Installing rollbar in '61 Comet. suggwestions on floor plates to be welded in. (I'm decent body/sheet metal mig'), Are unibody floor plates typically continuous bead or stitches at intervals around edges to floors?. Not required to be sanction organization legal. Fun car not a race clone... thanks
Sheet metal is not strong enough to weld a cage to. Sandwich the floor between two plates with bolts and then weld the roll bars to the plate. 6" X 6" X1/8" or 3/16" should be adequate for a street ride. Good luck.
check SCCA rules for production classes - they have complete instructions on putting cages/rollbars into cars with unibody construction
If doing it with two plates ALLWAYS make one of the plates bigger. One of them should be atleast a half an inch or more larger so the don't sheer the floor sheet metal like a knife.
You may not be building it as a true race car, but I would suggest that you take a look at an NHRA rule book. If you are going to build it, build it to code then you know it is safe. As I recall NHRA required the rollbar to be welded to a 6" x 6" plate that was fully welded to the floor ... keep in mind I said "as I recall" ... it would be best to check an actual and up to date rule book.
I just got my Mustang certified to 8.50. I used 6" X 6" plates welded to the floor, no stitch welding, no plates under the car. It's a pain to weld 1/8" plates to the floor
All good replies, For 8.50 cert. with welded plates, I need to ask: whose rules and cert.?. Backup plates underneath are complicated by sub-frame rails and torque box but bar plates weld to them. Pain to weld because...? Thanks
because your welding thick stuff to thin stuff. nhra requires the above listed 6x6 plate welded to floor. if you hit something hard enough to rip it loose you got other things to worry about.
i did a 90 mustang years ago. seems like i used 6x6x.187 plates welded to the floor... on the main hoop i actually cut the floor pans in the rear and plated in 2x2 outriggers to the inner rocker panels.. you've spent the time to bend the bars up nice, they look good, dont cheap out on the final installation.. might as well do it right. when your setting your welder up for the sheetmetal and plate welding, you'll know when you get it right. the weld will actually pull into the sheetmetal and plate. i would actually call it stitch welding, your just stitch welding around the entire plate.. bzzzzt, bzzzzt, bzzzt, bzzzt,bzzzzt,bzzzt,bzzzzt all the way around the plate..
Most of the concern with roll bars is not with them pulling out, but for pushing them through the floor pan. The 6" square plate spreads the load of the tube out enough to reduce the likely hood of the bar pushing through the floor pan. With a good (not rotted through) pan and a 6" plate with a good weld, even pulling the bar off the floor will create a huge hole, and will probably deform the tube first. I've been involved with enough dirt track unibody cars to tell you without a doubt, apiece of tubing welded to a 1/8" thick, 6" square plate welded to a floor pan distorts a lot of material (absorbs a lot of energy) before it would separate from the rest of the floor. Like someone said earlier, if you pull that plate off the floor, you have a lot more things to worry about. Its interesting to note how many people think a roll bar welded through a hole in the floor pan and welded to a car frame that is probably 1/8" thick and about 4" wide is stronger then a roll bar welded to a 6" x 6" x 1/8" plate that is then welded to the floor pan. When stuff starts to bend, you want it to spread the energy to as much area as possible. The purpose of the 6" plate is to spread out the energy. Gene
I use 6"x6" 1/8 plates continuous weld with a 250 mig with no plate underneath and everyone that I have done has always passed NHRA cert.
I built rollcages for years as my shop specialized in chassis work, mainly for oval track racing. As stated when I did the occasional drag car I used the 6"X6"X 1/8" or 3/16" plate for the floor mount and never had any rejections from any sanctioning organization. I did a continuous weld all around the plate.Stitch welding doesn't get both pieces of metal hot enought to completely fuse them. This is my opinion derived from hundreds of hours doing this work. practice/experience will allow you to set the machine just right and be able to weld thick to thin in one continuous pass. Frank
I agree wholeheartedly. It makes me cringe when I hear the words "stitch weld" in a thread about roll cages or chassis work. In real welding parlance, the terms "stitch weld" and "skip weld" are taken to mean an intermittent weld where you make a short bead (usually an inch, but maybe up to three inches), then skip a length along the joint, then make another short bead, and so on. However, what most people seem to mean by "stitch weld" on the forums is a long series of overlapping tacks (usually stated as a technique to limit distortion when working with thin material). This is a bad thing, especially when talking about roll cage work, because by making so many starts and stops, you greatly increase the chance of getting a cold start in the bead (IE a place where the filler metal makes a good looking bead on top of the base metals, while not actually fusing them together). You should weld your base plates down using a skip pattern, but make sure the welds are finished continuously. What I mean by that is to weld a short section, say an inch and a half, then go to the other side of the plate and make a similar weld there, then move 90 degs on the plate and make another weld, and so on, until its perimeter is entirely welded. I also believe it is good practice to start your weld away from the first weld you made, and then form the bead back toward the existing bead, stopping after you've remelted the initial starting point of the previous weld. Doing it like this you will very nearly eliminate the possibility of a cold start surviving into the finished product. You just have to work on your technique until you can properly run a bead on base metals of dissimilar thickness, getting good penetration without blowouts. I've always had the best luck by turning down my wire speed, slowing my travel speed, and keeping the majority of the arc time on the heavy plate. The movement pattern looks like a drunken snake's path, weaving back and forth, just dipping down onto the thin often enough to keep the molten pool moving forward, without letting it sag or blow out. You can control the heat input that way, so you can make a good penetrating weld without turning down the voltage on the machine (risking a cold seam). I do not agree with the above user who said that body mounting the cage was preferable to a direct frame attachment. If your chassis has an honest to God frame under it, you are miles ahead to attach your cage to it, both rigidity and safety wise. If you attach your seat and belts to the cage, not the frame or floorpan, you will be assured that no matter how the car and cage distorts, your seat and belts (and thusly you as well) will move along with the cage, so you stay inside the livable zone.
