Broaching
Selecting a broaching route: progressive teeth, push/pull and rotary tools, access and chip space, machine loads, material condition, and feature acceptance.
Tags: processes, shaping, broaching
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In the worked flat keyway, 24 teeth × 0.020 mm rise per tooth remove 0.480 mm of roughing depth. Across a 4 mm width and 30 mm work length, each tooth removes 2.4 mm³ before chip curl or compression. Use measured chip behavior and the actual engaged teeth to size gullets and check cutting force.
Linear broaches remove stock with a sequence of teeth. Specify internal or external geometry and tool access. Rotary broaching uses a different cutting action.
Cutting action and process variants
Mitsubishi Materials' C004G-H Gear Cutter/Broach catalog describes roughing and finishing edges arranged by size, with the depth removed per tooth and total stock determined during tool design. Its diagrams distinguish pull end, pilots, roughing/semi-finishing/finishing sections, tooth pitch, and chip space. This explains why increasing machine feed does not simply replace a different rise-per-tooth design. No issue date is assigned to this catalog here. Mitsubishi broach catalog
| Variant | Tool/load arrangement | Access question |
|---|---|---|
| Linear pull broaching | Machine draws the broach through or past the work; tool carries tensile load | Is there room for the pull end, cutting section, and full stroke? |
| Linear push broaching | Ram pushes the tool; guidance and unsupported length matter | Can the tool pass through without hitting a shoulder or fixture? |
| Surface broaching | External surfaces pass a cutting sequence, or the tool moves past the part | Can the fixture support the cut and provide tool clearance? |
| Rotary/wobble broaching | Profile tool works in a dedicated holder with inclined cutting action | Is the prepared hole or outside diameter compatible with the holder, depth, and chip space? |
| CNC reciprocating broaching | Repeated strokes with the specified tool/insert remove successive increments | Is the machine and return/relief motion approved for this operation? |
Pilot Precision supplies distinct push, pull, production, and one-pass tools. Its duMONT one-pass keyway tools use the appropriate bushing without shims, while production push tools have a different self-supporting arrangement. Those named systems must not be treated as one interchangeable broach-and-shim setup. Pilot Precision keyway tools
Starting feature, access, and chip accommodation
Nidec describes internal broaches entering an existing pilot hole, while surface broaches produce external profiles such as grooves and turbine-root features. Its product range includes distinct internal, surface, and fir-tree tooling. A conventional internal through-broach requires clearance for the cutting sequence and tool passage, rather than only enough space for the finished feature. Nidec broaches
Blind features require a specifically supported route. Slater's internal rotary-broaching preparation guide requires pilot depth beyond the broached depth for chip accumulation. It describes an optional bottom recess larger than the tool's across-corners dimension for chip breakoff and warns that trapped fluid in a blind pilot can create hydraulic resistance. These requirements concern Slater's rotary process; they do not establish that a conventional long pull broach can cut the same blind socket. Slater internal rotary-broaching preparation
Specify the permitted entrance chamfer, pilot size, full-form depth, runout/relief region, bottom geometry, and any material permitted to remain. The drilled depth is not automatically the usable profile depth. Check how chips will be removed and whether the inspection probe or gauge can reach the actual functional region.
Tooth stock, machine load, and material state
The cutting sequence divides stock among teeth, but more than one tooth can be engaged simultaneously. Pitch, work length, cutting width, chip thickness, material, friction, and edge condition influence the load history. Check both machine capacity and the tool/holder/fixture limits with the designer. A press's nominal force rating alone does not prove adequate alignment, stroke, guiding, or tool strength.
Pilot Precision's engineering section requires a rigid, square setup and warns against exceeding the broach's specified maximum length of cut. Misalignment can produce drifting, deflection, and breakage. Increasing the number of stacked parts changes the effective length of cut and chip demand; it is not merely a handling change. Pilot Precision engineering guidance, page 34
Identify actual material condition, not only the alloy designation. Nidec notes that overly soft steel can adhere and tear the finish, while harder material can shorten tool life. Its Constant Cutting Force Broach example is an involute spline tool for an S48C workpiece with 23.5 mm cutting length; its separately named burr-reduction tool uses another configuration. These examples do not establish a universal hardness limit or promise burr-free output on unrelated parts. Nidec material and tool-design guidance
Rotary broaching is a separate tooling system
Slater's FAQ identifies a 1° holder angle for its rotary holders, producing the characteristic wobbling action. It also warns that incorrect predrill/preturned preparation can increase pressure, reduce tool life, and damage holder bearings. Its material discussion makes feasibility depend on material strength and broached depth. Those statements do not authorize tilting a conventional broach or applying a linear-broach load estimate to a rotary holder. Slater rotary-broaching FAQ
Slater's preparation guide also ties adjustable-holder alignment to broach length and directs users to material-specific thrust information. Obtain the machine/holder supplier's limits and compatible setup. Cutting speed, feed, lubrication, and venting must follow the actual tooling application rather than a generic RPM or press-load recipe. Slater setup guidance
Original bounded calculation: stock and chips
Use the hypothetical flat keyway above. Ignore finishing allowance, rounded edges, run-in and run-out, and chip compression.
| Quantity | Calculation | Result |
|---|---|---|
| Total roughing depth | 24 × 0.020 | 0.480 mm |
| Undeformed chip section per tooth | 4 × 0.020 | 0.080 mm² |
| Raw chip volume per tooth over the part | 4 × 0.020 × 30 | 2.4 mm³ |
| Total raw material removed | 24 × 2.4 | 57.6 mm³ |
| Independent volume check | 4 × 0.480 × 30 | 57.6 mm³ |
Doubling work length doubles raw chip volume per tooth, even though rise per tooth remains unchanged. The 2.4 mm³ is not a sufficient gullet-capacity specification: curled chips occupy space differently, and actual chip formation must be accommodated. Neither the total volume nor the per-tooth chip section determines cutting force without validated material/tool data and simultaneous engagement. The calculation also does not apply to rotary broaching or to a round broach where diameter rise must be distinguished from radial stock.
Inspection, burrs, and production handoff
Nidec identifies rising force, adhered chips, edge damage, deteriorating finish, and size changes as tool-condition indicators. Use the approved sharpening route and verify output after regrinding. Nidec maintenance guidance
Separate width/size, depth, profile, location/orientation, straightness, surface texture, and burr requirements. A mating gauge may test function without revealing which geometric error exists. Define acceptable entry/exit edges and chip cleanliness; a tool marketed for burr reduction does not eliminate the need for drawing-based inspection.
A useful handoff contains four groups of information:
- Part and state: alloy, hardness/condition, prior heat treatment, stock, pilot feature, and production quantity.
- Feature definition: profile standard/edition where applicable, size/depth, datums, full-form extent, reliefs, chamfers, and surface requirements.
- Process compatibility: exact tool/holder, machine stroke and load capability, support/alignment, chip removal, and qualified cutting conditions.
- Acceptance: gauge/metrology method, locations, burr/cleanliness limits, sampling, tool-change controls, and traceability.
The cited manufacturer web guidance has no verified technical issue date. Website copyright years and PDF upload paths are not treated as process-edition dates; confirm current application instructions with the selected tooling.