How to set your router perpendicular to the table top

How to set your router perpendicular to the table top

This weeks Top Tip come courtesy of Jim Anderson of Texas.
 
One of the most important adjustments you need to make on your router table is setting the router perpendicular to the tabletop. If you don't have this set right the cuts you make will have slanted sides and any pocket you make will not be flat and look grooved. They will be made up of a series of ramped cuts. The biggest problem is you can't use a square to ensure the cutter is perpendicular to the table so you need another method. Fortunately there is a simple trick that will allow you to set the router exactly.

Here's how

After posting the video above it was noted that there is an error in the demonstration of how to adjust the Router angle. The video below covers the correct method to adjust the router with respect to the table as well as info on surfacing a tabletop for tramming the machine using a method that will eliminate the ridges caused by an untrammed router. This new video needs to be viewed after the one shown above as it provides supplimentary information.

Original comment prompting the above video

By moving the eccentric bushings your Z axis is no longer square to the table. 
The way to do it is surface the entire table with a small router bit with a small step over first. Remove the router and square the Z axis to the table using machinist squares.  
Re-mount the router and continue with the technique you showed but only adjusting the router mount to the Z axis.
Depending how much correction you made your parts may come out smaller or larger than predicted and have small steps in the sides.

Building the Jig

Photos and description courtesy of Jim Anderson


1. I took a piece of wood about 1x1x15 inch long 
2. Drilled a hole on one end to hold a straight shaft (3/8 dia.)
3. Drilled a hole on the other end to hold a pencil (1/4 dia.)
4. Drilled 1/4 dia. holes for bolts to apply clamping pressure
5. Slotted each end of the wood to allow flex for clamping
6. Used a 1/4=20 bolts for clapping pressure
7. Moved the router to the center of the mill table and Power Off the Mill
8. Placed the straight shaft in the router (I used a Forester bit)
9. Placed a pencil in the wood and the bolts and tighten to hold the bit and pencil
10. Slide the pencil to touch the mill table
11. Rotate the device 90 degrees and validate the gap under the pencil
12. Make adjustments to the mill so that the gap is the same for 360 degrees 

Pencil almost touching the table top

You can see here that the pencil is above the table top

The pencil is 1/4" above the table indicating the router is leaning to the left.

The router needs to be adjusted left and right back and forward until the gap remains constant under the pencil all the way around the table. Note that this process can only be done after the table top has been leveled at least once. A new tabletop could be sloping in any direction so an inital leveling profile must be run to flatten it with respect to the router.
The larger the distance between where it attaches to the router and where it is measured on the table the greater the accuracy so make it as big as practical.

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