Any tricks for tigging thick to thin?

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I am welding support plates on my car for a roll bar I am installing, and the plates are 1/8" mild steel and they are being welded to probably 1/16" or thinner sheet metal.  Any advice you guys can give me?Here is a pic to give you an idea of what I am doing.Miller Dynasty 200DX Tig Welder
Reply:I was taught to burn on the thinker metal and quickly drag down the puddle. Its easier to show than talk about. I'm sure there are other ways thats just the one i was taught
Reply:Yes,  run the bars through the body and attach them to the frame.  The body of the car is not a good place to attach a roll bar/cage - the plates will not help.
Reply:The Welding Web software clips any photos and the following text larger than 800 x 600.9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Try to keep most of the heat on the thicker plate and use the puddle to melt the thinner material. Do cars still have frames? I was always tought to run the cage to the frame, but that was way back when cars still had frames. I have no idea how you should support the cage on a unibody car, unless its just to make the cage cover all sides like a cube.BTW please resize the photos first. Thanks.
Reply:Originally Posted by DSWTry to keep most of the heat on the thicker plate and use the puddle to melt the thinner material. Do cars still have frames? I was always tought to run the cage to the frame, but that was way back when cars still had frames. I have no idea how you should support the cage on a unibody car, unless its just to make the cage cover all sides like a cube.BTW please resize the photos first. Thanks.
Reply:TSOR is absolutely correct. You do not weld structural members to sheetmetal.The body is made to be crushable to absorb some of the imact and  the rollbar is to give you ultimate protection. and keep your body secured with a harness.Cut or drill with a hole saw through the sheet metal and weld plates on the frame. THEN weld the roll bar to a plate that matches the other plate and bolt them together. If the roll bar is damaged you can remove the roll bar for repairs or remove it for sale .You can just buy tthe plates already stamped with the holes punched.Last edited by Donald Branscom; 03-10-2009 at 12:31 AM.AWS certified welding inspectorAWS certified welder
Reply:It's a Toyota MR2 guys, no real "frame" to speak of (unibody design).
Reply:Originally Posted by JonE30It's a Toyota MR2 guys, no real "frame" to speak of (unibody design).
Reply:In heavier areas, yes you can drag down from the plate to the sheet metal.  For the most part, I would just do a series of tacks/very short stitch welds.  Used to be a total nightmare doing cages in Acuras that way.  Keep an eye on the undercoating as well, it loves to catch fire, flare up, and wreak havoc on shielding gas coverage.  Spend the time with a hammer to get the plate/floor pan contour perfect.  Safer, and makes welding a whole lot easier.  In areas like the rear strut towers, the metal is usually considerably heavier than the floor pans and is easy to weld.  If you can, put a 90 degree bend in the floor plates and tie them into the rocker panels as well, as the metal there is also considerably heavier, or at least doubled up and spot welded from the factory.
Reply:Its a 91 toyota mr2 t-top car, there are two frame rails that I was able to tie the main hoop into, but in this picture is the rear firewall and behind that is the motor.  So there is nothing I can tie into behind it.  And it will be the same thing for down by my feet where two more plates are going.  Would you suggest that I just bolt these in, instead of welding them?Miller Dynasty 200DX Tig Welder
Reply:Originally Posted by SupeIn heavier areas, yes you can drag down from the plate to the sheet metal.  For the most part, I would just do a series of tacks/very short stitch welds.  Used to be a total nightmare doing cages in Acuras that way.  Keep an eye on the undercoating as well, it loves to catch fire, flare up, and wreak havoc on shielding gas coverage.  Spend the time with a hammer to get the plate/floor pan contour perfect.  Safer, and makes welding a whole lot easier.  In areas like the rear strut towers, the metal is usually considerably heavier than the floor pans and is easy to weld.  If you can, put a 90 degree bend in the floor plates and tie them into the rocker panels as well, as the metal there is also considerably heavier, or at least doubled up and spot welded from the factory.
Reply:By the way, I wouldn't bother TIG welding the floor plates in.  I'd just MIG them in.  It will save you headaches beyond all comprehension.  If possible, weld the bars to the plates FIRST.  It's nearly impossible to do so once they're already down there, depending on how close to the sides of the car they're tucked.
