I had the idea of building a bench for our staircase. The design should be kind of modern and should fit into the metal/wood look of our stair.
During browsing Instructables I came across the "Modern Garden Bench" from Carlh86 https://www.instructables.com/Modern-Garden-Bench...
That was the inspiration for the build.

Supplies

AmazonYou need

Wood (at least 200cmx60cmx5,5cm)
- As an alternative if you don't have a jointer, you could use 5cm x 3cm or 2" x 3" wooden slats instead
36x 8mm Dowels
4x M8 threaded rod (40cm)
4x M8 nut with countersunk (sleeve nut, Amazon)
10x Felt glider with Nails (Amazon)
2x 2,5x35mm stainless steel torx screw (or any other good looking screw)
Aluminum rod 25mm diameter, around 70cm

Tools

Drill press+ drill bits
cordless screw driver
Sanding paper
Belt grinder
Metal saw

Additional not necessary:

Table Saw (Not needed if you use wooden slats)
Jointer (Not needed if you use wooden slats)
Lathe (You can use the drill press instead)

Step 1: Design

I did a few rough drawings on paper and used fusion 360 to get an Idea of the finished bench.
Actually I haven't used fusion 360 in the past to plan furniture, but it is never too late to learn something new.

There are many great turtorials out there, so I guess it is not necessary to do the same here.

I would like to point out one functionality I do really enjoy the most since it works perfectly fine, the "cutting"-tool. I used it to add the 45 degree angle to the beams. First I drawed overlapping rectangles, added a line to connect both corners and used the cutting tool to delete the unnecessary lines.

Since it was my first attempt to make a 3d part in fusion 360, I guess it came out very nice and it was only around one hour of work including building up know how. The real sketching time was only around 15 minutes, so it is definitively comprable to a colored drawing.

For me it turned out that I will use fusion 360 more often in the future regarding 3d projects, also the rendering function is great:-)

Step 2: Prepare the Wood

If you plan to use wooden slats, you can skip the first step:-)

First I searched for wood that fits in size and that looks good next to the oak stairs we have.
I searched the wood we had in our shed, but I had no idea which kind of wood it is.
My dad and me took a plank that fitted in size and assumed it to be oak.
(today I think it is something else, but it looks good, so I don't care:-))

The plank had to be at least 2m long, 60cm wide and 5,5cm thick.

We used the old table saw of my grandpa to cut the plank into 5cm wide beams.
First I tried to get the beams straight just by cutting all four sides with the table saw, unfortunately the wood was too warped, so that was not working at all.

I tried to figure out other ways to do the job, but later decided to search for someone with a planer. Fortunately one of my coworkers helped me out.
Due to the warped wood, the beams came out way thinner than expected. Best my coworker could do was 38mm x 50mm.

With all the beams beeing dressed, I used the table saw to cut the parts to length.

Step 3: Cutting

Now we have to cut the wood to the estimated length.
I chose the bench to be 1,20m wide and 44cm in height.

The Seating surface consits of 9 woods that need a 45 degree cut on both ends.
We need 10 long and 8 short pieces for the sides.

I cut the wooden beams for the seating surface to 1,20m length with an 45 degree angle on both ends. I used the tablesaw with an angle stop to get the 45 degree.

If you are not sure if the angle is correct, just do two cuts on a spare part an check if you get a 90 degree angle when holding two parts together.

The side parts all need a 45 degree angle, but differ in length. I chose the feet to be roughly cut to 46cm, the fine cut will be done after assembly. The short woods are cut roughly to 11cm, also will be fine adjusted later.

After cutting you should have:

9x wooden beams with 120 cm length
10x wooden legs with 46 cm
8x wooden side parts with 11cm

Step 4: Build the Frames

It is time to build the frames of the bench.
To get more physical strength I decided to to a dowel joint with two Dowels for each frame.

At this step you should be sure about the design! It is more or less the last step where you are to change the look by laying out all the matching pars and mark all the parts that will be glued together later.

First I marked two lines on all miters to make sure that all Dowels are placed correctly. Then I adjusted the table of my drill press to get 45 degrees (so that I can drill 90 degrees to the miters)
I then built a quick jig to make sure to always hit the same spot and just repeated that step for both holes and all parts of the bench.

