Practical welding exam I performed on myself.

[karoldem]

Hi,
I have three days of experience in TIG welding and I want to ask you guys for opinion on my welds. I have several questions:

1. I'm going to weld myself a bicycle. Are these welds good enough for such an application or will my lack of experience cause some issues? Like, I wouldn't weld a gas tank, but I feel that for bicycle these welds are good enough. Am I right?
2. As you see I have "dimples" in my original material like in pencil drawing below. What are they called? What can I do to prevent it? When I lowered current it couldn't arch at all.
3. Do you see any other mistakes I made? What are they called and why do they happen?
4. What is your overall impression?

 

[chrismac]

Are you going to be using the material used in the photographs to build your bike, it looks like 1" galvanised sch 40 pipe. Its going to be a very heavy bike, if it is galvanising on the pipes this is very hard to remove and you really need to dig deep with the grinder to get down to clean metal.

Honest answer your welds are poor, more practice required, but they have stuck the 2 parts together and will probably hold.

question, are you proud of your welds? you should be when you are finished,

I would advise get your pipes cleaner, it will give you more chance and cleaner welds, if you have excess metal then you can always grind it back to tidy it up a bit.

The dimples are a defect called under cut, you need to either add more filler wire or drop your amps to stop it washing the weld/parent metal away.

For 3 days tig welding you have made good progress, keep at it.

 

[addjunkie]

As above..get some new clean shiney metal of the size your tend to build your bike with.

 

[Munkul]

the "dimples" as you call them is known as undercut. It happens when your material is dirty (its absolutely filthy), or when your tungsten is blunt/contaminated (I would imagine it is, with those dirty welds) or when you have too many amps, too big a wire, too slow a travel, bad torch angle, insufficient fill... the list goes on. Basically, bad technique.

Metal should be shiny bright clean. Any soot or spitting back on steel/stainless means you haven't cleaned it properly. Grind it back PROPERLY and that includes getting rid of all the galv.
Tungsten should be pointy sharp and clean. Always.
Filler wire should be 1.6mm or 1.2mm for that sort of work on plain steel. 2.4mm is too thick and will slow you down and give undercut.

Ideally you'd get a buddy who is a good TIG welder and get them to teach you how to do it properly.

It's not all bad though it takes many hours of practice to just learn the basics of TIG. It takes many more hours to get good at it, and it takes hundreds of hours to get really good.

 

[karoldem]

Are you going to be using the material used in the photographs to build your bike, it looks like 1" galvanised sch 40 pipe. Its going to be a very heavy bike, if it is galvanising on the pipes this is very hard to remove and you really need to dig deep with the grinder to get down to clean metal.

I have no idea how do you know this, but they indeed are 1 inch pipes. I didn't put it against anything of known dimensions. I bought them on scrapyard and I don't know whether they were galvanised, but they were rusty on inside and they were laying beside radiator.

As above..get some new clean shiney metal of the size your tend to build your bike with.

Are you guys sure? I grinded it so deep until it was shiny and bare as Eve. Around my weld at least. Pay attention that there is a discoloration around the weld with the same colour as paint. Can it be rust? Argon pressure was like 80% of what it was when the bottle was new.

And thank you all guys.

 

[Erie Fred]

I have no idea how do you know this, but they indeed are 1 inch pipes. I didn't put it against anything of known dimensions. I bought them on scrapyard and I don't know whether they were galvanised, but they were rusty on inside and they were laying beside radiator.


Are you guys sure? I grinded it so deep until it was shiny and bare as Eve. Around my weld at least. Pay attention that there is a discoloration around the weld with the same colour as paint. Can it be rust? Argon pressure was like 80% of what it was when the bottle was new.

And thank you all guys.

we know about allot of things.
we are trying to help you.

You need to practice on flat first, and get even consistent good welds, no undercuts.
Then move on, working up to the pipe joints.

suggest you use the same thickness in all your practicing (flat and round) as what you want to weld on your bicycles.

 

[Brad93]

Yellow soot is from the zinc

 

[Tangledfeet]

The vast majority of steel bicycle frames are brazed rather than TIG welded; my understanding is that TIG welding creates too great an HAZ (Heat Affected Zone).

 

[Seadog]

...which will lead to stress fractures.

 

[Mike Pinches]

The vast majority of steel bicycle frames are brazed rather than TIG welded; my understanding is that TIG welding creates too great an HAZ (Heat Affected Zone).

That always used to be the case but these days a lot have gone over to Tig welded, Five Land bikes up in Edinburgh weld frames for a number of companies including Cotic, and most imported frames are also welded. Reynolds and Columbus both manufacture air hardening tubing specifically aimed at tig welded bike frames. I think there are still more brazed frames being built for road bikes, Curtis are one of the few making brazed mountain bikes these days.

My only frame I have built is fillet brazed and personally I found it a much more forgiving process than tig, and the next frame I do will also be fillet brazed. I am thinking of Tig welding a frame in the future, possibly when I do a full suspension mtb frame. I have a length of 35x09mm wall 4130 steel tubing to practice welding on when I get a chance.

There are good threads on Pinkbike forum and on the ridemonkey forum for homemade bikes which are well worth a read.

 

[Munkul]

The vast majority of steel bicycle frames are brazed rather than TIG welded; my understanding is that TIG welding creates too great an HAZ (Heat Affected Zone).

