When cutting discs on a lathe, one often overlooked but important factor is the stylus rake angle—the angle at which the cutting stylus makes contact with the disc surface. In this context, we’re focusing specifically on cutting into plastic, not lacquer. Lacquer is a softer material and can tolerate a much steeper rake angle.
When cutting into PETG (the material all of our discs are made from), a rake angle of 8 to 10 degrees is typically required when using a heated stylus to remove material.
Since many users build their own custom cutterheads, each setup is unique. Similarly, though the Vinyl Recorder should have a hole in its torque tube at 8 degrees, meaning that when the head is parallel to the blank, your rake angle ‘should’ be 8 degrees, it’s worth checking as they are hand made, and variances can happens. Even small adjustments to the rake angle can significantly affect groove quality, surface noise, and stylus lifespan.
Measuring Rake Angle Accurately
Getting an accurate measurement of your stylus rake angle is very straight forward. Our good friend Joel over at Leadscrew Grooves shared a useful free tool that can simplify the process.
The tool is a Google Chrome extension called ‘Protractor’. Here’s how to use it:
1. Lower your cutterhead onto the blank disc.
2. Take a clear side-profile photo of your stylus in contact with the disc.
3. Open the image in Google Chrome.
4. Use the Protractor extension to measure the exact angle of the stylus against the disc. Make sure the disc is sitting nicely on 90 degrees on the protractor, set the green arm to 0 degrees, and the blue arm following the angle of your stylus. See the attached image for our example.
This method allows you to achieve a much higher degree of precision than simply relying on visual alignment. Once you have set your rake angle, you must fully recalibrate. Make sure that the stylus tip travels directly to the centre of the spindle, reset weights and finally measure groove depth. With PETG a depth of 50µm is a good place to be for playback and stylus wear. We have separate blog posts explaining how to do calibrate a VR here and measuring groove depth here.
