# Welding (not brazing) chromoly with O/A?



## bobbotron (Nov 28, 2007)

Hey all. I'm sure this gets asked from time to time, but I did a search and didn't come up with anything, so here I go - sorry if it's a groaner. (At least I'm not asking about Tig vs fillet brazing!)  I've read a bunch of places that O/A used to be the way to weld 4130. TIG seems to have taken over now, but I've seen a few places that still sell rods for Oxy fuel welding 4130. I was wondering if anyone has ever tried to weld a bike frame with an oxy fuel setup. 

Anyway, I'm not advocating it in any way, I'm just really curious if it's been done, and what the +/-'s of it are. 

What got me thinking about this is I did a O/A course over the winter, and we did lot of practice welded joints with 1/16" mild steel and R45 (RG45?) rod. It was super fun, and the welds were super strong. We also did aluminum brazing, which was interesting but really quite difficult.


----------



## dr.welby (Jan 6, 2004)

I welded a single-speed cyclocross frame with OA just for giggles a few years back. It was all heavier tubing - probably .9/.6/.9 stuff. The bike got a lot of commuting miles and general trail beatings and the welds have held up fine.

I also used it to make this semi-lugged front end.

It's more nerve-wracking than brazing so I don't see a ton of value in the technique for framebuilding but I guess it's a good technique to know. It might be good for people who are offended by the sound of the word "flux".

The general references you will want to look up are:

Tin Man Technologies sells OA welding videos and supplies, primarily to the home-built aircraft market.

L. S Elzea's Aircraft Welding book is a 1930s trade school manual for airframe welding.

Jon at Thursday Bicycles OA welds some of his frames.


----------



## bobbotron (Nov 28, 2007)

Neat, rock on!  Huh, that makes me want to try my hand at 4130 welding some day for kicks. Like I saw, I've done some O/A welding, including a repair of a garden hook for a friend, and some garden art out of an old steel fence. Once I got into the zone I found it fun to do.

What filler rod did you use?



dr.welby said:


> I welded a single-speed cyclocross frame with OA just for giggles a few years back. It was all heavier tubing - probably .9/.6/.9 stuff. The bike got a lot of commuting miles and general trail beatings and the welds have held up fine.
> 
> I also used it to make this semi-lugged front end.
> 
> ...


----------



## dbohemian (Mar 25, 2007)

Sure you can do it. 100's of thousands of airframes can't be wrong:thumbsup: 

RG 45 or ERS-60 or something like that are the preferred rods.


----------



## dr.welby (Jan 6, 2004)

bobbotron said:


> What filler rod did you use?


Thanks! I used RG-45.


----------



## unterhausen (Sep 28, 2008)

I probably could do it if I practiced. I used to weld extra bits onto lugs and fork crowns, but it really is a lot of work and brazing works just as well for that application.

I'm surprised dbohemian didn't dig out his picture of the welded joint again


----------



## bobbotron (Nov 28, 2007)

dr.welby said:


> Thanks! I used RG-45.


Rock on! I didn't realize you could use RG-45 for 4130. I thought it was just for really mild steel.

It's interesting to get such positive comments on this, I was expecting to be told to not bother/it's not worth it, which is fine. I was wondering what the reasons given would be and was going to leave it at that.

I have to say I'm pleasantly surprised; an internet thread with helpful info and no flames. Superb! :thumbsup:


----------



## dbohemian (Mar 25, 2007)

bobbotron said:


> Rock on! I didn't realize you could use RG-45 for 4130. I thought it was just for really mild steel.


The strength of the weld is not wholly dependent on the filler. Standard practice is to use a filler that is somewhat milder than the parent material you are joining. Surely there is some debate about this but welds should be ductile. If you are not heat treating your assembly after welding (and few of us do) then one can use lets say a high elongation stainless rod for welding high strength steel (ex:880 or 312) or mild steel for 4130 or 3/2.5 for 6/4 Ti and so on.


