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How strong is a brazed frame? I know many many frames were brazed when new before they went to welded frames. I'm looking at (buying then) modifying an A65 frame, the main area of modification being the rear frame tubes that normally hinder twin carb models having a longer tract. I intend to alter these and am wondering if brazing would be strong enough? The alternative would've TIG welding which I know would be strong enough. Both types I would have to practice before I mod' the frame and I would have to invest in a TIG, as opposed to investing in some flux as I have the rest of the kit already for brazing.

I would have no issue running a home made brazed frame IF I did the brazing.

In principle it is much the same as soldering in the fact that there needs to be a substantial mechanical coupling prior to the braze.
Technically if the material is strong enough to support the load it was designed for a single rivet thru this coupling will keep it together, and the pieces would be fine forever. The strength is in the mechanical coupling, and NOT in the braze.
Butt join brazing I do not trust unless there is a plug/sleeve between, fastening the parts mechanically prior to the braze.

For learning, the best thing you can do is PRACTICE for hours/days before touching the frame. Too hot burns the flux, creating carbon that prevents the "wicking action of the molten metal. Too cool, and you get no wicking but instead what loos like a decent bead that is is supporting nothing.
Just as in soldering the molten metal will follow the heat so if you want to fill between two coupled parts, put the heat where the metal is intended to go, and not on the pool of metal itself. The braze that you do not see is the important part. The braze you do see is an indicator of how the unseen has flown/flowed (?).

Short answer is... Yes, I trust brazing. Long answer... I already did.

Brazing in frames was only really ever done by poking the tubes into holes in the frame lugs, and brazing them in there. Thats the only way to get strength with a brazed joint - frame lugs with the tubes.

When frames went to welded, they were either bronze welded, or used steel filler wire.
The weld can build into fillets, thats where the strength comes from.

Frame tubes merely brazed together will soon crack apart, there is very little intrinsic strength in brass - which can't build fillets.
Hopethishelps.

Invest in the TIG, if you already stick weld you will be amazed at how tidy it is.

I should have added that as well. If you're going to invest in a tool, and have to learn how to use it anyway... TIG is the way to go. You can control-ably repair almost anything. Practice on a beer can if you want to really impress people.

In my case I never run out of cans to keep trying on.

I was just pointing out the merits of brazing above.

A super-light-gage Seeley frame with a built 920cc Norton motor is proof of the brazed frame worth. Proven over decades over thousands of racing miles, with any motor you can imagine.

Braze , but few have the skill

.

The bike in your pic Quinten, is that brazed or Bronze welding?
AFAIK brazing is only viable with lugged construction, its big boys soldering , whereas Bronze welding allows butt to tube construction because the joint is strong, no need for a lug.

To the OP, good cycle / pushbike frame makers use very high spec filler materials, if you need to join butt to tubes see if there is a boutique cycle frame constructor handy and have him do the welding. Some contain silver as a filler ( welds at the lowest temperature) for the exotics like renolds 720.

Pushbike frames ( and Manx Nortons)use much higher spec steels like renolds 531 and more exotic, these steels do no weld easily, the temperature must be kept down or the joint gets locally brittle , so special Bronze welding was developed for this ( at Renolds by Ken Sprayson ) I think.

Your BSA frame isnt exotic stuff its regular mild steel or "gas pipe" as it is cheekily known by frame snobs, and will weld with normal steel methods, however using a higher spec like bronze welding would do no harm.

If you are chopping at the frame rails its mostly about the quality of fit between the two sections to be reunited, watch some vids on pushbike frame construction in Renolds steel to get an idea. Accurate curving mitres can be cut using wooden jigs and hole saws.
Another useful tool will be a round Tungsten Carbide burr about 1/2" in a "windy gun".

Unless I was doing a lot of these I would do all the prep and take it to a good welder, it takes a lot of practice to get good, I am still "sloppy welder 2nd class".

Heres a link to Colin Furze who does some innovative garage builds, The jet bike should amuse, but if you watch some of his construction vids you will see some cool stuff.
https://www.youtube.com/watch?v=bKHz7wOjb9w

I dont know , just a pic snagged from the net .
I'd call it a Fillet-braze . (Regionalism ?) Not welding .
There should be capillary action , in the tight miter joint , tinning of parent material and fillet build , all going on .
The cleanliness of that pic could be from tig-braze .
I have seen where a root pass is welded and a braze build pass is flowed on top



Some/many ? May call a brazed-fillet , bronze-welding , but the action is happening at lower temps than weld/welding
... where there is Melting of the parent metal .
In my mind , if braze rod is used and the parent metal is only heated enough to
Melt the filler , its a braze .
If braze material is used to build a fillet , it's still a braze .

Raw oxy fillet braze looks like this .

The frame looks like it was tig brazed to me.
If you purchased a tig inverter you could rig weld and electric arc weld + tig braze.
Have a look on YouTube for tig brazing.

Uhmmmm...
_I_ never tried it, but a former employer could TIG weld cigarette pack foil...

