Author Topic: Hello, and terrible sad news. Pix added. Welded and repaired! Thanks!! (Read 4816 times)

efxguy · « **on:** August 24, 2009, 09:54:27 am »

Hello everyone, I live in the Chicago area and have a Pro-Flex 955 that I've been riding since it was new. It is a polished aluminum frame with and unusual parts group.

I have been not riding for a few years since I was so busy with work. In May, both my wife an I became unemployed and snce we had a lot of time on our hands, I cleaned and tuned our bikes and we have been ring nearly every day for the past few months. The days we don't ride we walk, about five miles. Needless to say we are both feeling a lot better about ourselves and a looking it too!

Last week my 955 started creaking fro the bottom bracket area, which has happened in the past is is not that unusual. This morning I got around to tracking it down. I pulled and cleaned the cranks and chain ring bolts and the pedal threads. When i got to checking the bottom bracket, I noticed a crack in the seat tube. It is a horizontal crack between the BB and the front derailuer bracket on the drive side. The crack travels up the swing up gusset weld, then horizontally again halfway across the tube on the non drive side.

The probe points to the crack, it goes to the left and follows the TIG weld up and then at the top of the weld goes around the tube halfway.

I am so sad about this! We've really been enjoying riding again and really look forward to it every day. But I think that my Pro-Flex is now unsafe to ride.

Has anybody any suggestions? Can it be welded? Is there a source for another (needs to be cheap!) frame? Everything else on the bike has been kept up, replaced as needed and is in really good condition. I'd be heart-broken to have to just let this old friend go.

So this is a bummer of a first post here.

Best regards,

Michael
Elgin, Il
USA

orange · « **Reply #1 on:** August 24, 2009, 01:30:07 pm »

Bad news fella

Terry (member: Shovelon) is an expert welder - he may have some ideas... expect him along shortly.

shovelon · « **Reply #2 on:** August 24, 2009, 04:16:15 pm »

Well here I am.

Can't really envision where that crack is, but if it were mine, I would weld it.

But I would be careful who does the weld. I do know that your frame is 6061 T6 alloy, and will detemper at the blink of an eye. So it has to be welded quickly with the high strength filler(5356), and make sure the person knows this. If it is welded quickly enough, seeing as the frame is already at T6, it should strain harden somewhat. Then over the space of a few months it will naturally age.

Terry

efxguy · « **Reply #3 on:** August 24, 2009, 07:13:01 pm »

Terry,

Thanks for the tips. And in the photo, you can see the bottom of the front derailer in the top of the photo to get an idea where the crack is located.

I may try to weld it my self, I have a 300a square wave TIG welder. Do you have any further tips on settings, preheat or what ever. Electrode size, cup size, anything! I've done a lot of tube tig welding, but I obviously can;t do any coupons or test welds of this material.

Otherwise, what should be my search criteria for looking for a welder? Aircraft? Race car? Aerospace? I think that it may be beyond my current means to hire a really good welder....

Edit to add, I'm in the Elgin area around Chicago if you have any suggestions.

Thanks again,

Michael
efxguy

shovelon · « **Reply #4 on:** August 25, 2009, 08:45:10 am »

Michael, your 300 square wave has a foot control right?

Get some 6061-t6 strip to practice on. About 150 amps AC, 70% straight polarity, medium arc balance. Run about 15 cfh argon, with 3/32" x 2% thoriated tungsten ground to a pencil shape point. Trust me on the tungsten, and don't ball back the tip or I will have to slap you.

With your practice strip, if you think you need to take the gas flow up to 20 or so, do it but stop there. Don't forget to use 5356 rod, 3/32 diameter.Try to get full penetration into the joint, but stop every 1/2 inch or so to let the heat dissipate or you risk taking the weld into solution which will allow it to soften too much. Remember 6061 alloys take minutes to detemper instead of hours like 7005. If you are doodling in the weld pool and the part overheats, you have cooked the heat treat out of it. To illustrate, say you strike an arc, tack a piece and the tack cracks because it froze so fast that it over aged. If you take longer, the tack area will retain some heat and the tack will cool slower and be softer, but won't crack. Doodle in the tack, and the whole area will eventually go dead soft. Just don't let your weld go dead soft. If done right, the metal will fall from t6 to t0 during your weld, but the heat rushing away will allow the area to strain harden and bounce back to t2, then age to t4.

Oh man, my brain hurts.

Now go practice.

Terry

efxguy · « **Reply #5 on:** August 25, 2009, 09:00:23 am »

Quote from: shovelon on August 25, 2009, 08:45:10 am

Michael, your 300 square wave has a foot control right?

Get some 6061-t6 strip to practice on. About 150 amps AC, 70% straight polarity, medium arc balance. Run about 15 cfh argon, with 3/32" x 2% thoriated tungsten ground to a pencil shape point. Trust me on the tungsten, and don't ball back the tip or I will have to slap you.

