Best way to weld this:

[Bill Edwards]

Stick over MIG here (fine to use it for tacking though as planned). 150a is about at the limit on 5mm, and you're talking box section - to use MIG you'd be with a low wire feed and moving slowly to compensate and as Richard says, putting a lot of heat in while moving slowly.
Set the stick welder fairly high and quickly blast away.

Having everything machined right will be a big help, poor fit up would usually be the biggest concern.
Don't underestimate how much box section warps when you weld on one side, it can be turned into a banana in no time.

And as Kent says, move round to spread the heat as you do it.

 

[MattH]

I dint say or mean that last thing you quoted me on
What I said was opposing tacks then when you weld it follow the same opposing principle with consideration of travel direction welds pull in line with travel direction
The more you weld on it they're it pulls. The bigger the gap you fill
the slower you get it done.
The less you clamp it

I'm sorry, I'm missing the distinction. Are you saying don't tack the entire thing but just tack individual junctions and then weld them and then move on to the next junction??

 

[Spark plug]

A good idea May be to weld the two long sides together back to back first, then weld the flat to them and allow to fully cool (overnight) before splitting them. This will mean that the forces will be even and balanced hopefully leading to minimal distortion and give added strength to the frame when you come to weld it up.

 

[Spark plug]

I'm sorry, I'm missing the distinction. Are you saying don't tack the entire thing but just tack individual junctions and then weld them and then move on to the next junction??

With any frame like this you need to tack the entire frame before starting to weld, as has previously been said box will distort horribly if it's not tacked well and if you put too mutch heat on one plane.

 

[MattH]

With any frame like this you need to tack the entire frame before starting to weld, as has previously been said box will distort horribly if it's not tacked well and if you put too mutch heat on one plane.

Which I what I was saying when quoting Kent.

 

[Kent]

I'm sorry, I'm missing the distinction. Are you saying don't tack the entire thing but just tack individual junctions and then weld them and then move on to the next junction??

No tack everything then weld everything sequence can make a big difference
By tack I mean tack just a little bib of weld not a stich and not a weld just a tack
It's hard for stuff to move if it's tacked but yes it still can likewise whole frame clamped

Ok If I was doing it I would have it on the right size bench with clamps all over it. Likely in a make do fixture and still follow the procedures mentioned tacking and welding. I wouldn't plan on correcting anything afterwards but with some jobs that's what happens

There is only one square and only one flat at the end of the day

 

[Bill Edwards]

Yes, having a good bench would be lovely! I'm currently building some heavy gates and wish I had enough to do to justify making a bench...

You do need to have everything tacked and then weld in a careful sequence. As you keep a close eye on it while doing so you can often work out where the next weld should be, exactly as Kent says things still move.

And as well as distorting while welding I'll echo whoever said that box isn't necessarily straight, it often isn't.

 

[MattH]

No tack everything then weld everything sequence can make a big difference
By tack I mean tack just a little bib of weld not a stich and not a weld just a tack
It's hard for stuff to move if it's tacked but yes it still can likewise whole frame clamped

Ok If I was doing it I would have it on the right size bench with clamps all over it. Likely in a make do fixture and still follow the procedures mentioned tacking and welding. I wouldn't plan on correcting anything afterwards but with some jobs that's what happens

There is only one square and only one flat at the end of the day

Yep, we're on the same page there Kent. Thanks for the advice.
I have a welding bench that is big enough, it's 40mm box frame with a 10mm AR Steel top. I don't know how truly flat it is though hence thinking about using the surface plate even though it's only 600mmx600mm. I worries me that the frame I'm welding is heavier duty than the bench and could therefore distort the bench. Whereas the surface plate is about 1" thick CI with 2" of webbing underneath.

 

[Spark plug]

I wouldn't weld it on the surface plate as the part of the frame that isn't on the plate may sag or twist. If you find your bench has any low spots you can pack the frame up with large washers under the clamps to try to keep it right.

 

[Kent]

Yep, we're on the same page there Kent. Thanks for the advice.
I have a welding bench that is big enough, it's 40mm box frame with a 10mm AR Steel top. I don't know how truly flat it is though hence thinking about using the surface plate even though it's only 600mmx600mm. I worries me that the frame I'm welding is heavier duty than the bench and could therefore distort the bench. Whereas the surface plate is about 1" thick CI with 2" of webbing underneath.

10 mm plate is a good top 40x40 frame maybe not but it's way better than an undersize bench

 

[MattH]

I tell a lie, it's 50mm SHS. Not much difference really though.

 

[ukracer]

I haven't mentioned Tig as I've not really practised with it much but I do have a Transformer TIG that will go to about 140A, I hadn't considered it as I presume this is to low.

Although I don't need much of an excuse to buy a decent DC inverter TIG!

Just up the road from you as well

 

[MattH]

I've been waiting on a long series endmill to turn up so I can have a play welding some of this 120x60 RHS.

First I squared off the end of a piece of RHS with the mill, flap disc cleaned the weld areas and used diagonally opposed tacks in all 4 corners:



I then checked for squareness:



I then ran a bead along the top and bottom of the short edges (I haven't touched my MIG in over 6 months and I need a bit of practice on the start and stops!).



After this I ran a 1/3rd length bead along the middle of the long sides:



I then cam back and did the other 2/3rds (always switching back and forth between sides).



Here's a pic showing the heat affected zones:



It turned out nearly spot on 90deg at the intersection:



And doesn't appear to of twisted from vertical:




This was all done with my Clarke 160TM at max so 150Amps. I will try another test with the ARC at another time.
Obviously I need some more practice on the MIG before jumping into the full frame but I do hold out some hope that I can get it together all square and true.
FYI, I was playing about with wire speed settings a bit whilst doing this, I was varying between about 8.5 - 9 - 9.5. it was happier at the higher settings but was leaving a fairing humped fillet (I suppose because of the lack of power on this 5mm material).

 

[Richard.]

Here's a pic showing the heat affected zones:

Heat tint!
HAZ cannot be seen without cut and etch.

Nice start by the way.

 

[MattH]

Heat tint!
HAZ cannot be seen without cut and etch.

Nice start by the way.

Roger that.

 

[Member 66061]

I like how you are taking time to make test pieces to get best results making the frame.
Very logical way to go about it, definitely time well spent. I hope your frame turns out good.