Circular Stairway-Side Children's Slide Conundrum

This stair-builders' thread about how to fabricate a slide that wraps around the outside of a spiral staircase morphs into a more general expert discussion about spiral staircases and handrails, with lots of nice photos. November 2, 2010

I have an inquiry from a builder friend as to how to lay up this rather interesting slide that wraps around a circular stairway. Any suggestions? The best that came to my mind was to just add laminations to the outside stringer - first tall ones, then shorter ones for the bottom, then taller ones for the outside, and finally come back with a rasp wheel on a 4 1/2 inch right angle grinder and grind out the profile.

For the moment, let us not discuss the code/liability/child safety issues.

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Forum Responses
(Architectural Woodworking Forum)
From contributor M:
Sure hope my granddaughters don't start cruising WOODWEB...

From contributor D:
I am familiar with a similar stair built in mahogany. The fellow that built it was somewhat inexperienced and bid it at 1/15 of what a national stair shop bid. He laid up veneers in a U-shape and then tried to join them. Took him over a year.

The photo you show looks to me like it was made as a strip canoe would be - staves. The vertical ones and bottom are simple, but the ones at transition from vertical to bottom of the U would have to be sawn curved.


From contributor U:
Jeez, can you imagine the speed that child's going to be traveling when it hits the bottom! And with that polished floor, it's going to keep on traveling until it wraps itself around a door post. Do you sell tickets to watch?

From contributor H:
I might attack this with a series of 2" wide U sections top to bottom. Since that would make a rather butcher block appearance, it may or may not look very good. But it would solve the problem of creating the 1/4-round transition between bottom and sides.

From the original questioner:
Would you be making the glueup for the individual U's with the grain running all left to right, all up and down, following the U, or along the run of the slide?

From contributor H:
Grain running left to right across the slide. The individual 2" to perhaps 6" short run U components could be strip laminated on a press. They would be extremely strong, and there would be no weak end grain glue joints involved. That is, each individual U section would be strong. The next issue is bringing them together into one long spiraling slide.

However, as I said, I'm not sure about appearance. Perhaps the individual U components could be machined to accept a twisting 1/4" thick layer of wide inserted veneer, so to speak, which could be added after assembly of the individual U sections.

Or maybe this U construction assembly could act as a frame and narrow thin strips could be laminated lengthwise to give a top to bottom running grain appearance (preferable, I would think).

If anyone could find out more about contributor D outstanding example, that would be great. I'd love to see how that was made.

From contributor D:
The example I posted is not the best way to go about this. Yes, it worked, but the U-shaped elements put together edge to edge were not consistent in shape and even when together, a faceted effect was dominant. Then plies were run lengthwise, but they presented a whole new set of problems since they do not run flat except at a few points. Lots and lots of sanding and sand-throughs and re-layering - gallons of epoxy and several thousand staples - not fun. Then, trial and error not quite pie shaped veneers were run from upper inside rim down to the bottom and up to the upper outside rim.

The better way is as the original questioner suggested, and as the stair in his post shows: strip laminations. Perhaps 3/8" x stringer width (height), decreasing to 2-1/2" or so tall across the bottom, and then increasing width up the outer side. The form would have to be female U-shapes that fanned out and provided clamping surface for the plies. Boatbuilding techniques. Then a grinder or some way to level the tops and bottoms of all the strips. Or maybe a large router riding on a jig that rides the rails to blend the strips - the inside being more challenging than the outside.

Now that I know how to do it, who would like one?

From contributor J:
Interesting project. I think I would "cold-mold" this spiral slide over an inverted female form. The form itself could consist of regular ascending plywood uprights with a semicircular or elliptical top. These uprights would then be fastened together with bent longitudinal sticks to form the inside of the helicoidal surface.

The first wood layer would be set diagonally over the form with subsequent cross-lamination layers (typical cold-molded process). The trimmed edges of the completed slide would then be capped along with solid end pieces, as in the picture.

This kind of a construction method will produce a uniformly thick cross-section as well as a much lighter, stronger and molded monolithic structure. (No rasp wheel grinding required). Since the construction methods are the same, the polished inside surface of the slide should look like the inside of a traditional wood canoe (without the ribs). I think the first layer should be pointing inwards as you slide down?

After you've finished with this project, keep the form intact since you're now set up to do another. Of course eventually you will need both a left and right hand form. (The Old Town Canoe Company has been using their same forms for a generation or more.) Sounds like fun to me... and maybe a unique business venture.

From contributor T:
I can about guess what our local code officials would say! But looks like an interesting project.

