*** EDIT : Please note that this is an old thread, and the question has long since been addressed. ***

If you are making a roll 10-point cage, and are following the FIA guidelines, which material would you use?

I'm debating between 1.75 x 0.120" DOM and 1.75 x 0.95" chromoly. I'd like to use the DOM because of the pricing, but wondering if it is legal. I'm not too clear on the following guideline :

I'd appreciate any help or advice!

Thanks a lot!

Pic for views : This is the initial 3D sketch ... It will differ in some areas, such as the lower braces that go from the rear shock towers to the bottom of the cage etc ...

 

What car is it for? They have Ontario build rules here

http://www.casc.on.ca/document...8.pdf

 

page 61/85

 

what app did you use to make that drawing?

 

I'd add a main hoop diagnal on the same plain as the hoop.

 

im not a fan of all those bends. you could eliminate 8 - 10 of them.

 

I would think it means, that the main hoop and if you have a hoop in the front (A pillars, windshield top), they would have to be done from the thicker part. The others can be the smaller tube.

Thats how I made it for my car, though havent been in events with it (as its only bolted on), but it was made from material (I suppose you're finnish from your name) specified in the AKK handbook, which I think is same as FIA norms.

I used seamless cold drawn tube, chromoly AFAIK needs to be heat treated before installation.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">im not a fan of all those bends. you could eliminate 8 - 10 of them.</TD></TR></TABLE>

I only counted 10 bends in total??? Maybe I misunderstood you

Adriano

 

theres more

 

I count 12 but i can only see being able to eliminate 2 ?
Iam no roll cage expert but it looks good to me.

 

yeah, i got either 10 or 12 depending on the joint at the top of the a-pillar. perhaps cjack can enlighten us as to which 8-10 bends could be removed?

 

Thanks for the input guys.

My main question was regarding DOM vs. CHROMOLY.

The design was made when I was learning some new features in Solidworks. The actual design is different now. I honestly don't know how I could eliminate any of the bends, as they are all necessary to the design. I can understand if you were referring to the two bends in the top of the A-pillar bars, but only because the rest of the roof bracing is not pictured.

I'm totally open to any suggestions on the design, if anyone thinks it's bad for any reason.

Thanks!

Here is a more recent design, though there are still some errors in the design. I need to connect the lateral bars to at the same point as the back stays, and the door bars should connect to the bottom of the main roll bar, and I'm sure there are other mistakes. There is also too many bars, but not sure which I will eliminate just yet.

 

too many bars.
main hope, a-pillar bars, and the rear bars are fine.
only need 1 diagonal cross bar for the main hope.
you can weld a bar to the diagonal cross bar for the harness bar instead of making a separate one that bends around it.
I'd elliminate the 2 bars going from the side of the main hoop to the rear strut tower mount (or wherever you choose to weld it).
you don't need the extra support bar to reinforce the a pillar bar.
single bar connecting the a-pillar bars at the time along with the X is more than enough. don't need bends up there.
the reinforcement from the a-pillar to the main hoop isn't needed, but you don't need to remove that. i think taht's about it.

 

all the bends could be replaced with straight bars and tite nodes if you wanted to. to me a unsupported bend = weak

im sure it works fine but i like to criticize

 

You need to rethink the door bars. I do not like any type of two three piece X, especially if it is not reinforced by taco gussets. It will collapse.

If you want to use an X (which I like), use two pieces of tubing and bend them down to the X. Then scab steel plate on both sides, plus add some gussets in the corners. You should also look at reinforcing the joints on the main hoop and A-pillar down bars so the door bars don't tear the material out of those joints.

Like the drawing. That is pimp. I need to get my Solidworks stuff back up in action and play with that feature.

 

is that a 25 5 spec cage ?

