First roll cage need advice

[dfink]

I know there are a lot of roll cage threads and I have read till I cages in my sleep. My tubing finally arrived today so I am actually getting ready to start. I would like to build a cage similar jhelgensen's in the Ultimate roll cage thread. I am thinking however that I would like to place the main hoop more verticle instead of leaning back as most cages do. To facilitate this the main hoop would terminate pretty much in line with the front of the back seat. This allows full back on my seat and lines up really well with the bolt holes in the "B" pillar area. The car is a cab so may be constructed slightly different from a coupe.

Here is kind of where I had in mind. I am also concerned if this is still considered the sill area. SCCA rules dictate the hoop terminate on the floor or sill.

[Tyson Schmidt]

No worries. That is still considered the sill area.

The only down side to doing it that way is when you go to make the side bars, and you make the outward bends to clear the seat, you will probably have to cut into the lower part of the B pillar.

Make sure you trial mount the seats before you get too far with the cage, or you may end up with some serious seat fitment issues.

[dfink]

Thanks for the advice on the side bar. That may be the decideing issue. I will probably place it where everybody else does. The seat is actually in the car now and appears it would clear the hoop and the harness bar. First lesson in bending even after a few trial bends came up short. I still just don't quite have the calculations down yet. Bender didn't come with any hints. It is a 7" radius bender. useing 1.5" tube.

I guess I will have to check out some the 4X4 sites to get some measurements and insite on what is going on I thought my test bends would tell me what I needed to know but I must be missing something. As is I will just add what need to the last screwed up measurements and it should come out.

[Chuck Moreland]

You can do that. But be sure to keep the main hoop in a single plane.

As you've drawn it, it is two planes and is compromising strength. Probably failing most clubs rules.

[CRNT918]

Buy a conduit bender, some conduit, and practice with that. It should give you an idea about radius and shrinkage allowances. Also, hydraulic tubing benders would work, but are not as inexpensive as the conduit and benders.

[dfink]

Originally Posted by Chuck Moreland

You can do that. But be sure to keep the main hoop in a single plane.

As you've drawn it, it is two planes and is compromising strength. Probably failing most clubs rules.

Thank for the single plane advice. Drawing sucks and final would be in single plane no more than 4 bends. I am pretty sure I will wind up going in the same more forward position everyone else has. The other location looked good upon first inspection but after using my screwed up first hoop as a test. [Hey it fits one side at a time.] I think it will fit better in the forward location. Gee wonder why everyone put it there.

Also on measuring. Perhaps this is where I screwed up. I wanted 40" across the top at the outside of the bends. I my testing I thought I got 11" from a certain point to the outside if the test bend. So I sutracted 11" from 20" or 1/2 of the top. I thought when the bend was done I would have 40"
Now I wound up 8" short. Here is what I think happened
Instead of the 11" gain I was expecting I think I only got the7" gain from the radius. This would explain the 4" in each side. It does however take 11" of tubing to make a 7" radius bend. The circumference of a 7" radius or 14" diameter is 44" so a 90* bend should take 1/4 or 11"
Here is one I didn't consider. Is the "7 radius on the inside or the outside of the tube. I assumed the inside as they call it a 7" radius die. If the 7" radius is on the outside of the bend that would explain what happened on my first bend.
If you have a box that is 14" on each side you have 28" on two sides so if you made a square corner you would need 28" of tubing to cover two sides. Now if you make a rounded corner and you have a straight leg of 7" then it takes 11" of tube to make the bend then you have another 7" leg so 14"+11" indicates that you would only use 25" of tube total. So when measureing for total tube length you would measure the location with square corners then subtract 3" for each 90 degree bend.
When making the actual bend you would determine the length as if doing it square then subtract 7" from that point and that is where you would positition the tube in the bender at the starting or 0* point.
I am still not sure where I got the 11" gain from in my test bends. Also if the radius is on the inside of the bend then everything I said above is wrong.
Any insight.

[ninesixfour]

I would terminate the hoop on the sills rather than the floor. The floor pan is paper thin and the sills are much stronger.

[dad911]

There are a few free online programs available to calculate the bends:
http://www.jd2.com/bendsoftware.htm

I also once found a site that would calculate the angle cut for you. You would enter the angle, and the tube size, and it would print a profile. Wrap the printout around the tubing and cut along the line.

edit: tube coping calculator: http://metalgeek.com/static/cope.pcgi

[Chuck Moreland]

Bend radius is measured through the center line of the tube.

