Disc blade RPM

[Marco M.]

Hi everybody,
I bought a groove assembly with two 47.6mm diameter and 6mm height tungsten carbide tipped discs (see picture). The discs have no key nor screw that prevents them from spinning w.r.t the arbor, only a nut at the end.
The assembly is mounted on a 400W mini mill with manual feed only.
I would like to cut a very soft wood (fir/pine).

Now the questions:

1. Is it correct to mount the two discs at 60° degrees w.r.t each other? Would it be better to align them?
2. Since the mini mill vendor suggests to use 500 RPM for a 20-30mm mill on wood, I selected 250 RPM. The machine is really noisy and sometimes the discs stop spinning. Would it be safe to go faster? At this speed it's really hard to keep a steady feed rate by hand.

Thank you

 

[RJSakowski]

The cutter sounds like what we call a shaper cutter. https://www.grizzly.com/products/C2158

I would stagger the cutters to reduce the impact load.

Generally, it has been my experience that faster is better with wood. Grizzly's shapers run at 7,000 - 10,000 rpm. This produces smaller chips and better finish. A higher rpm will also reduce slippage of the cutter as the cutting force will be reduced due to smaller chips.

The maximum rpm is of course limited by the cutter itself. Too high an rpm and the cutter could disintegrate. But 500 rpm sounds low for wood.

 

[Hukshawn]

Those are rabbiting cutters. 500 is way to slow. You have a higher chance of the cutter grabbing the wood and tearing it. I would max the speed, but depending on the size of the cutter, under 3” would be in the 12,000 rpm area. This may not be a good idea...

 

[Mitch Alsup]

Pine: 1.2 MPSI 0.017 lb/CI
Oak: 1.7 MPSI 0.029 lb/CI
Aluminum: 10 MPSI 0.097 lb/CI
Steel 30 MPSI 0.283 lb/CI

So, basically, the load on the cutter is 1/8 that of aluminum and 1/24 that of steel; while the amount of material in a single bite of a single tooth is 1/5 to 1/14.

I would spin the cutter as fast as the machine allows for woods.