With your practice strip, if you think you need to take the gas flow up to 20 or so, do it but stop there. Don't forget to use 5356 rod, 3/32 diameter.Try to get full penetration into the joint, but stop every 1/2 inch or so to let the heat dissipate or you risk taking the weld into solution which will allow it to soften too much. Remember 6061 alloys take minutes to detemper instead of hours like 7005. If you are doodling in the weld pool and the part overheats, you have cooked the heat treat out of it. To illustrate, say you strike an arc, tack a piece and the tack cracks because it froze so fast that it over aged. If you take longer, the tack area will retain some heat and the tack will cool slower and be softer, but won't crack. Doodle in the tack, and the whole area will eventually go dead soft. Just don't let your weld go dead soft. If done right, the metal will fall from t6 to t0 during your weld, but the heat rushing away will allow the area to strain harden and bounce back to t2, then age to t4.

Oh man, my brain hurts.

Now go practice.
Terry

Now THAT'S news I can USE!

Big thanks Terry!

-Michael

orange · « **Reply #6 on:** August 25, 2009, 02:43:10 pm »

^^^ I was going to say all that but Terry got in first

DugB · « **Reply #7 on:** August 26, 2009, 01:00:32 pm »

LOL Orange :-)

Terry, that's some serious welding intelligence, and conveyed via text no less! I'm the most amateur of welder, grinding off most of the metal I lay on, and hope to one day know the skill about 1/8th as well as Terry & EFXGUY seem to. Man, I learn something new on this list like everyday!

- Doug :-)

efxguy · « **Reply #8 on:** August 26, 2009, 03:26:54 pm »

Well thanks everyone, especially Terry. I got the frame welded and reassembled today.
http://i28.photobucket.com/albums/c209/spclefx/blobbyweld.jpg

It looks a lot less blobby and uneven in person, I swear! Not my best welding as I've never used that filler rod before and I practiced a lot too. I only had mild 6061, not T6 so I don;t know if that made a difference, but my test welds looked very good, better than the finished product actually. The ends of the weld look cratered as I was hesitant to crater fill and add more heat in one spot. I can tell you I was moving pretty fast to keep the ehat down.

Now of course comes the real test, I rode around the neighborhood, slow and easy and the creaking was gone and it felt good. I bounced hard on the suspension and torqued hard on each peddle in turn. Visual inspection after showed no changes.

I hope that if I did indeed screw this up and it fails, it won't be a catastrophic failure at high speeds. Wish me luck.

Best to all,

Michael
efxguy
ProFlex 955
Chicago-ish, Il

sammydog · « **Reply #9 on:** August 26, 2009, 03:34:48 pm »

Good to here it is all sorted and rideable again.

You've got me all paranoid about creaks now though.

efxguy · « **Reply #10 on:** August 26, 2009, 03:42:44 pm »

I really meant to mention this earlier, and wonder if some kind of sticky should be made and posted.

I have been consulting casually with an aerospace design engineer from a famous aircraft manufacturer. He has kindly been helping me design some reinforcing gussets for that part of the frame.

In his words, quote:

I'll bet every other bike like this one has a similar crack if it has
been ridden much. The crack starts at the top of the weld bead, right
at the end.

The bracket puts an prying load normal to the tube wall at that point
that causes one of the secondary moments I mentioned in the thread, and
this bending plus the stress concentration at the change in area caused
by the weld bead and the bracket causes this failure. The bracket on
the left side might not have a symmetric joint, but it's hard to tell
from the photos.

The bent seat tube aggravates the problem by causing a primary bending
load that is eliminated by using straight tubes.

End quote.

So, there you have it, any one with that type of frame should carefully inspect the seat tube / swing arm mount for cracks. My crack was mostly hidden by a bike shop sticker.

Best regards,

Michael
efxguy

shovelon · « **Reply #11 on:** August 26, 2009, 04:32:31 pm »

Quote from: efxguy on August 26, 2009, 03:42:44 pm

The bracket puts an prying load normal to the tube wall at that point
that causes one of the secondary moments I mentioned in the thread, and
this bending plus the stress concentration at the change in area caused
by the weld bead and the bracket causes this failure. The bracket on
the left side might not have a symmetric joint, but it's hard to tell
from the photos.

The bent seat tube aggravates the problem by causing a primary bending
load that is eliminated by using straight tubes.

Modern Poetry

shovelon · « **Reply #12 on:** August 26, 2009, 04:35:03 pm »

Excellent job grasshopper!!!!!

Now leave it alone for a week so it can age up.

Terry

wolverrine · « **Reply #13 on:** September 18, 2009, 10:02:35 am »

Great forum here guys. I heard some creaking at the bottom bracket area on my bike also. I checked it out and sure enough there was a crack in the swing arm. So now I have to follow Terri's advice and get my bike back on the trails. Thanks to efxguy...I would have never known there was a crack in the swing arm until it was to late.

Thanks all,

Mark

efxguy · « **Reply #14 on:** September 18, 2009, 04:19:37 pm »

Mark, can you post picks of the crack on your bike?

Thanks!

Michael
efxguy

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Author Topic: Hello, and terrible sad news. Pix added. Welded and repaired! Thanks!! (Read 4816 times)

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