I dislike knife blocks with dedicated slots for each knife—they never fit what you have, and there's always a slot missing or an empty slot. So, I took a look at various designs out there and tried to come up with a solution that works for any knife.

The design utilizes slots where you can insert your knife. The slots are flexible and grip the blade or utensil (like a meat fork or a cleaver) to hold them in place.

Since I love Gridfinity, I made the block compatible with it. For those who don't want to use Gridfinity, there's a flat bottom for use with regular felt or rubber feet.

Size of the block is 5x3x35U (~ 126x210x210 mm)

BOM

• Roughly 600 to 750 g of generic filament (PLA, PETG, ABS—whatever floats your boat)
• and 150 g of flexible filament (TPU or similar is recommended, but PETG works. In case of an emergency, you can use PLA).

Printing

A print profile for Bambu Studio is included—here are a few hints:

• body
  Print it however you like. Two walls are okay, but if you want a solid piece, go with three walls. Ironing on the topmost surface is a nice touch.
  
• bottom
  there are 4 options: you need to print only one: either gridfinity or the regular bottom and a drainhole or a closed bottom
  
• feet (optional)
  There are four options; you only need to print one: either the Gridfinity or regular bottom, with a drain hole or a closed bottom.
  
• top inserts
  This is a bit tricky since not every knife has the same thickness. I experimented a bit and found that the following configuration works best for a broad range of knives.
  
  
  middle and bottom piece: 0.4 mm (hollow) from a rigid yet flexible filament—I recommend PETG or ABS here. PLA works, but I'd avoid it since it tends to creep under load.
  
  topmost piece: 0.8 mm (solid) from a flexible filament like TPU, with 3 walls and a bit more infill than usual—ironing gives a nice touch here as well.
  

In my case, I have thin carving and boning knives that weren't held firmly in place by the upper two layers, but I also have a cleaver in the block that needs slightly wider gaps.

If in doubt, I recommend printing a few test pieces (just a slice of the models provided) to see what grips your knives best. If you find that two layers are enough, you can print the spacer piece and call it a day—but you can always add another layer later.

Assembly

All parts are designed to be friction-fit with tight tolerances in the corners. This design is necessary because the long side of the block would flex and not hold the pieces in place without glue.

Beware that the top spacer pieces can be very difficult to remove once they are pressed in. If the friction is too high, use a deburring tool or a thin blade to remove some material until they fit properly.