Building a stairway

[Lee]

Hopefully someone can shed some light on my question. I have to build a pair curved staircase stringers out of 3x12 boxed stainless tube. The angle is approximately 30 degrees with an outside radius of approximately 10 ft. I am assuming that if the material is fed into the roller at the 30 degree angle, formed to a 10 ft radius, it should come out about right. More than enough material will be rolled in order to allow for removal of the end "flats" left by the rolling process. The inner radius is about 6 ft. So the same would also apply to that one also if I am correct. Am I? The treads wil be made of wood, built and installed by another contractor, and the stringers will only be connected at the top and bottom individually. This is for a very expensive beach house in Florida, so I would like to avoid the cut-form method. Any input would be appreciated. Thanks.

[Flores]

I have a few answers, but it probably isn't what you want to hear. We have made some, but found that it is more accurate to weld 4 pieces of material than using rectangular tubing. In other words, for each side of the stringer we rolled a top, bottom, then an inside and outside piece to form the tubing, then welded it and cleaned it up. You mentioned an inside radius of 6 ft. That sounds a little tight, but I guess it would be okay if you were making a "spiral" staircase. (Actually it is a HELICAL staircase because a spiral has no height, and has an increasing radius)
I am not sure if the laws are different for residential as they are for commercial, but here in Texas the stairs have to have an incline of about 32 degrees, too much more and it will be deemed unsafe to climb. (This is what we were told anyway)
That being said, from a top view, if you have a radius of 6 ft, the angle at 30 degrees, and a height of 125", your incline will be pretty steep.
I don't have my calculator handy, but from the dimensions given so far, and to end up with an incline of let's say 36 degrees, you will need an inside radius of at least 20 feet. Refigure your numbers. Also, the inside stringer and the outside stringer will have different radii, and will have to be fed into the roll at different angles also. We also used wooden steps from the original building we were working on, 2 7/16" thick x 13" wide. We welded structural angle to the stringers to hold the steps. The wooden steps had to be cut into "wedge" shapes, and we had to overlap the steps nose to nose by 1" Our stringers were not attached to each other in any way with the exception of the steps.
You didn't mention if the handrail will be metal or wood. If it is metal, we just rolled pipe, and fed it in perpendicular to the roller, not at any angle. When you tilt it after it is done rolling, it will make the "helix" shape. Don't know the formula to find the correct radius for that, just hit or miss. Any other questions, post further.

Sorry so long,
Flores

[Lee]

Thanks for the input. One problem I have is that the material was ordered by someone else, and has already arrived. Kinda like; Ready, Fire, Aim! If I had the machingery to do it myself I probably wouldn't worry about it so much. But I have to figure out what I need done and have it done somewhere else. What I received was a 12" "C" channel with 2" legs, bent from sheet stock, with an 11-7/8 flat piece to cap it with. So it looks like a 12"x2" stringer, despite what I was originally told. I agree with you on using 4 pieces, I think it would be easier. But I have to work with what I have now. The 30 degrees was a guestimate on my part, but I was told a 10ft outer and a 6ft inner radius. That would make for a 4ft wide stair. I did managed to get a peek at the house being constructed, and I think the 10ft radius is probably pretty close. But the 6ft radius is probably closer to 7ft, as the landing on the second floor looks to be no more than 3-1/2 ft wide. The stairs follow the radius of the wall on the main floor. It's definately a tight area. I'll have to make a trip out and do some checking and measuring myself to be sure. They have a back-asswards way of doing things where I work here in Florida compared to Michigan, so I am a bit flustered. The handrail will be 1-1/2" stainless tubing, so yes, just rolling it and turning it on it's side will work fine. The stringers are like the ones you described, not fastened together other than by the wood steps. So you fully understand what I am talking about. I did just finish and install a spiral(helical) staircase, but I designed, laid out, ordered the materials, and built it myself. I had no problems at all with it. But when you have too many fingers in the cake, as in this case, it always winds up a mess. So if it winds up being 32 degrees, do you feed the material for the inner stringer into the roller at 32 degrees? If so, the outer stringer would be less than that, as you said. As I said earlier, I have never done one of these before, so it is definately a learning experience. I'd just like to learn the right way of doing it. Thanks again.

