Any welders in the house?

[rick74304]

Hey gang, as it stands now, my entry in the bbo is in jeopardy. In order to use the front end I want, i've had to weld the bearing cups to the frame, and stretch the fork stem the same length. The problem is, the welds keep cracking :x
I'm using a mig welder with flux-core wire, heat set on high, wire feed set slow. I've cleaned the metal down to a bare surface, beveled the edges so my bead has a valley to fill. I switch sides every half inch or so, cleaning flux between each weld. I am using different thicknesses of tubing (gas pipe vs regular bike stem) and have blown through the thinner tubing in 1 or 2 spots trying to make sure the weld is sinking in.
Seems every time I clean up the excess bead, I find the seam i'm trying to weld.

I've used the bench grinder and my hand held with a flap wheel to clean with, same results.
I'm thinking it's the different cooling speeds of the 2 metals causing the cracks, but i really dont know, as the frame and bearing cups did the same dang thing.

All i know is unless i get this figured out, i'm sunk, as this cannot be trusted to ride, and I dont build bikes to be all show and no go, if I cant ride it, i dont want it.
Rick

 

[icyuod2]

hey rick cant you just replace the fork stem with one thats gonna work? or get a stem thats too long cut off the extra?

how come your having to weld the cups to the frame? you just trying to lengthen the tube? or ya cant find any to fit the frame? looking at the bike/forks, it looks like it should be a easy fix with the correct parts.

i used the same supercycle tree's for this build.

i replaced the entire head tube with a piece of pipe to fit the fork tube/bearing cups.

worste case, instead of screwing with the bearing cups etc, weld the headtube from the old bike to the new frame.(or just use a piece of pipe)

 

[icyuod2]

btw is it a threadless headset right? if not, it would make life alittle easier.

 

[sojudave]

Maybe try setting your heat to low. I use a cambell hausfeld mig that I got at bargain. Anyway, I still have alot to learn but after experimenting with the settings for me I seem to have the best results with low heat and wire feed at about 4-5. Mine is a 110v welder, so the low settings keep me from throwing the breaker. I seem to get pretty go penetration with the tack welds, my problem is that my aim is off and I really need to work on laying a good bead.

 

[2manybikes]

The problem might be related to the composition of the two different metals. Typically bearing cups are very hard so that they don't wear out. The steel used in the frame is softer so that it can take some deflection without breaking.
The two metals also may have different thermal expansion properties. If one grows more when it is hot then when it cools down it will shrink more and cause cracking.

 

[JLarkin]

In broad terms, one amp of welding current should be used per .001" thickness of steel. That said, a 1/8" steel (0.125") needs about 125 amps for good penetration. This is the metal (wall) thickness, not the tube diameter. If you can measure the thickness, you can then find the right heat range on your welder to match. I am going to guess that steel frames are 16 gauge steel. This is 0.0598" (0.060" rounded up) which is slightly less than 1/16" (0.0625") Therefore, you'd need your welder set on 60 amps to be a close setting.

 

[MonsterMetal]

Is it cracking where you weld the cups or where your welding the head tube to other tube? Did you clean any chrome off the bearing cups?

Wire welding the bearing cups is going to be problematic at best... If they are hardened you will get carbon localization which will make them brittle at the weld .
Make sure your running reverse polarity (always with FC wire on thin material) Also called direct current electrode positive (DCEP) Thats a counter intuitive term... What it means is the electrons in the welding current are flowing from the wire to the work not the work to the wire (which you do use sometimes for somethings :? )


This is what I would do.... Im not saying its right.... or its the only way to do it.... Its just what I would do :lol:

clean the parts REALLY good.....This time when you weld it turn the heat (amps) on the welder up as high as it will go and the wire speed down to about 25% of the dial.
Make a space between the parts your welding together... about a 1/16 of an inch and weld it in pulses.. basically a series of spot welds all the way around. do the first one then move 180 deg to do the next.. then 90 deg from that one then 180 deg from there (so now you have a spot every 90 deg.) Keep going rotating 180 Deg till its done all the way around, That will keep down the heat and distortion. By doing a short pulse with the welder on max amps you should get a little weld that burns through the gap and sticks inside the tube. This would work better with hard wire and you'll need to brush the flux off the spots before you go to the next one to try to minimize inclusions. This will make the weld much stronger as there will still be some weld left inside when you do your grinding. you cant weld for more than a 1/4 or so at a time or you'll melt the tube. Also put all the heat (start on) the thicker tube when your welding. After you start the puddle push the weld to the thinner material, you'll have better penetration and control... If your welder has a solenoid valve to run gas shielded wire you would have way better luck with some ERW-70S6 wire and a 75/25 or 95/05 Argon Co2 mix The hard wire makes a much cleaner puddle on thin stuff like a bike frame its pretty tough even if you know what your doing to get a good weld with flux core.... If they where parts you could send to me I'd TIG weld them for you free... just cost you the shipping both ways... If I can help feel free to shoot me a PM....
Larry

 

[rick74304]

To answer in order;
Leigh, I cant swap the head-tube, the frame I pulled parts from is aluminum, and the build off rules state "no substantial frame chops/mods. The only way to use the parts I had on hand was to weld the larger diameter bearing cups to the schwinn frame, and lengthen the fork tube correspondingly. Again, keeping it rat means keeping it low-buck, so I wasnt planning to hit the bike shop trying to find a reduced diameter fork neck.Yup, threadless headset.
Soljuhdave, my heats on high, feed speed low, my welds are sticking to both pieces, just not holding it together though.
2manybikes, i'm thinking along those lines, so while I can take the expanded neck tube and pop it in the oven for a while, I cant do the same with the frame :roll: Maybe applying heat with a propane torch, then slowly reducing it?
Jlarkin....math? ewww :mrgreen: same as above, welds are sticking to either peice, but just not holding together (i'm pretty sure i'm hot enough, as I burned through the thinner tubing)
Larry, all paint was removed and parts wiped down before clamping. I used the grinder to make a vee shaped valley for the bead to fill between parts. Welder set on high, wire speed way down. I was doing about 1/2 inch beads, swapping sides as you said (i'll try again with 1/4 ich beads) My son was looking inside the headtube, and could see that both bearing cups and headtube were getting nice and red.
I might have to take them completely off the frame and heat them red hot with a torch, then let them cool to take the temper out (do I have that right?) then try welding again.
As far as the fork tube goes....i think I managed to get it to stick, after the 3rd time, I ground everything down, didnt see any cracking, to I took it and slammed against a steel dumpster a few times, then took an ond seat post. slipped it inside, and pried on the same dumpster. I was able to rock the dumpster, but stopped before I bent anything.
I planned to work through the 1st roll of flux core wire to improve my technique before buying a spool of regular wire and a gas bottle (my mig is gas compatable, but didnt come with the extras.
Hope i get this figured out soon, or i'm outta the game.
Rick

 

[cycle junk]

stop whining and just go buy a tig :lol: I will be over the next day.

 

[Bigdaddy101]

It ooks to me like he ground the weld to much. Looking at the weld above, it appears that the heat was to low and got little penetration, or he was moving to fast. Either way, there was no penetration. This, the bead did not spread. It just lumped on the steel. so when he went back to clean it up, he ground to much on steel that was not welded adequately. Structural welders elieve that grinding a weld weakens it. It is thought that it puts micro fractures or fissures in the weld. Either way, slow down and let the puddle spread. Oh yeah, and don't burn through....

 

[Fireproof]

My two cents . . . I think that if you anneal the bearing cups in order to weld, the bearings in the headset will be able to pound divots into the surface of the cups. The problem, then, is after that happens you won't be able to replace the cups because they are welded to the headtube.

Also, when working on something highly-stressed, like a fork steer-tube, you should sleeve the tube (inside or outside depending on the application. In your case, it would need to be inside if you can still have clearance for your gooseneck).

Good luck! Let us know what happens.