How strong is strong enough, how much is too much?

**mountain eagle** · 05-15-2011, 11:12 AM

As I've been making structural things I can only guess what the right sizes of steel are to use. Like the gate I did yesterday.... 2"x3/16 angle on the post with the frame out of 1.5"x3/16 in a basic three horizontal and two end caps arrangement. No angle bracing as I laid in 2x4 wood to set the pickets to.

Plenty strong. I could hang on it. But should I have used a smaller less expensive size? Should I have used tube?

On a similar note, I've been welding every seam point of contact. I figure I need the practice anyways. Tho can't imagine a professional does that as I see things mostly tacked in spots with one or two main joining lines with a full weld seam.

Welding seams..... how much is too much? How much is enough?

**mountain eagle** · 05-17-2011, 11:05 PM

Really? There's a post based contest going on and I still can't get no action? Though, this one........... well I guess it's a silly question? No?

**INSANITY** · 05-18-2011, 09:28 AM

Not really a silly question. Too much or not enough is something you will come to learn the more you fabricate. But, build it the way you want to build it! Who cares what everybody else thinks! Build it till it makes you happy. Unfortunately many "Professionals of all trades" build stuff completely half a$$ed because they don't care and we are not there to tell them any different, yet we get stuck paying for their crap!
I could keep going but I really hate typing!

**Bluesman** · 05-18-2011, 10:00 AM

I tend to weld all points of contact solid when I'm building things that will be load bearing or critical. To me, I don't care how strong a tack is, I just don't think a tack will suffice when I need something I can put some umph behind.

**Charley Davidson** · 05-18-2011, 10:23 AM

If it's structural or outside where water can get inside I say weld it tight

**mountain eagle** · 05-18-2011, 10:32 AM

Okay, good to hear............ I figured it was just my neurosis which I rationalized by saying I needed the practice......

**Bluesman** · 05-18-2011, 11:19 AM

Things like a trailer hitch, I don't do in one solid weld but in a series of shorter welds. Welding instructor friend of mine at the JuCo suggested this. I wasn't quite sure what his point was until he explained it to me. He says that on things like a trailer hitch that are crucial, welded up all the way around is good, BUT it would need to be in a series of short welds with evident start/stop points. He says that if you do it like that and a stress crack ever occurs, it will more than likely stop at the end of the affected weld, whereas if it was one continuous weld the crack would likely grow and the whole welded joint would be comprimised.

**Tritium** · 05-18-2011, 02:55 PM

I like the advise on a trailer hitch. Great info to know.

Thurmond

**SICFabrications** · 05-18-2011, 08:42 PM

this is what happens with a "stitch" weld as bluesman explained...... when you weld stitches, you are giving the parent metals some room to flex. the weld bead is sooooooo much stronger than the parent steels, that you can create stress points. for example a-36 carbon steel (typical steel you buy from the steel supplier unless you ask for a different grade) has 36,000 psi tensile strength a 7018 stick rod has the abilities to achieve 70,000 psi tensile strength. do the math. 572 grade 50 steel, grade 60, grade 80 then into "AR" and the "t" alloys, the list goes on and on and on and on you get into higher and higher carbon, manganese, nickel and other alloying agents to greatly increase the steel's tensile strength, but at a sacrifice of specialized welding procedures and consumables...

as for the op question a general rule of thumb is this.... the more dimensions that a shape has, the stronger it is... for example: angle iron has 2 dimensions say, 2x2 it has 2 sides. angle iron is NOT a load bearing shape, but designed for push-pull applications, although it is widely misused and abused as a load bearing shape (take a look at the trailers for sale at home depot or lowe's) channel: 3 sides great load bearing but very little torsion resistance (meaning it'll twist) i-beam (or w-beam as its called in the industry and dont ask me why cause i dont know why) has also 3 sides top and bottom flange and the web. even better load bearing, but even worse for torsional loads (meaning it'll twist easier than channel) square and rectangle tubing has 4 sides, 4 dimensions... best load bearing and best torsional resistance, but at a cost.... it's more expensive per pound than other shapes.

i built a flat bed for a 1-ton a few years ago out of 1.5x1.5 11ga. square tube for the frame and runners and then sheeted it with 14 ga diamond plate... lightweight and hell-bent for stout...

rectangle tubing will carry a load better than square, but the square resists torsion better....

round pipe (with the seam) has em all beat until you split a seam, then yer screwed...

DOM (drawn over mandrel) tubing aka gun barrel tubing is seamless round tube can come in various sizes and wall thicknesses, is VERY expensive, but the strongest of em all. custom built chopper frames are made from DOM...just sayin....

**Tritium** · 05-18-2011, 08:48 PM

I love this. I am learning more here than I knew I needed to know. I would rather read about mistakes (so I can avoid them) than make them any day.

Thurmond