MIG capacity: plate size vs bar size

[domga]

Hi folks

I am looking to begin a new hobby welding steel ornaments. Never welded before so thinking this should be fun!

Decided probably a MIG welder would be best for an amateur. So now trying to find out what welder I will need. MIG welders give max current and the max thickness of steel plate that can be welded. But I want to weld mostly round steel rod. Does anyone know how to calculate the amperage needed to weld steel rods - "T" and "X" joins?

I worked out that a round steel rod of diameter D has an average "thickness" of D*pi/4 = 0.78*D. So if I created a plate of 6mm rods side by side, the mean "thickness" would be 4.7mm. But presumably I need much less current to weld four x 5mm square rods into an X than to butt weld two 5mm thick plates.

If someone can tell me how quickly (mm per second) they can butt weld steel plate with MIG (current and plate thickness please) I can try do some calculations (heat diffusion - Poisson equation!).

Or better still, if anyone has a proven conversion formula (plate to bar) that would be great.

Thanks!
Dominic

p.s. I know I could just go out and buy a big 160A/200A machine and do even big stuff, but for just playing around it is hard to justify £600+ if a £250 welder is all I need especially as it will get only occasional use. Hence my question.

 

[Wozzaaah]

No need for all that scientific rubbish Dominic, down here that's known as 'going all round Bristol to get to Bath'.... a mig welder of about 180 amps will cope with just about anything you're likely to want to do at home.

Welcome to the forum.

 

[julianthegypsy]

No need for all that scientific rubbish Dominic, down here that's known as 'going all round Bristol to get to Bath'.... a mig welder of about 180 amps will cope with just about anything you're likely to want to do at home.

Welcome to the forum.

What he said!
If you want to do thin stuff as well, look at how LOW the welder will go. Cheaper welders always quote maximum amps as it sounds powerful but then you find you can't turn it down low enough to weld nice thin fiddly bits.

 

[cumbriasteve]

I thought a Poisson was something you had for a posh breakfast.

My welding is now all hobby/ornamental work (nearly) and my trusty Clarke 135 manages great, of course something more powerful is always nicer to have but I simply don't require it.

It made the handrail shown, not now my normal work but I was pestered.

It's 40mm box with 12mm square bar inserts, shows they are a capable little machine.

 

[BrokenBiker]

way too much maths there. its a lot easier if you just consider that some 8mm dia bar is 8mm thick. adjust settings accordingly and pull the trigger.

for ornamental work using round stock or small section solid square stock you are only going to be tacking anyway.

also I have found that you can do all the maths you want, at the end of the day each machine is different.

I have a sealey 100 amp mig, and my father in law has a snap on 150 amp mig. both set to same voltage and current (tested with meters) they both perform differently (not including duty cycle)

the bigger mig seemed to be able to weld a lot quicker and had a bit more penetration than the smaller, yet the settings were identical.

grab a mig, learn to use it and go from there

 

[domga]

Hi brokenbiker - yes agree that "grab a mig..." is best. And yea any amount of maths will not equal real life. But you miss the point - I am trying to work out what mig I need to "grab" (buy). Don't want to end up with one that doesn't do the job. On the other hand don't want to waste money on something that is way bigger than I need.

 

[cumbriasteve]

Hi brokenbiker - yes agree that "grab a mig..." is best. And yea any amount of maths will not equal real life. But you miss the point - I am trying to work out what mig I need to "grab" (buy). Don't want to end up with one that doesn't do the job. On the other hand don't want to waste money on something that is way bigger than I need.

Easy answer to that:

Give the members an idea of what you are making, what materials you are using and is there a budget limit.

You will find suggestions from experienced welders of specific machines suitable to your requirements will be forthcoming.

Simply knowing from a calculation you need for example a 150 amp machine won't be any help at all without the knowledge of what to avoid in that power range and what is recognised as a good machine.

 

[domga]

Hi Cumbriasteve

plan is to weld round bar 5mm & 6mm diameter, in T and X joints. If I were welding 6mm plate there are lots of tables to look up current needed. But no tables for other geometries :-( Am avoiding a specific budget - don't want to spend too little and regret it, but don't want to waste money either. Have been offered a 2nd hand Clarke 100E. I need to decide if that is up to the job. Unfortunately neither I nor owner know how to weld yet so I can't even do a test on it.

If anyone can tell me what speed they can make a butt-weld on say 3mm or 4mm steel plate (mm/second) and with what current, I can make some estimates for the rods.

Thanks!

 

[chunkolini]

Welcome aboard mr Dogma, this is The Place to learn about this game and there quite a few arty farty metal botherers on the site, check out the sculpture section in Projects.

I spent six years abusing a 130 amp clarke welder making sculptures up to some pretty big stuff.
Most of my work was made of a mix of 8mm bar and 3mm strip.
After it croaked it's last I shelled out for a 180amp welder and am now using slightly larger sections.
A 100amp welder would struggle with these sizes.
for butt welding bars and strips there probably is not a hard and fast method, it varies according to the angle you are joining things at and the appearance you are looking for.
I do a load of butt welding like this. eg

All made of 8mm bar.
or this

Made of butt welded lengths of 10 and 15 x3mm strip, oh and some 20x3mm strip. Lots of grinding at the end.

For this kind of work the main thing you need is patience not maths and theories or powerful welders. Every joint is effectively different. Time per weld? impossible to give a figure. A simple butt weld in say 15x3mm strip takes a few seconds unless you want to flow the edges in like on the giraffe.

 

[domga]

Hi Chunkolini

wow beautiful! Not sure I'll have the patience for things that size.

I agree patience is sometimes better than maths. But I have a physics background - alas I can't stop myself thinking about current flows and resistance and energy conservation thermal diffusion - kind of fun to me - weird eh? Sorry if it scares you all. For sure all your welders follow the laws of Physics, so if I had all the information about each join, and the characteristics of each welder one could in theory tell whether a weld was going to work or not. Problem is of course that I don't have those characteristics so the theory is can give nonsense if not careful. In my day job we would say that the model needs "calibrating" with some measurements. I'll shut up now before someone pulls my plug out...

 

[chunkolini]

Chill out and have a go.
I can remember being told that my 'toy' welder was not up to the job.
I knew nothing and gave it a go.
I like to understand things as well, lifelong science nerd but I also love learning by doing things.
Working at this scale like this is a bit daft but it gets a great result and avoids a lot of complicated metal shaping.

 

[cumbriasteve]

Hi Cumbriasteve

plan is to weld round bar 5mm & 6mm diameter, in T and X joints. If I were welding 6mm plate there are lots of tables to look up current needed. But no tables for other geometries :-( Am avoiding a specific budget - don't want to spend too little and regret it, but don't want to waste money either. Have been offered a 2nd hand Clarke 100E. I need to decide if that is up to the job. Unfortunately neither I nor owner know how to weld yet so I can't even do a test on it.

Thanks!

For 5 and 6mm bar the Clarke 100E may manage fine for ornamental work where full penetration does not carry the same importance as strength critical work, if it's cheap it may be a good first machine offering the chance of your money back when you decide to get something better... and if you enjoy the hobby, it's a near certainty.

Personally though I think you would soon find limitations in it's capabilities so I will begin the suggested models that should suit you as follows.

A Clarke 150, excellent machine and very capable for your mentioned sizes.

A Portamig 185, a machine leaning towards a more professional design, well respected on the forum and more than capable for your need's with a bit extra for backup, this machine I think would fit the saying of 'buy once and buy right'