I have decided to start a thread to document my rebuild. The MAX IV will get new axles and sprockets, engine mods, changing of the shift levers and such to tie rods. New roll cage which will tie in to the frame and outside rail to prevent body sag. Relocation of battery and removable seats for cargo storage, etc.
That being said I am looking for input on roll bar tubing sizes:
1.) what is the typical roll bar tubing size and wall thickness?
2.) How about the angle iron used around the frame?
The roll bar tubing used by Recreatives is 1 5/8" black pipe.
"Looks like you have a problem with your 4 wheeler........you're missin' two wheels there"
Been doing a little research today. The area I live in does not have a good supply of steel sales companies (for round roll bar tubing for example). Thus most stuff has to be mail ordered. I decided to look at the cost of different steel options for tubing. As such there are some advantages using Cr Moly 4130 for roll bar tubing particularly for strength per pound, and in some cases strength per dollar. I put together a simple spreadsheet (see link below) that compares the performance of the steel offerings from Aircraft Spruce 4130 tubing as a function of cost per foot, weight per foot, cost per pound, tensile strength per dollar (how much force it can take on axis (for one foot length) per dollar), and bending strength per dollar. Results are somewhat interesting and I ended up landing on 1.5" x 0.083" at $4.95 per foot for my roll bar ($3.89 per pound, $0.15 dollars per foot per 1000 pounds of yield strength in tension)
https://docs.google.com/spreadsheet/...UFtV0l6U0lfM0E
The problem with statistics is you can make them say anything you want to. The strengths listed are from a test lab, not real world. The problem with thin walled tubing is it dents easily, and once dented it loses it's strength. .083" is probably fine for an amphib that is not likely to barrel roll, it would probably just roll once. The next issue is welding. Chro-moly is best welded with a tig welder.
Often the best place to buy roll bar tubing is a race car shop.....they go thru alot of it.
Fortuntely there were no staticstics involved in the spreadsheet.It is just basic strength of materials math which looks at ideal strength of 4130 steel tube in pure tension or bending. Really just a way of comparing different sizes of 4130. When considering the type of steel to be used it is a matter of preference. All steels must be suitably and appropriately welded. Generally 6x6's are used recreationally and are not in the same class as high speed racing thus most steels (ERW, HREW, DOM or 4130) would be suitable. To each his own. I am just informing the forum what I am going to do and why.
Given the high strength of 4130 (90,000 psi rated yield strength) it will be less susceptible to "denting" then a lower strength mild steel in the same thickness. Proper use of 4130 can result in a lighter cage for the same strength. In the aircraft industry where strength to weight is paramount, you will see the use of 6061 and 7075 Aluminum and 4130 steel used.
Most racing sanctioning bodies permit (and encourage) the use of 4130 in addition to 1020 mild steel. Please see the rules for SCORE (Score International - Off Road Racing, sanctioning body for the BAJA 1000 race), NHRA, SCCA shown in the links below). 1.5" x 0.083 is suitable for vehicles under 1500 lbs (less driver) in racing conditions. Some sanctioning bodies require TIG welding (NHRA) of 4130 and some permit TIG or MIG welding (SCORE). SCCA requires additional thickness for steels which have a weld seem (ERW, see link below) "1501-2200 lbs 1.500 x .095 DOM / Seamless / Alloy or 1.500 x .120 ERW". Again we are not "high speed racing" but the recommended materials and methods by the below referenced sanctioning bodies (developed over many years of competition and accidents) can provide general guidelines for construction.
NHRA:
http://www.nhra.com/UserFiles/file/G...egulations.pdf
SCORE:
SCORE RULL CAGE RULES UPDATE
SCCA:
http://sports.racer.net/docs/rules/2...s_2002_gcr.pdf
I can appreciate you wanting to get the most "bang for your buck", but unless the goal is "overkill for the buck", I'd stick with plain-Jane welded-seam tubing. I respect your interest in safety, and there are a lot of interesting specs you've laid out above. I've made a few roll cages for comparably lighter Attex race machines for myself and a few other folks, and the stuff holds up just fine. The extent to which they've been tested has been limited to low speed (<20 mph) events, but JP, GeoJem and I have repeatedly stressed similar back-yard designed and fabricated units with the most damage being scuffed paint and a few reflected curse-words (Rustoleum semi-gloss seems to deflect several combinations of four-letter words the best.... additonal test results to follow).
I'll have to admit that the CREW steel lends itself to a heavier cage overall, but for the quantity used in a Max IV cage, what's the overall weight savings using the 4130? You're absolutely right when you say it's a matter of preference. I think JP's cage is composed of old rejected gas pipe picked up at a scrap yard at $0.35/lb. Ride hard JP.... ride hard.
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