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Discussion Starter #1
We were discussing in another thread about what tube thickness to use where. Historically I overbuild but I'm getting better. Of course to start with I follow the rules for UROC because this is a comp buggy for UROC/east. All is round tubing and DOM. Main frame rail is 1.75x.120. Main cage supports around driver is 1.5x.120. Anything else in my buggy that needs strength is 1.5x.095wall. This includes door bars, dash bar, engine cage. For things like dash or floor outline I use something in like a .050-.060 wall. For my bellypan I outlined the last one with 1.75x.120 and skinned it with 3/16" plate. The last buggy held together very well competing in EROCC. It's a good thing too, because I couldn't keep the tire side down:rolleyes:
So, what are acceptable thicknesses for other places? Seat mounts, Coilover hoops, bars used to trianulate the cage? I think this could be informative to alot of people.
 

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Thank you.

Also another question I have is once you know how much your going to weigh how do you know what size tubing to use for your halo?

3000lb buggy - 1.75" /0.120 wall ???
4000lb buggy - 2.00"/0/120 wall ???

I am just really guessing but I either read or was told that 2" is what I want for a 4000lb pound rig. I would love to be able to ditch a bunch of weight in the entire rig and if 1.5" - .095 wall is strong enough for X's and in the chassis then I would love to use.

What thickness is being used on areas that are on the rocks often like "rockers" (I guess ??) I have read here that many people are sleeving thier tubing or spliting tubing and then stitch welding the split tubing to these areas. I was thinking about using some angle iron in these areas but that too also adds weight.

Also not a tube question but what thickness plate are people using for belly skids. What holds up and what has to be replaced? If 3/16" holds up and lasts then why use 1/4"
 

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Discussion Starter #3
my last buggy was heavy at 3800# and the halo was out of 1.75x.120. Rolled it plenty of times pretty hard and no damage what so ever. For the belly you can go with 3/16 if you brace it across the top of it to keep from bending
 

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We use a lot of 3/16" AR (abrasion resistant) plate for skids, it's super hard and pretty strong, it's basically heat treated chromoly sheet. We've used some 1/4" 6061T6 AL for skids too and it works well, it's just grabby and gouges easy compared to super hard steel.

Most of the material selections depend on how it's applied to the chassis, as much as what loads are on it. Long spans of tubing may need to be thicker or larger diameter. Some areas of the chassis need to be thicker to resist dents, like anything on the outside that can be hit by a rock. Interior bracing can be thinner wall since it won't be dented but long spans that could buckle either have to be suported or should be larger diameter.

In general, we're using .120 wall DOM for the outside tubing, stuff that will get smacked. We've started using .188 wall for rockers, since they get hit all the time, sometimes pretty hard. .095 wall for interior stuff seems fine, and I've even looked at using some .065 for some bracing in short spans.
 

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The AR plat eis a great suggestion for rocker guards. Just remember if you plan on making "L" shaped guards, you need formable AR plate, there is non formable, it just cracks wide open in a press break.

This is a great thread and i hope a lot of the chassis builders chime in. Its building season and I would like to take everyones opinions and experiences into consideration.

What thickness is everyone using on their seat mounts?
 

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What about using the Aluminum plate and then lining it with the plastic.
What plastic? I don't think there is anything that sides much better over rock than AR plate . thats why they make loader buckets out of the stuff.
 

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Discussion Starter #8
The Twister said:


What plastic? I don't think there is anything that sides much better over rock than AR plate . thats why they make loader buckets out of the stuff.
Yeah I really don't think the plastic would slide any better. Maybe a thin piece of sheetmetal to skin it??

So, you think .065 is strong enought for 2 foot spans on the inner structure?

For another example, I used 1.5x.065 square tubing for my floorboards and fuel cell mount. It was very sturdy. I'd say you could easily go with 1"x.065 square for that.

Somebody has got to have a recommendation for seat mounts. I'm thinking the .065wall.
 