 

I have a couple of criticisms but keep in mind that i offer them as 100% constructive criticism and in no way am trying to sound like an a hole. if i saw that exact cage in a car i would hardly be stuck on the criticisms and i would be more impressed with how intricate it is, but nevertheless, there are a few things that i feel could be improved upon.

front to back...

i have mixed feelings about the vertical a pillar support bar. based on my understanding of roll cages i would say right off the bat that they are a bad idea. my reasoning behind this is that in a rollover I worry that as they deform they will push outward on the door bars which can't be the best case scenario.

now i hesitate completely pissing on that portion of the design because the aston martin dbr9 gt1 alms car is virtually identical in that regard and while it can be treacherous assuming that the pros are always right (take a gander at many of the supposed pro cage builders in the import scene and you will see plenty of examples of how not to build a cage) but i think it is safe to say that anything prodrive does can be considered gospel... until you consider that maybe they felt that was a safe design in relation to some specific aspect of the astons chassis that your car may not posses. a perfect example would the way that the bmw motorsports body in white m3 lemans car's roll cage changed drastically from the e36 to e46. (if i recall correctly) it was that body style change and not the previous generation) it wasn't that the realized that the did it wrong the first time. it was that the newer chassis was remarkably different and it required them to build a different type of cage. even between such similar cars it is hard to keep the exact same design. in short, i don't think I would risk it. i have mixed feelings about those bars.

----------------------------------------------------------------------------
i would rethink/ simplify the whole roof portion especially at the top of the windshield.

it seems as if you are combining two different methods and i worry the end result would be less effective that either of the original concepts. the methods i refer to are that some people choose to make the a pillar section function the same way as the main hoop (starts at floor goes up, across, back down to floor) except that it bends toward the rear of the car to trace the a pillars.

other choose to build a half roll bar that runs longitudinally and starts at the top of the main hoop, traces the side of the roof line longitudinally, curves down, traces the a pillar, and shoots down to the floor. it seems you've mixed these together.

if you choose to go with method one, all you would need is one longitudinally mounted "connector" pipe that runs from the main hoop top corner to the a pillar hoop top corner to tie them together. if you should go with method 2, then a a single transverse "connector" tube would run across the top of the windshield to tie the two sides of the longitudinal half roll bars.

let's assume for conversation sake (and because i think it is better, lol) that you go with method 2. all you need do across the top of the wind shield is use a straight piece of tube to tie both sides together. if you want extra reinforcements in the corners you can whip up some gussets and call it a day.

------------------------------------------------------------------

the x brace that runs across the roof is a good idea but it really needs to terminate into a corner. the way it runs through the diagonal windshield corner connectors and then terminates into the side of the a pillar tubes is totally counter productive and maybe even a recipe for disaster. the x brace on the roof is the first thing that gets touched if you were to lay the car upside down and you do not want them transferring energy into anything but the strongest possible joints, certainly not into the side of a bar like that. i think it creates the possibility to shear. maybe a remote possibility but why risk it when doing the way i suggested is simpler, less risky in terms of safety and i would bet my left nut that it makes for a more rigid chassis.

------------------------------------------------------

the windshield plane diagonal reinforcements (dont know what else to call them, but the things that run from bar that jumps the corner where the windshield bar connects with the a pillar bar... for the record i talked about them a few sentences ago and that may be confusing but you made i am referring to them separately as I am separating the "two in one" roof X/ windshield plane diagonal reinforcement hybrid that you designed. hope that makes sense) need to be included in the design but they do not need to be part of the roof X. the purpose of these tubes is to create a shear plane in the windshield area. to really capitalize on this you can do the same thing on the bottom of the windshield as well creating sort of a flattened diamond shape. this is totally a measure for strengthening that plane for the purpose of stiffening up the chassis. naturally the stiffer the chassis the better the cage works for safety purposes, but this is really more about chassis stiffness than normal roll cage duty.

--------------------------------------------------------

contrary to what others have said, i would do double diagonal bars in the main hoop forming an x. one is all you need for safety but 2 really adds a lot to the chassis rigidity equation. every alms car does this and that's not a coincidence.

----------------------------------------

it may not be possible within your cars unibody, and or may not line up properly with your rear suspension towers, but if you can make it fit, i would move the back stays out (away from the transverse centerline of the car) so that they attach to the main hoop at the same point that the roof X and rearward part of the transverse half rollbars attach. that would really tie that whole thing together.

you would then have four tubes terminating in the same spot on the main rollbar as opposed to two different spots. also the back stays would be on the same plane as the transverse half rollbars the same way that the door bars are on the same plane as the rear pointing lower supports for the back stays effectively making it all one big lattice work on the same plane. worth it's weight in gold in my opinion.

--------------------------------------------

your harness bar seems overly complicated. considering the limited room on account of the main hoop x diagonals it doesnt look like the seat will be able to recline far back anyway so it would appear that the harness bar can be on the same plane as the main hoop. you could just run a transverse bar that is parallel to the ground straight through the middle of the x in the main hoop. you end up with better support for your harness bar, another link tying one side of the car to the next, and effectively six tubes terminating at one single point on the same plane. that's the stuff wet dreams are made of my friend. lol.

