spiral stairs

[T.T]

how do you calculate the length of stringer required and angle which to roll it at

[lotechman]

Pretend that you are building a straight stair stringer. Using total rise and run you would use Pythagorus to find the length . The rise over run is the tangent value which is your angle.
For the spiral the rise stays the same however the run changes. If you know the diameter of say your kick plate or stringer and the total angular turn from bottom to top you can calculate the circumference of one turn (360 degrees) or any part of the circle. That is your run.
You can now unwind that spiral in your mind and find tangent value giving you the angle and length using Pythagorus.
Give us some numbers and someone here can walk you through your first calculation.

[T.T]

Originally Posted by lotechman

Pretend that you are building a straight stair stringer. Using total rise and run you would use Pythagorus to find the length . The rise over run is the tangent value which is your angle.
For the spiral the rise stays the same however the run changes. If you know the diameter of say your kick plate or stringer and the total angular turn from bottom to top you can calculate the circumference of one turn (360 degrees) or any part of the circle. That is your run.
You can now unwind that spiral in your mind and find tangent value giving you the angle and length using Pythagorus.
Give us some numbers and someone here can walk you through your first calculation.

rise=3000mm or 3m
dia=2000mm or 2.5m
angular turn=180 degrees
cheers

[lotechman]

Originally Posted by T.T

rise=3000mm or 3m
dia=2000mm or 2.5m
angular turn=180 degrees
cheers

the circumference is simply pi X Dia and for 180 half the answer. I get 3141.6

Rise over run is 3000/3141.6= .9549 which is your tangent value.
That works out to 43.679 degrees.
Someone check this.
If it is wrong I have a cat to blame.

++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++339+.
Good thing she can't work a mouse!

Nope the cat did it wrong I am sure! I think I missed something. I am getting second thoughts that there is a mistake.

[welderjim]

Thank goodness I am only a welder..aye my head hurts

[lotechman]

No worries Welderjim, All you do is have a rolling shop do the numbers for you. Give them the particulars and they will roll it to suit. They do it all the time. The one we use actually gives the rolling machine operator a print out sheet.
This picture may interest some. The stair was fourteen feet high. We only have sixteen under the crane hook so built it on the horizontal. It was for a movie set.

[T.T]

wow;;;;;complecated looking.the actual stairs that il be fabricating will have an inside and outside stringer made of 150mmx10mm flat and the treads will be bolted to 50x50 angle,thanks a millon lotechmam i now can take the first steps to fabicating my stringers

[lotechman]

Originally Posted by T.T

wow;;;;;complecated looking.the actual stairs that il be fabricating will have an inside and outside stringer made of 150mmx10mm flat and the treads will be bolted to 50x50 angle,thanks a millon loch i now can take the first steps to fabicating my stringers

I hope your stringers are wide enough to support the stair treads. Keeping a sweeping staircase the correct shape as you build can be difficult. The easiest way I have used is to build it on a one inch or heavier plate set on the floor. You can draw your circles on the plate and as you erect your stringers you can drop a plumb bob to confirm the correct curvature. You can tack the bottom of the stringer then jack up or pull down to change the twist. Channel is common for stringers.
Be careful of code restrictions. If it is a primary stair they are very particular about it because one day someone will have to be carried down the stairs on a ambulance stretcher. Often code will not allow extreme stairs as the primary. access.

[lotechman]

Originally Posted by lotechman

the circumference is simply pi X Dia and for 180 half the answer. I get 3141.6

Rise over run is 3000/3141.6= .9549 which is your tangent value.
That works out to 43.679 degrees.
.

I didn't go far enough. To calculate the length of your coiled stringer you have to take total rise and run to find the length of your stringer. Using Pythagorus and leg lengths of 3000 and 3141.6 your hypotenuse on the helix will be 4343.92
Split that length into the number of risers to find your spacing of treads on the spiral. I find a fifty foot tape and several old speaker magnets helpful to hold the tape to the shape. Regular tape measures do not lay flat on the stringer. Erecting the stair over a circular layout that you can drop a plumb bob helps. Murphy is lurking on these jobs so as you install your steps triple check to your layout and between nosings to make sure you didn't read a tape wrong or bump the plumb bob.
Don't ask how many times I have had to break the tacks on an incorrectly located stair. I couldn't tell you. The number is WAY too high.

