Suppose you have a simple railing design, made from 1-1/2"x.120" wall steel tubing. The railing is 12 feet long, and 36" tall. There are 4 vertical pieces,
2 at the ends and 2 more spaced out 4 feet, in other words there are verticals at 0, 4, 8 and 12 feet. There is a horizontal rail at the top (of course) and another whose bottom edge is 4" from the floor. This is a thought exercise, not a real problem, by the way.
The question is exactly what steps do you follow to make sure the railing comes out as square and planar as possible?
Assume the fabrication is to be done on an ideal welding table; i.e. flat, planar, and level. You have enough clamps. In particular, you don't have any sophisticated jigs and you don't have any access to robotic help or anything computerized.
I suppose bad ASCII art is indicated: (I labeled the 8 vertices)
A B C D +---------------+---------------+---------------+ | | | | | | | | | | | | |E |F |G |H +---------------+---------------+---------------+ | | | |
My real world problem is I've built a few similar structures and I've never felt I really had the right process.
I would tack the thing at A, D, E and H, rough-square it with a carpenter's square, then bang it around until the A-H dimension equaled the E-D dimension. Then I'd tack it a bit more firmly and bang it around a bit more. Then I'd weld in the middle rails (carefully to prevent warping) and check again, possibly banging it (or losing my temper and cutting it up for scrap). Then I'd go back and weld up the ends right and tight (or start over).
Of course I'd be doing this on a cement floor, not a fancy welder's table.
I have made thousands of feet of fence/rails of the configuration you described. A long description follows. For the short answer, skip to the end paragraph.
You can only get it so good, then reality takes over. There will be distortion in any weldment due to heat input and subsequent cooling. That said, the following things are helpful.............
Clamp things down to a flat welding table. I use a 4' x 10' made out of 2" x 3/8" angle. There's a rail 12" from one side and 18" from the other.
When you weld, try to have the heat set a little high so that you get a good weld without having to make two passes. Try not to make too large a puddle, but rather a smaller hotter one. Jump around in your sequence. Weld everything you can before turning the piece over. Let it cool for five minutes before flipping. When you turn it over, you only need four clamps to finish the job. Weld it out.
You are going to have some distortion. Clamping, welding with a jump sequence, not putting too much weld metal/heat into the piece, allowing for cooling, and multiple clamps helps.
A word on clamping: I lay out my top and bottom rails side by side. I mark where the spindles come in with soapstone. I spread them out. I put the spindles in line with the marks. I then start from one side and clamp it down making sure there aren't any big spaces I don't want. I go around then and tack the pieces with very hot tacks. Once that is done, I check everything and weld it out.
You are working with some stout tube. The application has a bit to do with it, too. For long pieces, you will have more distortion/warpage/sagging. I made a gate yesterday for our cabin. It is 15' wide and 4' high. I made the outside frame out of 1" x 1" x .065" tube, so it is very noodly over the fifteen feet. I filled in with several bark embossed rods throughout to make it look like foliage, and welded on about 75 metal leaves. I put two round laser cut images on there, and finally put two vertical decorated 1" bars for rigidity.
BUT, on one side, I made the pole 6' high and put a cable and turnbuckle to the center top of the gate.
Point is, sometimes just the weight of the weldment will cause it to sag when installed, and additional support is needed. Plus, it is good to have a banjo string on there, or a dolly wheel for when fat little Junior wants to get on there and take a couple of rides with his fat ass.
Sorry for posting more than you wanted to know, but it will be helpful for those who are making this stuff.
The simple answer to your question: Measure first to make sure you got it right and square paying particular attention to have the diagonals match, clamp on a flat table, stagger your welds, let it cool adequately before unclamping, and don't use too much filler metal or heat.
I would space the uprights away from the rails by about 1/16th of an inch. Then weld the one of the uprights to the rail on the side that would be vertical when on the table. With it welded on one side it should still be able to have the angle changed. So I would set the angle so it is almost a right angle, but so when I tack welded the side opposite to the one already welded the shrinkage will pull it to 90 degrees. Then I would tack weld it. And check the angle. It ought to be real close, but if not see if it can be moved to be right on. If it can't be moved, get out the grinder and grind out the tack weld and try again. Once you get the angle as good as you want it, weld the sides that you have not welded. Then back to the side that was only tack welded. After doing the one leg, I would weld the rest of the legs to the same rail using the knowledge I gained form the first leg. Then weld the legs to the other rail. Again spacing a bit away from the rail to allow for shrinkage and doing the sides vertical when laying on the table first.