I have done this and it is difficult. The above photo looks like a silicone bronze TIG weld. The weld flows similar to TIG welding aluminum but you do not need the AC current to weld. I have (when working in the feild) had to weld bronze rails to steel with TIG and the joints are very strong.

If I had my choice though for frames I would TIG all of the joints with a steel filler wire as long as the frame material isnt anything exotic.

A GREAT welder can name his price in my book. To ME welding is something that you feel inside, and know when it is right. You don't have to be a chemist or a physicist to understand what is happening at the core of the process but a great welder knows right down to the molecule.

I know I can weld much better than I do but I get lost in the time vs. function aspect. I'd rather spend my time balancing cir-clips, wrist pins, and pay a welder to do what he does. Flow that puddle.

Allan,

I think the simple answer is "yes" brazing is strong enough for the mods you are undertaking. Usually the issue is one of using a similar or compatible process that will work with what was done originally. If the frame is fusion welded (melted together using filler material) you can braze tubes onto the same area, but it is hard to revert to plain welding because the braze will contaminate the weld. So, if you choose to braze it is best to stick with it. If the frame is brazed, it is fine to stick with brazing, just don't overheat any brazed joints. I don't know about your frame, but many old frames were assembled on a jig and pinned. They then went into an oven and were brazed when removed.

As discussed here you can braze with an oxy-acetylene torch or a tig torch. I build frames with a tig. Tig is quite versatile. You can spot weld and weld stainless or aluminum. If you want to continue fabricating it is a great tool, but it is expensive for a single project. I like working and welding with steel because I feel I can work it and rework it to exactly what I want.

David

If you go the tig route, it is easier to tack the parts with steel filler wire and braze the joint afterwards.
If you intend to weld aluminium at a later date your tig plant will need to be a AC/DC plant.
Alloy is welded on AC, hope this is a help.
All parts need to be very clean and free from oils to braze.

The welding current required depends on the type and thickness of the metal as well as the type of joint (butt, fillet, etc.). But, as a loose rule of thumb when shopping for a welder think of needing 1 Amp for every 0.001" thickness of metal. Actually, when you get to thicker metal the requirements deviate from this so 200 A will weld 1/4" steel or Al. However, the higher thermal conductivity of Al demands more from a welder.

For what it's worth, just about the only welding I do is motorcycle-related and there isn't much on a bike of thickness greater than 1/4". So, I can recommend a Miller 200DX with a water cooled torch since mine has yet to meet a task where the 200 A has been insufficient.

That said, for most things pure (relatively inexpensive) Ar gas is all that's needed, but adding (expensive) He to the mix adds significantly more heat to the weld which helps a lot when pushing the 1/4" "limit." The difference He makes is really noticeable for thick pieces. Because of this I have an Ar tank normally connected to the welder plus a 50/50 He/Ar tank to swap to the unusual times when I need the extra horsepower.

The following post shows a 3/8" Al bracket I recently welded using the He mix:

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=550065&page=13

Another important spec in deciding on a welder is duty cycle, which the industry defines as the number of minutes of welding possible to do every 10 minutes without overheating the unit. My 200DX is rated at something like 20% duty cycle when used at the full 200 A, which means I can only weld for 2 minutes at that power before having to let the unit rest for 8 minutes. If I were using it in a production environment and needed this much current this would be a problem. But, seldom have I needed the full 200 A, and those times I haven't needed to weld for more than 2 min. anyway. I didn't time it so I can only guess, but the longest bead on the bracket shown in the above link probably took no more than 30 sec.

One last thing for people in the U.S., my welder is plugged into a 30 A, 220 V circuit. If you only have 110 V available check the specs of any welder you are considering to see what the limitations are. My 200DX works on 110V as well but at reduced output.

Thanks for the info, I currently use a Snap On MIG at work, connected with Ar/CO2 mix, ironically I have been using it all day (literally all day and got a few more days work,welding up a van back to MOT requirements)

I tend to weld on a very high ampage unless the metal is wafer thin, but so I do t blow holes in everything I will give the joint enough time to cool sufficiently ( so that it is still a dull red) before striking again. I can get the welds to fuse together nicely like this and run flat, using a lower amp means you have to hold over the same area for longer otherwise it will build in layers but not fuse as well or form a strong enough joint.

I've put a lot of hours into welding in the last 12 months mainly with the MIG and gone from a terrible welder to being quite proud of my work and having confidence in it. I am confident in that I would be able to braze or TIG with good results with enough practice. I certainly wouldn't put mine or anyone else's life at risk with an insufficient weld.

I suppose I could use weld for the application but I don't believe it is the neatest or strongest solution.


The TIG would get a lot of use, and after following the Spitfire thread it has given me encouragement to weld aluminium and other metals that I could only dream of doing.

Allan,

I use the exact same Tig welding set up that MagnetoMan uses and it has worked well for me.

Good luck.

David

A few months ago Miller came out with the replacement 210DX. I haven't looked at what new features it might have that aren't on the 200DX (because I don't want to risk making myself feel bad) but this probably means there are 200DXs in inventory at various dealers that could be had at significant discount.

The frame above is a replica Suzuki XR69 by Trident Engineering in UK. Pure motorcycle porn