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This is what I was refering to skin the belly with....

"Ultra High Molecular Weight Polyethylene, or UHMW, is used in a variety of industries ranging from food processing/packaging to bulk solids handling, recreation, and many more. With its unique blend of properties – high impact strength, low coefficient of friction, chemical-, moisture- and abrasion resistance – UHMW products help reduce maintenance expenses, part replacement costs and downtime due to its long wear life."


There are quite a few places you see this just and don't even notice it.

On place I remember seeing it often it on deck trucks that lower the deck off the truck and slide the entire deck back over the frame rails with a load on. I have only ever seen it in white but it is often used on tire carriers (swing away) to reduce noise and make it easier to open and close. I have also seen it used on the sides of conveyors (sp) to help guide the items on it.

http://www.redwoodplastics.com/BrochurePolyethyleneUHMW.pdf
 

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Sapper said:
I have only ever seen it in white...[/url]
Black is also common, and for a minumum, they can do colors. I'm trying to figure out a way to use this stuff on my bumpers and sliders I'm designing. They use it in the bottom of big triax dump trucks too, so the load will slide out easily.

The stuff is so hard, that it is more difficult to cut than the same thickness of steel on a hydrocutting rig.
 

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AR plate in not chromoly or heat treated BTW, it is just high carbon, high manganese, it actually looks similar to the 1541H that many people make axles out of.

SCORE and BITD (Best in the Desert) are two of the main sanctioning body of off-road desert racing. They have minimum roll cage design requirements, I only have acces to the BITD rules (SCORE is $20) but they both should be similar. The BITD requirements for an open cockpit vehicle using seamless mild steel are as follows:

Under 2000 lbs: 1.5 x .090
2000-2999: 1.75 x .120
3000-3999: 2.0 x .120
over 4000: 2.25 x .120

They just tell you to check the material specification to find equivalent strengths for using alloys such as 4130. I don't know how they enforce the rules. I have never seen a trophy truck (most are over 4K lbs) with 2.25 OD tubing for the cage, most are 2" or 1.75", but they are using 4130 so that is how they are getting away with it, however there is no way to check what material they are using.

This if for reference only, keep in mind this is not rock crawling, it high speed racing with multiple roll crashes at 80+ mph.

I commonly use .120 wall for external cage tubing or anything that will get hit, just so I dont have to cut it out when a thinner wall would be dented. All interior tube and diagonals can be thinner wall. I use alot of .065 or thinner 4130. On diagonal members that will be subjected to compression loads, you should use larger OD to keep it from buckling, but tension members you can get away with smaller OD.
 

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Hmmm, my EMJ reference lists their AR360 plate as virtually identical chemical makeup as 4130 plate and it is most definitely heat treated. It's listed with a brinell hardness of 360 and a tensile of 177ksi. From working with it, I can tell you it's HARD, we can't really punch holes in it and bending involves slitting the bend line with a torch, bending what's left and welding up the crack. Looks like chromoly, feels like chromoly.....
Big problem is finding 1/8", the thinnest we can find in AR plate is 3/16". They seem to only make the AR360 in plate and they define plate as 3/16" or more. I think we have to go to 4130 for 1/8" and get sheet, then have it heat treated.

I know some guys that are really happy with the UHMW for skids, I still have a hard time seeing that it's better than a hardened plate designed for handling rocks all day everyday. The plastic is lighter though and experience is showing that it works pretty well, so maybe it is good.

When you're tying brackets into thinner wall tubing, gussets become more important since you want to spread the load over more of the tube to prevent tearout.

One idea we've looked at also is using thinner wall tubing in rock strike areas where it will be covered with a skidplate. Basically, there's no reason to run a thicker wall to prevent dents if you have a skidplate on it that will prevent dents. We went with .188 wall on my bro's rocker tubes and then ended up running his alum. skids over it, so it was just an added 15# that we really don't need.
 
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