----------------------------------------------

lastly why not add a transverse connector tube across the rear strut towers. you will tie both sides together just like a strut tower bar only a billion times better on account of all of the other triangulation. also, it ties together your back stays and once again makes a super rigid plane.

i would say that your design is pretty damn impressive. it's 90% there and just altering a few things would make it way easier to build, stiffer, and even safer.

p.s. i don't have, nor do I know how to use solid works. if i draw out a roll cage design I am working on can you solid works-ify it for me?

 

Wow, thanks so much for typing all of that out. I read every word.

Certain things you said I had noticed before, and others I hadn't even realized. But thanks so much for the constructive critism!

I actually intended on those taco-style gussets, but not really sure how to draw them out in solidworks. Not entirely sure on how to fabricate them efficiantly / quickly. Any suggestions?

Thanks to everyone else who offered their opinion / advice.

 

that is going to be a lot of welding. i'm curious what you are going to quote this at markku.

 

I would start at $3000 for the basic structure and go up from there.

 

To be honest, not really sure how I'm going to price it. I'm going to cut the guy a deal because he is a driving instructor at the local track, and his STI gets a lot of exposure. He's also a famous downhill skiier gold medalist who knows a lot of people.

I've got another guy who wants a 6-point roll bar with 1 diagonal in the main hoop. I think I may have quoted too high for a simple roll bar. Trying to be careful not to undercut the hours, but trying to stay reasonable.

 

i have never heard of this in the fabrication world, but the law firm I work for does a lot of online advertising and we recently hired a company to revamp our website. they gave us an estimate that basically states that x is a ballpark figure that they think will be the total cost based on y amount of dollars per hour. so to use numbers they say that they will bill us at a rate of 80 bucks per hour for 31.25 hours for a total of 2500.00

they will do the work in good faith based on the estimate of 31.25 hours but if the actual time it takes them to perform the work goes runs over the estimated time by x percent of hours, they then have to charge us for additional hours but at a reduced rate of 40 bucks per hour.

in other words, they think they know how long it will take and quote us a ballpark price for that work with the understanding that if it runs a few extra hours over they will take one for the team, but once it goes so many percent over the estimated time (to account for "**** happens" and last minute customer requests, etc) the customer has to be understanding enough to pay for additional hours at a reduced rate.

i found this to be quite fair. maybe you could work something out like that

 

that is fair but, anyone can build a 31.25 hr roll cage in 40 hrs and charge 8.75 extra hrs of labor. how is the customer going to know the service they are paying for 31.25 hrs of doesn't take 25 hrs? do you think the company is going to deduct 6.25 hrs? absolutely not! they will say it took exactly 31.25 hrs. i think the OP should do a couple cages, and give an exact price quote per cage, based on how extensive the work entails. and if the customer waants to add/subract any part/labor then adjust accordingly. (hrs are just for reference, i dont know how long it takes to build a a cage)

 

its called Flat Rate. you charge what is about normal for an operation (a job) and you bust your *** to get it done faster. i charge around 300.00 labor to do a manifold back exhaust. if i get it done in two hours, you do the math. on the other hand, i have been stuck doing some exhausts that take all day because of clearance and other issues with the car. it sucks, but more so than not, i get some money in my pocket.

you just have to try and think everything through on a quote. theres nothing like quoting some one x amount of hours then finding out it took 15 more hours to do the work than expected. at most shops, labor is anywhere from 50 to 120 / hr around me. the shop im at is 99.50 an hour labor. customers like flat rate knowing they wont have to pay more than orginally told. Flat Rate is the way automotive industry runs.

 

If you run a high quote (bid 30 hrs when you know it will only take 15) you run the risk of losing the customer when they see a high bid. More than likely, the customer is going to be getting bids from multiple sources, and part of the decision they will make includes cost. If you want your company getting the reputation of high-balling, you better do REALLY good work to make it worth the premium price.

I've grown up in a family owned residential construction company and the custom built homes work the same way. Customer wants to build a home, and you have to give an estimate of how much it will cost. With something of this magnitude ($300k+ and 3-4 monthes of time) there are bound to be things that come up that slip schedule/cost. Try to minimize your own mistakes, and changes brought on by customer they end up paying for.