I’m cutting a guitar body that is 1 3/4 thick. I’ll be cutting it with a 1/4 up cut bit but I’m wondering what length I need to be using.
You need the bit extended shaft to be minimum 1-3/4" long. The cutter length only need to be larger than your depth per pass value.
If you are making a fender style guitar, the deepest cavity ( the control cavity)would be 1.5" inches deep. You can buy longer bits at toolstoday.com. If you examine the drawings ,you can see dimensions that call out the depths for the neck, pickups, and control cavities.