Autocad + Laser Cutter + my old staircase replacement

Something completely different now (and maybe for a number of subsequent posts).
And what could be the relation between Autocad, one Laser Cutter and my old stair?
Well I own an old house erected back in 1918.
Since 2001 I have started to renovate the house and due to financial and time restrictions this effort will last maybe for a number of years in the future.
One critical part in this renovation project was a wooden internal stair leading from the entrance of the house up to the first floor. (Height between floors 4137mm , a rather tall house!)
The stair has suffered heavy injuries since its life has been passed between two world wars and a lot of foreigners who rented the house in the mean time.
The first idea was to make a copy of the existing stair, wooden again, so I collected offers from local carpenters.
All of them asked a price around 6.000 Euros.
I agreed with one of them and i designed the stair using Autocad.
After 15 days I went to inspect his work and I see a stair completely different from what I have designed. (All corners had been converted to arches in a strange combination of country and gothic styles).
After not so good words between me and the carpenter I decided that I wanted something different.
A sturdy staircase with a modern, open, light and stylish look, using simple materials such us steel frame combined with wooden stairs and the ability to assemble it as a D.I.Y. project during my summer vacation.
The economic consideration was a factor too. What if this stair cost me around 4.000 Euros? Why not spent the rest 2.000 somewhere else in the house?
With these considerations in mind I started to design the stair using Autocad.
Partly because I wanted to show my Mechanical Engineering ability and also to experiment with the accuracy of the laser cutter, I decided for the assembly to be a completely bolted one. And as you will see in the next posts there were a lot of holes that should be concentric each other in order for the bolts to pass correctly connecting the staircase parts each other .
The photos from the laser cutting phase and also from the erection phase are in my Nokia N73.
I present here the drawing I prepared for the steel frame of the stair.

Material:                            St 37
Thickness:                         10mm
Length of the longer piece: Around 4800mm

In the drawing you can see also part of the railings and also the interconnecting pieces for the parts of the frame.