Tread Return Details for a Free-Standing Curved Staircase

Here's a complex and detailed discussion of stair tread fabrication for a high-end custom curved staircase, open on both sides. November 26, 2007

I am building a curved freestanding staircase on-site. The treads will have returns on both sides. What do you think is the best way to rout the tread returns? I've built curved stairs with no side returns before, but this is my first time doing returns on curved radii. I think I would prefer mitered returns because the grain makes the tread look more professional, but I don't know what the best tool and/or method for the job is.

Forum Responses
(Architectural Woodworking Forum)
From contributor H:
We cut them with a band saw or by hand. Round them over and sand the tread after they are attached. This has worked for us for many years.

From contributor D:
Make a male and female template and use a pattern bit to route the tread and return.

From the original questioner:
Thanks. This would give me a bullnose on the tread itself, but the wood pattern would look off on the curved sides of the tread. I've seen treads where the returns are mitered and glued on with the pattern side exposed on each side of the tread and was wondering if there is a simple way to do that.

My other thought for bullnosing the tread itself was a long radial arm attached to a router with a pivot at the center of the radius of my curved stair. That would help me cut a near perfect radius on a tread template or each one of the treads themselves. If I went the template way, I would use the template as a guide to cut and rout the rest of the treads.

From contributor D:
The template cuts a sweep on the end of the tread, then the matching template cuts the same shape in the return material. It comes off looking mitered with a .25" radius at the base of the miter.

From contributor H:
We are losing something in the post here. The treads are longer at each end by the amount of overhang you desire. In our case a 40" wide open 2 sides curved stair will have treads that are 42 1/4" long. We make one template and stay true to it. Mitre both ends of the tread and apply matching returns.

A steady hand on the band saw or shaper with template and bearing will work. I personally do not like the shaper method because it leaves the inside on the mitre return round. Too production-like for me. Perhaps someone near you with a CNC could cut them quicker and more precisely, but that would add costs.

I have always viewed curved stairs as a job that takes time. Much of it still is done the old fashioned way... by hand. Curved returns on treads is one of them.

From contributor R:
This is what I do. It's not too involved and is done right there, on site. First, scribe and fit the tread (I leave a 1 1/4" overhang nosing - it works out just right for the under tread trim), leaving tread about 3" or so long on the open side, or in your case, both sides. Since you are doing both sides, I would put a locating pencil mark on tread and riser. Scribe a line along skirtboard curve and a few inches along riser line, onto tread. Flip tread over, and from scribe marks lay out miter line from riser line. Now I use a 12" Dewalt slider, and I turn it to 45 and lock the slide, then put a spacer along fence (I think it's a 2 3/8", but spacer is somewhere in trailer and I'm not; you will want to use test piece to figure yours out). Then putting tread bottom up on MS, I cut down on line, cutting a 45 that is long on bottom, but just to line on top of tread. I then take a piece of a cutoff from tread (since curved treads are pie shaped, I make wide blank and cut 2 treads from 1 wide glue-up, scrap in center is return material). Cut return material to about 3" or 4" wide and a few inches over long. Miter one end.

Flip tread over (top side up), match up miter in return material to miter in tread, leaving daylight between miters (about a playing card). This is because after you cut, the return is going in a kerf width distance. Clamp return stock to tread (I use those small vise-grip pincher clamps). Flip back over to bottom up (where your pencil lines are). Cut along curved line with a jig saw, from rear tread to miter, cutting both pieces at same time. I didn't mention it, but after fitting return material, cut it to be 1 1/4" longer than tread width, and you either need to draw continuing curved line on return overhang, or eyeball it (I eyeball it). I use Bosch 101B blades (I think), as they are coarse, not much set, and are thick and hardly flex. Return should fit right in like a glove and be 1 1/4" longer than tread width.

Temporarily lay tread where it belongs, hold return to it and scribe a line 1 1/4" out along skirtboard (I have a 2" piece of 1" square wood that, when I tape a short pencil to it, gives me a 1 1/4" offset, for scribing). Then either using a small band saw or jig saw cut to line, you should have a proper return, 1 1/4" wide and 1 1/4" longer than tread width, and curved to stairs.

Put glue on tread end and return (I use TB II), pre-drill and install 2 #6 or 8 finish nails in return (hand drives). Put one nail in just rear or miter and second about 1 1/2" farther back (still allows tread to move). It is important to center nails on thickness of material, and sink deep, as you still have to route. Fill nail holes, in about 5 minutes wipe off any glue squeeze, and sand joint (sanding dust will fill any not-perfect fit, but it should fit right). And of course sand smooth the side of return.

I do a few ahead to give glue time to set, then route a 1/2" radius around tread and return (generally do some climb routing about the miter area to keep from blowouts). If all went well, tread should fit right in there with pin fit along sides where return goes past riser. After a couple for practice, they should be right on. Curved returns are more time consuming (hope you allowed money for this), but after a couple you get into a groove and it moves faster.

From the original questioner:
I think a CNC machine would be my next investment, but you are right, contributor H - curved stairs take time and patience. And yes, the treads will overhang 1 1/4" on all sides.

I am about to start the project and I am all for figuring out new methods, especially with these kinds of projects. I'll keep you posted on how it goes. I think I have to improve my jig and band sawing skills for this one.

From contributor R:
I'm a big believer in using templates and such to make things easier. However, I have found that on circular stairs, even factory built under ideal conditions, once the rock and skirtboards are on, or just skirtboards on a freestanding type, the inside and outside curves have a way of not being exactly the same on every step. This comes under "sh#t happens." And to get the best in premium fit, there are still some things that have to be scribed and fit one at a time. After all, nobody installs a 20-30 K circular stair in a production home, and they get a little more particular on fit and finish on a 2M and up home.

From the original questioner:
You're absolutely right. My brother and I build 1m and up homes and I do the finish and carpentry. I've also noticed that the higher the price of the home, the pickier they get on the details. The stairs, however, are the first thing they fall in love with. A lot of builders go with the supported stringer curved stair, but nothing impresses people more than a free standing curved staircase. That's what really sets the house apart from its peers. Again, thanks for sharing your method with us. I think I am going to have to spend more time and give attention to detail on this one.