Four serial ports in one bracket

When I build my new server I found that I had plenty of PCI and PCIe slots, but not enough brackets. The only way to fix this was to have more then two serial ports in one bracket. Multi serial cards with breakout cables do exist, but they are expensive. So I build my own.
I used a bracket with one DE-9 and one DB-25 connector. The DB-25 is used for three serial ports with one common ground. For ground I used the central pin, which is pin-7. The DB-25 is connected to three ribbon cables connecting to a (six port) multi serial card. A DIY breakout / fanout cable connects to the DB-25;

               Bracket
               ┌──
               │
 IDC10--------DE9
               │
 IDC10-----\   │    /-----DE9
            \  │   /
 IDC10--------DB25--------DE9
            / ♂|♀  \
 IDC10-----/   │    \-----DE9
               │
      Ribbon       Breakout cable
      cables

Internal

     ┌───┐
  2  │o o│◁ 1
  4  │o o└┐ 3
  6  │o o │ 5
  8  │o o┌┘ 7
 10  │o o│  9
     └───┘    IDC-10 Female
  1. Find out which IDC-10 pin corresponds with which DE-9 pin (there are only two standards).
  2. Cut three 9-wire ribbon cables to length and crimp an IDC-10 to each, not using pin-10.
  3. Connect the three ribbon cables to a male DB-25, using pin-7 as a common ground for all three cables. The table below shows a practical way of doing this. The ribbon cables are labelled 'A', 'B' and 'C';

Pin side view

                       1
     1 2 3 4 5 6 7 8 9 0 1 2 3 
   ─────────────────────────────
   ╲ ● ● ● ● ● ● ● ● ● ● ● ● ● ╱
    ╲ ● ● ● ● ● ● ● ● ● ● ● ● ╱
      ───────────────────────
                  2
      4 5 6 7 8 9 0 1 2 3 4 5
PinCableSignal
Top row
1 A DCD
2 A RXD
3 A TXD
4 A DTR
5 B DCD
6 B RXD
7ABCGND
8 B TXD
9 B DTR
10 C DCD
11 C RXD
12 C TXD
13 C DTR
Bottom row
14 A DSR
15 A RTS
16 A CTS
17 A RI
18 B DSR
19 B RTS
20 B CTS
21 B RI
22 C DSR
23 C RTS
24 C CTS
25 C RI

Solder side view

Except for ground, one cable connects to the left (C), one to the centre (B) and one to the right (A). This way the physical layout is more or less the same as that of the original IDC-10 to DE-9 cable, so you can copy most (all except ground);

           1
     3 2 1 0 9 8 7 6 5 4 3 2 1 
   ─────────────────────────────
   ╲ ∪ ∪ ∪ ∪ ∪ ∪∪ ∪ ∪ ∪ ∪ ∪ ╱
    ╲ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ╱
      ───────────────────────
                2
      5 4 3 2 1 0 9 8 7 6 5 4

Corresponding signals;

        C        B        A

     D T R D D T G R D D T R D
     T X X C T X N X C T X X C
     R D D D R D D D D R D D D

     ∪ ∪ ∪ ∪ ∪ ∪∪ ∪ ∪ ∪ ∪ ∪
      ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩

      R C R D R C R D R C R D
      I T T S I T T S I T T S
        S S R   S S R   S S R

         C       B       A

External

Connect three 9-wire shielded cables to male DE-9s. Connect the shield to the connector shell;

Pin side view

     1 2 3 4 5
   ─────────────
   ╲ ● ● ● ● ● ╱
    ╲ ● ● ● ● ╱
      ───────
      6 7 8 9
PinSignal
Top row
1DCDData Carrier Detect
2RXDReceived Data
3TXDTransmitted Data
4DTRData Terminal Ready
5GNDGrouND
Bottom row
6DSRData Set Ready
7RTSRequest To Send
8CTSClear To Send
9RI Ring Indicator

Solder side view

Connect the other ends to a female 25-pin connector. One cable to the pins at the left (A), one to the centre (B) and one at the right (C). Connect all three ground wires to pin-7;

                       1
     1 2 3 4 5 6 7 8 9 0 1 2 3
   ─────────────────────────────
   ╲ ∪ ∪ ∪ ∪ ∪ ∪∪ ∪ ∪ ∪ ∪ ∪ ╱
    ╲ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ╱
      ───────────────────────
                  2
      4 5 6 7 8 9 0 1 2 3 4 5 

Corresponding DE-9 Pin numbers;

        A        B        C
     1 2 3 4 1 2 5 3 4 1 2 3 4
     ∪ ∪ ∪ ∪ ∪ ∪∪ ∪ ∪ ∪ ∪ ∪
      ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩ ∩
      6 7 8 9 6 7 8 9 6 7 8 9
         A       B       C

Connect the shields to the connector shell.