From the original queestioner:
I am not sure what code problems there are. It is attached to a stairway, but it is not a stairway, nor does it stand in substitution for a means of egress, so I would argue that the stair codes do not apply. (Consider what the case would be if someone built this in a playroom and not next to a stairs.) I am not sure it even comes under the building codes at all. (It is just built in furniture.)

I presume there is a code for children's playground equipment, but I haven't looked to see if it applies indoors and in private (as opposed to a public slide).

I am sure that some clever bugger might file a lawsuit if his kid breaks an arm, but I am not sure there is a safety code that prohibits this. We live in an age where we expect to see a government regulation for everything, but maybe we could still build a slide for a kid without being blocked by red tape?

If there is someone out there who actually knows of a building code section that applies, please cite it.

From contributor J:
I would build something like this in compliance with local "home playground equipment" building codes. The problem I see right away with this slide is that some big kid (like me) will try to surf down the slide in his socks and wipe-out through the glass window. (If it could happen, it will.)

The high-sided slide picture looks much safer.

From contributor H:
Yes, I too was wondering about the glass in that first picture. Seems tempered all the way around would be either required or at the least a good idea.

From contributor D:
Code will require that any glass within a certain distance of a stair be safety - tempered or laminated. So will common sense.

We have supplied non-conforming stairs to projects and had no code problems as long as there is a code conforming stair in the house. The mahogany slide/stair was one of three stairs in the house (to the same level), and the other two were code conforming and very conventional.

Anyone that builds stairs will agree that stair code interpretation and enforcement varies widely from not only jurisdiction to jurisdiction, but also inspector to inspector. The house with the mahogany slide annually contributes about 400k in property tax to the local authorities, so they were all there at the open house, awaiting their turn to go down the slide, and being very accommodating.

From contributor G:
Isn't it a laundry chute!?

From contributor B:
Very cool. We routinely make helical handrails from solid blocks of wood. So I would use that approach for the bottom of this slide. Starting at the inside I would make a rectangular "handrail" with a solution for that radius and pitch. Followed by another with a solution for the next radius and pitch. Repeat until you have enough rectangular handrails to glue up the bottom of the slide. I would glue them up and work that bottom glue up with hand tools.

We have developed the ability to fabricate helical glue lam-beam stringers. So I would use that method for the sides of the slide. You would have 2 different solutions for the GLB stringers, but it is very doable. Here is a photo of some rectangular handrail pieces being worked on our CNC.

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Here is a picture of a stairway with a structural glue lam stringer. I think it would work for the sides of the slide. Having said all of that, it is still going to be expensive.

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From contributor B:
You got me thinking about this crazy slide, so how about this? The bottom of the slide could be made from a series of winders. The winders being basically pie shaped steps that are thick. You could carve the top side of the winders on the CNC, so the top side would look like a propeller with a flat on a very small part of the uphill edge. That is where you would glue the next winder. I just did a quick sketch and it looks like this too could work. The key of course is to carve each winder on the CNC machine prior to assembly. You could leave the bottom surface of the winders stepped. Again, glue it up and get after it with hand tools. This could be very cool.

From contributor H:

Contributor B, that is an outstanding solution to both the slide and the spiral structural stringer. Extremely clever I would say. Very simple and very elegant.

Did you get that stringer structurally certified by an engineer? I would think a building inspector would require that.

On the CNC, are you using a full rounded ball nose bit for the undercut side of the spiral rail, or are you planing it parallel to the right hand side after it comes off the CNC? Or is there some other method you are using to get the undercut side machined?

Thanks for posting this. I find this work very impressive.

From contributor B:
Thanks for the kind words! You just made my day. Yes, the GLB stringer was sized and certified by an engineer. The cool thing about the structural GLB is that we cut all of the pieces on the CNC and drilled indexing holes for dowels in each piece so that when we glued it up, we did so without a full size template, or full size jig or anything.

For the handrails, we turn the piece over and machine the other side on the CNC. Typically we leave some wood in the cut so that the two sides do not connect and, most importantly, the piece is still held in place. We have also left tabs to hold the piece in place, although sizing and placing the tabs requires more luck and thought because the piece can flex when using tabs. For our handrail pieces that also have a profile (they all do), we have one more process/machine that we use to cut that profile on a helix.

From contributor J:
Contributor B, strange mix of high tech CNC handrail and timber-built stair (cir. 1850). You're wearing a lab-coat and coonskin cap at the same time, so you must be a stairbuilder. Nice work in progress I am sure.

From contributor B:
Not a work in progress anymore!

