For solid carbide tooling, usually yes. A carbide end mill can typically be reground several times at a fraction of replacement cost, and the economics improve with tool diameter and price. The judgement is whether geometry can be properly restored and whether the resulting change in diameter and corner radius is acceptable to the process. For inexpensive tooling and for tools where dimensional change is unacceptable, replacement is simpler.

Because a cutting tool works by presenting specific angles to the material. Rake controls how the chip forms, relief prevents the tool rubbing behind the edge, helix affects chip evacuation and cutting action, and the corner condition governs finish and edge strength. A tool given a keen edge but incorrect angles will rub, deflect, work-harden the material or chip, and will often perform worse than the dull tool it replaced.

Its diameter and usually its corner radius, both reduced by the material removed, and its overall length if the end has been taken back. Those changes must be measured and carried into the CNC program and the tool table, since a program written for a nominal diameter will cut oversize or leave stock if the actual tool is smaller. Reground tools are best kept identified and grouped rather than mixed with new stock.

To regain their original performance, yes. Grinding removes the coating from the reground surfaces, and an uncoated carbide edge will not match a coated one in tool life, particularly in abrasive or high-temperature materials. Proper practice is to strip the remaining coating, regrind and re-coat. A reground but uncoated tool is still usable, but expect reduced life and adjust the process rather than assuming equivalence.

A manual universal machine uses fixtures and operator skill to present the tool at the required angles, and is well suited to occasional sharpening, simple tools and one-off form tools. A five-axis CNC tool grinder generates the complete geometry from a program and can manufacture tools from blanks as well as regrind them, with consistency a manual machine cannot match. The choice follows volume and the range of geometry required.

Yes, and drill point geometry is one of the more valuable things to get right: point angle, lip relief, web thickness and the symmetry of the two lips. Asymmetric lips make a drill cut oversize and wander, which is the usual reason a hand-ground drill produces a poor hole. Dedicated drill grinding attachments and CNC cycles both handle it; freehand grinding rarely produces symmetry good enough for accurate holes.

Diamond wheels for carbide and cubic boron nitride wheels for high-speed steel, chosen by grit and bond for the balance of finish and removal rate required. Wheel condition and correct dressing matter as much as on any grinder, and using the wrong abrasive for the tool material wastes wheels and produces poor edges. Coolant is important, since edge quality on carbide is easily damaged by heat during grinding.