Alternating Tread Stairway

[ururk]

(posting this for the third time... I sized my images down with the hope it accepts my post)

I've been building a workshop for several years now, and within the last year acquired a few Festool tools ("festools?). I had been coveting the KS 120 REB and just needed the weakest of excuses to get one - snagged a refurb last year to cut some 8" boards for my flooring - but it turned out to be a requirement to cut my stair treads. The other tool I got that came in handy was the ETS 125 REQ-Plus - this I purchased to sand the frame of my shop and ended up using it on these stairs as well.

I built these stairs as I wanted to minimize how much floor space it took - I won't be using these daily, although when in the shop I may end up using them multiple times.

Mockup with pine - wanted to validate the concept and verify stair tread depth. Made a few alterations to the final shape.

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Each step was CNC'd - being nearly 2" thick I was pushing the limits of my CNC (belt-driven Shapeoko), the 1/4" collet on the router.

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After CNC'ing, did a few operations on them - cut them to length with the KS 120 - my previous saw was a 10" delta chop saw - the KS... I know some people have issues with it but it's such a nice saw. Sanded with the REQ-Plus, routed the edges, hand sanded.

I pocketed each step in the stringers 1/4":

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Finished pocket

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This was a tough decision - mortise and tenon or screws. Then visible screws or screw+plugs. I decided on using HeadLok screws as they have a nice industrial look to them. I 3D printed a jig to hold my drill guide for proper/even placement. I used a ruler to align the jig with the pocket - I drilled from the outside of the stringer - was worried the drill might splinter where it exited.

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All the steps while I was coating them. I used Bona Traffic Naturale, three coats, sanded after the first and second coats.

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Installed, sans railing. Railing will be done... not sure when. I'm still putting floor boards in - but hopefully sometime this year.

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[woodferret]

That looks nice.  I had always like the look of those alt steps.

You probably already know this, but for sake of potentially others, one trick if you're hitting CNC limits is to just go deep enough to embedded its own templating profile.  Jigsaw that channel and then go to town with a bigger router.

 

[Muttley000]

Those look really nice, I also like the framing of your shop!

 

[ururk]

Those look really nice, I also like the framing of your shop!

Thanks! I did not make the frame (though I raised it with the timber framer) or put the foundation in, but otherwise did the rest. Much bigger project than I had conceived, and am still trying to finish it.

 

[jimbo51]

For me with uncertain knees some days, that design would be disasterous.

 

[Packard]

It looks nice.

My concern is that the stepping side is only supported on one end.  I remember cracking 3/4” pine boards with my fists when I took Tae Kwan Do.  I would worry that a heavy adult might snap off the tread.

Of course other species might be less prone to cracking, but it is just a few inches wide and probably not as wide as the punching boards we used to use.  It looks thicker.  But still, I would worry.

 

[ururk]

For me with uncertain knees some days, that design would be disasterous.

I'm not certain what the long-term outlook will be with them for myself - but you walk up them step over step, albeit slower because the total stair depth is condensed. In 20/30 years - I might have to change them.

They can be ascended multiple ways:

Normal up/down, like a "normal" stair, walking the center of the stairway, touching every step
Descend backwards, a variation on the one above
Along one side, "walking" up them like a ladder, touching every other step
"Leap frog" by going one step at a time with both feet, touching every step, but requires coordination
Going up or down at an angle, requires less precision, sort of like marching in place, touching every step

With normal stairs I either take two steps at a time or run up them - these I am forced to walk like the average stair user... this is good from the perspective that, it's safer to ascend at a normal pace, but my usual "hyper" stair climbing is not possible.

 

[ururk]

It looks nice.

My concern is that the stepping side is only supported on one end.  I remember cracking 3/4” pine boards with my fists when I took Tae Kwan Do.  I would worry that a heavy adult might snap off the tread.

Of course other species might be less prone to cracking, but it is just a few inches wide and probably not as wide as the punching boards we used to use.  It looks thicker.  But still, I would worry.

The boards were finished to 1.8" thick - at the narrowest end each step is supported 4.25" (total depth is 5") - I also used a static load calculator to compute sag/deflection for a heavy point load. My primary concern was how wide the stairs were - alternating tread stairs are typically 20-24" wide - but I wanted them to match the floor joist opening, so the boards were cut to 31" wide. I would have preferred narrower, for a variety of reasons.

They are missing two things - a bar between treads and railings. The stairs aren't complete, but I want to finish the floor above before I move on to the railing.

 

[Packard]

I was not talking about the sag.  I think it is fine for the sag.  My concern was the wider section is only supported on one side. 

If you step on the wider portion near the unsupported side, I worry that it will split along the grain on the wide side. 

After looking at images of other applications, they all seem to have added support on both ends of the tread.

A failure of the tread could have serious consequences. 

Take a look:
https://www.google.com/search?q=alternating+tread+ladder+wood&tbm=isch&ved=2ahUKEwiok4GKh4j6AhU_n3IEHcfjAgYQ2-cCegQIABAA&oq=alternating+tread+ladder+wood&gs_lcp=CgNpbWcQDFDIPFjIZmCEnwFoAHAAeACAAWGIAeYGkgECMTKYAQCgAQGqAQtnd3Mtd2l6LWltZ8ABAQ&sclient=img&ei=t18bY-jbCL--ytMPx8eLMA&bih=712&biw=1121&client=firefox-b-1-m

Addendum:  Not all do add support:

 

[ururk]

I was not talking about the sag.  I think it is fine for the sag.  My concern was the wider section is only supported on one side. 

If you step on the wider portion near the unsupported side, I worry that it will split along the grain on the wide side. 

Now I understand. I've seen both styles (some sort of center support or free), but I'll look over my boards to make sure the grain doesn't run in a way that makes that split possible. I could always laser out some steel plate to reinforce the bottoms with.

 

[Packard]

My first thought was to drill a 1/4” diameter hole across the grain from front to the back of the tread.  Then run a threaded shaft and place the width of the tread under tension.  Then plug the ends. 

In my mind, this would keep the tread from splitting.  But I am not an engineer, so I am not sure.

Or drill a 3/4” hole and use a 3/4” long dowel to support the end of the tread.  That is actually the easiest.  Stack the treads and drill through both.  Glue and cross pin. 

But I am not sure it would look very elegant. 

That is the strength of your design.  It is spare and elegant.  It appears to have everything that is needed in a ladder and nothing that is not needed.  Adding anything that is visible would work against the elegance of the design.

 

[smorgasbord]

Just wondering - are you a lefty or a righty?
In snowboarding circles they talk about regular setup and goofy setup, where the regular is Left foot first and goofy is Right foot first. So, sorry to say, you're a goofy.

 

[ururk]

Just wondering - are you a lefty or a righty?
In snowboarding circles they talk about regular setup and goofy setup, where the regular is Left foot first and googy is Right foot first. So, sorry to say, you're a goofy.

Righty - both in hand and first foot on the stairs. That nomenclature probably explains a lot about me

 

[ururk]

I looked at the grain for each board - none have grain that goes from top to bottom perfectly - all the grain goes at an angle. I'll keep an eye on things though and if it seems like they are drying/warping badly (I bought KD, but still, wood is wood) will consider the threaded rod. There was a part of me that wanted to make the treads out of a laminated product (LSL's in particular look nice when viewed across the grain)... but anything other than a solid wood felt "wrong". I'm going to be covering the OSB on my walls as soon as my second floor is in, so there won't be any visible manufactured wood.