Tube Penetration Question From New Welder With Pics

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Hi Folks.  I am a new welder that has been practicing.  I will be welding together a very lightweight 2x2 3/32 tube frame for a teardrop trailer with a DC stick welder.  I have been practicing on the 2x2 stock, running beads and butting pieces together.I am not having too much trouble running an OK looking bead when I get myself all setup correctly.  My concern is penetration.  After I lay a bead down if I look at the back side, most often I have a good bit of discoloration and flacking of the metal, but rarely am I getting real surface penetration.  The bead does not break through on the underside.This picture shows typical penetration when I am not trying to get it to pop through.  The angle of the rod is not as vertical, the rod may be smaller, and lower amperage.This picture shows a bit more penetration, although uneven.  It gets hotter half way through the weld and is starting to sink more toward the end (left side).When I do build enough heat to get enough penetration, the weld will start to sink, showing on the backside, but flattening out and widening considerably on the weld side, making for a much less attractive weld.   And it is darn close to burning through, and I have to increase my speed greatly when the weld starts to sink.  Also, since the welds are short on this 2x2 stock, I rarely get that type of full penetration during the start of the weld, because the metal is not yet hot enough, but do in the second half.  Getting that type of penetration is proving inconsistent across the weld length.Here are some practice beads.  These typically don't have full penetration through the backside.  I am trying different rods and amperages.In the next picture, the middle bead shows when the bead starts to sink in resulting in full penetration on the underside.  Although I don't have a picture of it, the penetration on the underside has almost more bead protruding than on the topside (at least through part of the weld once it got hot and sank).So here is my question.  I believe I have a strong enough joint if I weld with enough heat that it just barely does not break through the back and the weld does not start to sink into the surface.  And then the weld looks better and is easier to control.  But should I be trying for 100% penetration.  And if so, how to I get it for the entire length of the short weld, particularly at the beginning.I have been experimenting with 6013, 7014 and 7018.  I have run 6013 5/64ths rod on normal polarity, and I get about the same results running 7014 3/32ths rod on reverse polarity. Thanks for your insights.P.S.  What is the significance of a really shinny weld compared to one that is not?
Reply:The only time you should get 100% penetration is when doing a butt weld with a gap. What you should be aiming for is 100% fusion, when the filler metal is mixing with the parent metal creating the weld. I know people use the term penetration but for some like yourself, it has brought some confusion, so I think the term fusion works better. I would definitely go for using 3/32" 7018 for its strength characteristics and be running at 75-90 amps.
Reply:Jay O - Thanks for that.  I was a bit confused.  Now I feel better about it.  I need good "fusion" as you call it, but don't need so much heat the weld starts to sink.  That is a relief, because it seemed too difficult to control and looked ugly.  Question.  On tube this thin, when butt welding, is there any reason to bevel the joint? It seems unnecessary to me. Question.  On ending a weld I was instructed to pull the stick back over my bead and pull away.  But with 7018 this seems to leave a little pin hole with slag in it.  I had intended to tack the four corners on the tube, and run my beads between them (after cleaning up the tacks).  So should I just run into the corner tacks and then pull away to the right (welding from left to right)?
Reply:If you are building a trailer that will go on the road you need to be able to do welds in all possitions that could pass bend tests. You are nowhere close to that yet from what you posted.If you are butting tube together with tube that thin you should be getting 100% pennetration. Proper prep and joint configuration would help. If you bevel the edges you will get better penetration on one pass. You could gap the joint and use a backing tube so you get good penetration as well.One thing to watch when tacking corners is that you make sure your welds wrap the corners when you make the final welds. If not you run a high chance that you will leave weak areas in the corners where cracks will start.Please note that building trailers is not a beginner project. It's an advanced project for someone who already knows how to weld well. be sure you practice in all positions not just flat. You usually will need to do at least some out of possition welds even on a small trailer. Vertical and overhead welds usually give people the most trouble getting good welds. If you haven't, I'd seriously suggest a class at a local tech school to get up to speed the fastest. When you sit down and figure out what materials, rod, electric and so on would cost you, not to mention the instruction, a class is stupid cheap. I'll see if I can dig up the links to a few threads on bend tests so you can get an idea just how good your welds actually are..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Originally Posted by gpweldJay O - Thanks for that.  I was a bit confused.  Now I feel better about it.  I need good "fusion" as you call it, but don't need so much heat the weld starts to sink.  That is a relief, because it seemed too difficult to control and looked ugly.  You are "melting through" which is too much heat for the base metal to retain it's shape.Question.  On tube this thin, when butt welding, is there any reason to bevel the joint? It seems unnecessary to me. There is no reason for a bevel on light gauge.Question.  On ending a weld I was instructed to pull the stick back over my bead and pull away.  But with 7018 this seems to leave a little pin hole with slag in it.  Then, don't do that.  I had intended to tack the four corners on the tube, and run my beads between them (after cleaning up the tacks).  So should I just run into the corner tacks and then pull away to the right (welding from left to right)?
Reply:gpweld everybody does things differently, you'll have to find what works best for you. I've never tried welding any tube that thin, but if I had to, I would start off with a 1/16 inch gap, and maybe a slight bevel, (but I doubt it) some 3/32 inch Hobart 335A 6011 at around 60 amps. Tack all four corners. Thin, and ramp the tacks with a die grinder, start on one tack and run to the other, with a cut and fill technique. Whip forward for the cut, whip back and pause for the fill. You'll want the inside to look something like this. Attached ImagesDon’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:DSW - Thanks.  I do plan on lots more practice in all positions on every weld type and thickness I am going to be using.  I have no intention of trying to put this together until I am happy with the results and have cut it all apart and done strength tests.  I am not in a rush and am enjoying learning.  I will also start out with some smaller projects that are non-critcal.CEP - Thanks also for the pictures.  I have tried some 6011 3/32, but for steel this thin it appears to penetrate too much without a lot of speed.Ok.  Thanks all.  Lots more practicing coming up.
Reply:3/32" wall tube is far too thin for a trailer. 1/8" or 3/16" would be much better.
Reply:Originally Posted by gpweldI have tried some 6011 3/32, but for steel this thin it appears to penetrate too much without a lot of speed.
Reply:CEP - Thanks.  I will try it again with the 6011, but I think the 7018 has been working best for me.  And yes, that is exactly what I am doing.  Trying lots of different things to see what gets the best results and strength for each area of the build, before I build anything.metelmeltr  - normally I might agree with you about 3/32 being too light for a trailer, but this is unique situation where the body of the teardrop trailer forms most of the strength of the frame.  The tongue and other areas on the trailer will be of a thicker gauge steel.Most folks who build teardrops in fact go way overkill with a heavy steel frame, and then bolt on a very solid wood structure to the top of that, and then also solidly attach walls.