Reply:Originally Posted by SupeBy the way, I wouldn't bother TIG welding the floor plates in.  I'd just MIG them in.  It will save you headaches beyond all comprehension.  If possible, weld the bars to the plates FIRST.  It's nearly impossible to do so once they're already down there, depending on how close to the sides of the car they're tucked.
Reply:The 110v MIGs work perfectly for this sort of work, no need to get anything high buck.
Reply:Originally Posted by SupeThe 110v MIGs work perfectly for this sort of work, no need to get anything high buck.
Reply:This is how it is typically done on unibody cars.  A lot of sanctioning bodies are now specifying GTAW now that the process has become widely available.  With that, they ban all other processes.  Check with your sanctioning body or do a search for cage requirements at SCCA, NASCAR, NHRA. or others.As said before, start the puddle on the thick plate maintaining the proper torch angles and bring the puddle over to the thin until it wets into the sheet metal.Most auto sheet metal is 19 gauge, about .042"  and the 1/8 is  .125".  So the heat required to melt the 1/8 is more than twice the amount used for the autobody sheet metal using the 1 amp per .001 rule of thumb.  The sharp edge of the 1/8th will melt at a lower setting, so experiment a little with the heat.  Roll cages are also where lift arc rules!  This came up with a quick google search:  http://www.blackhawkfarms.com/rollbar.pdf  Lots more out there!
Reply:Originally Posted by TSORYes,  run the bars through the body and attach them to the frame.  The body of the car is not a good place to attach a roll bar/cage - the plates will not help.
Reply:I am going to pick up a mig welder, which should make finishing up this project much easier.  I will post up some more pics in the photo section.  The roll bar itself looks sexy!Miller Dynasty 200DX Tig Welder
Reply:Originally Posted by Fat BastardThen why is it in the rules for NHRA IHRA SCCA ASCC that way?How about for cars that have unibody chassis? To the OP I would go with the first reply you got. Good and more photos please
Reply:Originally Posted by TSORShow me said rules that state the OP is doing it correctly.
Reply:Donald and TSOR Not that your thought are not a better way (more structurally sound) it is simply over kill for the application. In NHRA IHRA the ET of the car dictates the construction of the car. In road racing it is the speed potential of the car the is the deciding factor, a production based car (in theory) will not achieve the speed of a purpose built car. Another factor is that in road racing we attempt to match car mass to car mass meaning it is dangerous to race a 3000 pound car with a 1200 pound car. So while the advise you gave is valid, in this instance it might be  unfounded. It really depends on who he is racing with and what type of racing. For road racing with my club ASCC he is following our rules vary well.Last edited by Fat Bastard; 03-11-2009 at 01:17 PM.
Reply:I have been building this to NHRA rules.Miller Dynasty 200DX Tig Welder
Reply:What ET class will it be running in?
Reply:I am expecting mid 10's at around 130-135mphMiller Dynasty 200DX Tig WelderThe way the OP wanted to do it is exactly how most sanctioning bodies dictate you attach roll cage tubes to a unibody.  The large square of 1/8" plate distributes the load over a wide area.  Having said that, it pays to spend a lot of time looking at the placement of those plates.  There are usually areas with more layers of sheet metal than others that would be a better place to to tie into.  A great way to tell is look for places with a LOT of spot welds very close together in the unibody.  I generally try to do as a poster above suggested and tie into both the floor and the rockers.  My main hoops usually land in boxes the tie into the floor, rockers, and rear firewall/bulkhead.I have both tigged and migged the base plates in.  If the car is really nice or still has interior in it I go for tigging them simply to avoid the sparks and splatter.  But it is far easier to mig them in.  With either one you have to spend most of the time on the base plate with a quick movement of the puddle onto the unibody each time you move forward.  There are many pictures of this kind of thing throughout my galleries found here:http://tubularfab.com/gal2/main.phpLook at the Mazda RX7 bolt ins for tigged base plates.
Reply:Tubularfab, I am in awe everytime I see your work.  BTW, off topic, I have a few pieces of that Monster Garage DeLorean, though that Panoz build was outstanding.