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From contributor H:
Sheesh, you can get dizzy looking at that picture! Neat staircase though. We need to get more stairbuilders onto this forum so we can learn a bit more. I will hold onto the thought of that stepped spiral stringer.

What software are you using to generate the spiral handrail? I can see doing it with Enroute and the 3D revolve tool.

Also, a little more on your "other" machine for profiling the spiral handrail. Share that with me and I might even share our "Tilt-O-Hussey" design with you.

From contributor J:
I am dizzy "up the down staircase." Very nice. I can see where you were headed with this now. My own coonskin cap is off to you.

From contributor B:
I am using the same software for that circular stair handrail as I am for this one.

Tilt-o-Hussey, eh? No, don't think I can go there. I will tell you that we can profile pretty much any shape handrail, level turn, helical or fittings (upeasing, etc).

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From contributor J:
How long does it take for your CNC to hog out three handrail blanks like the one in the picture (oak)? Is that faster than using the bandsaw?

From contributor B:
You asked about time to carve the handrails using the CNC versus a bandsaw. Here is the longwinded answer.

Those pieces are not simple curves. They twist while they curve. The curve and the twist are not organic. They can be defined mathematically. And for our purposes there is only one correct solution. We define solution as the combination of curve coupled with the twist. The twist happens on all faces. Top and bottom as well as the 2 sides.

Cutting that shape out on a band saw and having the correct solution is a daunting task. Just drawing it on a slab of wood works my little brain. We used to do exactly that. Bandsaw and carve the billets by hand. It was extremely time consuming. Doubly bad is that it also took a journeyman to do it correctly. So we would have myself and my senior shop guy completely immersed in carving the billets. Really it is about the client and their willingness to pay for that labor.

To carve these shapes on a CNC still requires the effort of myself and my CNC operator, but in such a different manner that there is just no comparison. And while the CNC is carving, its costs are minimal (electricity and cutters and depreciation). While the CNC is carving, everyone in the shop is working on something else - call it simultaneous fabrication. It may take 3-4 hours to carve 3 billets from a blank of wood. It would take us far more time to do it manually. And at the end of the day we would not be near as accurate as the CNC. Finally, the hours on the CNC are not equal to the hours it cost to pay a senior craftsman.

Here is another project where we used this approach to craft a handrail for a client. This photo was indeed taken in progress.

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From contributor H:
What about the CAD/CAM time? I'm not suggesting that the bandsaw would be quicker... It's just that you didn't mention that part of the equation.

From contributor B:
Indeed, there is time needed to draw and model these types of handrails. We track that time and we charge for it as well. Nothing is free. I hear an underlying question: is it faster to build this digitally or by hand?

So this is my opinion, based on nearly 4 decades of being a carpenter, of building by hand and then building using the very best technology that I can afford. The technology wins every time.

The very best of my efforts and the efforts of my crew, using manual techniques, can not come even close to competing with me and my crew utilizing appropriate digital techniques. It works for us, and I know it does not work for everyone, but here you have it.

From contributor J:
It normally takes me about 1 1/2 to 2 hours to square a single wreathed handrail blank (not billet) from square-cut stock. I still use the band saw and hand tools, but after that it's ready to be machine shaped.

I think our total manufacturing times may actually be comparable, but you're right. I am the only person in the shop that can do this.

Your stair with the twist balusters is very pretty but I think it would have been a bit nicer with wreathed turns at the corners (not so much jumping up and down) What do you think?

Your methods are uniquely your own in that you utilize CNC to square the stock but not shape it. Unless you're prepared to elaborate on this process, you might just mention that there's already fully integrated CNC machines and system-software available for this kind of work (and let it go at that).

After reviewing your pictures and methods, I would say you're definitely bullish on big chunks of material both for your stairs and handrail. Materials, though, are cheap compared to labor, so whatever works for you.

From contributor U:
Again, the quality of the work you guys turn out has blown my mind. That stairway is superb. Beautiful. Fascinating to see its construction stages in the earlier picture. That was one hell of a job.

From contributor B:
Thanks for the dialogue. Being stuck in the middle of nowhere (we have to drive 70 miles to find a 4 lane highway), it is nice to talk to people doing similar work.

The methods we use are completely homegrown. I am using a medium duty 3 axis CNC router (Warthog) without a tool changer, coupled with a 3D modeling program from Delcam, called Designer. The part is then exported to another Delcam program called Featurecam. Both of those are really developed for metal working. I am actively exploring Rhino 3D as a replacement for Designer.

