When I was satisfied that the pickguard CAD drawing met all my design criteria, I exported the shape from TurboCAD as an STL file for import into MeshCAM which is the software utility I use to generate the machine toolpath as GCode (a long list of XYZ rectangular coordinates plus information on feed rates). I cut numerous pickguards with minor changes throughout my Brian May Red Special build project and I settled on a three-stage process which works well on my system. This involves the following steps:
- Cutting the apertures which have 90 degree edges (i.e. for the neck and bridge, pickups, parallel slide switch actuators and potentiometer shafts) using a 2 mm diameter single flute solid carbide end mill. These toolpaths are produced using MeshCAM.
- ‘Drilling’ countersunk screw holes using a 2 mm diameter single flute solid carbide end mill. I have developed an Excel spreadsheet to manually compile this entire GCode toolpath using the G02 command to cut pure arcs. This has three advantages over using CAM software: it gives me full control over the dimensions of the conical countersink and the cylindrical screw shaft hole, saves a lot of lines of code and can be easily customised simply by changing the XY co-ordinates of the screw position.
- Cutting the pickguard outer edge. To obtain a 45 degree bevel, I use a 90 degree carbide V-groove cutter at 0.25 mm depth per pass to minimise vibration. The cutter kerf is around 1.0 mm even with a sharp tip so I make allowance for this in MeshCAM by calculating the toolpath with a 1.0 mm cutter.
The embedded video which is speeded up 20x illustrates the following CNC cuts:
- The three-stage CNC cutting process of the pickguard itself from 3 mm gloss black perspex
- The neck pickup surround from 2 mm gloss black perspex
- The back plate which covers the tremolo cavity from 3 mm dark red translucent perspex thicknessed down to 2.5 mm using a 6.0 mm two flute solid carbide flat end mill
- The mounting plate for the six Switchcraft 46200LRX series DPDT parallel slide switches from 3 mm gloss black perspex
I use a spindle speed of 7,500 rpm with XY feed rate of 1000 mm/min and Z plunge rate of 30 mm/min with both cutters. The cutting depths per pass are 0.25 mm for the outline using the 90 degree V-groove bit and for the 2.0 mm diameter single flute cutter: 0.50 mm for apertures and 0.10 mm for the fine rounded over cut on the pickup surround edges.
I must have bought almost every brand of Brian May Red Special control knob available over the years and have found that none of them have every dimension or aesthetic detail authentic to the ones Brian made himself for original Red Special. That said, I was pleased that Brian May Guitars changed the ones which they sell for a very reasonable £19.99 plus shipping from a shiny version with a sharp knurl to the version fitted to the Brian May Red Special Super guitar. These are the correct dimensions, have a knurl with the correct spacing which is the full height of the central grip and have a dull finish. I recommend that you buy the official versions but please bear in mind that they are designed to fit a potentiometer with a knurled shaft and require drilled out to fit a 6 mm or 1/4″ (6.35 mm) plain shaft potentiometer such as the Bourns PDB181-GTR02-254A2 items I use on all my projects. I used my mini drill press to prepare them as follows:
- Degreased the cast iron bed of my mini drill press with acetone or isopropyl alcohol.
- Adhered the top of the knob to the drill press bed using low viscosity cyanoacrylate superglue.
- Centralised the chuck in the shaft hole by eye using a 5.5 mm solid carbide jobber drill.
- Changed to a 6.0 mm solid carbide jobber drill to bore out the hole.
- Changed to a 6.0 mm two flute solid carbide flat nose end mill to flatten the conical end of the hole left by the jobber drill.
- Changed to a 15.0 mm three flute solid carbide flat nose end mill to mill a rebate for the potentiometer upper securing nut.
- Released the knob from the drill press bed using an electric heat gun.
- Removed dried superglue with solvent and abrasion from a fingernail only.