TIG welder for a small bicycle company

[Engineer]

Looks very interesting...............but personally I would want to make it out of steel tube, as you would find the structure was a lot stronger, less likely to have any sort of problems with cracking, and easier to build.

If you want to stick to aluminium though, I would carefully investigate issues to do with strength and possible long term fatigue failures, and the possible improvements that would result from using heat treatment in the production process,

 

[roadsidecycles]

Engie,

the main issue we face, is the lack of quality tubing available.

The only few companies that sell proper 4030 CRO-MO tubes or anything similar in durability, don't sell them for our tube size(around 20-30mm) and if they do, the wall thickness is atleast 2mm. Building a 30x2mm tubular frame like that, it would probably weigh around 2x as much, which would bump up the weight of the bicycle alot(currently around 30kg).

as stated before, im not concerned about the durability, i'm pretty sure that if the first and second generation frames have held up, the third generation will be even better.

I did however take a look at some MIG welders. would it be feasible to use MIG welding instead of TIG?

 

[Engineer]

Exactly the same problem faced by the Spanish motorcycle industry back in the 1970s.............they made frames out of gas pipe, which tended to be very heavy and not that strong!

Like it or not though you probably are going to have problems with an no hardened alloy frame over an extended period of time, unless you look at the design pretty carefully and add gusset plates to the most highly stressed areas.

Depending entirely on your level of skill it is quite possible to gas weld aluminium, which may be worth investigating if money is very tight, and you have the confidence to give this a try. Special torches which are ideal for this process are available, and cost a lot less than Chinese TIG sets, which may or may not work reliably for a reasonable period of time.

 

[Shox Dr]

Aluminium bicycle frames, if built correctly will stand the test of time. A MTB frame raced hard will last maybe 3-4 yrs/seasons before any noticeable difference in ride is noticed. ie the ride becomes harsh, once this starts to occur cracks will soon follow, however most frames can be re-heat treated, extending the life of the frame. Pace cycles are one company that springs to mind that offer this service, for their own frames RC30 etc it used to cost 75quid.

 

[Engineer]

Aluminium frames which have not been heat treated will have typically have material strength reduced by around 1/3rd in the HAZ. Problems here can be overcome by using thicker gauge material, or fitting gusset plates to spread the load in high stress areas.

I would say the OP's design should probably be fine untreated, but he would need to look very carefully at adding gussets to reinforce areas subjected to very high loads.

 

[hotrodder]

I did however take a look at some MIG welders. would it be feasible to use MIG welding instead of TIG?

Not with your budget. With 30x2mm ally tube TIG is the way forward unless you can spring thousands for one of those fancy synergic/pulse MIGs. With a traditional/basic MIG once things like wire feeding issues have been sorted you'll probably still have problems with things like bead profile (high travel speeds + small diameter tube) and cold starts- pull the trigger on a MIG and you start depositing wire immediatly but aluminiums thermal conductivity means you need to begin hot/slow and either speed up or back off the amps as the part becomes heat soaked.

 

[NTwoO]

Interesting design. As an owner of a bike by www.velomobiel.nl the subject matter regarding these kinds of bikes are well known. With the right pricing the sales could happen, but those windscreens are not ideal. Take a look at the Go one, for instance. They moved away from a windscreen due to the blinding effect it has in traffic. If the sides are not enclosed, the windscreen is an aerodynamic disaster causing immense drag and resulting in a very inefficient bike. Try and make a steady transfer from your current profession to this. The advice of using steel is not that bad. Then you can use a decent reliable TIG rig that is DC only... or even MIG. That should give enough of a basis to move on to a more advanced production once the sales start to flow.

 

[NTwoO]

Oh, and btw. spoke your back wheels with the full 36 spokes. Trikes have high side load on the wheels and using only 18 spokes is absolutely not advised. Bicycle spoke patterns are not built for side loads. Check out old english cars for examples on how a wheel should be spoked for side load.

 

[roadsidecycles]

Hey hey, thanks everbody for having a great discussion going .

So the option is either TIG welding the alloy tubes or going for steel tubes instead. I'll give it an another go to see what kind of materials we have available.

NTWoo - those pictures are from the summer of 2008. Since then we've made a second iteration of the bikes and also changed alot of the features around to make it better.

We havent decided if we want to move away from the windshield, since some people have regarded it as the next best thing after sliced bread and some people would like to have it removed. Personal prefrance i guess.

As for the hubs - we ran into and issue with the rear axles and hubs we initially designed for the bike - we made the flanges just a little too small so the spokes came in short as well. We ordered new hubs and decided to try out how good it looks with the 16 spoke option. It looked great, but not that steady.

 

[Engineer]

531 type cycle tubes made in SE Asia may be an option, as i would think these are reasonable quality and price would be ok. Another option would be some form of 4130, but with either of these tube sets you will need to braze them together, but a gas torch and a couple of bottles are going to cost a lot less than a Chinese TIG set, which might have a very short life anyway.

 

[roadsidecycles]

Well this is awkward - turns out there is a company in Estonia that is selling ultra strong steel tubes, very thin walls, 0.8 and 0.9mm thickness. Pretty much same properties as 4130 CRO-MO tubing, yet has half the elongation factor(only 8% compared to 4130).

So if it turns out that the steel tubing works, does pretty much any el-cheapo DC TIG do the job? or is it best to still spend around 500-700 pounds on a proper machine?

Is 4130 not TIG weldable?

 

[Engineer]

4130 can be tig welded no problem, but ideally you do need to buy it in the annealed state as this will increase the max elongation and reduce the possibility of cracking. To reduce costs its also well worth looking at brazing, which is a method of frame construction which has been used for many years, and will be effective even if joint fit up is less than perfect.

Steel frame with lightweight tubes should be lighter than 2mm aluminium, but worth looking at increasing tube OD in very high stress areas, as you really need to be looking at a frame which is substantially stronger than the ones at present, as you need something able to withstand serious abuse over a long period of time.