Reply:Originally Posted by TubularFabThe way the OP wanted to do it is exactly how most sanctioning bodies dictate you attach roll cage tubes to a unibody.  The large square of 1/8" plate distributes the load over a wide area.  Having said that, it pays to spend a lot of time looking at the placement of those plates.  There are usually areas with more layers of sheet metal than others that would be a better place to to tie into.  A great way to tell is look for places with a LOT of spot welds very close together in the unibody.  I generally try to do as a poster above suggested and tie into both the floor and the rockers.  My main hoops usually land in boxes the tie into the floor, rockers, and rear firewall/bulkhead.I have both tigged and migged the base plates in.  If the car is really nice or still has interior in it I go for tigging them simply to avoid the sparks and splatter.  But it is far easier to mig them in.  With either one you have to spend most of the time on the base plate with a quick movement of the puddle onto the unibody each time you move forward.  There are many pictures of this kind of thing throughout my galleries found here:http://tubularfab.com/gal2/main.phpLook at the Mazda RX7 bolt ins for tigged base plates.
Reply:I don't know what the wire feed numbers on a new fangled digital Miller welder are, but I generally set the volts on mine at 17.5 for welding 1/8" plates into car sheet metal.  This is definitely hot enough to burn through, so make sure you keep the heat focused on the 1/8" plate.  Make sure you clean the unibody very well getting rid of all the pesky seam sealer, paint, and E-coating as these will gass and screw up your shielding.  Most modern vehicles have sone form of rust prevention coating on them - ford calls it E-coating - that will act a little like a galvanizing when you try to weld through it.  The stuff does not come off well with a powered wire brush even, so I usually scuff it off with a coarse 80 grit roloc disk in an angle grinder moving it around very quickly so I don't thin the sheet metal any.Nice welder!  I'm jealous!  My mig is an older Miller XMT 300 CC/CV power supply connected to Miller S54 wire feeder.  So I at least have digital readouts for volts and amps.  I also need to get a smaller gun for mine as the 400 amp Tweeco that came with the feeder is overkill and less than ideal doing cagework.  Talk about bulky!
Reply:I bet that 400amp gun is huge!  You should definitely replace that for as much use as you give it.I tried out my new welder today, I had much better luck welding with the MIG welder.  I had it set to 16.5 volts, and 115 wire speed.Miller Dynasty 200DX Tig Welder
Reply:I'd used a thinner plate.  For NASA, the rules say 0.083 min.  I'm not sure about NHRA, but I'd use thinner than .125.  It doesn't make sense to me for the mounting plate to be so much thicker than the base.  The thinner stuff will form to the base coutours better which will make the weld better.  More important than the base plate, IMO, is ties to the verticle part of the body.  The verticle ties will be loaded in shear which will be stronger and stiffer than a plate that can just bend. I'm in the middle of putting a cage in my car.  The thickest plate I will use are 0.095.  I found that in the scrap bin at the local metal mart.  My tubing is 1.75x0.095, so I think the 0.095 plate is a good match.Racecar FabricationOld Miller 320 A/BP TIGMiller 140 MIGwww.f-bodysport.com
Reply:NHRA requires .125 platesMiller Dynasty 200DX Tig Welder
Reply:If you are gonna do it then do it BY THE BOOK and save yourself the pain of doing it over again..From the 2009 NHRA Rulebook.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Originally Posted by zapsterIf you are gonna do it then do it BY THE BOOK and save yourself the pain of doing it over again..From the 2009 NHRA Rulebook.....zap!
Reply:No not at all..Did'nt know if you had the info available.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Sweet cars man! I drive a 04 Sti with a ton of go fast goodies (18g, TMIC, water/ meth, etc), but I am thinking about going to the darkside and picking up a Evolution X GSR. I really like your MR though.As far as the question, I would think I would focus my heat on the thicker material and walk the cup toward the the thinner material. You would have to fiddle with it a little with it and find the right amps obviously. Sounds like a fun project!
Reply:Dont weld the whole plate, I do 1 inch or so stitch welds. There are many strong tie in points on uni bodied cars, you just need to find them. I am not sure on an MR2 though, my mustang I ied the main hoop into the floor and rocker panel, and the down bars go to the rear shock towers which are beefy.HTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.