I’m working on a set of stairs that has a rake wall that starts out curved then transitions into a standard, straight rake wall. I don’t think the framing was done very well and have a couple of questions that I am hoping someone with some experience can shed some light here.
I am going to build the top cap first and use it as a platform to lay up the bent handrail. Building stairs has a way of amplifying mistakes, so I want to make sure I am going about his in the right way before I get too far along.
Here are my questions:
1) If the top cap (the piece that the balusters will land on) were laid up in one piece should it have a slight twist to it, like a corkscrew, or should it follow the same plane ( i.e., if it were removed and laid on the floor would it in essence be flat as if it were cut out of one solid piece?)
2) The rake angle of the straight section is around 36°, is there some way to check the curved portion to tell if it were framed correctly? Initially I used a strait edge to project down the straight run and found the nose of the wall to be 4″ shorter than I thought it should be. However, using a piece of ordinary paper and fashioning it into a similar shape, I realized that my method of checking is incorrect. The radius portion drops in a different manner.
So I initially laminated the top cap out of strips and clamped it to the curved part of the wall, but it came out with a twist in it. I may be wrong, but I don’t think it should be twisted. I think it should be flat, so that the top cap is level.
Any advice on the subject would be so welcomed right now, additionally feel free to add in any additional info or methods that you think might help getting this thing done. I am open to any and all ideas.
Thanks,
KH
Replies
"1) If the top cap (the piece that the balusters will land on) were laid up in one piece should it have a slight twist to it, like a corkscrew, or should it follow the same plane ( i.e., if it were removed and laid on the floor would it in essence be flat as if it were cut out of one solid piece?)"
KH: I was asked a few years ago to work out the radius of curvature and development of a helix. This Helix Calculator is the result.
That's the theory ... the folks I did the work for never did build the stairs so I never had the opportunity to see the math put into practice. But there are other forum members who have worked with curves in space who will be along to help you with the practical side of things. I'm looking forward to their input as well.
Btw, that calculator and formula are for a helix wrapped around a circular cylinder.
Edited 5/17/2006 10:29 am ET by JoeBartok
Edited 5/17/2006 10:30 am ET by JoeBartok
The 36° angle can be constant for both the straight and circular parts, but the length of the run on the radius portion has to be calculated as part of the circumference of a circle. Cut a cardboard tissue paper roll and flatten it out, and you will see what I mean.
(Is that curve a circle when viewed in plan? Or am I jumping to conclusions?).Joe Bartok
KH
So I initially laminated the top cap out of strips and clamped it to the curved part of the wall, but it came out with a twist in it.
That part makes sense to me, it should/would have a twist.
Whats your profile of your handrail?
If I was glueing up a handrail for that rake I'd be doing it like everybody else, right on top of that wall.
What are your plans for profiling the rail? Or were you going to use the already made stuff?
You should be able to flaten the bottom of the rail using a porta-planner, that would make your bottom parallel with the cap, I need to know what your doing for profile after the glue up. Maybe others have a better idea of what your trying to accomplish but I'd need more info.
Doug
Now there's a good question: how does one deal with that "twist"?
I have made a cardboard models to test the formulas and while the radii and lengths work out dead on the helix will twist just like in the diagram.Joe Bartok
Doug,I'm not so worried about the handrail, I'm figuring that if I get the top cap made correctly then the handrail will follow. My concern is that the wall is framed poorly, but don't know enough about this type of handrail to make that call. And even if I insisted the framers came back to fix it, I wouldn't know what to tell them.At any rate, the photo is the type of grab I'll be fabbing up.kh
KH
Ok, I went back and looked at the original picture of the wall. If you put a level on that top plate of that curved wall does it fade away as it goes down, hard for me to tell in the picture.
Maybe that's what your concern is, if so you can put a piece of ply on top of that wall, shimming it to level, and then glue your cap up on that. Does that make sense? That way your cap would be what I think you are wanting. I'd screw the ply down as I went, shimming as necessary.
You'd have to deal with hiding the wall not coming up to the top cap but that's really incidental for a job like this.
I hope I've interpreted what yours saying correctly, if not ask again.
Doug
From the picture it looks like you have the worst case scenario, twist, curve, and change in pitch. When I build curved stairs I always try to avoid a change in pitch, because it makes the handrail and/or capping very difficult to work with.
While there are some people on this forum that can handle a situation like this, it is unlikely much help could be passed along in the written word.
Seek some help from someone that has been there.
Bear