While reading the thread on tubing benders, I thought about a practice that I do whenever I weld up any structures out of tubing. I picked up the practice years ago somewhere, probably from a book, but wondered if most people working with tubing even know to do this? What I do is, on any piece of tubing that will wind up being fully welded at both ends, I drill a 1/8" hole somewhere in the middle of the piece of tubing. When I'm finishing up welding the ends of the tubing, the little hole gives a place for the pressure and smoke that builds up inside the tubing to escape. I usually leave the little hole there until I'm totally done and know I won't be welding anymore on that length of tubing, then I spiral a little quick weld on the hole to close it up. A lot of times that hole serves double as a midpoint to take measurements from, so I'll leave it there until everything is done. If you don't drill that little hole, when you get to the very last part of weld that seals up both ends of that piece of tube, the pressure building up inside the tube can push or splatter the last little puddle of weld back out again, making a half-ass weld there. I think a lot of people probably don't even think about that and don't bother with drilling a little hole. How many of you actually go to that extra trouble? I think I read it's standard practice for things like aircraft tubing, but I wonder how many people making tube cages do that? I read somewhere that some people even squirted a little oil into the vent hole to cut down on corrosion inside the tubing, and then welded the hole shut. That seems kind of dangerous though. Anyone ever hear that too? The 2-ended stub point drills used for drilling sheet metal studs in buildings work well for drilling those 1/8" holes. The stub point makes them a lot less likely to break.
I do it when both ends will be closed but I thought it was mandatory for chromoly. Something an old timer taught me years ago. He claimed for the exact reasons you said.
I drill the vent hole in the piece of tubing that the piece is welded to, inside the joint, so that it vents into the next piece of tubing. That way all the tubing is vented together. If the whole weldment wind up being air tight(no open ends) you can just drill one little hole somewhere to vent the whole thing the next time you need to weld on it. For small jobs like adding a small tab, there's usually enough enclosed air volume to allow the hot air to expand that you don't even need to vent it at all. And yes, I wipe out the tubes and spray a rust preventative inside. Started doing that when I was putting compressed air reservoirs and etc inside the frame, now I do them all.
I have built a number of 4130N aircraft structures...fuselages, etc....and have welded with gas (oxy-acet) and TIG. In fifty years of this I have always drilled a hole, .125" in the center of each tube at the location for the adjoining tube(s). When the entire structure is finish welded, I drill one last hole on the uppermost location. Then I fill the entire structure with either linseed oil or similar. It can take a LOT to fill it. Then that last hole gets a rivet....self-sealing Cherry Max. That's the way it was done in the aircraft biz in the old days. Still works.
Some of the race car frames do this too. All the frame tubes are interconnected by small holes. The whole thing is then pressurised with compressed air (or dry nitrogen), A small pressure gauge is then fitted. As long as the pressure gauge reading stays up, you KNOW for sure your tube frame is not cracking anywhere.
That sounds really heavy, do you leave the oil in? Some race cars, notably birdcage Maseratis, and some aircraft have the whole structure pressurized and a gage is installed. If the air pressure drops, it means a crack has formed somewhere and a search is begun to find and fix the crack. The pressure aids in the search, just like a hole in a tire.
Cool. I've been doing it right then without even knowing it. I started out of necessity when the welds started spitting at me. I drill a small hole (1/8") at tube joints where the will be hidden by the next tube. OT - watched a guy weld onto a 2x4 tube steel machine one time, and it really blew when he hit it with the stick welder... turned out it was used as part of the air supply to the machine.
Same here, makes everything purty, no unsighty hles out in the open, However if using any part of the chassis as a vent and or pressure line remeber not to drill it!!
Yes, the holes are put in there for a reason; 1. So air pressure doesn't mess up a weld, or equipment. You see, if your doing really super critical stuff......there's places you need tubes to be vented to the atmosphere....oh, lets say high altitudes, underwater stuff is like that....yada, yada, yada.......... 2. Also, to let the condensation dry out so the piece won't rot out from corrosion. 3. So you can pressure test it....... But mainly for the first 2 reasons when doing general welding. PPPPSSSSSSSSST............its a good place to hide fuel if your racing too!!!!!!!!!!!!
Drill holes like this on chromolly to be able to shield the backside of the weld with argon/co2. Not necc. for mild steel. Carl Hagan
The Jalopy Journal
