Arc welding a bicycle frame

[GeorgeB]

I'm just about to try this and thought I should check whether any type of welding is compatible with the steel likely to have been used for a modest 1980s era road bike frame. I'd prefer to use an arc welder if I can.

The existing frame had 26.25 inch wheels fitted. It's difficult to find tyres for these wheels, so I want to swap the wheels for the more standard 700C size wheels, which are a bit larger (i.e. greater diameter). I need to extend the length of the front forks by up to an inch, so the larger wheels will fit and line up with the brakes. This looks relatively easy but safety come into it, because the front wheel will be depending on any welded joint I put in, when I'm flying down some hill at up to 25 mph.

 

[the snooper]

my mayes old man welded a pushbike frame with an arc welder in the 80s and it never snapped or cracked. if thats any help

 

[gavuk]

My old man welded my racer,a "sun".back in the 80's when it was not very old,he arc welded it through necessity ,it was all we had access to at the time,through choice he would have brazed ,tigged or migged it together,whilst it was possible to weld with stick the danger of slag inclusion blow through and increased haz zone due to more heat,it would be the worst process to use,in his words "a good welder,can select the right tool for a given material and application as well as actually weld it !" .How do you intend to extend the forks? if you attempt to weld it like you did your car ,tacks all the way round and then run a bead ,you may introduce too much heat ,causing grain growth and structurally changing the material,not ideal if its holding a wheel....is it possible ?yes,but there are better and safer options

 

[GeorgeB]

My old man welded my racer,a "sun".back in the 80's when it was not very old,he arc welded it through necessity ,it was all we had access to at the time,through choice he would have brazed ,tigged or migged it together,whilst it was possible to weld with stick the danger of slag inclusion blow through and increased haz zone due to more heat,it would be the worst process to use,in his words "a good welder,can select the right tool for a given material and application as well as actually weld it !" .How do you intend to extend the forks? if you attempt to weld it like you did your car ,tacks all the way round and then run a bead ,you may introduce too much heat ,causing grain growth and structurally changing the material,not ideal if its holding a wheel....is it possible ?yes,but there are better and safer options

Gav - thank you for raising some good points. I prefer to use arc for extending the bicycle forks because:

- brazing can't be anywhere near as strong as a half-decent arc weld.

- TIG must be best but, for this job, it's probably overkill, and I haven't yet mastered it, or even started out.

- MIG I have, but I prefer arc on any steel above about 1mm, and expect to get a higher quality weld (penetration, etc) with arc.

The technical aspects do concern me, like the affect on the forks of all that heat, like you point out.

How do I intend to extend the forks? Photos to follow...the OEM forks have an end 'plate' joined to the down tube (fork). The wheel is slotted into this end plate (flat plate steel). I hope to make the plate a bit longer by welding on a bit more metal. The plate must be about 3mm thick. I won't need tacks. A MIG welder might struggle with steel that thick, unless it's a powerful one.

the snooper - thank you also.

 

[gavuk]

In truth George,i thought you were intending to extend the tube part of the fork,at 3mm arc welding does come back into the game .....i would stick with mig up to 3mm personally if equipment is up to the job,as for braze ,strength,depends a lot on the joint, if the application was tube inside tube ,the capillary action of braze can produce a very strong joint.....hopefully others like chunko will reply with some first hand knowledge of welding such materials,look forward to the pics

 

[chunkolini]

Welding forks?
Very dodgy.
No very, very dodgy
If you butt weld them you will probably die.
Best way is to sleeve them, still not very sound practice, I have done this several times but I would always sleeve and braze, a lap weld using the sleeve method can also work.
The safest sleeve is to get another set of forks, lop the legs off them, then lop the dropouts off the forks on the bike, just below where they become less tapered, then cut the new forks so they slip over this leave about 1-2" overlap. Not very scientific but it can be done accuratelyish. Befre making the join bolt the legs together with a length of threaded bar

making the endplate longer sounds like a very bad move to me, I would not do this myself, no redundant material and no chance for a gradual collapse in the even of failure.

Keep any joints on the fork as near th bottom as you can, the further up the more leverage and the greater the chance of faceplantitis.

I would say your safest option would be to get hold of another fork, these old(ish) road bikes all had 1" stearer tubes, I'd scratch around for a replacement, that should be easy enough to find.

Good luck.
Report back.

Chunko'.

 

[GeorgeB]

making the endplate longer sounds like a very bad move to me, I would not do this myself, no redundant material and no chance for a gradual collapse in the even of failure.

Thank your for your suggestions and warnings. You know a lot more about bike frames than I do.

What do you mean by 'no redundant material' please?

To clarify, I'm not talking about extending any part of any tube. I propose extending the small end plate. I can arc weld all 4 sides of the join. The two pieces of metal should be fully fused together. I may then add new plate over the top, to add further strength, because that end piece is not designed to extend out as far as my modification.

Risks as I see them:

1. Alignment may be a challenge, so the front wheel still sits properly after my fork extension.

2. Metal fatigue if the entire assembly becomes brittle, or something, through all that heat. But people weld huge areas on cars, e.g. sills and don't consider it a big risk. I can hammer it and try and assess whether the joints seem strong enough before starting to ride the bike again.

 

[Paul-n]

George

[ Almost ] All mountain bikes have 26" wheels , just get one or two from freecycle !

