The PTC Guitar

Finished Guitar.

Iroko Hardwood frets - Oak Neck.

This is probably one of the hardest projects I have ever encountered. It hits you from all angles and continues to beat you into submission at every turn. So don't take it on lightly unless you are determined, used to painting yourself out of a corner and a masochist.

This is a labour of love not a ready to go project.

The first severe learning curve was Pro-Engineer it in itself is a very powerful and initially evasive piece of software but like its predecessor Pro-Desktop it does start to get easier as you clock up the hours.

The shape of the guitar has been governed by the originators of the drawing i.e. PTC. The body of the guitar is based on the PTC logo.

The neck has the Pro Engineer logo cut into it and the gear head is intended to be the wildfire profile.

Step 1. Choice of materials.

Iroko was chosen for the body to give a number of properties - Good machining, Good Colour and finish.

The neck was initially made from oak but it has a very stringy nature when machining so it was replaced with ash in the later models. (Five were made in total.).

The neck needs to take the pull of all six strings without bending. A back strut helps it with this by transferring some of the bending stress into compressive stress.

The fret board was made from Sapielle to give a nice depth of colour.

Step 2. Send the files from Pro-Engineer.

The files were exported in high resolution STL format to be imported in GEOCAM.

Step 3. Machining.

It was evident that the very rounded shape or the body was going to make machining eventful at best.

It was elected to machine the pocketed side of the body first so that the holes used for the Humbucker Pickups could be used as locators for pins on a jig to ensure the second side was machined in line with the first.

Step 4. Machining side 1 of the body.

Due to the STL being not being positioned for the best use of material the first test was done in blue foam. This allowed us to place a template over the finished foam to find the smallest wood blank that could be used whilst leaving the wood grain more or less in line with the neck.

The blue foam was used then to locate the blank before it was clamped for each of the four copies..

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Step 5. Machining side 2.

This was undertaken using the jig discussed earlier and double sided tape the curved nature of the first side made the hold very tenuous and care had to be taken not to over cook the matching which would result in movement or detachment of the block.

The jig allowing a fixed offset to be entered to ensure the two halves match.

Multiple machining locations.

Machine layout (Jig not included).

This picture is displayed to show how multiple jobs can be setup at any one time on the same machine. Using either a datum offset or defining the position as a fixture allows drawings to be machined at any location on the bed.

The neck was also machined in two steps, the first being cutting the fret side of the neck out of the block.

then the second on a location jig again using double sided tape..

Finally the fret board was made by sticking the 10mm thick blank to a wooden jig with marker placing using double sided tape.

The fret cuts were made with an engraving bur that was conical and finished at about .2mm.

Using the Boxford tool definition system it was possible to define the tool and make the cut speed slow enough to allow the waste to be ejected before the tool became hot. It was a slow process but rendered fret slots that worked first time with the fret wire.

The facing was made from laser cut acrylic sheet.

Finished Body.

Neck With Frets.

We are awaiting a finished fully strung guitar from PTC and as soon as this arrives we will add the pictures to this project.