Fence rails sagging

[eddie]

Well, I finally decided on the design of my fence.

2-1/2, 11 ga, sq tube for posts
Punched channel for the rails...2-1-1/8 with 4 in between pickets; 3 rails per section
Pickets - 3/4 pressed spears

I put up a 6 ft section on Saturday but didn't bother to check the rails for sagging because I thought the channel was pretty stiff (and it's heavy).

Well, I tacked a lot as I went along...got through and there's a noticeable sag in the rails...I'll have to rip this section out and start over because these types of things bug me...like a picture not level on the wall.

Anyway, I'm looking for suggestions on the next section. Maybe I shouldn't have let all the pickets weight rest on the bottom rail before locking everything together.

Do I just take it really slow..a picket at a time..tack , tack, tack?

I'm assuming if I'm able to get everything plumb and level and lock everything together that I shouldn't have any sag? I've seen flimsier rails than this with no sag.

thx
Ed

[dda52]

Would you perhaps be able to post a pic? I am thinking you are having warp issues rather than sagging. Seeing where the bow is versus the weld placement would be telling. 6' is too short to have a sag.

If it is warping, it can be reversed. I'm gonna tell on myself now.:o The last fence panel I did warped all over the place. I got in a hurry and didn't restrain it properly when I welded it. All I had to do to fix it was flip it over...restrain properly and apply heat on the other side. When it cooled, it pulled itself back into 99% of its original shape. So, if it is a warp issue, you should be able to fix it without starting over.

[eddie]

dda552

Here's a pic; the fence isn't off kilter; my camera was held an angle; but I think you can see the noticeable droop.

Maybe it is warping but before I hit it anywhere with actual welds I was doing a lot of tacking...but...maybe not enough.

I'll probably just chopped this section off and put it around at the back where it doesn't show so much. But if I were to try your "straightening" suggestion, would't I have to break the welds on the pickets for the thing to have freedom of movement?


Ed

[DrIQ]

Eddie,
If I read your post correctly you assembled and tacked the fence in the vertical position. You need to lay the panels out and weld them on a flat surface and then set them up between the post. By tacking and welding the pickets in the flat position you should eliminate the sag when you put the panel in position between the post.

[Jim-Tx]

It might just be the pic, but the bottom rail appears to have more bow in it than the top 2. Are all 3 rails the punched channel? If you are welding the pickets on the top side of the channel it will bow towards the weld which would cause the problem I see in the pic. Like the previous post says, if at all possible lay the panels out flat and weld them.

[eddie]

All three rails are punched.

For the bottom rail, I epoxied a flat on the underside so that when I passed the pickets thru the top two rails, they would rest on the bottom rail while I tacked away. Again, I think this may have doomed me from the start in that the pickets weight was resting on the bottom rail...unsupported.

You're right the bottom rail is bowed the worst, then the top rail. I noticed only the bow in the second rail to start with and using some clamps to try and straighten it before finishing the welds...I can live with the second rail but other two are right out there close to the street for anyone with some real expertise to see. :o Can't live with that. :D

Maybe for the next section, I can shore up the bottom rail until all is tacked.

For me, doing it piece-by-piece seems better than trying to lay it all on the garage floor and work with...tough on the knees and back. And I suspect that one piece would be quite heavy to manuever

[dda52]

Ok, that is better. Yes, the welds are contributing to the sag....actually causing it is more like it. I assume you are welding them all the way around? If so..there it is. Many times that type channel will warp like no ones business when you pour on the heat. It is just not heavy enough to hold itself in place when the heat is on. From the pic, it wasn't apparent...did the top sag as bad as the lower?? That is important as you will see later.

The Doc has it...weld them flat. Restrained if possible. That is how I would do it. I would clamp everything to my table and tack it all and weld slowly...and definitely not all at once straight across. That is a sure recipe for warpage. Restraining the panels will help...esp if you let them cool almost completely before releasing them. If you skip weld, weld a few skip a few and then hit a few on the top or middle and take it slowly, that will also help. The key is to avoid pouring all the heat at one time and in one place..or a slow progression across the piece. Bad thing is you can do everything humanly possible to prevent it...and it still happens. Channels and square tubes can be the worst. So, you just have to do your best to prevent and also get proficient at fixing.

In your case, some things come to mind. A heavier tube at the bottom would help any saggage. It has more heft to keep everything straight. If the bottom has sagged and the top is relatively straight, cut the bottom channel loose with a zip wheel and reweld. I would probably weld the pickets on just two sides. That would help with the heat problem and besides...they wouldn't be going anywhere like that. ;)

The best way to fix warpage is by applying heat to the side opposite to the direction of the sag. In your case, use a torch to heat up the top of the lower channel at the welds and get it almost red. (Very important...the heat must be applied evenly where the sag is the greatest...and progressively less as you move out. Otherwise, you will be creating another problem.) As it cools, it will shrink up and draw the channel straight(er). Sometimes it takes a couple of times to fine tune it. It will not make it 100% perfect, but it can get dang close. Now, if your top rail is straight, doing that will warp the top most likely.

If you do not have a table to restrain it and must be welding them in place, you can prestress the channels to the rough amount of the sag..in the oposite direction. That way, it would possibly draw up straight after you weld it straight across. In other words, prebend it and weld it the same as you did before so when the heat warps the channel, it will straighten it out instead of making it sag.


Sorry, I wrote a book and bet I am contradicting meself.:o I am doing several things at once. Lemme know what I got messed up if anything guys and I'll fix it.:p Gotta get back to work now.;)

[whateg0]

You don't really need to have a big table to weld this type of thing. If you have a couple of sawhorses and some heavier tubing, you can use that to make a makeshift table that you can clamp to. You really only need to have the horizontal pieces clamped.

As far as moving the assembled panels, buy your neighbor a case of beer. ;)

Dave

[Zrexxer]

And I suspect that one piece would be quite heavy to manueverEh, around here if you need help you just park your truck at the corner of the Home Cheapo parking lot for about 3 seconds, and it will be full of all the help you can stand! Better brush up on your español though :rolleyes:

[Jim-Tx]

Don has a good tip there. If you can't do it any other way, then prestress the channels a tad. I do that with gate frames where I weld cattle panel to one side. I let the weld pull the frame back straight. It's MUCH easier to prebend and let the weld do the work than it is to try to straighten them after they are welded and bowed.