Overengineered?

pstoffers · Post by **pstoffers** » June 7th, 2009, 8:56 am

CR500R7 wrote:I can't for the life of me, work out why the frame spars would crack on top of the spars.
Unless these are just vibration cracks.

sonic22 · Post by **sonic22** » June 7th, 2009, 11:35 am

dannygraves wrote: what gas are you using? what rod, exactly? there are many grades of al/mag alloy. On my mig, I believe I used 4340 with an H25/argon mix.

i am using pure argon (99.9%)
the rod is AlMG4,5Mn (aka 3.3548, aka AW5183)

i am in the market for some XG253 (Alu 5%Si) which (acording to the seller) is ok for 6061 alu.

dannygraves · Post by **dannygraves** » June 7th, 2009, 11:47 am

sounds like the rod is the problem. but also AL is VERY picky about the power used. its easy to melt through with too much, make a minor change and not have enough power.

sonic22 · Post by **sonic22** » June 8th, 2009, 1:32 am

yeah i know...

i am using a foot pedal to control the current.
It is not easy to say the least!

bearorso · Post by **bearorso** » June 8th, 2009, 9:02 am

CR500R7,

Here's my take on the cracks on pstoffers frame -dannygraves ones being a big part as well ( I assume the "being made to fit "refers to SH's work as I understand this is a SH from pstoffers previous posts ) - especially the one about the hammering that HC bikes take.

I did my Dip.Mec.Eng over 25 years ago & couldn't resolve a force vector equation on paper to save myself nowadays, everything left in my head is experience / practical, so this isn't too cerebral.

The two cast swingarm pivot to shock tower plates, with the shock tower welded in and the cases/swingarm attached is an immensely strong & Rigid structure . It isn't going anywhere fast. The top spars, as strong as they are, with the bend in them (when looking from above) are quite flexible in terms of spreading/bowing out - the curved tube going from the spars to the down tubes as well. Those tubes also attach only slightly forward of the plate/spar junction - that area is a big point of force convergence. So you get an essentially solid structure attached to a flexible ( predominately in one plane, re the bowing ) one. Under harsh bottoming , which would be generating massive forces with a std swingarm, let alone extended ones ( I've not seen this sort of cracking with std swingarms, but still could happen ) but also that of the front end, forces are going into that area of the spars where the round tube is attached & the cast side plates. It would be interesting to see if it required welding on the inside - it would seem probable. The top of the spars has a tighter radius than the bottom , plus ( I think ) the internal bracing is aligned with the line you see on the spars, so the lower section is stronger/more rigid so the crack will spread/develop @ that weaker point. The top of the spar would have a tendency to twist outwards when it bowed = frame cracking in that area, the top & outside as its surface is put in tension. The jacking out of frames that some people do delivers big forces to this area as well - Aluminium isn't a good material to take beyond its yield point - that perhaps may be what dannygraves was referring to.

I've repaired many linkage bike swingarms over the years - people are puzzled that the cracks are inevitably on the Top of the swingarm - thinking that it should crack on the lower side from bottoming. But what is happening is the linkage is redirecting what you'd think are compressive forces into tensile forces, so tearing apart the arm in a way that seems impossible at first glance.

Sorry if this doesn't read well, please give me some lee-way, I took a low hanging branch to my head on Sunday so I'm thicker than usual.

Have to say , Hill Climbers are Sick Puppies that I think would be a bit "worrying" to be near.................

sonic22 · Post by **sonic22** » June 8th, 2009, 10:54 am

if i understand what you say correctly (and to decode it a bit)
it is not because we have vertical forces on the top (or bottom) of the beam
but because we have forces from the inside towards the outside of the beam.
(in other words the oval shape of the frame (from above) tries to became more round)

in more simple language when huge forces reach the upper frame that part tends to push the beams outwards, but because they are "solidly" connected to the rest of the frame torque is generated and then wrapping of the frame at that point which finally leads to tares on the beam.

it is like twisting (holding bottom with one hand and top with the other) a soda can to the point it splits open...

did i get it right?

sonic22 · Post by **sonic22** » June 8th, 2009, 11:04 am

i even made a sketch about it!

brown are the forces coming from the front or the back
blue are the reaction of the frame to the brown forces (oups...)
red are the twisting forces that are generated because the frame has strong front and rear mounts and there is less give in those arias.

i believe the frame finally gives near the rear mount not because that is where the maximum torque is generated (that is in the middle of the beam), but because there we have the upper part of the beam twisting while the lower part stays still and that create stress to the metal.
And alu does not like to be stressed.

hope all this is in the right direction.

p.s. the original photo is not mine but i think i found it here..
p.s.2 wonder if i should bang my head on tree brunches more often...

bearorso · Post by **bearorso** » June 9th, 2009, 4:50 am

Got it in one, Sonic!

