Thread: Best welded joint type for novice?

Metal thickness? Application? What sort of welder do you have?

Given that its a good weld it will be based on a few factors as Master splinter alluded to.

If you select 1.6 as a wall thickness you might find all sorts of grief trying to weld it with say a transformer a stick welder.
The coped joint illustrated may be strong but overall its no stronger than a mitre joint for instance. Visually it looks great but it is more complex and time consuming to cut.If there are a number of joints and they are left and right hand joints it's all to easy to make an error.

New welders make mistake of assuming that the more weld that is deposited,the stronger the joint becomes.
Not so!

Again, if a good weld is deposited, any structural failure will always occur in the base metal( perhaps near a weld but not in it) before it happens in the weld metal.The (good) deposited weld metal is about 10% stronger than its parent metal if properly matched. As an example it follows welds torn out of the base metal are not failures as the base metal but a design failure of the joint and material thickness application.

Depending on the design of the structure any extra welding can cause distortion of light wall tube and be very difficult to rectify.

A lot of work I do in box section is just tacked in the correct number places and is still be well within the strength /loading parameters of the job.

Some of us can recall the Volvo ad where the entire weight of the car was supported by a single spot weld as it was hung from a crane.
The same principle applies.

A successful outcome for welded joint is dependent on a number of factors.Its a combination of all the factors

Material selection as in profile and wall thickness
Joint design
Process used - stick,mig, oxy
Operator skills


Grahame

What about if I am welding case hardened plasticine out of China made from recycled sardine cans?

As a welder - I'm damn fine carpenter!

If I could JUST get over the reaction to 'jump' every time the stick starts to melt, and the helmet visor goes dark...

And I seem to have a little trouble feeding the stick into the weld at a constant rate - the gap between rod and material seems to grow as the stick melts.

In theory I know what to do sort of...and I've had a fair bit of practice....but for the life of me the sound just scares the crap outof me - do you EVER get used to it? I just get it started good before I jump and stop it again.

Am I doing it right to slightly waver the stick side to side a little across the two pieces I am joining?.

When I have it in a vice and chest height, and can rest both hands to steady them...and do the sorta wiggle bit - I got a nice bead the other day, where the slag all stayed in one piece and sort of curled up off the weld to leave a REALLY neat bead of weld without slag holes and looking like cocky shyte...

Now I want all my welds to look like that, but i must have just jagged it coz the very next one looked crap doing the exact same weld!

I have doubts I will ever make a welder - and to top it off, dunno how but when grinding, with my glasses and safety goggles over the top - hot metal somehow got inside and burnt a little blister on my eye lid!

It's a bloody sight harder than others make it out to be!

As for vertical welds or fillets - fuggedabowtit! I ain't there yet!

I've used Mig in the past and that's more like using a silastic gun.... a fair bit easier!

I went to one of those one night learn to weld classes...and under the watchful eye of the instructor - made the mistake of wearing my photochromatic (self tinting) prescription glasses inside the welding helmet (coz I couldn't see jack without them) and started to weld something on the steel bench, but I started out OK and as I progressed the glasses just got darker and darker until I couldn't even see the weld or the piece I was welding or the bench... all i could see was a feint glow where the hot metal was so had no reference point of what I was welding. Much to everyones amusement I welded the test piece to the bench top, such that the tutor later couldn't get it off even with the grinder...and had to break out a gas axe to fix my stuff up! (Yeah all the while calling me for everything under the sun - and suggesting I stick with making sawdust in future - to the rest of the classes, and my bro in laws, complete delight)!!

Everyone was saying "keep going, keep going" & I thought i was doing a sterling job... until I stopped and took away the visor helmet thing and my now jet black glasses...

I knew how a blind man must feel!

I have serious doubts I'm ever going to make it as a welder.

Any advice? (Besides stick with carpentry)?

