Slot milling is a machining process in which a rotating cutter fully engages with the material to create a channel, groove, or keyway. Unlike side milling, where only part of the tool is engaged, slot milling requires the cutter to be fully buried in the workpiece, making it a more demanding operation in terms of cutting forces, chip evacuation, and heat management.

Cutting Parameters in Slot Milling
Slot milling is characterized by full-width engagement, meaning the radial depth of cut (ae) is equal to the cutter diameter. Other key parameters include axial depth of cut (ap) and feed per tooth (Fn).
- Radial Depth of Cut (ae): In most cases, ae = cutter diameter, meaning the tool is fully engaged across its width.
- Axial Depth of Cut (ap): Determines the depth of the slot per pass. Deep slots often require multiple passes to avoid excessive tool deflection and heat buildup.
- Feed per Tooth (Fn): Controls chip load per cutting edge and must be selected carefully to balance tool wear and cutting efficiency.
The material removal rate (MRR) for slot milling is given by:
MRR = F × ap × ae
where:
- F = feed rate (mm/min or in/min)
- ap = axial depth of cut (mm or in)
- ae = radial depth of cut (mm or in) (typically equal to the tool diameter in slotting)
Challenges and Considerations in Slot Milling
- High Cutting Forces: Full-width engagement generates more force than side milling, requiring careful selection of cutting speeds and feeds.
- Chip Evacuation: Chips have limited escape routes in a deep slot, making coolant flow or compressed air essential.
- Tool Deflection: Deep slots increase the risk of tool bending, affecting accuracy and surface finish.
- Heat Management: High engagement leads to increased heat generation, requiring proper tool coatings and cooling strategies.
- Workpiece Rigidity: If the workpiece is thin or unsupported, vibrations can reduce accuracy and tool life.