----------



## HomeGrownSS (Jan 18, 2006)

id like to see some examples of a nice clean O/A welded steel joint, especially on a bicycle. i havent done too much O/A welding, mainly just experimenting with it, and it did not look pretty! since i was just fooling around i used coat hanger for my filler rod.


----------



## dbohemian (Mar 25, 2007)

HomeGrownSS said:


> id like to see some examples of a nice clean O/A welded steel joint, especially on a bicycle.












Coat hanger.....

I thought sometime I might just weld up an entire frame this way. I know Jon (thursday) does and I see no reason it the tubing selection is right that it should not work great.

Would be a wonderful response to those guys who berate me about being too fancy to then hit them with a oxy/fuel welded bike frame:thumbsup:


----------



## MrCookie (Apr 24, 2005)

OA welding seems to be becoming a lost art. There is a lot of "why bother" attitude regarding gas welding. Got that vibe from my teachers at the local community college.


----------



## edoz (Jan 16, 2004)

I've used ER70s6 with success.


----------



## HomeGrownSS (Jan 18, 2006)

are there any advantages of O/A welding?


----------



## edoz (Jan 16, 2004)

HomeGrownSS said:


> are there any advantages of O/A welding?


Comparing TIG to O/A welding, it's the same joint strength using the same filler assuming both operators are of the same skill level in their respective processes. An O/A setup can be bought with a couple hundred bucks, and it requires 0 powergrid. It's more portable, and less consumables are used. Also, a torch setup is more versatile than a welding machine. You can heat, braze, cut and work with stuff like glass and plastic.

I'm not knocking TIG, but a torch is a damn handy thing to have and if I could only have one I'd want an O/A torch.


----------



## dbohemian (Mar 25, 2007)

MrCookie said:


> OA welding seems to be becoming a lost art. There is a lot of "why bother" attitude regarding gas welding. Got that vibe from my teachers at the local community college.


Yeah, it is really too bad. TIG welders rock....but, there are still instances that an OA torch excels and not teaching it IMHO is wrong.

Heat control is heat control and often OA welders have an easier transition into TIG welding. Add to that all the reasons stated already and in some rare cases OA is actually preferable.

For instance. OA welds are very ductile and soft, which is perfect for finishing sheet metal either steel or aluminum. For restoring old cars or aircraft where you have to weld and then planish and form the piece you just can't do it with TIG. The weld will crack almost right away. With OA you can form it without worry.


----------



## ampeirce (Apr 3, 2009)

Agreed, it's the 1st metalworking tool I bought 16 years ago.I used it for everything for at least a year or more,cut, weld, braze. I made a dozen rather ornate bar stools and 3 serving carts for the restaurant I worked for at the time, plus lots of other stuff. It taught me more about welding and heat control than anything to date. I still use it today. Makes me want to go o/a weld a joint!


----------



## dr.welby (Jan 6, 2004)

Anyone have a sense what the lack of a purge (and/or backpurge) means for O/A joints? As mentioned above I've built a frame with the technique and know that it was (and evidently still is) used in favor of brass fillets for airframes, but I wonder what difference it might mean for the modern framebuilder.


----------



## MrCookie (Apr 24, 2005)

I think there would be arguments for all different methods. 

According to an old mechanic/logger I worked with, part of the driving force behind moving to TIG was increased speed over OA.

Brass/bronze bazing often leaves behind corrosive flux which may be difficult to remove, and if the joint fails, it must be thoroughly cleaned before repairing, especially if being followed by a weld (any residual braze will contaminate a weld).

A good braze fillet will distribute stresses better, and is less likely to result in a brittle heat affected zone.

My guess would be that back purging an OA weld isn't as necessary? It may have to do with the OA flame being neutral or reducing vs. oxidizing? Maybe the OA temp is lower and less reactive to impurities in the air than the plasma column created by arc welding? How many Tig welders back purge steel? It certainly should reduce refractory oxides, but if the joint is tight, there shouldn't be much contamination from the back side?