You've arrowed the forces well - as you can see, the cast uprights/shock tower sure as hell isn't going anywhere, so to speak, so the bowing & the twist you've indicated is spot on & it concentrates right at the spar//tower interface. The "twist" is why it cracks on top & sides. We don't have HC here in OZ like you guys - I'd be interested to hear if this happens to HC AFs often - I've only encountered this on one bike, used by a FMX lunatic, never on a std CR/CRF/CRFX or AF.

Perhaps I didn't explain it as badly as I thought - I spent most of today in a succession of bloody big machines that go ping as I fell over a few times this morning - apparently I've got a high grade concussion from my encounter with the tree . No riding for a while according to the docs

A QUESTION FOR PERHAPS OLDER & WISER BLOKES THAN ME:

How in fucks sake can you win with Women? I'm seriously in the dog house with the love of my life - she's freaking out about all the damage I've done to myself over the years & how she has to worry about me - meanwhile , I've been patiently coping with her going through about 4 years of menopausal Psycho Woman, being as much of a snag ( well, as much as a bloke called Bear can be ) that she requires.

At least my grand daughter's a cool little thing - she's upset that an Ent (she's been watching Lord of the Rings) hurt her Nonno Orso ( granpa bear ) - although grandma told her it was because it thought I looked like an Orc

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » June 9th, 2009, 6:03 am

just tell her: OK you win, from now on i'll ride you up the hill.

sonic22 · Post by **sonic22** » June 9th, 2009, 6:04 am

bearorso wrote:I spent most of today in a succession of bloody big machines that go ping

http://www.youtube.com/watch?v=arCITMfxvEc

feel better man!

CR500R7 · Post by **CR500R7** » June 13th, 2009, 5:03 am

A big thank you to Danny Graves, pstoffers and bearorso for explaining that, I was looking at that all wrong, sure makes sense now.

guys

gregrobo · Post by **gregrobo** » June 13th, 2009, 7:11 pm

cr500r7 230+ posts and no pics come on dude enlighten us on this project

CR500R7 · Post by **CR500R7** » June 15th, 2009, 5:13 am

Just as the user name suggests, how is that for enlightenment.

FattyFive · Post by **FattyFive** » June 16th, 2009, 6:26 pm

WheelyGene,What year is that 125 frame? That is exactly what mine looks like.

Wheelie-Gene · Post by **Wheelie-Gene** » June 16th, 2009, 6:43 pm

2nd gen...2001.

I would have never converted a 125, but it's all I had.

FattyFive · Post by **FattyFive** » June 16th, 2009, 7:31 pm

Is it complete? Any other pics? Thanks for the info.

Wheelie-Gene · Post by **Wheelie-Gene** » June 16th, 2009, 8:07 pm

It's getting there.......
My crank came back from STR and it's time for reassembly. Now there's a lot of little issues to take care of.
Seems the last 10% takes 90% of the time.

I started a build thread a long time ago and lost track of it so I started a 2nd one.
http://www.bannedcr500riders.com/board/ ... php?t=4579

Some people have seen it, many haven't.
I'm living proof that it's best to keep shit simple.

Click on a pic for my build album. It's in chronological order.
Hope this helps.

Before:

As of last week:

Post by **AlisoBob** » June 16th, 2009, 8:09 pm

LOVE the dry clutch!!!!!!!

4Z · Post by 4Z » June 16th, 2009, 9:27 pm

A true work of art!!!!

sonic22 · Post by **sonic22** » June 16th, 2009, 11:07 pm

wow.. nice job...

i can't help but saying you should paint the frame and swing arm black or red... (anodizing would be super but expensive)

CR500R7 · Post by **CR500R7** » June 17th, 2009, 2:56 am

CLASS ACT for sure Wheelie-Gene.

dannygraves · Post by **dannygraves** » June 17th, 2009, 6:59 am

AlisoBob wrote:LOVE the dry clutch!!!!!!!

Wheelie-Gene · Post by **Wheelie-Gene** » June 17th, 2009, 11:08 am

Thanks....

The plastics used to be red....hence the red trees.
I just thought the black/aluminum combo looked more tasteful. A black frame would be overkill. I'll eventually strip the trees to match.

AlisoBob wrote:LOVE the dry clutch!!!!!!!

It'll play hell w/the toes.

Post by **AlisoBob** » June 17th, 2009, 1:03 pm

Wheelie-Gene wrote: It'll play hell w/the toes.

Brits been riding it...

ktm 620 · Post by **ktm 620** » June 17th, 2009, 1:32 pm

i think this shouild be called coolest conversion ever not that peac ov crap over waight yam wat you guys think

BannedCR500Riders.com

Overengineered?

a