Broken Buggy

I thought I had my breakage problems with the PL Bigfoot buggy worked out by switching over to Flexifoil parts. I had everything Flexi except for the BF front fork so I could use a Bigfoot light tire. I even managed to use a Flexi downtube and connect it to the PL Bigfoot fork. Then yesterday I was making a slow turn on a gradual incline and....

The siderails must have already been cracked underneath from previous bumps.

I was able to splint together the two halves with a piece of wood I found and my two ground stakes so that I could tow it back to the truck a quarter mile away.

Quote: Originally posted by rtz

I'd just inspect the welds before or after a session and look for hairline cracks in the welds. The shiny stainless makes them easy to see.

Don't look at the bead, the cracks WILL happen right next to the weld. I mean right NEXT to it. There is something called the" heat affected zone" ,that is the metal on the edge of the metal that melted. But this metal got ALMOST hot enough to melt but did not. As a result it became weakened . Even the "weldngod" creates a HAZ, it cannot be helped . But, it can be reduced by keeping the heat input down to a minimum. These are production buggies and the guys that weld them are not in the same category of welder as me. They may even get paid by the piece. Which means they are gonna "throw the coals"at it to get as many done as they can. Which WILL create a huge HAZ. Also if the re-entrant angle is too steep it will create a STRESS RISER, and that can create a crack as well. Put both together and disaster ensues.
Just my professional opinion
WG


edit: Also ,by getting stainless too hot. It creates carbide precipitate on the backside of the tubing/pipe. It looks like black sugar, and it is a defect.

Quote: Originally posted by rtz

I think Van's rails are a thicker material and not being stainless; potentially stronger:

According to the Metals Handbook of the American Society of Testing and Materials, 316 Stainless has a tensile strength of 85,000 pounds per square inch.
Ordinary Strength Steel is 70,000 pounds per square inch.

I'm curious where they get these parts made, cause this is a NASTY weld ,complete with undercut. Whomever welded this,is no welder. Looks to me like a child welded it. Do they make them in Bangladesh, in a child labor sweatshop???

Quote: Originally posted by Crash then swim

Not that I have broken my Flexi, or any buggy I'm just trying to pickup some welding tips!:wee:

I have an idea on how to repair it. But it is metric and I'm not sure if I could come up with the right material to make the repair with. Basically, a heavier wall sleeve that fits inside of the tubing then getting beveled and welded to the flange. With a couple of plug weld holes in the tubing to help it become one.

But, this may only move the stress riser to the end of the heavier pipe.

The real problem is "fatigue" and the material is borderline for this application. There is a lot of flex right at that point and all the flexing is breaking down the metal. Just like bending a piece of wire over and over until it breaks. The heavier you are ,the sooner it will happen. Or rugged terrain could do it as well. There is a reason my stainless "Homebrew" buggy weighs 131Lbs. It is NOT made from thin wall tubing. I wanted it to be built like a tank. Even my Aluminum buggy that I was told was not a good idea and would not last ,weighs 87 Lbs. and it is still going strong 4-5 yrs. later.
Strength by design !:alien:

WG

We have replacement frame rails in stock if you need to get it back together quick.
http://www.awindofchange.com/product/plframerails.html

Quote: Originally posted by WELDNGOD

Quote: Originally posted by rtz   I think Van's rails are a thicker material and not being stainless; potentially stronger: According to the Metals Handbook of the American Society of Testing and Materials, 316 Stainless has a tensile strength of 85,000 pounds per square inch. Ordinary Strength Steel is 70,000 pounds per square inch.

But Stainless is definitely far more brittle than non-stainless. At least the tubing I would use if I still had access to my old iron-working stuff.

Just sharing my knowledge with my kite family. I don't want to see anyone hurt ,and if I can teach someone enough to do it better/right ,then I have been a benefit to the community.

The results from todays ride:

rtz, what brand is that? I would like to personally call them out on this .That is disgraceful.... And extremely unsafe . A weld needs certain things in it's make alloy. That is where "filler wire " come in,but it's not just filler. Some things make it more durable,less prone to cracking. Without it you get what we have here.

NAME AND SHAME the culprit. They should NEVER be allowed to sell another P.O.S. to anyone else.

Don,
Seeing as you are reviewing crappy welds, how about this one on lower brace of fork from a supposedly reputable buggy.. I have to wonder how (well?) that buggy tracks at speed. I will leave it up to you guys to figure out which brand, but the flexi classic fork does not have a brace and the libre special isn't stainless.

S

I would say he never tacked it all around before production welding. That is awful...
Here is my weld on my siderail to downtube connection. I gaurantee it w/ my life. Notice the difference?