Ah yes, I forgot some details... let's say aluminium square box (2mm - I was considering 1.5mm but thought that would be trickier to weld?), angle and sheet (3mm). The welder is a 140amp MIG. This little project will be a light duty work bench.

So when talking about a "good weld" that would mean no voids, contamination etc.? As well as good/correct penetration?

From what I've read it seems that a steel weld should actually be stronger than the surrounding material? Is that true of aluminium also? And what is the general opinion on grinding welds? Is that a definite no-no on structural jobs (just for reference)? How about adding extra weld to fill a section that had a concave weld finish? Is that type of thing considered okay for home/DIY stuff?

Interesting info about just tacking the right spots Grahame. Is that type of thing just temporary? Or it can be permanent depending on the usage?

Timless - you could try wearing ear plugs? Otherwise put on some heavy metal (music, that is) and get in the right frame of mind to murder the metal - it ain't your friend! Hard to be scared of it then. Haha. (It works for weightlifting.)

I can't offer you any advice other than to understand very well the process of welding, and what is happening when things either go well, or go bad. Looking at other peoples mistakes and learning how they fixed them seems to be a good way to get a different perspective on things. If you have a good understanding you will be able to diagnose your own work, and you just keep improving from there... I did exactly that when I learnt to spray paint recently. After ever part I sprayed I went back to a troubleshooting checklist just to see what I could do to improve. Not that I made any big mistakes aside from the first time spraying clear, but if you aim for the perfect job it changes your whole approach and mindset, and the results reflect that. At least that is how I did it, and plan to take the same approach with welding!

For the grinding - all I can say is don't put your face directly over the job, and be mindful of where the sparks are all flying! Maybe you're better off with a face shield than goggles?

As for the rest just keep practicing and learning, that's how everyone else does it...

Mugget,

A simple 45 degree mitre joint would be the best from a practicality standpoint and for most purposes will be just as strong as the rest of material.

Obviously the thicker the tube the better for both weldability and strength.

Grinding your welds flush with the surrounding material is 'OK' as long as your welds have full penetration, but in reality - how will you know? (particularly with MIG) when welding a closed section. On a 2mm section, you haven't got much thickness to play around with, so I wouldn't grind it down - if you practice enough your welds will look really cool, and you'll be proud to show them off, rather than grinding flush. Adding weld to a concave area is also 'OK', but beware of aluminium losing temper if it is heated too much repeatedly (and cools slowly) - the area around the weld will go soft and you may lose structural strength. Also beware of cracking in aluminium welds (if the weld is concave, then there may not be enough wire filler being deposited, which is a real risk factor for cracks).

I haven't tried MIG welding aluminum - but I reckon this will be a damn hard way to learn. It'd be a great project for a TIG though .

- Mick

Mmmmmm... a good ESAB square wave TIG welder on aluminium is fun.

If you've no experience on aluminium (unlike steel, it doesn't change colour when red hot. It just turns into a puddle held together by aluminium oxide) it's probably the hardest thing to learn on, except perhaps learning how to do vertical up on copper.

For thin stuff (say under 5mm) try these: ULTRA BOND aluminium repair rods - Robson's Tool King Store and a propane torch.

See: Durafix Aluminum Welding Rods - YouTube

And then watch in awe at this: How good is your TIG weld? (weld strength & oxy acetylene torch welding aluminum) - YouTube

OH MY GOODNESS!!!

I love you Master Splinter! Thanks for those links. I never knew you could weld like that using just a torch with aluminium repair rods or flux & wire. That made my day... I am one happy camper now...!!

It's a long story, but I never intended to weld ally. I bought the MIG and thought I would just start off making a few things from steel (but it turned out that other projects came up and it sat unboxed for over a year!). I wish I had a TIG instead, I've watched videos and after seeing how it's done, I "get it". Using the torch and repair rod or flux & wire looks pretty much like the same method as TIG (separate heat source and filler), I have no doubt that I can do that after some practice. I don't know what it is about that, but somehow having separate heat & filler makes a lot more sense to me.