6" x 6" 1/8" will be fine . The main loop must be one solid piece . I have done plates and also welded to the frame through the floor IF the frame was there ! You also need a SOLID CONTINUOUS weld around the tube to the plate if you can make it in one pass . So make sure you are in a good position so you can make that continuous weld . THIS IS NOT SHEET METAL WELDING ! NO tack welds stitched together on any roll cage bottom line ! That's for sheet metal ONLY ! Just remember if something goes wrong , that cage is the ONLY thing that is going to protect you ! You need to check the books on where you are racing to make sure you have the right tubing and cage requirements for that sanctioned race track . Most are all the same but best to be sure ahead of time . THEY will check your cage to race ! Also don't be cheap and install a 4 or 6 point cage . They are for show . Protect yourself . The extra weight , welding and money for a stronger cage is with ever dollar if something would go wrong . That is just one of those areas you DON'T want to try to save a money on ! Personally I would go with a 12 pt. cage , but that's me . It's your life in that cage you are building , just remember that ! Safety First ! Now enjoy your drag car and post some pictures ! Just my opinion ! Retro Jim
Build it to pass inspection. The guy buying it later won't want a "fun" roll bar. This includes the material, how it's built and welded and where it's located. Do searches on how to assemble it so you can do full welds at all joints, including the halo and A pillar bars. They will often drill holes in the floor and drop it through so they can weld the top, then lift it and slide the plates under. Check your insurance. There has been some discussion of some companies that won't cover a car with a cage on the street. No point in paying for something where they deny when you need them.
Thanks for the replies. ' ready to light up the MIG now. I liked the crown pipe welding suggestion of dropping through floor and then slippng plates under... AC welded for many years , sheetmetal or tubing, MIG makes steel fab easy as copper soldering for most jobs. Cleaning the car's 50 year old tar body coat for welding is the hardest part . Have Fum
What's with the bent rear kicker? That tube will be much stronger if it were straight. The diagonal in the main hoop would also be much more effective if it ran from lower right (down at the floor) to upper left (into the main hoop right behind the driver's head). You'll need to split the horizontal harness bar and that right kicker to keep the diagonal continuous, but otherwise, it shouldn't be a big deal. Having the diagonal like you've got it doesn't really help much to stop vertical crushing (which is pretty much what the roll bar is there for). Just a little constructive criticism. Please don't be offended.
I think you should take a look at a few real pro cages, there's a few spots there where you just are not getting optimal protection. Some of the loads and forces are not being compensated for. If you are going to do it do it to shut down all critics and make it safe, it's your life, protect the shit out of yourself. Typically the rear bars will tie in to the top of the hoop or roll bar, they will cross and form an x to absorb forces coming in to the chassis from each side, they want to go to the top of the bar to resist load at the roof not just at your shoulders, what goods shoulders if your head is smashed? I would also run the door bar proper and the roof bar as a separate unit and cross brace them at the window line, in some cases a bar across the midroof on an angle front to back is very nice to have. If you really want to boost the factors of safety don't be negative on gussets, they show you care and add good safety to the car. In the end you may have a bit of extra tube but you are doing this for fun and safety anyhow, have fun. That's what it's really all about.
Most all sanctioning bodies i have dealt with require outriggers or the cage to be directly welded to the frame whenever a full frame exists. Also in the event of subframes a minimum size metal is required to tie the two together depending on the speed of the certification. Although not hamb friendly one of the most common are the ones S&W sells to go through the passenger compartent of fox body mustangs.
Thanks again for the replies, 'will indeed be using gussets, This S&W kit does basically tie the subframes to the bars, and will taking another look at the safest configuration within compromises of a street car. Thanks
just think oof this,,, even without a wreck ,, just going down the average road,that car twists and flexes so much that you really need to plate underrneath as well, use bolts, and if possible connect your front and rear sub frames ,, that way you take a lot of flex out of the car and flooor boards will live longer
I slice a slot in the floorpan, and install a piece of 2" x 4" x .120" wall rectangular tubing welded from the frame rail or subframe connector to the rocker. I also completely weld the edges of the 2 x 4 to the floorpan. This is much stronger than 6 x 6 plate: This is how the diagonal in the rear hoop should look:
I like the landing pads, those are well done. I still don't understand the bent rear down tubes. Why not make them straight and several times stiffer? With a cage like that, it's not like you've got to take rear passenger space into account.
Lots of great advice and help, but this is not one of them. You don't need a plate on the bottom. Show me ANY street car, or race car for that matter that pulled plates from the sheetmetal due to twisting and flexing. Pictures. Not being a dick, just minimizing wrong information. My 91 Super Stock Olds Calais has several thousand 9 second passes on it, and a friends 88 Camaro Super Stocker has more. Both unibody cars, both with NHRA certified and current legal cages. Both use plates on one side only.
That cage came from Autoweld, and that is the way they build them. This car will see street duty with a back seat in place, baby car seats and all.
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