[rsscotty]

There are some cage pictures in this thread I replied to recently.

Pictures of E and F class 911s

Hope this helps.

[dfink]

Originally Posted by Chuck Moreland

Bend radius is measured through the center line of the tube.

Well I guess that would explain why it didn't work to figure inside or outside.

I did get a second main hoop made. Did the top bends OK then messed up the side bends. School is expensive these days. I was able to straighten my screwed up bend and then rebend but this will only be used for testing. I will remake the main hoop once I figure out where I want it and hopefully how to bend it. My wife is bringing my camera and is going to help me put the top back on. I will take some pictures and see what people think of the placement. To me anyhow the main hoop is the most important and hardest to fit. It has no point of reference. Once the main hoop is in you really have no choice but to make the other pieces fit the main hoop.

Also you are correct on hitting the "B" pillar. It looks like all that would need to be trimmed is the gutter that holds the inside carpet.

It looks like I can make the top part wider and not have very much bend on sides. Or a least less bend on the sides

Camera has arrived.


Top off



a little adjustment after the top went on.



Seat clearance the seat is all the way back



clearance to top

[dfink]

Perhaps I should just extend all the way to the floor and come in just ahead of the sill area. Maybe I can weld on a couple of extensions to my test hoop and see how it would work going to the floor. Might make seat clearance tougher.

[dfink]

OK I extended the legs and positioned it just in front where I was before. There is a small sill there. I think it was worth the trial. Appears to me to fit much better in this location. I can weld a box to the floor weld and weld several spots to the "B" pillar. If I did roll it would have to be spectacular to budge that bar. What do you guys think better or go back to the other design. It looks like I would have just enough room for the horizontal bar. I generally have the seat a few inches forward when driveing. Would only be back to max for egress. Not sure what would be needed at the base the sill there is pretty small.












Not sure what to do here

[ischmitz]

are you going to have a roll-cage blessing ceremony like this one

[dfink]

No but what do you do with screwed up roll bar material. Here are a few bits of the old one I took out. Also the one I am useing to test with I thought I would place on the for sale board as a bed headstand. Somebody surely has a kid that would love to a roll bar for bed headboard.

[barney911rs]

Here are some shots of my SCCA legal GT class cage. We moved the base up the sill a little to make the hoop more vertical like you were asking about.



Note the line of the hoop compared to the B pillar.

[dfink]

I could swear I posted this already but since it is not here will do it again. I got the main hoop completed can set in place. It is only resting against the support bolts I put in so can be moved if needed. It lools like it will clear the seat OK. I normaly have seat forward a couple of inches when driveing. Is is shown in the max back location. So what is the next step. Should I make the base mounting plates. I think a couple pieces of 1/16 X 1.5" angle would actually work well. Weld to the sill then weld to the leg or weld to the leg then weld to the sill. Then should I do the diagonal first or the down tubes first. I guess the diagonal can go about anyplace but if I want to line up with the down tubes perhaps I should do them first. Maybe tack the legs to the base plate or if I weld the legs first tack the base plate.

Here are the pictures.

[barney911rs]

You'll want to weld the base plate to the car, then weld the tube to the plate. You'll want to have a single plate that goes from the top and wraps around the side to add strength. You sure that spot is strong enough?? Not sure what you mean by down tubes. You talking about the rear supports? Yes you would want to do them first.

[Rob B]

I have a valuable tip which I'll try to explain. Start by wrapping a thin piece of cardboard or a thick piece of paper around a piece or roll bar scrap. Tape the paper tube to itself so that it can be slid along the roll bar. Now you can slide the paper tube partially off the roll bar scrap, trim an accurate bird mouth with scissors, and you'll have a perfect template to transfer to the actual roll bar tube.
Hope this make sense, Rob

[Lukesportsman]

We've all seen the body contour "duplicating" tool that has say 8-12 inches of sliding metal pins or the toys that will make an imprint of your hand by displacing pins at different levels. Someone makes this for tubes also, though the company escapes me right now. Essentailly a more expensive reuseable faster method than Rob B describes. I guess it depends on the time/money ratio that makes sense for each individual.