As far as a canned solution to our handrail and stair building needs, I just do not know. We fabricate a lot of different things. Even our handrails are all over the map. The designs, configurations of our projects are typically a collaboration. Architects, homeowners, metal fabricators all contribute. The stairways are almost never just simply circular in shape. The profiles, species, balusters, and connection methods all vary widely. And every project has a strict budget.

The stairway with the twisted balusters was made of white oak grip rail and reclaimed spruce balusters. The stairway with the limestone treads handrail was made of white oak grip rail and 1 1/8" square solid bronze balusters. The dark stairway with the killer chandelier was made of walnut treads and risers, sapele skirts and grip rail and forged steel balustrade.

Every one of these examples took weeks to collaborate on the design. Size of every part is questioned and modified, shapes of all transitions are looked at. Somehow I just do not see a canned solution working all that great. I will say that a 6 axis machine with tool changer would be way cool. But as it now stands, all of my machines are paid for and I do not worry too much if something is setting idle. The peace of mind is worth something.

From contributor P:
You guys are the rocket scientists of the wood industry! I remember when I got into the CNC thing, a stair guy came over and played 20 questions about CNC, but at his shop he was very secretive about his alchemy. Thank you for sharing.

Contributor B, what math are you using to arrive at your solutions? Are you profiling the handrail on a shaper?

From contributor B:
You asked about the math. Let me tell you, it is not pretty. When we were carving these rail billets by hand, I figured each part using math and some drawing. For the last 3-4 years I am simply modeling all of it on the drawing programs. In a way it is figuring the math visually. They used to call it something like dimensional geometry.

One of the challenges that we have experienced is that the site conditions are not what they are supposed to be. For example, a circular stair is not really circular. Or the rise of a stairway varies. To address that problem, we purchased a digital measuring device called a "proliner." It is capable of measuring pretty much anything in 3D. It produces a DXF drawing/point cloud while you are measuring. Accurate to .015" over 40 feet.

So for the handrail for the stairway in the picture below, the process went something like this. The project was 800 miles or so from my shop, so I flew out, taking the proliner with me, to gather field measurements. I spent around 6 hours on site measuring and a few hours in the hotel looking at the drawings to ensure they looked good and that I got good field measurements.

I flew back home. It took the client about 6 weeks to finalize the design and cut us a deposit check. During that time I did not look at the job or the drawings at all. Once we got the deposit, of course the client wanted the handrail as soon as possible. So we fabricated all of the pieces in our shop. Level turns, straight rail, transition pieces, helical pieces and a lamb's tongue to terminate the rail. The rail started in the basement, up one flight of circular stairs to the main floor, traversed that floor with a level turn, went up another circular stair that transitioned into a section of straight rail, continued up the straight stairs and transitioned into a 2nd floor guard rail that was straight for a ways then had 3 level turns of differing radii. Whew!

One of my journeyman carpenters and I drove to the job site and installed the rail and the 1 1/8" square bronze balusters in one run. We did our end zone dance and drove home. I just could not have done that job without the digital fabrication methods I have described. The clients were happy and so am I.

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Here is a final picture of that handrail where it starts in the basement, with a lambs tongue.

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From contributor A:
Did you have any formal training in CAD/CAM drawing or was this knowledge all gained the hard way? Your work is absolutely first rate.

From contributor U:
Didn't used to work for NASA, did you?

From contributor J:
I'd really rather be compared to an 18th or 19th century woodworker than a rocket scientist. Today our machine technology is much, much better, but are we? Whenever I start feeling prideful about some of the work I've accomplished, I run across a real "gone with the wind" staircase someplace.

Most of the work being done today (including mine) is plain and repetitive compared to the highly stylized, handmade woodwork of the past. Most of our work is but a poor or cheap impersonation of these classical period pieces.

One of the companies I am currently associated with is working hard to develop robotic manufacturing systems to produce stair and handrail components. Their move is now away from simple CNC to fully automated robotic HOA.

This is rocket science that will undoubtedly blast off and leave me far, far behind. Me and my hammer will become a dinosaur display. This is another slippery slide that we're all working on today. I ain't so proud.

From contributor B:
Contributor J, methinks you are too harsh on yourself. All of us are a product of the water we swim in. It's that simple. If you lived back in the day, you would have been producing the products that your clients wanted back then. And in the future you will also produce the products your clients want, or you will be a dinosaur, as you suggest.

There is no value judgment in any of this; it simply is how it is. If you are producing work that is of good quality and you are supporting yourself and your loved ones, you have every right to take some pride in that. And if we can have some fun and friendships along the way, we are living the dream.