I want to knock up a harness bar but am not sure what to make it out of. Steel is strong but heavy so I'd prefer Aluminium, or at worst Chromolly. There seem to be reports of people using all of them. No sense in putting in heavyweight steel simply because "it's the strongest don't gamble with your life!" if Ally is perfectly up to the job. 2+0 blokes run harness bars off of their aluminium strut bars, though that alone is of course not sufficient evidence to prove they're up to the job. Thoughts? -A
Are you looking for functionality or looks? You can use chromoly but also cold drawn seem less for legit applications. If it's only for wank and nothing intended for racing or function. Alloy will be ok..
You're not wrong on titanium, but if aluminium's up to the job it's the same weight at 1/5 the cost Functionality. It won't be that visible. I am going to strap harnesses to it and will rely on it with my life if I crash... I came across their site, one of a few I looked up. I've used RaceTech before and they have a good range of chromoly that I'd probably hit up: http://racetechsteel.com.au/4130-chromoly/round-tube/31-8mm-tube-products I haven't heard of cold drawn seamless construction before. I'll have to do some digging, sounds good.
CAMS no longer allows alloy roll cages for good reason. Best (safest / lowest cost) option would be CDW steel welded across the wheel wells, though that may be too low (should be no more than 10% from the horizontal on your rear belts). If you're going to go with a harness you should run at least a bolt in half cage, otherwise in a rollover you are at greater risk due to not being able to collapse forward. You can then have the harness bar welded in at the correct height. The problem with chromoly is the welding, if not welded correctly the welds can easily fail. Have been a few chromoly race cages that have failed over the years. Only recommended if you've got the money to get it done by a pro.
Thanks for the insight Shane. I don't see DOM being what I go for, heaps of weight, I'd rather chromoly. I'm not welding it in anyway so I don't have to worry about how well it meshes with the chassis metalwork. I can only "weld" mild steel, so regardless of what I end up picking up I'll have it tigged up by a pro. The answer to any question is always titanium... but shit is this stuff dear https://www.imetals.com.au/index.php?route=product/category&path=497_518_519&sort=p.price&order=ASC A roll over will see way more force than a crash. A lot of people seem to use ally bars without horror stories, but it's the internet so you never know... what's the deal with using harnesses without a cage in event of rollover? something something they can't get you out?
With a standard seat and a lap sash belt you can collapse forward if the roof collapses, with a harness holding you upright not so much
I hate to say it Chili but I dont see anywhere where Anti was saying cost was the major factor, he did say functionality - Which I took to be what is excessive overkill and what is a suitable practical material. Of course the "Wise Olde Saying" is absolutely correct. That all said I have no idea as to the answer I would assume Cams would have a stipulation in what ever is there code for rollcage materials and requirements.
He wants an analysis of the properties of aluminium alloys and their suitability for use as a harness mounting point. Aluminium is far more expensive than steel so your 'truthful' saying would suggest that is the better material, counter to every knowledgeable comment here. On topic, remember those alloy strut braces you tested for rigidity Anti? No doubt with appropriate engineering you could design a brace made of aluminium that could handle the loads but it looks like they require more bracing to avoid having to have excessive sized tube so you'd lose cabin space.
All general tube and pipe is a flat sheet of steel that is rolled and welded seam section. In any shape, i.e. round oval etc etc, in all materials. look inside a tube, you will see the weld line. These can crack along the seam line, which is why you never press/bend along the seam line on your inner radius. This ranges in grades up to 250g C.D.S. cold drawn seamless. Is a tube cold drawn process through dies etc to get shape dia etc. Is considered stronger and lighter than seamed tube. There is no weld seam. This process doesnt invole heat, which voids modifing the base molecules(product deteriation), which happens when steel is heated. this can induce cracks after the base material is modified from its original form.(hot cracking/cold crackinge etc etc) this is generally 350g and up. Roll cages start at this point. chromolly is a mixed material, chromium mollebendium alloy. It is considered an alloy being its a mix of components included into the iron build up. These can be either hot drawn or cold drawn, strong and light, non seam welded. Generally used for roll cages, chassis building, work sites where medium strength with good light weight properties can be beneficial. This start at 410 grade steel All the above are Ferrous steels and are easily welded. Aluminium is a non ferrous metal, so is not considered strong as the above. This lives in the family of copper, brass, lead etc etc. So is soft and mallable as these. Aluminium tube/pipe is roughly a third in strength compared to our ferrous metal friends. so look at the strength/stress grades of normal steel and one third of that is the equivilant for ALU. The bonus on this is the major reduction on weight. cast ALU is the same as cast iron, is strong compound, though is weak with impact stress. ALU is graded by H ratings and T ratings, generally T6061 is the most used ALU in car and aircraft structures. ALU must be tig welded for structual applications. Basically titanium is too hard/expensive to get for the average back shed fabricator, so i wont worry about that. So theres some information for you to ponder. Either way you go, your going to either have to weld it to the car, or weld brackets to the piece your trying to make. So lets hope your a good welder, or you use someone who is. Being able to weld doesnt mean you can weld.
Thank you. I just want to do things properly. If that means lead wiping, I'll suck it up with the weight, but if a harness bar can be made light weight, then I want to it properly and have it light. That's true. All I need is a 1.5" or so diameter straight tube though. Some thick wall stuff with no bracing elsewhere, point to point across the top of the rear strut towers. Thank you! That's good info. What would you use?
The forces applied to a strut bar are very different to the forces that will be applied to a 'harness bar' in an accident.
Indeed, for others reading this without the relevant context I was pointing out that Anti had previously tested some aluminium strut braces and found them to be pretty floppy, if they bend with a couple dozen kilos on them there's no way a similar grade/size material would hold together with the hundreds of kilos worth of force applied in a crash. Need to be pretty chunky and likely an expensive alloy to be suitable.
If your going to weld it yourself, cds steel. 45-50nb by 2.5 wall, with 3mm mounting plates. If your going to get someone else to weld it, t6061 alu, as a solid rod, triangulated and braced, with the triangulation facing forward. So the impact stress goes through the forward facing triangluation bars. the stress force going along the bars will be absorbed better than across a single bar, which will reduce the harness bar flex. remember alu must be tig welded in stress related applications. Reason being the weld procedure on alu, nothing like mild or stainless. As you've done testing on the strut bars, it's already showing you how weak alu is... where is this going in the car? in a 4 seater aswell? The best option would be a cds bar across between top front seat belt mounts if in a 4 seater? not that I've seen in a 4 seater. I still don't see the purpose of this in a street car though?
Stu, Thanks for your comments. Whilst "Cost" was not expressed by Anti as a "major factor", it was used on several instances as a "contributing factor for making a decision". After spending many years working with persons who have suffered severe debilitating injuries(and seeing the traumatic results of many "seemingly unlikely events")my advice/comments are definitely based on the "worse case" scenario(and a genuine desire to NOT SEE similar incidents occurring to my fellow Forum Members/Friends).:zlove::zlove:
