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Thread: welding

  1. #1
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    welding

    Im wanting to mod my BSA 20 and a few other bikes.

    Ive got an ARC welder.
    Im going to try to mount brake studs to the chainstays.
    The bikes I have are all normal plain steel.
    I was gonna cut up old MTBs to get the studs off them. Maybe cut the studs and part of the frame including the bridge and then welding all of that onto the inside of the chainstays.

    I got a new packet of 1.6mm arc welding rods. But have been trying to join scrap bike tubes together. No luck. Theres plenty of orange glow on both sides of the metal. But when they cool, it falls apart.
    I sanded the metal to shiny bare finish. And I profiled the tubes to fit snuggly together. I cleaned the terminals on the machine and made sure the earth is getting a good firm hold. I managed to get a tube to bridge a set of chainstays. But when I clean up the weld its a bunch of round lumps. Not a line of weld.

    Do I have to set the machine up to a different power?
    Do I have to move the rod at a different speed?
    Do I need thicker welding rods?
    Or do I need to get a mig welder?
    Ive been thinking of getting a mig. But they are a fair bit of money

  2. #2
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    By arc welder I assume you mean a 220 volt stick welding machine, or what? If it is a 220 volt machine with at least a 20% duty cycle, you could use a carbon arc torch and brazing rod. It is a much more forgiving process than trying to get good penetration on your weld without blowing a hole in the tubing. (A 115 volt stick welder does not have enough power to operate a carbon arc torch. I tried it.)

    Remove any paint or rust at the joint so you see bright bare steel. Basically, you buy some 1/4" (about 6 mm) carbon rods at a welding supply shop. The torch holds two carbon rods in a "V" formation. You set the welder to about 60 - 80 amps and bring the tips of the rods together by squeezing the torch handles. Hold them together for a second or two and allow them to spread a couple of millimeters so a brilliant blue arc jumps the gap. (You want your welding helmet protecting your eyes during this.) Heat the joint and bring the brazing rod into the arc flame. The braze will flow when the joint is hot enough.

    You can make a carbon arc torch for very little time or money. The carbon arc torch I made has two wooden handles of 1" x 2" pine about 6" long and joined with a hinge at one end. A piece of steel rod 1/4" dia. about 6" or more long sticks straight out of the other end of each handle. I welded about 2" of 3/8" pipe across the end of each steel rod to make a "T" shape. Drill and tap the pieces of pipe near the end closest to where the carbon arc will be. Insert some thumbscrews to hold the rods tightly. Fit a compression spring between the two handles and restrain them so they cannot open enough that the spring flies out of place. I used a nylon cable tie that runs through the center of the spring and through a hole in each handle. Use #10 stranded copper wire with plastic covering and attach an electrical connector to each steel rod. Put a bare end of the #10 wire in the stinger and in the ground clamp. To make things easier for you to handle, you might tape the two #10 wires together every foot or so along their length.


    You might have to bend the steel rods just a little so the tips of the carbon rods touch when the handles are squeezed. Have at least 2" of carbon rod between the arc flame and near end of the pipe that holds the carbon rods.

    When you set the torch down after using it, place it with the hot tips of the carbon rods facing up. Do not set it on anything metal or sparks will fly.

    One other word of caution, when brazing anything with threads near to the joint, you may want to get a carbon compound to smear on the threads so any melted brazing rod does not fill in the threads and render them near to useless. I do not know what it is called, but you can ask at a welding supply shop.
    Last edited by twobikes; 01-24-08 at 06:58 AM. Reason: add another detail
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    Hey thats very informative.

    There is a thing like that in the stuff thats with the welder.
    But wasnt sure how to use it.

    Have to examine it to see if its complete and safe
    Do I need a different strength of protective sheild in the mask?
    Have to get some brazing rods for it.

    Might look at Youtube to see if theres videos showing that

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    Alec,

    I forgot you are in Scotland and your standard current at the mains is 220 volt/50 cycle current. What I said about a 115 volt machine applies only to the USA. I saw some home welding machines in Germany that put out around 100 amps or a bit more at the top and can run off of a standard household outlet. I would expect that is similar to what you have.

    The machines I saw in Germany also had a carbon arc torch included, although some of them were a little on the light duty side and used a smaller diameter carbon rod. In the USA you can sometimes find 5/16" or maybe 3/8" rods, but usually 1/4" rods and the 1/4" rods work well.

    A helmet lens you use for welding is very adequate for work with the carbon arc torch. You will quickly become accustomed to using the carbon arc torch. You can tell by the sound of the arc and its appearance if you have the rod tips too close or too far apart. When the flame seems weak or deflects off to the side it probably means that one carbon rod tip has burned back more quickly than the other. Shut off the welder and align the tips again. Be careful. They are HOT at the end and can burn skin quickly. But, you can manipulate them at the "cold" end while wearing good welder's gloves.

    The frame tube will likely heat up more quickly than the stud. You can manipulate the angle and application of the flame to make them heat more equally. With practice you can get the braze material to go where you want it to go. If you get really good at it, you can even get the braze material to build up more where you want it. (I am not that good.)

    Be a bit careful. The torch flame is hot. It can make little molten puddles of steel appear and eventually burn a hole in the tube. Just adjust the heat a little to the low side of what you need and keep the flame moving over the joint area so one spot does not get too much heat.