For butt welding plates, we built dams that would fill with shield gas to reduce contamination from the back side.


----------



## edoz (Jan 16, 2004)

MrCookie said:


> How many Tig welders back purge steel? It certainly should reduce refractory oxides, but if the joint is tight, there shouldn't be much contamination from the back side?
> 
> For butt welding plates, we built dams that would fill with shield gas to reduce contamination from the back side.


Purging chromoly isn't necessary. Some guys will tell you it is, and it won't hurt to do it, but if you read up on the regulations for aircraft and motorsports like NASCAR and NHRA, there's nothing that requires it. If there was even the tiniest possibility that landing gear would fail or a race car would fall apart at 300mph then those organizations would require it.
What is required is full penetration of the weld into the base metal. That means no matter how tight the joint is, your weld goes all the way through and you will have a bead on the back side. Most guys will run a "keyhole" which means you are actually melting a hole completely through and you're filling it in from the back as you go. The molten metal on the back side isn't where the arc is, so it's fine. The the puddle under the arc is what needs the gas coverage with steel. Like I said though, it won't hurt.


----------



## HomeGrownSS (Jan 18, 2006)

hey guys, dragging up this older thread.
i completed a few pending projects, so i finally got the time to try my hand at O/A welding.

i like it, a lot. by the 5th and 6th joint things really clicked and i got into a rhythm. 
it is really easy to blow a hole in the mitered tube if you get slow and sloppy with the torch.

cut the 6th and best looking one apart, didnt get penetration at the root of the weld, i could see where the 2 tubes met and there was not filler material all the way through, im assuming i should see filler all the way through to the inside? im using a victor 00 tip, the smallest i have. im thinking a 000 might help to really get into the intersection of tubes, but ill see how it goes with the 00 for a while, practice, practice, practice!

for filler rod im still using coat hanger, but should be getting some real rod in the mail tomorrow. oxweld no. 7 was recommended for what im doing.


----------



## dr.welby (Jan 6, 2004)

I had a "practice sculpture" just like that! - the first welds were all scabby and lumpy, and then it clicked and I got something resembling a weld.

I also used a 00 tip. I'd like to know how a 000 works out.

The one thing that totally changed the game for me was to watch one of the Tin Man videos on airframe welding. When I originally learned how to O/A weld in metalshop, they always had you start and heat up a puddle and then add rod. Whenever I tried to do that I'd just burn through. In the Tin Man videos they have you head up just to red hot, and then melt a little lump of rod onto your hot spot, then turn that into a puddle. That made all the difference in getting the bead started.


----------



## HomeGrownSS (Jan 18, 2006)

dr.welby said:


> When I originally learned how to O/A weld in metalshop, they always had you start and heat up a puddle and then add rod. Whenever I tried to do that I'd just burn through. In the Tin Man videos they have you head up just to red hot, and then melt a little lump of rod onto your hot spot, then turn that into a puddle. That made all the difference in getting the bead started.


that is good advice, ill give that a shot. 
to start i have been heating up then then adding filler just as the puddle starts to form on the un-mitered tube, where i am directing most of the heat. once the filler and the puddle combine i hit the mitered tube with just enough heat to join it all together. i've been doing 4 tacks like then, then connecting them all.


----------



## bobbotron (Nov 28, 2007)

That's super neat, HomeGrownSS, thanks for posting that! I've been meaning to give this a shot, I have some Fourney RG45 rod, but haven't had the time to make some mitres to test it out. Only tried it once so far, and blew a hole through the un mitred tube super quick, whoopes. 

When I was doing T joints in the welding course I took, I remember it was wretched until you figured out the right torch angle, then things really clicked. I'd say keep at it, and maybe try to run a slightly smaller flame, and try some easier joints (like lap or T) to get the hang of it.