[Hanz]

Wow, Lee- I was wondering after your first post if bending that large thinwall tubing would be possible without it 'crumpling,' and now that you have it changed to channel, are you not concerned about it? I don't have a huge amount of bending experience, although have worked with rollformers, and I don't see how that could be done without a form die to keep it in the correct shape...Good luck, keep us posted!

Ps- If it was me, I would ask the person who designed it and ordered the material, 'So HOW do WE do it?' If you attempt it yourself and waste the material, won't you be responsible for it? Bet it wasn't cheap...

[Flores]

Let me give you the express version of this. First you will have to layout your helix into a flat pattern. You can use the older way of finding this out by using parallel-line developent used for making "T"'s in rolled pipes. Which involves drawing your top view, your front view, dividing your circle into equal numbers, and start playing connect the dots and drawing vertical and horizontal lines. (maybe this isn't the express version)
First you will you will need to find your arc-length of your helix. The formula to find an arc-length (for any circle or arc) is:
Arc Length = (pi/180)*radius*angle

For the 6 ft radius:
(pi/180)*72*30=37.699
Draw a horizontal line and label it 37.699
Draw a vertical line at one end of the horizontal line and label it 125
(which is your height)
Now draw a line to close this triangle.
Use the pythagerean therom to find the angle of the inclined line.
(A square) + (B square) = (c square)
square root of ((37.699 sq.) + (125 sq)) = 130.561
130.561 is the true length of the inclined line here.
Now figure your angles.
The angle between the horizontal and the vertical line is found by:
Invert Tangent (Base/Height)
Invert Tangent (37.699/125) = 16.78
A triangle equals 180, and 2 are known, one is 90 and the other is 16.78
180-16.78-90 = 73.22
If you are using AutoCAD or something, it should be easy.
Basically, the vertical line would be your roll, and the inclined line would be the angle your piece will need to be fed.

Double check my math.
Now do the same for the other stringer radius.

As for rolling a channel without crumpling, we used UHMW to capture it.
We didn't do a helical stairway with this, but I have done arches in atrium windows with this setup.
You would need a piece of UHMW wider and thicker than the piece you are rolling.
You would cut 2 slots for the flanges on the c-channel, but you would need enough meat below the slots to keep it from breaking apart. Now you place your channel into the slots in the UHMW and roll them both together. You want the slots to be a little loose, but not too much, or it will be hard to remove it from the rolled piece. A dead-blow hammer can help remove it. As you roll it, your piece will want to crumple, but the UHMW will help support the wall and keep them from collapsing. You may get a little crumple, but it may be able to flattened out with a dead blow and a bunch of tack welds.
Maybe 2 four ft sections of this will work, roll part of it but not all the way out that the UHMW falls down. Put the second piece of UHMW in place, then roll it through.
One word of caution though, UHMW is a little expensive, but we charged them for tooling in the quotes.
Just some suggestions, take what you can.
Hopefully this helps because I am tired of typing [img]/ubb/images/graemlins/crazy.gif"%20alt="[/img]

Flores

[Lee]

Well I did it! I was right in rolling the material at the angle of the stair. The outer stringer was rolled at 33 degrees( the larger diameter one) and the inner one at about 41( the smaller diameter one). For ease of assembly, the 2" legs on each channel were cut at 2" intervals the entire length of each 8' section. This made for a wobbly channel to say the least. The sections were then tacked together in pairs, and hung at the actual height after the angle was cut where they join the upper landing. I then added enough channel to reach the point where they are to land on the floor, tacked each cut in the sections, then added the flat sections to cap the channels and form the tube. Right now it's all tacked together and I've begun the final welding. I think doing it this way would be easier than using 4 seperate pieces, but then again, I've never done it that way either. I'll just be glad when it's totally done and installed! I have taken a few pics of it "in process" and will take more after it's finished. I'll post everything when it's it's completely done and installed in the home. Thanks for all the help, I needed all of it I could get. This was definately a challenge!! And all this time I thought the other half of my brain was there to keep the one from falling over.......