After that I put a 8mm Dowel with glue into each hole and pressed the parts together by using screw clamps.
Make sure to get the correct 90 degree angle by measuring the length of the top and compare it to the bottom length, or at least try to do the same mistake on all frames:-)

I repeated that process and built nine frames, five with long, and four with short legs.

Step 5: Build the Connection

To connect the frames with each other I used an 8mm metric threaded rod.
I wanted the connection to be invisible from the front view, but it should be possible to disassemble or readjust the bench if the wood would shrink.
Therefore I decided to use a stainless steel countersunk nut that will be visible from the back.

To make the front connection I drilled a 3mm hole, 10mm from one end, in the middle of the threaded rod that will be used for a holding screw that stops the rod from turning or beeing pulled out.

Next was to drill the holes. Therefore I layed all frames on the floor so that they are aligned perfectly and marked four lines where the parts will be connected.
Make sure to keep the correct order, since you have to be sure about the first frame at this step!

I again used my drill press to drill the holes with an 8,5mm drill bit into the frames that later will be the middle of the bench.

The first and the last frame receive a different treatment.
The holes for the threaded rod in the first / front frame must only be drilled around 30 mm deep. On the same height, a 2mm hole must be drilled from "inside" the frame.

The last Frame can be drilled with 8,5mm all the way through, but from the back, a 13mm hole for the countersunk nut must be drilled. After that, the countersink has to be drilled so that the nut sits flush in the frame.

With all the holes drilled, we can prepare the aluminum distance rings.

Step 6: Prepare the Aluminum

It was time to prepare the aluminum and cut it to the desired length.
In my case I had the possibility to have access to a Lathe, so it was kind of easy to do that.

First I drilled a hole of 10mm diameter in the middle of the aluminum rod, therefore I used a center drill bit first and slightly increased the size of the drill bit until it was 10mm.

If you don't have access to a lathe, you can drill the holes with a drill press also, just make sure to secure the aluminum rod perfectly! Also I would cut the longer distance parts before drilling.

After I was finished at the lathe, I used a metal saw to cut the rod to the needed length:

16x short distance rings, cut to 10mm width with a Center hole of 10mm.
8x longer distance parts, 58mm long with center hole 10mm (2x 10mm distance + width of the wood, in my case 38mm).

Pro Tip: :-)
If you mixed up the frames a bit, you have the possibility to change the length of the aluminum parts to get the frames perfectly aligned. Be aware to note the length of the parts to not mix up during the assembly.

In my case I had a various length between 57mm and 59mm

Step 7: Finish the Parts

Now it was time for the first assembly. I recorded the process for the finished bench in the last step, so feel free to have a look there.

After that I had to cut the feet to the finished length. Therefore I used the table saw and set the fence to 44cm.

The bench must be placed on the short side on the table saw and be pushed sligthly through the blade. Repeat that process for the other side to make sure that the finidhed bench is perfectly aligned.

I don't have photos of that process since it was kind of dangerous. If you don't know how to cut the feet to the desired length, just mark the same length on every frame and disasemble the bench to cut every frame independently.

To finish the parts I used 150 grid sanding paper with my band grinder to get a rough finish on the parts. Keep in mind to follw the grain! I also used the belt grinder to get a small round edge on all parts. I finished all parts with my 220 grid sanding paper by hand.

After that I applied the same high solid oil that was used for our stairs. Due to the fact that the bench was build for usage, the finish had to be sturdy. After two passes on each part, I was done:-)

All that was left to do, was to mount the felt gliders. I drilled a 1,5mm hole in each feet and used a hammer to attach the felt gliders to the feet.

Step 8: Assembly

The assembly process was pretty straigthforward.

First i layed the front piece on my trestle and mounted the threaded rods. Then I placed two short distance parts on the upper rods and kindly pushed the next frame on the rods.

Now again put two short distance parts on the upper rods and put two of the longer ones on the side rods. Take the next frame and push it simultaneously down on all four rods.

Just repeat that process until you have to put the last frame on the bench. It could be that you have to apply a bit of force to get the counternut in place. Use an allen key to tighten the nut and secure the bench.

Congratulation, you are finished!