    Also, the greater the surface area between the two members of the joint, the stronger the joint. If you need to attach a threaded stud, perhaps you could use a bolt with full threads and grind the head to the contour of the tube to which it attaches. That would be a stronger joint than the end of a round rod stuck onto a tube.
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    As far as welding tubes togerther with a stick amchine is concerned, it isn't a problem. Sounds like your machine is running on too low an amperage, that is normally what I look for when I get the blobs as you describe. If you are a beginer, you probably aren't holding the trode at the right height. You scratch or tap up an arc, pull it away to avoid getitng stuck, and end up shooting trode metal all over the place in globs. Also, not seeing the puddle, and having the right height can be a problem. I started welding just as I sorta needed reading glasses, and I often couldn't see what was going on, and didn't spot it because it was new. Whatever the reason, not seeing what is happening is a problem. Using an auto helmet can help, because the start is hard for the beginer, and you don't see anything with a regular helmet until you strike a good arc. On the negarive, you get a lot of flashes without dark with an auto, since you are starting up all the time. I split the difference, and close my eyes with an auto when I start, if I don't feel I need to be looking during start-up.

    For bike type work, I normally get special rods designed for sheet metal work. Nominally they are about the size you are using, but in fact they have more flux and less wire. They are very easy to start, and I normally cut them in half so that they are stiffer, which allows me to control the presentation better. "twigs" tend to attach themselves to the surface where they want to and you don't get good control.

    Where you put the ground makes some difference. Like on a fork the fork is the big piece, and you need to weld more over on it's side, whcih means you want the clamp on the brake mount, or in this case the jig holding it. That can be hard to arange, but it is the kind of detail you need to get best results.

    Major issue with stick is you polute everything around you. If you lay down tacks, you may need to clean up after every single one. You chip away the flux, and you wash everything. When you are starting out, you probably make a bunch of mistakes, and with every false start you have to chip wash sand and wash everything. So with a tube joint, you may have to tack four times, and weld four quadrants, if you are good, that's 8 wash cycles as you go, though in some cases you can skip a few since you cross from one side to the other and with luck you didn't contaminate the far side.

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    Quote Originally Posted by Peterpan1 View Post
    For bike type work, I normally get special rods designed for sheet metal work. Nominally they are about the size you are using, but in fact they have more flux and less wire. They are very easy to start,
    Are you writing about 7024 rods? If not, what number code are they?

    I am not sure what the globs are you wrote about. I was describing little molten puddles that begin to form when a carbon arc torch is held in one place too long. On thin tubes this is a precursor to blowing a hole in the metal all the way through. I was not at all talking about using a welding rod or electrode.
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    "I am not sure what the globs are you wrote about."

    OP:

    "But when I clean up the weld its a bunch of round lumps"

    Could be spatter off the stick, or just discontinuous weld beads.

    The stick I was referring to is called something like easystrike. Of course it isn't 4130 specific, but then neither is the OP example. I would probably use it on 4130, but I wouldn't recommend it. For the usually thicker mild steel one could use regular welding rods the material is stout enough. The easystrike is very easy to use which makes it nice for running tacks and lots of starts and stops inherent in tubes. It even worked reasonably well with those 100 buck AC machines, as long as the voltage was way high.

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    Ive got a sturdy metal desk with a vice attached.

    On the tubes Ive been experimenting with, I clamp them in the vice. I have a good enough earth through the vice so I can stike an arc on the desk. Maybe handy if Im using the desktop to lay out the tubes. Not handy if Im putting the torch down..

    I think Ive been moving the torch too slowly. And at a low power setting. Its got a power indicator line. It moves with rotory control. It says that for 1.5 diameter its got to be at minimum. Think its 40 to 140 amp power. But I have it set to a higher power about a quarter on the scale.

    I got a packet of 2.5MM rods today. There cheaper than the 1.6MM rods. Geuss theres less of them in there.

    I got a scrap tube. Its a thick wall, about motorbike bar size. I ground a slot in it with my angle grinder. Then folded it over. I managed to weld that. With my 1.6mm rods.
    I hand filed the welds down. Got to watch when using my grinder, sometimes sets the smoke detector off, even though theres no noticable smoke. Anyway the weld just looked like the steel tube. No bubbles or slag in it. I tried to break the weld. I pushed and pulled. The tubes a foot long. Didnt break.

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    Globs like you describe can also be caused by holding the stick way to far from the work making a very long arc.

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    I was trying my 2.5mm rods today. Trying to get the tip near the metal. Was better. Got a proper join. Still looks rubbish. More practise, will get better.

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    Is it DC or AC? With AC you need nearly twice the amps per thou of material thickness (with DC its about as many amps as thou). so .035 would be 70 amps, and electrode would be around .035 if you could find it. It's the art of the possible, and you just have to work out what works for you.

    The thing about where the ground is, is that the arc tries to close the loop, and you want the major heat in your heavier part. So if that is your fork you want the clamp on the boss, But if you can hold on the boss and still get a good blob go for it.

    I have a few bikes where the canti boss is about 1/8" off the fork, presumably held by a jig, and they just blobed the gap, probably with a MIG, though you can get that done with a stick too.

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    Is just a cheap machine, so presumably its a AC machine.

    I try to keep the ground near the weld.
    I had it inside the end of the tube yesterday, and was welding up to the end of the tube.
    So cant get much nearer

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    Whatever is working for you now, keep doing it! I'm just sharing that if you were welding end to end two tubes, one to the left and the other to the right of you. Your clamp was on the left one, then your electrode would bias a bit to the right one and in closing the loop you jump the arc across the gap with a better fusion to both. If one of these pipes had a thicker wall it would naturally be the one placed to the right, in this example. At least that is the way I do it. It's not likely to be a big difference in cases where the fit is real tight, but that isn't all cases.

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    I had tube in the vice with the clamp on it. Was a top tube
    I had a seat stay that I tried to weld to it.
    I was holding it in my leather welding glove. Half way along the tube.
    With the clamp at one end of the top tube.
    The weld built up on the seat stay...thought it would go to the top tube.
    If not cause of the electric earth being there...it was also below...so gravity.

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