, preferably on the top close to an end. Once you get done welding the ends, then spot weld the hole shut.

If doing this, I see no reason that the tube couldn't be checked for leaks at the welds, then heated with a small torch to dry it out and force air out, then quickly weld the hole shut while it's still hot. Now there's less moisture in the tube along with less air, meaning less oxygen.

I used linseed oil in the last steel framed road bike I had. It had wall thicknesses in the seat stays of fractions of a mm or something silly sounding and I rode it in the rain all the time. I didn't want rust.