This is how I would do it, but if Randy Z recommends a different method, I would think a long time before I did it my way.
First off, make sure your cut pieces are right. Assuming that A to D is one piece, 3 pieces of E-F, F-G, and G-H, and 4 posts, make darn sure that your 3 short pieces are exactly the same, square cut ends, and are are the correct length to match the top rail. (side note: when we switched over to a robot welder, the fab shop quality control had to come up a LOT in order to make good welds. The robot couldn't handle the lousy fitup that the regular guys took for granted.)
Second problem is dealing with the top rail: 6" of weld on one side in 4 places, it will pull toward the weld an dbow up in the middle. It has to be clamped hard, I'd even reverse arch it a bit, maybe 1/2" or so???
Next is your fitup, you want to put the least amout of weld required to minimize distortion. .065" wall can be just cut square, .120" wall is fairly heavy to get full penetration without some weld prep. I'd cut a .065" x 45 degree bevel on each end that would be welded.
Clamp everything down. Start with a hard tack on two corners of each joint. Welds should be as small and fast as possible. If using a MIG, get some smaller wire, maybe even .023"
Weld sequence is tricky. If you can do nice vertical welds, you can do all the verticals first. Weld in a back and forth pattern, don't just go around the circle in each block. Downside of vertical welds is that frame will warp into a parrallelogram. I find that this is easier to pull into shape then one that is bowed from welding on one side.
If you have to do downhand welds, hard tack all corners on the first side, flip, clamp, do all the welds on the second side, do all welds on the first side, hoist it vertiall, do all the welds downhand, flip it upside down and do the last welds.
10' x 3/4" pipe clamps with some extensi> Suppose you have a simple railing design, made from 1-1/2"x.120" wall
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This is how I would do it, but if Randy Z recommends a different method, I would think a long time before I did it my way.
Geez after this I am getting a funny feeling. Believe me Grant when I say that I have flame straightened more than my share of handrailing after welding. The two most important things is for the welder to give the fabricator a bad time if he leaves gaps or other bad fits. It is best to do this at coffee time when the rest of the crew can appreciate it. :'))) Believe me I have been on the receiving end a few times. The smaller the gap, the less problems. As far as keeping things square during tacking I put one tack in then check for square over and over and over. A larger square made from light angle so that it can sit on the table helps. Don't hesitate to tack a diagonal on temporarily if you have an feeling things will move. One of the best tactics I have seen is to tack it as best you can on the table using SMALL tacks. I mean tacks as much as an inch long but no larger than a 1/8th fillet. Pushing the gun into the corner and wiggling it as you pull the trigger gives a gob that is not appreciated! If you have to weld over some fitter's gobs or stop and grind them down you will look forward to coffee time when you can vent. Stand the handrailing up vertically. Weld your joints in position. The vertical to top rail is a horizontal sloping down and under the top rail. As you finish underneath you blow the grape off if you have too much material. At the mid rail you start at the top and run downward and under again blowing off any grapes or excess molten metal. When I say "blowing off" you aim the end of the wire at the molten gob that is hanging and it will drop away as you release the trigger. Use lots of heat and move quickly. .035 wire is best for good control. By welding while it is standing up you can alternate side to side so that the heat balances out. Some welders take three foot pieces of channel and weld a six inch piece of smaller pipe vertically on it. The handrailing can be dropped over and it will stand by itself. Good luck, Randy
Good idea about standing it on end. The other thing your message made obvious is that bigger shops are likely to have a fitter and a welder. If you were doing the whole job, would you fit everything first and then weld? Or would you do the welding on some parts before fitting additional parts? And most important why you would do it that way?
