View Full Version : Gas welding questions

12-26-2009, 05:25 PM
New here so hi everyone on this great forum. Want to build a recumbent and all I have is oxy/acetylene. Searched the forum for info and couldn't find my answer. Question is what rods to use and what size ? Also do I need to use flux for better results ? If so someone please suggest a specific one. Thanks

12-26-2009, 07:23 PM
Depending upon what your base metal is will dictate your choice of rods.
Most Zombie hacks are mild steel so standard mild steel welding rods are the way to go. The small dia rods. No flux is needed.
If your doner bikes are chrome moly I cant help as I've only tigged that stuff.
Flux is only required if you are brazing and in that case you use brass brazing rods.
In Zombie builds brazing would be used mainly for the add ons such as brackets etc. If brazing a frame then its better to use lugged construction as butt brazed joints would probably fracture early (not saying its impossible but difficult to succeed)
From the sound of your question I would assume you do not have much experience in gas welding. This being the case then I would advise finding someone willing to show you as its very easy to get adhesion rather than complete fusion in the weld with catastrophic results later as the parts fall apart.
Do some practice welds and destructively test them for strength.
I like gas welding but it does produce heaps of distortion in thin steel sheet such as chain guards etc.
See if there are any classes being run in your local colleges/trade schools

12-26-2009, 08:19 PM
I think the rods I use are 1/8" - I'll check for sure in the morning.

More important is the size of your tip. It can't be very large, because it's easy to burn through 16 gauge tubing.

I have both gas and arc welders, and I like gas better, but usually end up using the arc welder. Gas welding is done slower so it's easier for me to control.

I'd suggest getting a junk frame and practice on it, including cutting it up and welding the pieces back together. It's harder to weld along an edge than it is to lay a bead along a plate or tube.

John Lewis
12-28-2009, 04:11 AM
I've brazed several bikes. Needs good cleanliness , plenty of flux and just the right amount of heat.

I used 2mm bronze rod but don't know what grade. It was what was commonly available. I fillet brazed the joints and have had no failures. One Tadpole trike, Several recycled recumbents and two Bentech SW's so far. Bentech and one RR have done round 8000 km each.

Paying attention to what Brad had to say about his designs, both my AZ builds were arc welded with a cheap stick welder.

It took some effort to learn to use the stick but I am satisfied with the results.

Now as you have oxy acetelene then you could fusion weld with filler rod (I never mastered that) and That would be just as good as arc and perhaps better on thin material.

John Lewis

12-28-2009, 05:02 PM
Hello Busabuck:
I am new to any type of welding and have decided on fillet brazing with oxy-acetylene to build my trike. I have found the Henry James website very useful. www.henryjames.com You can call and actually talk to Henry ("Hank") and he is extremely helpful. They sell 1/16" bronze brazing rod and Gasflux brush-on flux at reasonable prices. I have also tried a powdered flux from my local welding supply and it did not work nearly as well. So far I am just practicing joints on mild steel. There is much encouragement on the web to braze your bike, and several famous builders do this with fillets and not lugs and point out that brazing has a long successful history with bikes and airframes. You are right that a good number of the others here on this forum have long experience and are willing to help us novices. Build a good one!

12-28-2009, 07:07 PM
I have a stick, a wire feeder/MIG, and several gas torches. Given my druthers, I would choose the gas any day of the week, just because I prefer the aesthetics of the process. It is slower than the electric processes, but I am in this for the fun and relaxation, so "I got all day," so to speak. Its quite soothing and peaceful compared to the other two. In a production shop, I would choose the MIG. That said, I built my DW with a the wire feeder using flux core wire, because that is what I had at the time. I later got a used stick just to learn the process. Eventually I assembled enough bits and pieces off eBay and CL to make a nice oxy-acetylene kit. Unfortunately, they kind of grow on you, and I now have a Henrob, two Smith AW1s, and a Smith Little Torch. They become "collectibles" if you aren't careful.

I haven't built an entire bike using oxy-acetylene welding yet. I have done some frame modifications to my RANS Wave using the brazing process. I have also used it to do some "metal art," which is a lot of fun. I think you are wise to try the brazing first, since it is generally accepted as easier. I have used both paste flux and flux covered rods from my local welding supply. Both work, but require a slightly different technique.

You do need to be aware that joint design is important with brazing, as it is with welding. Most brazing fillers are only about 1/3 as strong as steel, so if you use one of those (there are stronger ones) you need to try to build up around 3 times as much thickness as your steel base if you are doing a filet braze. All of Brad's designs need to be modified a bit at the joints to take account of it, if you build them that way. The traditional brazers got around this by using lugs. The lugs gave the brass or silver a lot more area to hold onto. When you filet braze just mind your thickness at the joints. If you take a look at some filet brazed frames you will see the filet is quite thick compared to the steel tube thickness. I have also seen some clever use of inside sleeves where two tubes join to give the same strength as a lug.

