In this instructable I'm building a DIY Router jig that turns the Router into a thickness planner.

the simple MOBILE thickness planner can be used on any size of wood and on any length, Can be easily modified to match different widths or thicknesses (extreme sizes) and is portable - can be used on the spot of the project (eliminating the need to transport the slab/beam/whatever to the workshop and back).

Step 1: Available DIY Solutions

When coming to router jigs, there are lots of them, as can be seen in the following google photos search: https://goo.gl/irmR67 (see: https://youtu.be/Z9ECXZulTDU).

The majority of the jigs consist of a precise and solid frame, and a router that slides on a track and flatten the slab while moving.

Step 2: My Solution

After thinking on the requirements and constraints, I came to a conclusion that there's a jig that will do the job and will be portable and simple. The main concept is to take the zero "DATUM" from the table/workbench itself instead of taking it from the frame. this jig requires flat floor (quite common) - if there will be any issues with the floor ,they will be reflected in the planing result - so make sure to work on flat base !

I replaced the frame of the planer body with a small portable frame which is attached to the router itself, and move on 4 wheels. the wheels replace the sliders/bearings. The wheels height should be taken into consideration when building the jig to flatten a known slab, and the build is quite simple - as can be seen in the following steps: (1) Building the frame (2) Attaching the wheels (3) connecting the router (4) Starting to work.

Step 3: Building the Frame

As can be seen in the images, The frame is prepared from the following parts:

Two metal angle bars, cut to the required length (37 cm in my case)
Drills in the end of the bars in order to mound the wood plates (wheels base)
Plywood wheels plates

Step 4: Preparing the Router Mount

In order to connect the router to the frame, I removed the bottom plate of the router, and used it as a pattern for the holes locations on the frame. The 4 holes locations were marked and drilled in the bars, and the same bolts that connect the bottom plate connect the frame (4 x M4 bolts)

Step 5: Mounting the Wheels

Four (4) off-the-shelf casters (as can be found here: https://goo.gl/Zgtqeq) were attached to the frame, the usage of the SAME casters, mounted on the SAME level is the core of this jig's accuracy. so please be strict on that on any variation of this Jig.

Step 6: Full Assembly and Planing / Milling

The last step is to mount the router to the frame, using the same 4 bolts (4xM4 in my case) and milling a wood.

As can be seen in the photos, there's a freehand milling option in the wood, in exact TWO HEIGHT LEVELS (Could be more) while this feature is not optional using the reworked wood piece as a reference and also can not be achieved (free hand milling) using all kind of frame based jig mounts.

So, Summing the advantages of the DIY Router planing Jig:

Simple, DIY, and re-configurable.
Portable
Enable features that can not be achieved in any other jig (free hand milling, multiple level milling)
Spares the need for full size planer when using for small volume tasks.