Machining
Broaching vs Milling
Broaching pulls a multi tooth tool through the part in one stroke, each tooth cutting 0.025 to 0.15 mm deeper than the last, finishing an internal keyway or spline in seconds. Milling generates similar features with a rotating cutter over minutes. Broaching buys cycle time with expensive dedicated tooling.
| Broaching | Milling | |
|---|---|---|
| Tooling cost | $300 to $30,000 per broach | $50 to $500 per cutter |
| Cycle, 8 mm internal keyway | 10 to 30 s | 3 to 10 min with slotting or EDM assist |
| Tolerance | ±0.01 to 0.025 mm | ±0.025 to 0.05 mm |
| Internal forms | Splines, keyways, hex, serrations | Limited in through holes |
| Flexibility | One form per tool | Any profile via program |
| Material hardness limit | Under 35 HRC | To 65 HRC with right carbide |
| Break even volume | 1,000 to 5,000 parts | Prototype to low volume |
Choose Broaching when
- Internal splines and keyways at volume
- Cycle times under 30 s required
- ±0.015 mm on a repeated form
Choose Milling when
- Prototypes and lots under 1,000
- Hardened parts over 35 HRC
- Geometry that changes between jobs
The verdict
Run the volume math. A $6,000 keyway broach against 4 minutes of mill or slotting time at $85/hr pays back around 1,000 to 1,500 parts. Below that, mill it, shape it, or wire EDM it. Above 5,000 parts per year, nothing else touches broaching cost per feature.
Cost comparison
A standard keyway broach runs $300 to $800; custom spline broaches run $5,000 to $30,000 with 8 to 12 week lead times. Sharpening costs $150 to $500 and a broach takes 15 to 25 resharpenings. At an $85/hr shop rate, saving 4 minutes per part is worth $5.70 each, so a $6,000 broach pays back near 1,100 parts. Stay under 35 HRC; pushing a broach through hardened stock chips teeth and scraps a five figure tool.
Common questions
Can you broach a blind hole?
No. A broach has to pass completely through the part, and it needs a chip exit. Blind keyways and splines go to rotary broaching for shallow hex forms, slotting or shaping with a relief groove, or wire and sinker EDM. Design the through hole in if you possibly can; blind internal forms cost 3 to 10 times more per feature.