I believe that the brazing process was mainly used because they were welding chromoly tube which is crack sensitive when welded with TIG or MIG… for a long time I believe they liked gas welding for chromoly tubes for aircraft, because it’s a very slow process with lots of heat soak, which helped reduce cracking compared to MIG and TIG…

These days maybe better process allows TIG to be more widely used? I dunno…

 

[Tangledfeet]

I believe that the brazing process was mainly used because they were welding chromoly tube which is crack sensitive when welded with TIG or MIG… for a long time I believe they liked gas welding for chromoly tubes for aircraft, because it’s a very slow process with lots of heat soak, which helped reduce cracking compared to MIG and TIG…

These days maybe better process allows TIG to be more widely used? I dunno…

That always used to be the case but these days a lot have gone over to Tig welded, Five Land bikes up in Edinburgh weld frames for a number of companies including Cotic, and most imported frames are also welded. Reynolds and Columbus both manufacture air hardening tubing specifically aimed at tig welded bike frames. I think there are still more brazed frames being built for road bikes, Curtis are one of the few making brazed mountain bikes these days.

My only frame I have built is fillet brazed and personally I found it a much more forgiving process than tig, and the next frame I do will also be fillet brazed. I am thinking of Tig welding a frame in the future, possibly when I do a full suspension mtb frame. I have a length of 35x09mm wall 4130 steel tubing to practice welding on when I get a chance.

There are good threads on Pinkbike forum and on the ridemonkey forum for homemade bikes which are well worth a read.

I think I may have made a rushed comment and got muddled! I have a cousin that happens to be a lead design engineer at Brompton... I'll ask!

 

[Mike Pinches]

I believe that the brazing process was mainly used because they were welding chromoly tube which is crack sensitive when welded with TIG or MIG… for a long time I believe they liked gas welding for chromoly tubes for aircraft, because it’s a very slow process with lots of heat soak, which helped reduce cracking compared to MIG and TIG…

These days maybe better process allows TIG to be more widely used? I dunno…

I believe for aircraft they still specify gas welding for chromoly as Tig welding would usually require post weld heat treatment to prevent the cracking you mention. However it is now commonly accepted that for wall thickness of 1mm or less (ie bicycle tubing) heat treatment isn't necessary. Plain chromoly is now mainly used by homebuilders rather than professionals as they generally use the newer air hardening steels.

I think I may have made a rushed comment and got muddled! I have a cousin that happens to be a lead design engineer at Brompton... I'll ask!

Steel bikes are now a niche market with the majority being aluminium or carbon. There is a market within road cycling for high end 'artisan' frame builders trying to sell fillet brazed frames for upto £4000 a frame (lot's of them go bust).

 

[Tangledfeet]

Brompton Knowledge | Why Are Brompton Frame Parts Brazed

Discover why Brompton frame parts are brazed and how it affects your bike's performance. Learn about the benefits of brazing on Brompton Support.

www.brompton.com

Brompton (still) braze. Exhanged a few messages with him this afternoon; he's in Guangzhou after a loop that has taken him London to Ho Chi Minh and Shanghai too.

And all cattle class, such is the state of the bike industry.

 

[citizen kane]

I made a couple of frames some years ago, picture is the bottom bracket to seat post. Just keep practicing, you will get there eventually.

 

[chrismac]

I made a couple of frames some years ago, picture is the bottom bracket to seat post. Just keep practicing, you will get there eventually.

View attachment 476059

was the brass mandrel to keep the bottom bracket from distorting? if not how did you manage to keep the threads in position,

 

[jimbo84]

If you want some inspiration for steel bike frames have a look at this guy’s stuff. Brazed.

Demon (@demon_frameworks) • Instagram photos and videos

26K Followers, 261 Following, 856 Posts - See Instagram photos and videos from Demon (@demon_frameworks)

www.instagram.com

 

[Jelly_Sheffield]

Are you guys sure? I grinded it so deep until it was shiny and bare as Eve. Around my weld at least. Pay attention that there is a discoloration around the weld with the same colour as paint. Can it be rust? Argon pressure was like 80% of what it was when the bottle was new.

And thank you all guys.

When grinding galvanized materials, you initially take the surface off and expose a bright shiny layer of zinc.

If you grind further you remove the zinc and expose a slightly darker (comparatively blue-er) steel surface.

Because zinc boils at a temperature lower than steel melts any zinc you don't remove in the area that gets hot boils off leaving white, yellow and black residues, and in extreme cases whisky wool like structures.

Inhaling zinc fumes will initially give you an awful taste in your mouth, and if you inhale enough will cause a very unpleasant flu like illness lasting several days.

Whilst there are practical reasons why you might occasionally need to MIG or Arc weld galvanized materials, it's not something anyone would ever normally want to TIG weld, especially as TIG really depends on extreme cleanliness to give strong welds.

 

[citizen kane]

was the brass mandrel to keep the bottom bracket from distorting? if not how did you manage to keep the threads in position,

The sub assembly is tacked up in a jig and the brass heatsink is as you say to try and minimise distortion. The bottom bracket gets a final facing operation when all the welding has been completed

 

[tom2207]

have a look at Paul Brodie on you tube , he does a lot of frame work and a very interesting guy to follow , think Alan Milyard with a few cylinders missing.