[T.T]

can you do it out for me by formula for me would be much appreciated
pi x dia
i get lost half way through it ,another question when rolling it how do u check the spiral is right,do you check it by using a template the radius of the stairs,many thanks

[lotechman]

Originally Posted by T.T

can you do it out for me by formula for me would be much appreciated
pi x dia
i get lost half way through it ,another question when rolling it how do u check the spiral is right,do you check it by using a template the radius of the stairs,many thanks

Ok so I will start as if you were building a regular stair. You need two measurements and those are your total rise and total run. In the case of a regular stair it is easy. For a sweeping or spiral stair the total rise is still easy to understand however the run is a bit different. Imagine taking a regular stair and wrapping into a helix or unwinding your spiral stair to get a straight stair case.
The distance around the outside stringer is your run. (horizontal distance)
Circumference = pi X diameter
If your stair stringer has a diameter of 2000 mm then the circumference is 2000 X 3.141592654= 6283.185. You told me that the "turn" was 180 degrees. so 180/360 or 1/2 X 6283=3141.5 is the run.
Imagine a regular stair in your mind It has a rise of 3000 and a run of 3141.5 That is your spiral stair stretched out.
I will not go on until you say you understand so far. I am renown for being patient so if you don't understand say so and I will try another way to explain. There are not such things as stupid questions... only stupid mistakes.

[T.T]

i took a piece of scrap today and did atrial run,your measurements are near perfect,now i stand under you,thanks for your time much appreciated

[lotechman]

Originally Posted by T.T

i took a piece of scrap today and did atrial run,your measurements are near perfect,now i stand under you,thanks for your time much appreciated

Near perfect!!! With my Germanic heritage that will not do!! :'))
I found that if you intend to do the angles and distances for the stringer , kickplate, and handrailing, every time the calculations will have to be done for the slightly different diameters. I take mean diameters for all my calculations.
The most challenging for me was a handrailing on a sweeping curve of over fifty feet radius that was a sloped pedestrian ramp of some sort. It had several pipes of different radius's then inset welded wire mesh panels rolled to the radius. The things were for a stadium somewhere in the Seattle area.
I made a jig and built the curved top railing upside down with the sloped pipe posts angling upward.
Now if anyone can tell me how to develop a spiral inside a cone I would be interested... something like a cement mixer interior.

[stick]

An OT question here......anyone else ever work in a building with spiral stairs? I did for 15 years, and my knees and ankles are SHOT from the constant sideways motion required. I just SEE spiral staircases now and it hurts! I hate them with a passion!

[lotechman]

Originally Posted by stick

An OT question here......anyone else ever work in a building with spiral stairs? I did for 15 years, and my knees and ankles are SHOT from the constant sideways motion required. I just SEE spiral staircases now and it hurts! I hate them with a passion!

I totally agree with you!
Locally you cannot use true spiral stairs as the primary access from one level to another. Even curved/radiused sweeping stairs are frowned upon. I worked on some steel framing last year for a multi-million dollar residence. I saw some pictures of the site during construction and there in the middle of the floor area was the start of a spiral stair. For such an expensive house I couldn't imagine why one would create an inconvenience. Sometimes ego has more to do with design choices that logic.

[stick]

i never thought about it before, but it must have been a common occupational injury to lighthouse keepers back when they had to make multiple trips up and down to maintain the light. The places I worked in that had them were hydro generating stations. I only had to use them a couple times a shift. You'd think that a building made to produce power would at least have an elevator, but nooooooo! LOL!

[LayoutMan]

Originally Posted by lotechman

I hope your stringers are wide enough to support the stair treads. Keeping a sweeping staircase the correct shape as you build can be difficult. The easiest way I have used is to build it on a one inch or heavier plate set on the floor. You can draw your circles on the plate and as you erect your stringers you can drop a plumb bob to confirm the correct curvature. You can tack the bottom of the stringer then jack up or pull down to change the twist. Channel is common for stringers.
.

Hi Lotechman, i was searching old post about spiral staircase, especially how should i instal the setup in the shop, and found your old post like that! i can understand english good but im not writing as good, but here only if you want and its not a problem for you, do you think that you can do a little sketch of that ? i mean, a sketch that will show how to place the 1'' plate, the plumb bob, and with that plumb bob i never use it, i thought it was more a field tool, i know how its fixed with the string to a truss but in a shop how do you fix that ? and where do you put the plumb bob to see if your stringer is right curved ? do you put this at arround 6mm distance from the out side to stringer (when your spiral stairs is horizontal) and just turn the spiral stair to see if the plumb bob touch the stringer ?

hope you'll understand my bad english from quebec and you'll be able to help me!

Thanks

[lotechman]

I hope this explains how to locate stairs using a plumb bob. You draw your circle on the floor first before erecting.

[LayoutMan]

Thanks for this, i don't know why but i really thought it was used when you build the spiral staircase at the horizontal position (like your shop picture).

[lotechman]

Originally Posted by LayoutMan

Thanks for this, i don't know why but i really thought it was used when you build the spiral staircase at the horizontal position (like your shop picture).

The stair was 14 feet high.. too high for shop so we built using framing square bevels and a 2 foot builders level for each step location. I had to calculate the angle and then convert to bevel in 12 inches then set the spirit level on the square.

[Gjertson]

There is a book called a "treatis on stair building" It's pretty comprehensive.