Change of plan now - forget the MIG (who needs gas cylinder rental!?), I will get some of those Ultra Bond rods and a torch!

About the mitre join... I don't have a metal cutoff saw (or a mitre saw for that matter). So how about just butt joining all the tubes? While it may not be the "best" or ideal join, it's not going to be so much less effective (like half as effective), right? Considering I'm only using 2mm thick material (for the legs/frame), and seeing the strength of the Ultra Bond rods, since the bench will only see light duty work - I'm starting to think it would be fine?

Thanks for all the info.

A friction saw is the wrong tool to use to cut aluminium anyway - it melts the material and contaminates it, which is bad news if you want to weld it afterwards. You should use a cold-saw (tungsten-tipped blade designed for aluminium) or a hacksaw.

In answer to your question, a butt join should be fine. Just keep in mind that when using those brazing rods, you need to have a stainless-steel wire brush that is *only* used for prepping the joint just before heating - if you use the brush for anything else, you risk contaminating the joint.

Originally Posted by RustyArc

A friction saw is the wrong tool to use to cut aluminium anyway - it melts the material and contaminates it, which is bad news if you want to weld it afterwards. You should use a cold-saw (tungsten-tipped blade designed for aluminium) or a hacksaw.

Woodworking tools work very well for cutting ally. My BIL is a boat builder and he uses all woodworking gear including SCMS, routers and trimmers. Provided the work is firmly held while cutting, a woodworking table saw with negative raked tooth blade makes extremely clean cuts in ally. A trick my BIL showed me was to rub hard wax along the line of the cut which prevents any galling on the teeth.

To cut steel I recommend a small powered hacksaw - they are much safer and quieter that cuttoff saws and also don't spray grit and metal all over the place. Yes they are slow but you can safely leave them cutting and go do something else. Used ones can be had for around $100.

Even easier - Build with Qubelok - Aluminium Trade Centre

Oh, and you can buy argon gas cylinders from some suppliers now...Speed Gas - Products - Argon

Originally Posted by BobL

a woodworking table saw with negative raked tooth blade makes extremely clean cuts in ally. A trick my BIL showed me was to rub hard wax along the line of the cut which prevents any galling on the teeth.

On the odd occasion I need to cut aluminium profile, I just use my compound slide drop saw - it has a wood blade, and you do need to take care, but it does perfect cuts, and running it through some wood afterwards gets rid of any aluminium on the teeth. That said, I should try the wax trick next time.

Talking about woodworking mitre Vs. metal cutoff saw - are there any other differences aside from the metal saw has a sealed motor? Assuming you use the correct blade in each saw?

Well I have some Ultra Bond on the way, order some ally next week and see how it goes...

One thought of how my little plan may still come undone - since the Ultra Bond is kind of like solder, it will re-liquify when heat is applied again. So having to do multiple sides on the one piece could be problematic... but I'll see. At least I will be well stocked for any quick ally repairs!

What would you call the Ultra Bond method? Does it only qualify as welding if the base metals are actually melted? Would it be more along the lines of brazing? Surely you can't solder metals?

I have never been too keen on the idea of those plastic joiners...

I think steel-cutting cold saws typically run at lower RPMs than wood saws, but when it comes to cutting aluminium I'm not sure. Having the correct tooth rake seems to be the critical thing.

Those rods are more like brazing than welding. Given aluminium conducts heat away like crazy, there's little chance an adjacent join will disturb an existing one, but either way I'd be doing some test joints on scrap before doing the actual job.

Yes, it's aluminium brazing rather than welding.

And soldering applies to any 'low temperature' (well below the melting point of the parent metal) joining. (I suppose then you could argue that tungsten carbide tips aren't brazed, but soldered, as the melting point of TC is 2,800C and I don't think there are too many other commonly used metals that get to that sort of temperature!).