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Keith Mathewson
01-13-2010, 12:59 AM
I've been playing around with tread configurations for fitting a curved stair into a rectangular opening with a well hole such that a continuous rail can be used without gooseneck, upeasings, etc. as seen in some of the older homes. The first layout is a little too much tapering, I'd have tread 2 & 14 straight and start tapering from there. Does anyone have experience making one of these?

Riversong
01-13-2010, 01:27 AM
How about posting the picture or sketch in a common graphic format, like jpg or pdf so we can view it?

newman
01-13-2010, 01:57 AM
How about posting the picture or sketch in a common graphic format, like jpg or pdf so we can view it?


how about you download sketchup viewer


http://sketchup.google.com/download/gsuviewer.html

dave_k
01-13-2010, 03:27 PM
that's 11 treads doing a 180 degree turn which is 16.39 degrees per tread. (or something to that effect) Draw that out from the center point of your arc then superimpose the center post that will support the inside of the tread and ad 1" per tread for a nosing. Am I missing something???

Keith Mathewson
01-13-2010, 07:46 PM
Dave,

The difference on this one is that it is a square stairwell with a curving inside stringer. Here is a pic somewhat like what I'm looking at.

Riversong
01-13-2010, 07:47 PM
how about you download sketchup viewer

I don't eat ketchup, either.

Do you have stock in Google?

newman
01-13-2010, 07:58 PM
I don't eat ketchup, either.

Do you have stock in Google?


no, I'm just giving you a suggestion for viewing it.
I suppose you won't download a pdf viewer to view pdf files either...

dave_k
01-13-2010, 09:54 PM
Dave,

The difference on this one is that it is a square stairwell with a curving inside stringer. Here is a pic somewhat like what I'm looking at.

I see what you mean. The layout of the treads should still radiate from a point. The curved section should be 180 degrees starting from the 2nd tread. You would lay out your treads of the mid point of that line. 180 degrees divided by the number of risers through the curved section should give you the angle each tread is laid out at. The arc of the inside stringer is also struck off that center point. I'd have to draw it out to see exactly how it would work in your case. I have never drawn a stair exactly as the one you propose. Unfortunately I don't have CAD installer on the computer I'm on at the moment. My concern would be the run up the line of travel up the curved section being inconsistent with the straight run. I may still be misunderstanding you but as far as I know all simple curved stairs radiate off the center point. Elipses are a different story and I have seen curved stairs with curved treads that don't work quite that way

Keith Mathewson
01-13-2010, 10:39 PM
It would seem at first look that it would work in that manner. I've been reading Techniques of Staircase Construction which is devoted to laying out these types of stairs and from what I've read they need to be laid out much in the manner depicted to work with continuous handrail. The book goes into great detail on tread tapering and skirt ramp relationships. listing at least 5 ways to taper treads. The fitting of the treads is not so much the issue but how it impacts the rate of rise and fall of the handrail.

Stan Foster
01-14-2010, 10:14 AM
Keith- In situations like this,...I draw the walking line on the floor. I would find my top riser and bottom riser on this curve....then divide this elliptical or whatever non circular line it is...into equal segments. Now if this is at least 10.00 run...you have a consistent walking line run. The shape of the inside stringer 12 inches in will be dictated by the riser lines going through these walking line/riser intersections. You most likely will have a sinuous curve for the inside stringer. These can be faired out with gentle curves and will be very unnoticable.

The risers most likely will only be truly perpendicular to the stringers only at the top and bottom riser. The other intersections will go from acute to obtuse.

Stan

Keith Mathewson
01-14-2010, 07:06 PM
The manner for laying out the treads as described in the book have some considerations that I would like to incorporate in the design. First the tread at the apex of the curve which is referred to as the tapered tread centers on the facing wall, the 2 treads which span the conner should not end near the conner and should be nearly equal on both sides of it. Additionally the inside progression of expansion and contraction should be proportional to avoid any humps or kinks.
To address these restraints a number of methods for spacing the tread width at the inside skirt and maintaining a constant width at the walk line.

Keith Mathewson
01-14-2010, 07:13 PM
The method of laying out the treads as if it were a constant radius inside and outside curve is shown and what the string ramp would look like if produced in that manner.

