Hi All. New old guy with questions

[Vanners]

I've been lurking around for a bit in the background and gained an insight into mig; so I have have registered tonight to tap into your expertise.
So here the the questions - I am restoring an old motorcycle and intend to fit a home built sidecar chassis.
I don't envisage having to weld anything much more than 3-4 mm mild steel round tube probably slightley less. If I do need to go thicker I'll use my ancient arc welder. I know more is less but there is; as always a budget.£200 ish. Would a machine around the 90-100 amp range?
Secondly is there a technique for welding tubes at 90 degrees to each other and getting a reasonable joint. Do I need to flatten the contact point off to get a larger weld area?
Thanks in anticipation

 

[keith19]

Hi Vanners,

90A to 100A just won't be powerful enough for what you want. See here:
http://www.mig-welding.co.uk/clarke-90.htm

Unless you are lucky enough to pick up a decent s/h 150A Clarke or similar within your budget, I guess it's back to the stick welder. Which can be a pain joining small diameter tubing, I know.

Re 'flatten the contact point off' do you mean vee the joints, as in a butt weld?
Small round tube is usually cut curved to fit exactly, so don't need veeing.

Whatever, I wouldn't even attempt a sidecar chassis without a powerful enough welder; one day someone may have to ride in it... If I only had 100A available for working on 3-4 mm, I'd feel safer with arc than mig.

 

[Vanners]

I take your point, the tube I have in mind is 38-40mm and I can get it in 2 or 3mm. I would want to lay one tube on top of the other at 90 degrees (not weld the end of one tube to the side of the other) so I was wondering whether or not to flatten each tube slightly on its radious to give a bigger contact area.
4mm would only come into it to make tube clamps so I could use the arc for that. I want the mig for the more inticate welding.

 

[keith19]

See what you mean about the 90 degree cross, the actual contact area is quite small in proportion to the diameter of the tube. A slight flat depression in each tube where they crossed would certainly offer more welding area, which should make for more strength.
It's not a joint I have experience of with tube, so hopefully someone with more experience will be along soon.

I think you may have a job to manage the 2 - 3 mm with 100A. (The 130A m/c would be much better). You may have to do two or three runs to get the same effect as one run with arc. But as you say, mig is better for the more intricate stuff.

 

[cumbriasteve]

Its always hard to picture a project in someone elses mind but for the joint you mention I think I would be notching out each tube a little to give a stronger and more visually attractive joint thats easier to weld..unless of course the construction won't allow that.

 

[GrahamGKD]

If you had facilities to notch tubing I think you could make a very short section of tube notched one end and then notched at 90 degrees to the first notch the other end so that the two right angle tubes would sit in the notches and still touch each other. In terms of x,y,z planes the two crossing tubes would be x and y and the third notched very short tube would be in the z plane. Hopefully you can visualise what I am on about - I would struggle to draw it?

 

[Vanners]

Thanks for the advice, the project ( a light weight sidecar chassis) is still very much in the 'thinking' mode at the moment so I might review how the tubes will be secured at 90 degrees. It may be better to machine some clamps out of solid billet.
I have seen a local supplier offering 130 amp migs at less than £200. Bearing in mind this is limited use hobby welding ie no big runs and if I use an argon mix; would a low end mig unit suffice for welding on brackets, mounting plates and large clevis jaws in the end of tubes.

 

[keith19]

I'd say that you should be good for up to 3 mm with a 130A mig, maybe even 4 mm with veeing the joints, where possible. But 4 mm is at the limit of the 130A m/c, whereas a 150A should handle 4 mm okay, and 5mm with veeing.

More runs can be made on thicker material if you only have a lightweight welder, but the problem is penetration. Good penetration is critical for safety related components. Given the same amperage, on the same metal, a 'hobby' arc welder will usually give much better penetration than its 'hobby' mig equivalent. An inverter mig will do better for the same amperage, probably as good as arc, but these are not generally hobby machines.

As you're at the design stage, you could study both both trad and modern (If there are any!) chassis designs for the sidecar, to get some idea of the welding pros and cons of different designs. Sorry if you've already done this, I'm just thinking aloud as to what I'd do in a similar situation.

Something else to consider - especially if this is a one-off job - is cutting and fitting up the chassis yourself, then taking it to a well-regarded local pro welder to complete the job. You should have change out of your £200.

 

[pedrobedro]

I helped a friend fit an old Busmar sidecar to his Goldwing and the chassis on that was massively over engineered in my opinion. Any tubes we fitted to it were cut in a V with the angle grinder then shaped to a U. There is a program called tubemiter here, free and you put in your tube parameters and it gives you a template to cut round.

 

[Vanners]

I've collected a few pictures of sidecar chassis and more or less decided on the design. New chassis are available but are very expensive. So whilst I'm still in thinking mode I may look at the possibility of box section rather than tube. The majority of the chassis is hidden anyway. There are a couple of designs that have few welded joints so maybe thats the way to go. I think the 130 amp I've seen locally will do the job backed up by the arc, so I'll be doing some shopping shortly, Thanks again for the advice

 

[cumbriasteve]

Just had a thought.. new built trailers now have to comply with some build legislation..not sure what but will your sidecar be similar, laws and regs may exist that prevent you using it without having it approved to certain structural standards.

Using it without meeting any existing regs would leave you open to a world of trouble if an accident occured, even if you were not to blame

 

[Vanners]

Steve,
As i understand the outfit will have to comply with Constuction and Use regs as any other vehicle does. I would'nt be building it with a view to production or selling it thats a whole new ball park. Many people build/ modify there own vehicles, m/cycle frames and trikes without having to comply with type approval. There is some legislation being proposed in Europe that will prevent any modificatins to any vehicle from the manufacturers standard, but its not law as yet and is being opposed. There are many areas in engineering where building to approved designs or published plans is perfectley acceptable. But as you say its worth checking these things.
For this project I will probably use an existing design and just tack it together and have a qualified welder complete the structural welds; for my own piece mind as much as anything. First trick of course is to repair the frame and get the bike back together.

 

[cumbriasteve]

Yep..that French thing is what I remember reading..get it built fast