Attention PL and Flexifoil :Your buggies SUCK ! Filler wire doesn't cost that much ,even in China. Have you guys ever heard of "Quality Assurance"? Obviously NOT. I have patio furniture built better than that, and it just sits there.

I'm so glad I built my own buggies, I would have been pissed beyond belief ,if I'd got a buggy with welds like that.
And I wonder if someone got hurt because of a weld failure due to deliberate malfeasance, could they file a lawsuit against them?

@ Scud, that weld looks like a third grader made it. Oh yeah, that's probably what made it.

Nice lookin bead WG.

Quote: Originally posted by WELDNGOD

Quote: Originally posted by rtz   I think Van's rails are a thicker material and not being stainless; potentially stronger: According to the Metals Handbook of the American Society of Testing and Materials, 316 Stainless has a tensile strength of 85,000 pounds per square inch. Ordinary Strength Steel is 70,000 pounds per square inch.

Be careful quoting strengths if you are not familiar with what the numbers mean. The number you give is the UTS (ultimate tensile strength). This is the load per unit area which will pull a sample apart. Long before this occurs you will be seeing plastic deformation. Engineers base their designs on the yeild strength (YS) or the load required to stretch the metal so that it will not return to its original shape.
For 304 stainless the UTS is 73 200 PSI and YS 23100 PSI. The strain to failure is 70%.
For 1018 mild steel the UTS is 63 800 PSI and YS 53 000PSI. Strain to failure is 15%.
Stainless will deform long before mild steel, but break at a higher load. Strain to failure is a measure of ductility. From these numbers stainless is between 4 or 5 times as ductile as mild steel.

I have to assume my welding friends are unfamiliar with benefits of autogenous tig welding (no filler). Often used when welding thin wall tubing as it gives a smaller HAZ and less problems with composition gradients that can be associated corrosion at welds..

S

Quote: Originally posted by Scudley

Quote: Originally posted by WELDNGOD   Quote: Originally posted by rtz   I think Van's rails are a thicker material and not being stainless; potentially stronger: I have to assume my welding friends are unfamiliar with benefits of autogenous tig welding (no filler). Often used when welding thin wall tubing as it gives a smaller HAZ and less problems with composition gradients that can be associated corrosion at welds.. S There are no benefits, only rejections. It is NOT allowed except on sheet metal. The concavity created is called undercut, it is rejectable. Unless you are welding a spatula together or some galley sheet stainless, you better add filler or you will get FIRED ! I actually weld everyday, all day. You name a system on a ship ,and I have built one or dozens. All that book mumbo-jumbo don't mean jack on the deck plates Bro'. And BTW,that aluminum buggy I built is still kickin' sand. I even loaned it to Ragden @ WWBB. He has put some miles and some stresses on it. Guess what... Not a crack anywhere and still rock solid.:P "Strength by design,not material" WG Now go back to your desk,I got weldin' to do!

Quote: Originally posted by WELDNGOD

Oh yeah, if your buggy bends all to heck. It's still broken..... Even if it did not break in two..

Yes Don, absolutely true. This why is dangerous for you to use UTS as a design spec. It why engineers use yield stress.
Now there things that can be done to raise YS (work harden, heat treat) so yield stress number will will often state the material history. Ie as drawn tube or annealed.
S

Quote: Originally posted by Demoknight

But Stainless is definitely far more brittle than non-stainless. At least the tubing I would use if I still had access to my old iron-working stuff.

The specs for 304 stainless give a strain to failure of 70% and for mild steel (1018) 15%. Which one did you say is far more brittle?
Why would you choose to use a brittle material in an application of subject to tensile loads.
S

Quote: Originally posted by RonH

I've only seen one kind of pipe in Sean's hands...

laughed my ass off and then fell out of my chair funny.

This was a fun read! I'd want to talk to Sean and the welders if I had to spec materials and weldments for my personal buggy or one I wanted to sell with my name on. I think both sides have knowledge to offer. Just can't let one know you've been talking to the other!

Got it welded:

Hardwire stainless shortarc (a kind of MIG welding) . better than production.

BB was right this was an interesting read... Just some thoughts though, feel free to tell me I'm wrong.

I have both a Peter Lynn buggy and a mild steel VTT Hybrid buggy. Van provided me with rails and the current edition of my buggy has a homebrew downtube and back axle and the PL front fork. I'm am by far no Weldngod, but I do know how to weld mild steel, make it reasonably strong, and look pretty. http://www.powerkiteforum.com/viewthread.php?tid=27299

I was just thinking about this from the standpoint of USAGE... I'm not a speed demon and I'm not doing tricks (esp with big air). I live about a bazillion miles from Ivanpah, and I'm only on a beach for a very short amount of time during the year. My riding spots are all pretty small and I'm about 90% sure that I will never get over 30mph in a buggy (see my current PB below). As fast as 22 mph feels, I don't have much intention of going too far past that.