700c is actually rarer than 26".

regards Paul

 

[chunkolini]

'Redundant material'
A phrase we devised when building bikes, if there is obvious overengineering, say 6mm plate, massive tube wall thickness etc, or maybe like you describe stick a one piece back plate over the outside.
A sort of mterial insurance policy for lack of knowledge.

Another problem going up a size on the front twheel, you might find it catches your toes on real tight turns.

As Paul says how about going 26", a lot more common.

Then of course there are brakes to align. 'V' brakes or caliper? caliper brakes are usually easier to bodge for reach, but less efficient, V brakes have a fair bit of leeway, cantilever brakes? chuck them in the bin. A stupid design.

Brake bosses can be moved but have to be 'quite straight', not 'very straight', but more than a 'bit straight'. Sorry to use over technical language. Basically they can be adjusted in three planes so real worries.

Metal fatigue? do you ever see car sills twanging about all over the place? try this, ride over a rough patch of road and see how much the forks are twanging around, dont at this point crash. Fatigue is a cumulative affair.

Another point, how is the drop out fixed to the fork, they are usually brazed in place.

Then a roast dinner tastes great through a straw.

Chunko'.

 

[GeorgeB]

'a roast dinner tastes great through a straw.

I'm not sure what you mean by the above but the rest of your post was very helpful, thank you. I'll say one thing - you're a lot more helpful than the guys in two or three cycle shops I visited, asking if it's possible to change the size of the wheels. They said it wasn't possible and to spend £hundreds on a new bike. This was two or three years ago so I decided to try it anyway. It took me all of about 20 minutes and, in my mind, made the so-called professionals in the shops look like fools. That bike lasted several years and rode perfectly well, until something else brought it down. I simply drilled new holes to reposition the brakes. I propose using a different approach on my present frame by extending the end plates - drop outs I think you called them. Yes, they are brazed in place, so I hope the braze doesn't melt when I start welding in that area. I may replace the braze with a 'redundant' weld as the first step.

For road/sports/racing type bikes I feel 700C x 18-23C is the norm, so I really don't want 26" wheels.

 

[hotrodder]

'a roast dinner tastes great through a straw.

Chunko's talking about the broken jaw and lack of teeth that can result from face-road contact following failure of front forks

brazing can't be anywhere near as strong as a half-decent arc weld

Many of the brazing alloys are a fair bit stronger than mild steel, as said joint design is the key thing though- fillet size for bronze welding/fillet brazing and joint fit with capillary/lugged joints

Welding over/next to brazed joints will destroy 'em and make a right mess generally

 

[gavuk]

Welding over/next to brazed joints will destroy 'em and make a right mess generally

sure when i tried stick welding near a braze joint,the arc didn't take at all,splattery mess,........twas a long time ago

 

[chunkolini]

A proper brazed joint is about as good as it gets for bikes, look at the classic british bike frames, Curtis braze frames for nutters doing 20ft jumps, and BMX racers, let alone the beautiful road race frames by The Daves' and why are all frame builders called Dave and why do they all come fro Yorkshire. An aside.

Go easy, Chunko'.

 

[Tino]

Just a thought George, instead of extending the plates remove them (melt the braze and slip them out) and braze in new longer and possibly slightly thicker or stronger ones. You could use a 701 steel for extra strength.

 

[GeorgeB]

Just a thought George, instead of extending the plates remove them (melt the braze and slip them out) and braze in new longer and possibly slightly thicker or stronger ones. You could use a 701 steel for extra strength.

That's a very good idea, thanks but the problem is - I'm not geared up to do any brazing. I don't want to buy the gear and gas just for this small job. I don't think I'd even be able to melt the braze, to remove the plate, unless by accident during an adjacent weld. Perhaps a carbon arc torch would do the job, but I'd need to fabricate a torch/holder.

My main concern at present is alignment - how to position and cut the slots for the wheels to fit into on the new plates, so there is adequate alignment.

 

[hotrodder]

You'll probably suprised how simple the proper frame building dropout alignment tools are, easy enough to knock up something similar. Getting the dropouts square is one of the easiest parts of the job. Something else to bear in mind... From the mention of 26.25" wheels in the OP probably find that the dropout spacing is quite different to 700c wheels, well rear wheel at least so may have still have issues fitting different wheels- front wheel to foot interference has already been mentioned but depending on the dropout width might also be much messing about with rear wheel spacing and/or dishing maybe in combination with cold setting the rear triangle depending on current dropout width. More info here

 

[gavuk]

found this link interesting ...alignment

 

[Alec.S]

Yeah....i was about to say that 26 inches was the most common....so there might not be any point.....

alec

 

[GeorgeB]

found this link interesting ...alignment

That's a very good find, thank you. My task is even more difficult - to cut out the slots in the right place, in the first instance before I improvise a tool something like that to see if I'm anywhere near.

I'm fairly sure that 26" wheels are never used on sports/racing type bikes these days. It's all 700C. Anyway, they are the only wheels I have.

 

[volition82]

Before you go chopping around the fork (which is a very bad idea IMO) have a good search around on http://forums.mtbr.com/ . There are a lot of niche products made to get around problems such as yours, such as specialised brakes etc. If you can't find the answer via a search start a thread on the relevant forum with a few photo's explaining what you want to do and somebody on there will be able to find a fix for you and more often than not a cheap fix as well. If it's a bike and a slightly possible alteration someone on that forum will have already tried it.