In this part of the country I've not seen a curved stair in a rectangular hole. Perhaps it is more common in other areas. Here it is just a U-shaped landing. This looks like a nice option if one is called to a site where the framing is complete.

dave_k
01-14-2010, 07:32 PM
The fitting of the treads is not so much the issue but how it impacts the rate of rise and fall of the handrail.The handrail has to follow the pitch of the stairs. Wouldn't that be constrained by the stairwell? The total rise and total run are what they are. You MIGHT have enough latitude to add or subtract a riser. I can't picture the geometry that would let you adjust the handrail to allow it it to be installed without upeasing or goosenecks unless it happens to land that way. At least not a solution that conforms to modern building codes. My primary reference on stair building is "A Treatise on Stairbuilding and Handrailing" by Mowat which shows spiral and elliptical stairs with rails continuous to the landing as you describe. They appear to use the same railing height on the stair as on the landing. Our code requires a 31" to 36" high hand rail on the stair and a 42" high guard on the landing so it wouldn't work. At least not if you want the guard at the edge of the landing.

dave_k
01-14-2010, 07:44 PM
I just looked at your sketchup drawing in your original post and either you changed it from yesterday or it didn't load properly on my computer. I envisioned something completely different. The drawing I saw yesterday (at least the way it loaded on my computer) looked to me to be a simple curved stringer radiating from a center point with uniform treads. I don't have any experience with stairs of that nature. It looks like a challenging job though.

Keith Mathewson
01-14-2010, 08:07 PM
I didn't change the drawing, don't know what may have happened.

This all started with a customer who called me in after it was too late to change anything and wanted a handrail on a straight run U-shaped stair without standard goosenecks, upeasings, etc. We settled on wreath turned fittings at the various landings. In the process of looking at options I considered a curved section of the landing in an effort to make producing the fittings easier, found some pics of curved stairs in U-shaped stair holes and here we are now.

S.Joisey
01-19-2010, 09:18 PM
Keith,

To convert a sketchup file to .jpg; - Click File- Export- 2D graphic; it will export to the location you want. Then you can post it here as a .jpg

BTW - love your posts- fascinating and lots for me to learn.

Jim Baldwin
01-27-2011, 02:20 AM
Keith, as you may be aware:

As it concerns the handrail, the purpose for the dancing winders is to more uniformly distribute the pitch changes which occur between the straight flights and the curved section. The progressively smaller straight treads leading into and out of the curved section allows for sweeping and graceful (straight) ramp easements. These then connect to the curved wreathed rail which is also uniform in its' pitch and graceful in its' appearance. In the "tangent system" equal tangent pitches of the half circle plan is the "goal".

Typical uniform straight treads connected to regular radiating winders often results in a wreathed handrail with two (abrupt) easements within the curve (as well as a non-uniform walk-line of the stairs themselves).

Willibald Mannes (in his books) are producing wreathed handrail sections by orthogonal projection line layout and oblique-cut timbers. This method really requires very thick blanks especially for easements within the curve. The dancing winders effectively reduces the required size of the timbers and facilitates the work.

The dancing winder layout that you're considering is usually the "right way" to build these kinds of stairs (BTW, you're one of the few guys I know that might appreciate this).

Keith Mathewson
01-27-2011, 07:59 PM
In the "tangent system" equal tangent pitches of the half circle plan is the "goal".

Willibald Mannes (in his books) are producing wreathed handrail sections by orthogonal projection line layout and oblique-cut timbers. This method really requires very thick blanks especially for easements within the curve. The dancing winders effectively reduces the required size of the timbers and facilitates the work..

Jim,

When I first started doing stairs the stair layout drove the design of the handrail, which I think is the approach most people take. After awhile I realized that I had it backwards. The handrail should drive the stair layout. Changing the pitch of the handrail even a small amount causes an unsightly kink or requires a wreath and since the tread position dictates layout the relationship between the two has to be understood. Although trying to sell this to builders & architects is like being a BBQ sauce salesman in an ice cream store.

I don't know about the orthogonal projection line layout approach- thanks now I have some more research to do...

bellchippy
01-28-2011, 04:28 PM
Keith

If the design calls for balusters be aware of the spacing on the treads they might not be in the same position on each tread if the treads are different sizes at the string.

Keith Mathewson
01-28-2011, 07:20 PM
Good point. Dicristina has many drawings on lay out and baluster spacing. A great deal of planning needs to happen so you end up crying in your coffee...