brazing/welding???

[Fast Eddie]

what exactly is the brazing process? is it any stonger/weaker than welding together tubes? does anyone make their own jigs at home then have a shop cut/weld everything? just wondering, fast eddie outty

[Thylacine]

Think of this (http://www.google.com.au/search?hl=en&q=bicycle+brazing&btnG=Google+Search&meta=) as the start of your research.

[dlbcx]

Brazing is performed at a lower temperature than the melting points of the metals to be joined; the filler metal is used to attach the metals together and provides the joint strength. Welding, on the other hand, will melt the metals together; sometimes, a filler metal is used to reduce cracking.

[Fast Eddie]

that thylacine site is great! and i dig the name and "gimmick" of using an extinct marsupial, clever! my interest in custom frames is this, i build gravity speed bikes and i have to use and modify existing frames-usually 20" bmx frames-to do this. these frames work well because they are made to take a pounding, and since i bolt on 10-25 pound of weight on them (in g-sports heavier is better) the frames hold up well. the probem with these frames is the short wheel base. you'd be suprised how steady these frames are in excess of 60 mph (if built correctly) but because of the way these bikes are mounted if the rider is over 5'7" or so it is very "cramped" trying to mount them in a head first race tuck. ive come up with some mods to make to a 24" or 26" full suspension frame but i have not been able to try em yet, would be alot easier to just have the right freakin frame! there has got to be a relatively low budget way to produce a frame. since heavier is better that would lower the cost a bit in material (some guys even fill their frame tubes with lead buckshot to add weight) but i have not been able to find a low cost way to jig/weld a bike cuz they GOTTA be straight at the speed we ride em at. ive even had problems with "from the factory" frames not being straight enough for this application. any suggestions....anyone? fast eddie outty

[Thylacine]

Wouldn't you be better off on a trike recumbent with a fairing, like a Greenspeed or something? A big guy in one of those would be ballistic.

Got any links to a typical version of these bikes you're talking about?

[Fast Eddie]

gravity speed biked dont use pedals or any kind of propulsion, strictly gravity powered. my site has some pics and a brief definition www.freewebs.com/gravityracing/ and i am a member of the Gravity Bike Association based in California www.gravitybike.com

[Peterpan1]

You can certainly get someone else to do the welding for you, and they would probably be happy to work from your jigs as long as they were logical and didn't get in the way of the torch.

Welding is the universally prefered method of joining tubes and the prefered method of joining tubes in the racing world, except for bicycles. I assume it is also the prefered method by which the base frames are manufactured? So from a liability perspective it would appear the obvious choice. If weight isn't an issue then I can't see any reason not to weld frames together.

Temperature is often bounced around as a reason to prefer brazing or lugs over welding, but the critical temperatures for steel are in two bands (over simplification warning). There would be an advantage to a joining technology that was cold, possibly as low as 400 degrees or less, like epoxy gluing (would require very extensive lugs). Certainly by the time one is at 1000 degrees one is well beyond the range at which the temper of a heat treated tube would tend to be losts. The next bump in the road is the temperature at which steel burns. Gas processes shield the joints agains burning up so it doesn't mater that the tubes are heated to the melting point. The other thing about heat is the distribution of it. Arc welding done properly limits the heat affected zone. Brazing keeps pumping it into the joint so you may have a wider affected area, which is a negative, though the fact welding and brazing both work fine is evidence that these issues need to be identified but they aren't deal breakers.

[sngltrackdufus]

Brazing is performed at a lower temperature than the melting points of the metals to be joined; the filler metal is used to attach the metals together and provides the joint strength. Welding, on the other hand, will melt the metals together; sometimes, a filler metal is used to reduce cracking.
there is 2 types of brazing one is "solder brazing" the other "braze welding".
Introducing "filler rod" does much more than add "meat" to the weld one thing is it helps control the heat on material being welded.
A filler rod does not necessarily help reduce cracking. I have seen "hot tearing"(cracks) right down the center of a weld area many a times.
Then again ,I personally have cut a beer can in half cleaned it up & fused it together without it leaking when filled with water.

[Peterpan1]

Not trying to be argumentative, but aren't you talking about welding either tig or gas in your second example. Seems unecesarilly confusing to refer to that as brazing. If you fuse the metals it's welding if you melt them together it's brazing. If you use the same metal as the parent in the rod, roughly, it is welding, use soemthing significantly different with a much lower melt temperature for an essentially mechanical bond, and it's brazing. The fact one uses a rod in both is irrelevant.

[Jonny B]

If you fuse the metals it's welding if you melt them together it's brazing.

Wrong way round mate. If the tubes melt into each other it's welding, if only the filler melts and sticks to the tubes it's brazing (or soldering).

[Peterpan1]

I'm not sure it is the wrong way around, part of my brazing description was crap. The essential point is that welding uses a similar or identical metal fill metal (steel tubes and steel rod) and the parts are fused together. The tubes in a welded bike project don't necesarilly melt together, there is usually some root portion that does, and some portion that is joined with the fill.

[sngltrackdufus]

pffft