----------



## HomeGrownSS (Jan 18, 2006)

bobbotron said:


> That's super neat, HomeGrownSS, thanks for posting that! I've been meaning to give this a shot, I have some Fourney RG45 rod, but haven't had the time to make some mitres to test it out. Only tried it once so far, and blew a hole through the un mitred tube super quick, whoopes.
> 
> When I was doing T joints in the welding course I took, I remember it was wretched until you figured out the right torch angle, then things really clicked. I'd say keep at it, and maybe try to run a slightly smaller flame, and try some easier joints (like lap or T) to get the hang of it.


why try the easy stuff when i have to learn the hard stuff?  
this was my first time doing tubes, i did a little bit of 1/8" sheet metal repair on my friends off-road go-cart that really got me excited about it, and prompted me to try bike tubing.


----------



## dru (Sep 4, 2006)

*Coat hanger??*

Yeah, I've used it too....but seriously go get some 1/16" rg45 if you are going to weld up thin stuff. Coat hanger works fine, but requires a bigger puddle than you'd want for bike tubing.

Drew


----------



## HomeGrownSS (Jan 18, 2006)

dru said:


> Yeah, I've used it too....but seriously go get some 1/16" rg45 if you are going to weld up thin stuff. Coat hanger works fine, but requires a bigger puddle than you'd want for bike tubing.
> 
> Drew


haha, just got my RG45 in the mail today, laid down a few more beads. the 1/16" rod is a home run!


----------



## smdubovsky (Apr 27, 2007)

Looks good!


----------



## bobbotron (Nov 28, 2007)

HomeGrownSS said:


> why try the easy stuff when i have to learn the hard stuff?
> this was my first time doing tubes, i did a little bit of 1/8" sheet metal repair on my friends off-road go-cart that really got me excited about it, and prompted me to try bike tubing.


Haha, fair enough. 

Welds are showing some good improvement - you should try some destructive testing on them!


----------



## HomeGrownSS (Jan 18, 2006)

so ive been cutting the mitered tube off after each joint. gives me a good look inside. what should the inside look like? im also curious what the inside of a TIG joint looks like for comparison sake.

in a few places i can see where the filler came right through the tube intersection, but mostly it doesnt come all the way through. i quartered some of the joints, i can see that the outer is completely welded together, but not all the way through to the inside.


----------



## dru (Sep 4, 2006)

You are basically only welding tee joints welded on one side only since you cant easily weld the inside of the tube, can you? Thus you don't need penetration right through the base metal, unlike butt joints using the keyhole technique. You do need penetration into the base metal as close as possible to the intersection of the two tubes which is very tricky with a torch. Apparently it is much easier to achieve this with various electric methods. You are obviously getting a nice 'C' shaped puddle as you are working along the joint as can be seen by your photos. A lot of the time when I do mine, I have a big gap in penetration right at the intersection. It seems if I get too aggressive with the heat, the 'C' shaped puddle gets too big and I don't get penetration close to the joint. Maybe some of the actual welders can pipe in since I am a mere hack!

Drew


----------



## HomeGrownSS (Jan 18, 2006)

from cutting a couple up i can see im definitely getting penetration right into the intersection, but not all the way through to the other side. it seems like i cant expect that to happen but id like to hear from someone whether or not it is a reality.

im using a 00 victor tip, running 5psi on the oxy and the acetylene. i have the flame adjusted neutral, with a nice sharp inner cone, close too, but not oxidizing. 

i keep the tip real close and use that sharp cone to move the puddle where i want it. keep that tip cleaner handy, i barely ever have to clean the tip when fillet brazing, but this welding thing seems to dirty it up more frequently. 

i am welding forehand with the flame just about tangential to the tubing, aimed mostly at the unmitered tube, so i can get that puddle right where the tubes meet. 

still working on my filler rod dipping technique, to get it in and out real quick without the rod sticking, but keeping it in the flame region so i dont get an oxide buildup on the tip of the rod.


----------