Enjoy the torch - I know I do.

12-29-2009, 11:14 AM
Thanks to all for the great info. I'm really stoked now and anxious to get started on a project. My son visited me and demonstrated how to make great fillets with the gas torch. Curiously it was his first time to use oxy/A. However he has a lot of experience with mig and tig. Thanks again.

01-05-2010, 01:18 AM
I use silver brazing rod on any load bearing structure on the bikes.

Yeah it may be overkill, but silver braze is about 20% stronger than bronze brazing rods. I also like the way the silver braze flows.....much easier to get a good looking braze joint.

It is a little more expensive than bronze rods but in my opinion, well worth the cost for the extra strength it gives.

03-02-2010, 03:10 PM
New here so hi everyone on this great forum. Want to build a recumbent and all I have is oxy/acetylene. Searched the forum for info and couldn't find my answer. Question is what rods to use and what size ? Also do I need to use flux for better results ? If so someone please suggest a specific one. Thanks

Oxy/acetylene is a great system to use for building a bike.

For basic gas welding, no flux is used. I go to my welding supply store and buy R 45 3/32 copper coated welding rods for welding steel.

I prefer brazing over welding for building a bike. Easier to make good looking strong joint.
I use 1/8 inch low fuming bronze rods and use either the pre fluxed rods or use a can of brazing flux with the uncoated rods. It is a bit cheaper to buy the uncoated rods and a can of flux.

What is nice about gas welders is that you can bend steel with it. You can cut metal with it. Plus it can be used for plumbing and all kinds of other things.

John Lewis
03-03-2010, 05:04 AM
I've fillet brazed several bike builds. There have been no issues. The first was done with a big plumbers gas torch and a hearth made of brick to concentrate the heat. Later I got to use Oxy Acetylene. That was much better. I use bare rods about 1.6mm dia and powder flux that I usually mix to paste with water and apply liberally.

I accepted Brads recommendation that his designs were not done with OA in mind and not built any of my AZ bikes with OA other than to braze on cable stops etc and to make the mesh seats that I use.

John Lewis

04-01-2010, 09:45 PM
Gas Welding is a great way to go. I have a 2 month old Miller 211 Mig unit which I love, but probably will only use it for tacking the tubes together, then gas weld the joints.

Each welding process has its advantages and disadvantages, but in general, I like gas welding for thin tubes because I can make virtually perfect welds that would need little or no grinding. This is possible because with gas welding as with Tig, you essentially fuse the two parts together only adding the exact amount of filler necessary. I made a rear fork for the Warrior a couple of days back with the mig, and then ground the welds. It looked awesome. Unfortunately I am concerned that I might have taken a little too much metal away from the tube which could lead to cracking.

The second benefit of gas is that the welds are automatically stress relieved. With arc welding one should normally stress relieve joints after welding to minimize cracking in the highly stressed area at the edge of the weld.

The biggest downside of gas welding is the additional heat put into the surrounding metal, which can cause warping. This is controlled by using the smallest tip possible, and good clamping and tack welding. The second downside is that gas welding is slower than arc welding, but since there really aren't that many welds on a bike, this isn't really a problem. Secondarily, the slow nature makes it much easier to make very strong and attractive welds. It is easy to fix welds that may not be perfect as you can go back and rework areas without adding filler. You can't really do this with stick welders and migs as they are always adding filler, even if you don't need it.

Further, most of us are not professional welders, so we often don't really know the difference between a good weld and a bad weld. I assure you that it is very easy to make a weld that looks great with mig, that has virtually no penetration and strength. While it is possible to do the same with gas, it is very very difficult to do. If a gas weld looks good, it usually is good.

The bottom line is, don't feel left out, and don't rush out to purchase an arc welder for building bikes unless you just really want one. We have been welding aircraft fuselages which are also thin tubing with gas since the beginning and it is still done today. Yes some people weld fuselages with Tig, but then they have to go back with a gas torch and stress relieve the joints. You can kill both birds with one stone when using gas.

Every welding process has its place, and conversely you can make any of them work in just about any situation.

04-02-2010, 10:17 AM
Greetings Busabuck,

I have read through this thread and I think you have gotten great counsel. Speaking directly to your question on type and size of rods, we just completed a DeltaWolf trike which except for small fittings, was welded exclusively with oxy/acetylene. The rod was RG45 and the size was 1/16"

Best of luck on your project,

04-02-2010, 11:12 AM
my first build is being MIGed because it is available and it is quick. I enjoy gas welding since you can make it look real nice with a minimum of cleanup, but as was said before, warping is a concern with the thinner stuff. I still plan to buy a MIG welder and it would be nice to get a oxy/acetylene unit too. Its all good. :sunny: DaveC