We get a lot of questions about lathe setup and calibration, and one thing that comes up constantly is people asking about cutterhead weights and whether they are using enough weight, or too little. The issue is that the weight itself doesn’t actually matter. What matters is the groove depth that weight achieves, and that’s what many people aren’t measuring. The entire point of cutting a record is making grooves in a blank. Everything else like your lathe calibration, vacuum setup, mastering chain all exist to support one end result, which is cutting a proper groove at the right depth with accurate modulation. If you’re not measuring the actual groove you’re cutting, you’re essentially guessing at whether you’ve achieved the most fundamental need of the entire process.
Cutterhead weight is just a tool to achieve groove depth. The reason people use weights in the first place is because it’s a convenient way to read downward force to the cutting stylus, but the relationship between weight and groove depth isn’t consistent across different setups. Your lathe, calibration, dashpot, suspension, blank material, stylus all affect how deep a given weight will cut. So saying ‘I use 12 grams’ tells you almost nothing about what’s actually happening in the groove.
We’ve seen people cutting way too light along with people cutting way too deep and in some cases with people who all said they were cutting with 15 grams head weight, despite both studios having a huge difference in grooves. This shows just how inaccurate it can be relying on weight alone. It’s also entirely down to the user to take the reading, and with spring scales this can be off depending on how the user reads it.
For plastic cutting (we use PETG) a good target for an unmodulated test groove is around 50 to 70 microns in width. This gives you enough depth to cleanly cut. But you need to actually measure this. Get a USB microscope, measuring groove depth is completely possibly on a £50, 1000x zoom scope and a reticle ruler (we have other blog posts with info on these). Make a test cut with no audio and measure the groove width, which is how we determine the groove depth. Then you know what you’re working with.
Once you know your actual groove depth trouble shooting becomes way easier.
We should add, we get asked for a lot of support work, and the first question you will likely get from us is ‘what is your groove depth’ and we would need a photo of your reading. Without that it’s likely impossible for us to help.