Thread: A hyperthetical on grinding your welds

Good post Graeme.

Like anyone, the stuff I find trickiest is the thin stuff, like 1.6 mm SHS tubing. What's the real penetration with this stuff likely to be? When I look inside the tube at a weld sometimes it looks like like the weld bead has penetrated right through - other times you can't see anything except the heat scorch. This is also often the stuff one needs to have flush eg sliding one piece inside another.

Originally Posted by Grahame Collins

. . . . . .Imagine we are running a bead to butt weld two equal thickness plates together,say 6mm . Our small home machine ,say a 10 amp GMC can run a bead of 2.5 diameter rod at 110 amps down the line of the joint. Above the plate surface it deposits metal maybe a millimeter in height. Below the plate surface if there is 0.7 of a millimeter we have done well.

It's not an excuse for poor welding but in your example whether 0.7 mm is enough can depend on if a weld can be run on the other side of the joint and how much flex or force the joint needs to support. If I can get a solid bead down on one side I tend to be a bit more agressive with the grinder on the other.

Cheers

Thanks, Grahame, I like reading these threads, always adds to the knowledge base.

Now, converting that knowdedge to practice...

Hi Bob and Scooter

Real penetration (for 1.6mm box ) is likely to be anywhere between what I said around .7mm and burn through. Thats because of a heap of variables starting out with the metal volume,amps setting,arc length, electrode type and travel speed.Another factorI suspect compounds the problem (but am unable to prove) is that the initial arc strike that I believe jolts the arc voltage up increasing the heat factor and burn through on that 1st strike..

The Box section especially the light wall stuff is a PITA because of the wall thickness. The absolute small VOLUME of metal cannot absorb and dissipate the heat of the weld quickly enough.

The smaller the dimension of the box, the bigger the problem.ie low volume,less heat dissipation. By sleeving the box section you have increased the volume of metal and help conduct away that excess heat which will burn through.

I think I can help a bit more here.If we work smarter not harder ,we could improve the heat conduction by heat sinking with pieces of copper sheet say 1mm thick.

You might find some copper( to flatten out) from a bit of fairly big bore offcut copper pipe. The box section could be laid out on the copper sheet and also you could make right angle brackets which could be clamped on to support the joint in assembly and further wick away the heat.

If you didn't want to pi$$ around with bits of copper just dunk the work in a bucket of water intermittently.

I have had good results with it before and am confident it should work for others. to me welding problems like that are just pure physics.

Cheers Grahame

Guys ,
I have just had another brain phart and remembered this.

Welding a tee piece of thinwall hollow section can be a big pain.

Burn aways at the cut edge can be drastically reduced by coming from a low angle and away from the cut edge.

The rolled edge makes for a natural valley but the cut surface will burn away if directly arced on. 3/4 of the arc on the solid and the rest overlaps the cut side.

Are also factors

• Short arc,
• Lowest amps possible
• Quickest usable travel speed

See the pic

Grahame

Thanks for the excellent tips graeme, am about to do some SHS in the next few days so I will try your suggestions.

With the copper sheet idea, how badly does it mark/melt the copper especially if one does end up blowing a hole in the steel? I have some square cross section 3mm brass angle that I could use but don't particularly want to damage it in the process.

Cheers
Bob

Bob,
if heat is indirect probably no more than needing a buff up.

If direct heat there will be some marks.Brass reacts a little different to copper because of the zinc content which will vaporise as soon as anything over about 600 degrees is imposed upon it. save your goodies and just dip in water -often.

Grahame

I realise this is not going to be as good or as quick as a water dunk but I have taken to using a water squirter/spray for small stuff if I don't want to take the whatever I'm welding out of the vice, or it's part of a larger frame etc that is too difficult to dip into a tub of water. I usually keep squirting till it stops steaming and instantly evaporating and there is a film of water on it for at least a few seconds. The fact that it does not take a large volume of water demonstrates the large heat capacity of water.

Cheers

OK - took Graemes advice on SHS and here is the evidence.

I'm basically welding a T piece from two bits of 20 mm x 1.6 mm SHS.

This is about normal for me (bear in mind I have a condition called "essential tremor" which is just another term for shakey hands, and the more I concentrate the worse it gets). I call this my standard "turkey poo" welding, reasonable strength but not very pretty. Look at the ground off weld underneath - also not good.



Here is a second go. A bit better except for the pinhole. The gobby bit on the LHS is from another run.



Here's one that I think worked out pretty well.


Here I'm welding a small 20 x 60 mm rectangle of 6 mm thick steel onto the flat side of a 20 mm x 1.6 mm SHS.


Here's a bit better one of the same thing(I think I may need to move the rod a bit faster).


Getting there, slowly. . . . .
Comments, suggestions ? ?

Thanks Graeme.

nice pics Bob. Your right about the first one looking like turkey poop.

The last one looks the goods, probably because it was thicker steel. Your using an Arc right? How many amps?

Not bad Bob , I reckon your amps may be a tad too high though.

Originally Posted by martrix

nice pics Bob. Your right about the first one looking like turkey poop.

The last one looks the goods, probably because it was thicker steel. Your using an Arc right? How many amps?

Thanks guys,
This is all done using my $99 home welder - I could take the job to work, or around to BILs, and use a MIG, but for a simple job like this I find the cheapie does OK.

On the 1.6mm SHS I'm using 2 mm rods with the current set at 65A. On the thicker steel I'm using 2.5 mm rods with 85A. If I set the current lower than these settings I find it very hard to strike an arc. It could be my rods, they are more than a year old and they are not stored in airtight containers (just folded pastic bags). I also wouldn't trust the current indicator on my welder it looks like its been bent and restraightened.

What I'm making is a conventional outboard blade clamp for my small mill. I'll post more on this on the small milling forum.

Cheers

Hi BobL

Nice camera work!

Your travel speed is pretty close, Bob, but amps may be a touch high or arc length a bit long or rod angle to sharp. All 3 cause undercutting See the little undercuts on the rear side of the last pic? Its not a major fault unless its own a high strength job like a boiler shell OK!

Some welding rods don't like welding over their own slag.
A small chisel or something small and sharp driven into the slag holes to clean it out,(and rip it up it with a stiff wire brush ) will yield better results when you put another pass over it.

Grahame

Note the shape of the ripple pattern.Its about the right travel speed if it is crescent shaped -as Bobs are.

If I get my new MIG setup tomorrow, I will throw up some pics for your assessment too Grahame. I will be trying to turn a new leaf with my welding.......minimal use of the angle grinder.

Thanks for all the tips Grahame - very helpful.

I can certainy see my arc length is not always steady mainly because my hands shake - its worse with a new (long) rod so I have taken to cutting rods in half with pliers. I also find I can maintain a slightly steadier arc if I move the rod in little circles or small side to side swings.

I used to be quite good at this before the shakey hand problem but am finding it hard getting back to my former skill level.