Miter Lock

Cabinet :: Fabrication :: Miter

If you decide to go the route of building a Custom Pinball Cabinet from scratch, one of the biggest fabrication challenges you will face is how to get clean looking corners…

Most of the cabinet edges will either be covered with some form of trim, or not visible except from the bottom or from the back. The features that can’t escape attention, however, are the two vertical edges of the front panel on either side of the coin door. For a professional-looking quality Cabinet, these two corners will need some form of mitered edge, and the feature of choice for Pinball Cabinets has been to use a “Miter-Lock”.

The front vertical edges of the Cabinet are the most visible, and need a mitered edge in order for the Cabinet to have a clean professional look.

The front vertical edges of the Cabinet are the most visible, and need a mitered edge in order for the Cabinet to have a clean professional look.

A Miter-Lock edge is created on a router table with a single Miter-Lock Bit, with the two panels of wood being passed through the cutter either laying flat or standing vertical. Below are a set of images showing a typical Miter-Lock Bit installed in a bench-top router table:

Miter Lock Bit

Typical “Miter-Lock Bit” installed in a bench-top router table.

The bit itself is like a typical 45 deg cutter, but with two distinct jogs in the middle. These jogs create self-interlocking edges when two pieces of plywood are cut horizontally and vertically.

The panels that need the Miter-Lock are the two sides (front-edge only), and the front panel (both side edges). Since the side panels are very large and unwieldily, it makes more sense to run these flat through the router, and run the smaller front panel vertically. See the pics below:

Run the small, easer to handle, front panel through the cutter vertically.

Run the small, easer to handle, front panel through the cutter vertically.

Running the front panel through the cutter vertically (above), and the side panel through flat (below), creates a mirror cut that is self-locking.

Larger cabinet side panel being run through the router flat, cutting the front vertical edge.

Larger cabinet side panel being run through the router flat, cutting the front vertical edge.

When done correctly, the Miter-Lock Bit will cut two mirror-image edges, creating a self-interlocking corner. This process should only be done by those who are experienced with the equipment and use of a router table. Aside from the typical set-up, the important adjustments for this cut are to get both the height and offset equal and matched to the thickness of your wood panel (in this case, 3/4″ 7-layer plywood).

Any mis-adjustment in height or offset will cause one edge to stick out farther than the other. Not a disaster, but does’t look as nice and could cause the overall dimensions of the cabinet to be skewed.

Below are a couple images showing how each of the finished edges should look, and how they fit together:

 

Example of how each Miter-Lock cut looks, and how the two edges fit together to create a self-locking joint.

Example of how each Miter-Lock cut looks, and how the two edges fit together to create a self-locking joint.

One final tip I have is how to avoid having the vertical edge chip out during the routing process. Now, in a perfect world, we would have the grain of the wood running vertical along the cut line. But, because our side panels are just longer than 48″, it’s not possible to lay out the whole cabinet in one sheet when the typical grain runs length-wise. (Stay tuned for updates, I’m working on a slightly more compact cabinet that will rotate the layout to match the grain).

Below are a panel of images depicting a method that avoids the thin top laminate from chipping out during the vertical cut:

To avoid having the top laminate chip-out, you can pre-score the cut line with an xacto knife.

To avoid having the top laminate chip-out, you can pre-score the cut line with an xacto knife.

Here are the steps to avoid chip-out (the first panel is an example of the disastrous results of cutting across the grain…):

  1. Using a same-thickness piece of plywood as a guide, line up a straight-edge ruler 3/4″ away from the outside edge. Bear in mind that the face of the panel we are cutting is the inside, the “beauty” side should be face-down.
  2. Clamp straight-edge to the panel, preferably at both ends, and preferably to the table as well.
  3. Using an Xacto knife, cut along the edge through the to laminate layer. This will be about 1/16″ depending on what grade your using.

Tip: The metal straight-edge is to the inside of the cut line. This means if you make a slight mistake with the Xacto, you’re only messing up a surface that will later be removed. It’s best to use a new, sharp blade, but with a new blade you always need to make your first cut with a VERY light hand, and then come back with several passes to get the cut deeper. It is very easy to get of track with a new blade.

Good Luck and Be Safe!