Just finished putting in some new hardwood stairs in our house. They were unfinished white oak treads made by Young Millworks in Kentucky and stained to match the floors. Still need to do some touch up paint on the skirt boards, but overall it is pretty much done.
Before:
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The frame-up looks crazy and bending a rail is no joke, the ballusters are a nightmare but when finished, it looks incredible. Makes one ask the obvious -- why aren't all stairs curved?
A bit bigger than your typical wood working project and not even that common in homes not built by me, here is the underbelly of a wood-constructed circular staircase. It forms a quarter circle with inside radius of 7-feet and tread width of 4-feet. Look for my finished staircase picture also...