1. ## Max Cut depth

Is there any general rule for calculating the maximum depth of cut for a bit of a given diameter? What effect, if any does feed rate have on this calculation? I am cutting mostly softwood, using aK2CNC 9650 machine, with a Porter-Cable 7518 router.

2. It depends on the material and the quality and accuracy of cut you want.

For prefinished 3/4" cabinet plywood I use a 3/8" mortise compression bit and climb cut almost the full thickness of the plywood at 12000RPM (spindle) feeding at 6 inches per second (IPS) leaving just 1/32" of the plywood not cut. I then conventional cut the last 1/32". This enables me to compensate for bit and machine flex. I use mortise and tenon joinery on my cabinets so this cutting accuracy is critical.

When doing 2.5D carvings, I sometimes use a 1/4" ballnose (other times a 1/2" ballnose - depending on the size of the carving) to rough cut and in soft wood will set pass depth to 1/4" to 5/16" at around 4IPS. In hard wood (bubinga for example) I might set pass depth to around 1/8" to 3/16" at 4IPS. If I'm cutting a part in alder with a 1/4" compression bit, I will set depth of cut to around 1/2". For my finishing pass I use a 1/8" ballnose. It is only removing about 1/16" material so I buggy along at around 5 to 6 IPS.

What it all boils down to is calculating your best router speed and feedrate and matching that to your bit and material. It is a matter of trial and error as each machine will be a little different. If you go to Onsruds website, they post feed/speed calculation sheets for proper chip loads and you can start there and then fine tune for your machine.

3. Machine rigidity and spindle power are probably the biggest factors in determining depth of cut, along with material.

Typically, the larger the tool diameter, the deeper the cut. For harder materials, cut depth might be bit diameter or less. For softer materials, 1.5-2x tool diameter.