That said, is it reasonable to assume the most stress and force I put on a buggy is when I put my big fat 200 lb backside into the seat? ... Or is it reasonable to assume that if you intend a buggy for relatively light use, a Peter Lynn buggy (subpar welds and all) may be a reasonably well suited ride? It would seem to me like anyone who decides to take a PL buggy out to go 40-50 mph+ has some very bad decision making skills. I'm not sure if it's how they are marketed, but most people in the sport would tell you that a PL bug is a "starter" ... At least that's the terminology I heard A LOT, when I was shopping. I would think that when guys are making the decision to go out at excessive speeds and putting more strains and forces on a buggy, they have already moved into something that costs $1200 or more (Apexx, MG, Ivanpah, PTW, etc). If not, they may not be the brightest bulb in the box. It only takes a few seconds of stupid to undo years and years of learning, right. Or are the stresses and forces at 15-20 mph enough to do significant damage to a buggy?

It's obvious that there is something wrong with some of the welds on some of the PL buggies, otherwise rtz and yeldarb and some other folks wouldn't be having this problem because they didn't stand up to typical abuse. But there seems to be a higher percentage of PL buggies that are just fine.

And what about buggies made of mild steel? Are they significantly weaker? My VTT feels pretty stout, and I know there are a lot of Ivanpah's out there of mild steel. Are they more likely to get wrecked under the strains of high speed?

Just some thoughts I'm having about the discussion,... am I out of line? How much does the usage factor play in the durability of a buggy relative to what it's made of?

@BB,

Yeah, that's what I'm gathering from what WG said above. For some reason I was under the impression that cruising at speed with the forces at work making the buggy move were what was under question, esp. when taking buggy strength into consideration. I had not even considered how the "bumps in the road" tested the weld strengths. All my riding spots are grass fields, but are relatively bump less, but now I know...

And like G.I. Joe said, knowing is half the battle.

Quote: Originally posted by soliver

@BB, Yeah, that's what I'm gathering from what WG said above. For some reason I was under the impression that cruising at speed with the forces at work making the buggy move were what was under question, esp. when taking buggy strength into consideration. I had not even considered how the "bumps in the road" tested the weld strengths. All my riding spots are grass fields, but are relatively bump less, but now I know... And like G.I. Joe said, knowing is half the battle.

Like the welders and metals guys said above, the metal can give and take a little while stressed and bounce back to original. But push it really hard like on a hard bounce and you can push it past what it can recover from, especially with thin materials and substandard welding.

Having a failure is worse and worse as the speed increases though. If you broke something earlier but it hasn't shown itself yet, the torque on the buggy frame due to a high speed run could cause it to fall apart when you'd most like it to stay together.

Quote: Originally posted by ChrisH

Try this, take a piece of 12"x1"x.125" stainless and mild steel tubing, weld them both to a metal table and then hit them with a hammer and see which one moves/cracks/bends/breaks etc.

I've been thinking about this a lot lately. What if those same strips of metal were welded to a table of the same material for each strip. Weld the 1" end to the table so the 12" is pointing up. Now start flexing both materials back and forth and see which one work hardens and breaks first. I kinda think this is the case with the thin wall stainless buggy. It's flimsy and can only be flexed so many times. I think if it was stout and made of heavy wall material; it would never break.

But I still wonder about thin wall mild steel because bicycles don't seem to have the same issues but maybe there it is more of a design issue and difference. Plenty of "cheap" lightweight 10-speeds from the 1970's out there still being ridden.

Also too the design or manufacturing decision to use autogenous welding and take away material from each piece to fuse them together instead of adding more material from a welding rod; I don't think was the best choice. Peter Lynn really should reconsider that choice.

Considering the price these buggies are going for these days; they really should be top quality.

I thought the going price of $550 for the little folding model several years ago was outrageous then. Have you seen the current prices of buggies lately?

http://www.bigmikeskites.com/PeterLynn/Buggy/PeterLynnBuggy....

Two words ....... HEAT TREATMENT

Quote: Originally posted by riffclown

I will not jump into the fray more than to relate that I'm not sure what WELDNGOD did to the aluminum in MY buggy but it's built like a tank and I'd trust it with my life. In fact, I already do every time I sit in it. He cites "strength by design" and I'm sold on that concept.

Yes riff. WG's rides are insanely tough built!!