M758

So George is this what you were talking about?



Would I need a plate covering the lower front triange made by the 3 door bars?

RedlineMan

Hey Joe;

The door bar is a little convoluted, but it would likely be fairly effective, if you decide you don't want to remove anything. As for the plate gussets... no. Plate is not good for torsional loading in compression, which is what you would have at this point. Plate is only really good in shear or tension. I would think the ultimate would be to make a box from flat stock that filled the inner bend area. Instead of a single plate, you build a box; a plate on each side with a top plate, all solid welded. VERY strong in directions.

Geo

Joe, that's not it.

You end up with a little triangle at the very front below the horizontal bar and above the diagonal bar between where the two connect to the a-pillar brace. Those can be plates. They will work a lot better than John believes. It makes that area incredibly stiff. Install a wrap around gusset on the opposite side of the X.

For some reason my image manipulation software wouldn't load. I'll have to show you tonight.

M758

Ok..

Was this more like it?

Geo

That's exactly it Joe. I think the small ones at the bottom front only have to be flat plates. The other two should be flat stock wrapped around with the same radius bend as the radius of your tubing.

If you really want to get max strength, you could add gussets above and below the X as well. These sorts of gussets are incredibly strong and able to handle a lot of load despite their being formed from sheet stock.

You won't need it in this case, but when this type of gusset gets rather large, they really need a stamped hole that bends inward around the hole. These holes with the bend aroudn the edge not only save weight, but they add strength believe it or not. Doesn't work for small gussets however.

Geo

I should add that the gussets in the bend of the a-pillar supports are probably the most important ones because you have a bent tube that has no support for the bend. The gussets will add considerable strength at the bend.

RedlineMan

Ummm...

I knew that building boxed areas was very strong - as I stated - But, geeeez G... are you telling me I'm even more right than I thought?

It was my assumption that Joe was speaking of a single rib on the underneath centerline of the tube. Perhaps I read him wrong. Boxing in that area would significantly strengthen it and look nice, all with very little weight added. Doing so to any x-brace in a door opening will do the same, of course, and is an excellent idea. These box sections do take a fair amount of time to fabricate neatly, but they are indeed strong, and they look really nice if you have a knack for style. I'd like to say these were mine, but they're not. They are from the Factory!



You can also do the head tube junctions. These came out so nice they are hard to see!

Geo

Forgive me John, I truly misunderstood what you were saying. I had always assumed Joe was talking about the rolled gussets and that you were commenting on just welding a flat panel to the really small triangle at the X.

Yes, I fully agree with you that the rolled gussets are significantly stronger than a simple flat piece welded along the tube (such as you see in NASCAR bars on Nextel Cup cars). I think those little petite gussets you see on the Nextel Cup cars in the side bars are just plain silly.

RedlineMan

Hmmm...

Would you be refering to these?



In reality, these little dudes add a surprising amount of strength (and little weight) to the tube joint by spreading load past it into the tubes themselves.

Premier Motorsp

One more thing to consider when designing the door bars. Suppose you have a monster front end collision that moves the A pillar back six inches. The door bar is going to be in compression and is going to buckle. You need to make sure that it buckles outward instead of inward. If it buckles inward it is going to stab you.

This is a major flaw in many cages. Most of them don't have some sort of 'flaw' built in that causes the door bar to buckle outwards.

If you look closely at factory cages you'll see that they reinforce one side of the X more than the other, or they have slight bend in the correct direction.

Chris Cervelli
Premier Motorsports

Greg Fishman

Not saying anything negative about Redline's work but you have a great cage builder in Indy. You should see the work he did on a GT3 and and a 350z that races in Grand Am. Guys name is Greg Risk, and on top of the great work he is very reasonable.

fatbillybob

Flat plate gussets vs. sheet rolled boxed gusset: Correct me if I am wrong. The plates are about the thickness of the cage tube and offer equal or not statistically different strength as the boxed gusset usually made of 16g sheet. Assuming this is true then the only real issue is that boxed gussets look better, plates cannot be used where you may hit them so as to not act like a knife during impact, plates are better to use in areas where you can't get around to weld unless you do the professor drop the cage through the floor trick or cut the tin-top off and reweld the top later. Finally, what is the difference if you gusset say an A-piller bend with a straight piece of short tube ala the spread of a gusset? I think that looks the ugliest of all and is the heaviest. Comments? I'm here to learn.

kary993

Here is a link to my full cage. I agree with many about the gussets and think that the door crossing is far stronger than a single bar. Of course the NASCAR bars are even better. I also believe that a roof cross bar is required if you want to be more safe. Take a look at these before and after shots.

https://rennlist.com/forums/showthre...highlight=cage

RedlineMan

A good question, with a good answer;

Try fishmouthing a tube at the extreme angles befitting that spot and you will see the folly of it. It would not only look clunky, it would be very time consuming. Making a box section will also take time, but is easier to do and will also be more attractive.

RedlineMan

I almost hesitate to do this...

And I mean no disrespect whatosover, but I feel I want to comment on Kary's cage in one respect. I understand the reason for employing the "halo" type of cage - where the side and head tubes are made from one "C" shaped unit, and the a-pillar bars are seperate. That reason is it is INFINITELY easier to fabricate. There may be some other reason, but I can't think of what that might be.

Easier though it may be, I feel it has one deficiency, at least in this particular case; No arch on the side tubes. The side tubes running parallel to the drip rails have no arch, and therefore much less load spreading and crush resistance potential than a "traditional" side hoop style made of one piece. You could conceivably fabricate this tube with an arch over the driver's head, but that would seem to negate the "easier" part of their fabrication.

I may be wrong, but that is my gut reaction. Just my opinion, if you please.