You can also remove the appropriate faces in the component before exploding.
@Box I’m getting closer. I did a 64 sided circle for 16 steps, but when I extruded the curves for the handrail, the outer curves don’t quite line up and the inner rail has a jagged appearance. I also have a lot of hidden edges, even though I allowed for 4 segments for each tread. I also can’t use the Outer Shell option as it gives an error message that the components aren’t solid? I manually hid the lines, but don’t think this is the best way to do it. Curious why the inner handrail isn’t working like the outer rail. I’ve attached my model if you wanted to take a look. Thanks so much again 
SPIRAL STAIRS 2.skp (164.6 KB)
Close, but a bit of inaccuracy is throwing it off.
Go to View/Edge Style and untick Profiles.
Go to Window/Model Info/Units and Untick Use Length snapping.
Go to Camera/Field of view type 35 and hit enter.
Now you don’t have thick lines throwing things off, forced inaccurate snaps and a view that isn’t distorting the circle.
You say you started with 64 for 16 steps, but then your 16 steps are more than 360 deg and have 5 and a bit segments, and are ever so slightly not 30 deg nor flat. There is a tiny stray edge that is making them not solid. It’s also not a good idea to hide edges, you can soften them and turn their visibility on and off, but actually using hide on them can lead to problems.
Here you can see I quickly unhide any edges you have hidden and I remove the stray edge. The diagonal on the step itself is telling us it isn’t flat.
I would start again and try to be more accurate, easier than trying to fix it.
The thing with the number of segments is pretty important, you want to use the correct multiple for the number of stairs so that the wedge is correctly aligned with the vertices of the circle and you need to pull out your circle on axis so that everything lines up.
See how the segments of your arc are not all the same.
It can also be handy to rotate your original circle by half a segment, this makes the two end segments half the others but perpendicular to the edges, useful for follow me among other things.
Realistically you may want to change the number of segments on the inner as it does get a bit bent, or just use a pole in the middle.
That should give you something to work with.
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I made a simple one to make it a bit more obvious how the segments work.
This is a 24 segment circle, so it would make 12 steps in 360, 3 steps is 90, 1 step is 30 and one segment is 15.
So you need to calculate the number of segments that you want to make the number of steps of the appropriate size.
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When I do an operation like this I find the center of my arc bows outward which pushes the walls out of plumb. I can fix it by dragging the upper surface back into position piece by piece but is there a way to keep the walls plumb that I am missing with this method?
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@Box makes sense. Thanks very much. My stairs are now solid components, but even when I select the Outer Shell it still doesn’t remove the extra lines. Is there an extra step that I am missing?
It’s just softening.
I found an old file in my archives. It may gives you some ideas.
Spiral case handrail.skp (1.3 MB)
Not that I am immediately aware of, it’s not a method that is particularly accurate, but is a simple method for working without extensions. I vaguely remember a conversation, probably more than a decade ago, at Sketchucation on this subject and the general consensus was something along the lines of, if you want that shape use curviloft.
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If you want to avoid the bulge and make these accurate with plumb walls a manual stitch is pretty straight forward. This is with 2 segments, 4 would mean 3/4 then 1/2 then 1/4 etc. This is also a good use case for the new Stamp option of the move/copy tool, double tap ctrl to get the stamp, you can see the tiny icon change. You need the first segments to allow the pull up, otherwise it will drag the corners.
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@jean_lemire_1 thanks very much for the file. Greatly apprecite it
@Box thank you so much for all your help and assistance. I have finally created what I was after and am very happy wih the outcome. If it wasn’t for you taking the time to go through all this I would have been really stuck. Many many thanks again. This is what the spiral stair case looks like
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Looks good, well done.
There is an interesting progression of information in this thread. It is often difficult to condense everything into a single answer.
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I like how you intuitively found the halfway height for the center edges. Basic stuff that one needs to remember to save effort.
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