Saturday, August 2, 2014

Fourteen More Guitars

I've been doing more CNC routing of Wallace Detroit Guitars. Here are some details of the setup and cutting.

The blanks are made from wood recycled from abandoned Detroit houses. The wood is collected and scanned for metal fasteners by Reclaim Detroit. For the guitars blanks below the wood is sawn and glued up with the endgrain facing upwards. This makes the annual growth rings very apparent and creates a unique look for the guitars.


The blanks vary a bit in width and length. They are all exactly 1.76" thick. I had them panel sanded at B&B Heartwoods to get them just right.

The computer model which establishes the cutting has the origin at the bottom, center-line of the instrument. This allows me to precisely place the cut on each unique blank. Because the blanks are so accurately sized in thickness I cut the pockets as measured from the top. So when they are finished sanded (removing 0.01" of material) the pickups and neck are all aligned exactly right.

In order to set that on the router what's knows as the "NC offset" is used. For each blank the desired center point is measured from the edges.


Then the values measured are entered into the router's controller as an offset of where the 0,0,0 point in the computer model should align.

Sometimes this results in the guitar being centered in the blank.

Other times, in order to get the desired alignment, the shift means it barely fits. This really came down to if I wanted to lamination line to be centered, or a strip between lamination lines to be centered.

To miss defects (or sometimes remaining metal such as screws and nails on the outside of the blanks) I offset towards the top as well.

The variation in growth rings based on species and grain tightness make for some beautiful patterns:

The router has powerful dust collection so very few chips escapes the router bed during cutting. But there is also a very powerful vacuum holding the blank in place on the table. And with a down shear bit some of the chips remain in the cut groove. Even after the blank is removed!

These chips are quite fluffy - and almost no heat is accumulated in the tool.

They guitar is held within the blanks with small tabs. In this case I used 3/4" wide and 1/10" deep tabs. Here you can see two on the sides and one next to the neck pocket. These are easily broken away - especially because they are end-grain up.

Some of the wood is trim, rather than framing lumber. Below is a blank made from mahogany, walnut, maple, and cherry trim boards. It's also side grain so it has a much more conventional appearance.


Here's a sampling of the fully routed guitars:


Here's a video of the cutting process. Parts of the video have been sped up by a factor of 2.

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