In my case, I'm certainly the fitter, the welder, the helper AND the cleaner-up-after! :-)
By standing it up, you can also apply preloading to the tee joints, so they don't warp. I don't believe in the "heavy clamping" method, personally. The only thing that works for me is preloading. I used a small hydraulic bottle jack, a
2' piece of heavy square tube, and two 2' webbed rigging straps to bend the top rail up slightly on either side of the tee. It's easy when you're doing square tubing, the bottle can just sit on the tubing.
I think this is similar to 'herding cats' the trick is to make the cats think it is their idea and that it is just a coincidence that you want them to go where they ARE going. Pilots call it 'staying ahead of the aeroplane'.
Small gap = less metal needed = less heat input = less shrinkage.
This is another time where it is like 'herding cats', as you can stop halfway, and after cooling you can see where you can use heavier welds and welding direction to pull the work so it will be straight(er) when it cools.
Sometimes it is easier to do the assembly on site as you can then more easily compensate for out of level concrete (or steel) and the structure will tend to be more rigid, it is also easier to install and hide the mounting bolts, it is harder to paint though.
You will spend a lot of time shrink straightening with a torch before you learn about weld distortion. Often the best way to control distortion is with the design of the fabrication. I avoid attaching pickets directly to pipe handrails where ever possible, (don't ask).
Good luck, this is more of an art than a science and you will get better with practice, before you weld, think about shrinkage.
Always tack everthing up before welding. The only exception is something like a butt joint joining the top rail together if it is longer than twenty feet. A tack welded assembly will hold and brace against some of the distortion. If you made a mistake often it is more obvious when the assembly is complete visually. It is not unusual in large shops to tack something up, stand back to look at it and utter some sort of comment in disgust. It is so easy to break a few tack welds. That is not the case if the assembly is partially welded. There are few times when you should weld before completing the fitting. Randy
Yes, but an important point. Making the tie ins completely watertight is not a great idea. You will miss something, and water can infiltrate. If you have a pinhole at the top, and a good weld at the bottom, the post can fill with water and freeze, bursting the tube. Seen it hundreds of times. It's always a good idea to leave a little gap when the piece will be exposed to the weather. Even a very small gap or hole.
Little change of tack (?!!!) from previous line of posts:
To get a right-angle - a square corner, there is the 3:4:5 triangle rule. For the railings you are alright, because the uprights and the horizontals are the same length and meant to form a rectangle so "equal diagonals" is proof of squareness. But is is useful to know.
Any triangle with sides in the ratio of 3:4:5 - the corner between the "3" and the "4" side is a right-angle. So on site you can get a good right-angle (square) using a plank or a piece of string. What is "one length"??? The length of your boot; width of a sheet of paper ... whatever so long as you re-use the same thing 5 times to mark along your "measuring rule".
\ |\ | \ | \ 5 4| \ | \ | \ | \ -------- right 3 angle here
A colleague of mine who taught plumbing was really proud of a group of black African students with very limited English language skills who knuckled down to hard work and remembered the 3:4:5 rule. They brought a length of iron pipe from the bending machine, the lecturer laid it on the workbench at the corner and declared "It's not square - correct it". They waited a moment and checked the workbench using the
3:4:5 rule - and found the flame-cut bench-top was not square. Which that lecturer had been using for measuring squareness for some time. Oops!
They'd have mesured "3" along the width, "4" along the length and seen if the diagonal was "5" (isn't that right?).
Hi to you all, New to the group and just having a browse, one thing I do to help prevent distortion along the top of the rail is get a sturdy piece of structural section such as a piece of 150mm channel and clamp as best as possible the top rail to this whilst tacking and welding the railing. Make sure the section is straight of course. As most other people have alluded to here, make sure you stagger the tacks and welds. Remember as the tack or weld cools it will pull in that directions, sometimes this can be used to your advantage. One other thing about tacking, always put the first tack on the long point of whatever you are joining, this allows you to square the items a little easier. Regards Rod
When you fit up two pieces to weld it is likely that the pieces only actually touch at one point. If you tack at this point, then the shrinkage will pull the two pieces together fairly evenly. If you tack at some other point then when the tack weld shrinks it will try to pull the two pieces together. But if they are touching at the " longest point " the pieces will not stay in alignment.
If the fit up is such that the pieces touch at all points, then it is better to space the pieces slightly apart.