Question about new digital stepper controllers

[irving2008]

Thats a good article. Though I knew the info already it explains it in a really nice and succinct way.


In answer to the OP. Yes you can use some degree of microstepping as long as the cutting forces tangential to the stepper axis are less than the % of the holding torque.

By way of example:

The force required is dependant on the specific cutting force of the material and the area of the chip. Unlike metals where the specific cutting force is a constant, in wood it varies with the grain direction and hardwoods can approach the forces needed for machining aluminium when going across the grain.

Aluminium is 500N/mm2 cutting force, common woods would appear to be around 50-150N/mm2. A 3mm dia cutter taking a side cut of 0.1mm deep would experience/generate a 75N force in aluminium, maybe 7-25N in wood.

A common 3Nm Nema23 stepper, detent torque of .2Nm. 1 step = 1.8deg, resolution required 0.5deg therefore use 4 microsteps. %holding torque available ~ 40% = 1.2Nm less detent torque = 1Nm.

Radius of item being cut, say, 5cm (0.05m), means that the cutting force cannot be larger than 20N (and for safety probably 50% of this) before the work will move the stepper more than the microstep size.

The best solution to improving resolution, since rotary speed isnt an issue, would be to gear it down. A 10:1 ratio would give a resolution of .18deg and 30Nm of torque which would be good enough for aluminium at 5cm radius.

Like all things, this is theory, you need to try it in practice to find out what combination of cutter, cut depth, workpiece size and angular resolution you can truely achieve.