Any tricks for tigging thick to thin?

[mr2man]

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.

[landman]

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

[TSOR]

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.

[Craig in Denver]

The Welding Web software clips any photos and the following text larger than 800 x 600.

[DSW]

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.

[TSOR]

Originally Posted by DSW

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.

Build a subframe and attach it to that.

[Donald Branscom]

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.

[JonE30]

It's a Toyota MR2 guys, no real "frame" to speak of (unibody design).

[LarryO]

Originally Posted by JonE30

It's a Toyota MR2 guys, no real "frame" to speak of (unibody design).

Can you make a subframe connector and attach to that? Does it have front and rear subframe?

[Supe]

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.

[mr2man]

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?

[mr2man]

Originally Posted by Supe

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.

Thanks for the advice. I can probably tie into the rock panels for the front floor plates, but I can't tie the rears into the strut towers because I have an intercooler in the way on the one side.

[Supe]

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.

[mr2man]

Originally Posted by Supe

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.

Well, I guess it might be time to buy a MIG welder...

[Supe]

The 110v MIGs work perfectly for this sort of work, no need to get anything high buck.

[mr2man]

Originally Posted by Supe

The 110v MIGs work perfectly for this sort of work, no need to get anything high buck.

If I am going to get one, I might as well get a good one. I am thinking a miller 212 or 252.

[Jim Riley]

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!

[Fat Bastard]

Originally Posted by TSOR

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.

Then 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

[mr2man]

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!

[TSOR]

Originally Posted by Fat Bastard

Then 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

Show me said rules that state the OP is doing it correctly.

[Fat Bastard]

Originally Posted by TSOR

Show me said rules that state the OP is doing it correctly.

Show me the rules that say he is not

See http://www.scca.com/contentpage.aspx?content=44 See 9.4 E

NHRA IS SECTION 4:10

[Fat Bastard]

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.

[mr2man]

I have been building this to NHRA rules.

[Fat Bastard]

What ET class will it be running in?

[mr2man]

I am expecting mid 10's at around 130-135mph